Basement Vapor Barrier For Basement Insulation
Basement Vapor Barrier and Insulation
We’ve written several articles about basement insulation and a cost effective approach to basement insulation using foam board and fiberglass insulation. Since writing those articles we’ve received quite a few questions about when to use a basement vapor barrier and when not to. So we thought it might be a good idea to clear up some of the confusion.
Understanding Vapor Movement
Before we explain where to use vapor barriers it’s a good idea to talk about where the vapor comes from which ultimately makes the discussion easier to understand.
First off you need to think of your concrete (or block) walls as a huge sponge for moisture (water vapor). Over time and throughout seasonal changes in temperature concrete will “dry” out releasing a tremendous amount of water vapor. The adjacent sketch shows an unfinished, un-insulated, un-heated basement wall. We’ve shown arrows that indicate where the water vapor goes as the wall “dries” out.
Depending on the time of year it’s possible that all that humidity in the air will turn around and condensate on the cool concrete surface if the dew point is correct. The point here though is how moisture in the form of water vapor leaves the foundation walls and migrates into the basement space or outside above grade.
Hi Todd.
Not sure if you replied but i can’t find the page i posted my question on.
I was interested in following your article above on how to insulate the basement and vapor barriers, etc.I noticed how you said frame infront of the foam and to leave a one inch space between for air flow.
How do i help to keep the foam attached to the wall?? I was going to use an adhesive and then frame up against to keep it in place, but the air space you said was better.
Can i use wall anchors for the foam too?? I was concerned if they work on my old basement wall.
Also, my township requires horizontal and vertical fireblocking. How do i incorporate this into your instructions and diagram above and still be in code??
Note: i am not covering or finishing my ceiling. my head height is too low so i will just leave it open and paint instead.
Thanks for all your help.
Rob A.
@ Rob – We typically use an adhesive specifically made for foam board. The key is to put the adhesive on the foam and let it sit for a few mins before you apply to the wall. That allows a skim to form on the glue and it sticks better to the wall. I’m not sure the fire blocking is applicable in your situation. It’s typically applicable with balloon framing which you will not have in this situation. It’s best to check with your building inspector ahead of time and find out what he/she wants. Good luck.
Thanks Todd.
I’ll be using the blue foam and adhering the silver side on to the wall and blue side facing into the room, correct??
My township website shows a diagram of the fire blocking on a finished basement wall, and uses horizontal and vertical blocking. it says they require vertical fire blocking at 10ft intervals.
Seems unnecessary to me too, but i’ll need to talk to them first and explain what i’ll be doing then see what they say.
Thanks,
Rob A.
@ Rob – What foam product are you using? Without knowing which product it’s hard to say which face goes towards the concrete.
Hi Todd.
it’s the SUPER TUFF-R 1 1/2 In. 4 x 8 Polyisocyanurate Rigid Foam Insulation. it’s silver on one side and blue on the other.
Is this the best to use??
@ Rob – You have it correct. The product you are using is probably the top of the line…but certainly will do the job!
the blue side faces? in to the wall?
which product are you using? some of it is blue on both sides.
Hi Todd
I live in southern Missouri, cold but not extreme, I’d like to cover the poured basement walls. I’m thinking about glueing foamboard between 2×2 furring strips and paneling over it. Any reason not to?. I don’t think I need the additioanl insulation value a fiberglass-inside 2-4 stud wall would provide. Ceiling is insulated with plastic covered fiberglass and will be covered with drywall. Walls have been uncovered for 15 years so they are as dry as they will be. We use a de-humidifer ithe room. Most of wall area is completely below grade. Also if I can use this set up, do I need a platic vapor barrier under paneling? What type of formaldehyde free foamboard do you redommend? Thanks for your advice. G. Brewer
@ Gary – I would glue the foam board directly to the concrete. Then place your furring over the foam and secure it through the foam into the concrete. Either that or frame a wall in front of the foam. Be sure to tape the seams well. No need for a vapor barrier. Good luck!
todd,
my basement foundations walls were very poorly poured in 1952 w many honeycombs, air pockets, and poor adhesion between poors.when we would get as little as a 1/4 inch of rain i had water running across the floors. for this problem i have installed a complete interior seepage drain system in my basement that also has a lip that sits above the floor against wall that collects any seepage water off walls.i corrected any outdoor water problems-downspouts,improperly sloped concrete,terrain,etc. i have also applied hydraulic cement after chipping out concrete in any spots on walls that still had visible water seepage,i then applied dry lock paint to these areas. this has taken care of any visible moisture on walls or floors after heavy rains–(recently 3″)dry is nice. i have also put in a radon mitigation system that is sucking air from under my basement slab through the seepage drain system so any moist air is being removed off of foundation wall(the design was to remove radon but by incorporating it with the seepage system im also pulling air from the moist foundation wall through the earlier mentioned lip against wall). with all this being said i’m currently furring out the walls staying 6″ off foundation wall,treated lumber for bottom plate,fiberglass insulation in void between floor joists on sill plate against ribbon joist,below this foam board insulation-to prevent mold- from top of foundation wall 4′ down-not the whole stud space- flush with drywall face of stud. does all this sound ok and should i install vapor barrier between foam insulation and drywall. i know this sounds like a lot of information but i figured the more descriptive the better. thank you for your assistance in this matter.
chris
Sounds like you’ve been busy fixing the real problems which is good! I would recommend you read this article:
http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
It shows how I recommend you insulate the basement walls. I really don’t recommend only doing 4′ as you propose.
I would also recommend you read the following article on the rim joist insulation:
http://www.homeconstructionimprovement.com/rim-joist-insulation-insulating-options/
Good luck.
Reading your article has made me re-think my approach to insulating my basement walls. I live in Upstate NY, where the Winters are brutally cold. My 5-year old house has block basement walls.
I decided to experiment with one wall and installed the DOW 2″ rigid foam board, and am building a standard 2×4 wall as well. I intended to fill it with R-13 fiberglass insulation.
One question, however. I am not sure if I should use a faced insulation or not. According to your article, it seems unnecesary (since I am using 2″ foam), however I cannot find any rolls of R-13 unfaced fiberglass at the box stores! I can find R-13 pre-cut batts, but they are twice the price and will result in about 6″ of waste per batt. Any suggestions? Alternative include (1) using R-19 for 2×6 walls and compressing it (bad), or using R-13 faced rolls.
Many thanks for your insightful article.
-Todd M
@ Todd M – Thanks for visiting the site. The vapor barrier won’t do any harm in your situation. If that’s the cheapest product available then I say go with it. Good luck.
Hello Todd,
I am having my basement redone after a fire. The basement was previously finished with chip board paneling partially over framing and partially directly on the concrete. We will be using dry wall. The building contractor I am using for the rebuild has framed out the wall with TYVEX behind it. He says that it’s not necessary to put in insulation behind the dry wall because the air space and the soil around the foundation will provide all the insulation needed. The basement has never had moisture on any of the walls, but it is always colder in the winter and summer then the rest of the house. Is my contractor correct, or should I insist on insulation on the outside walls of the basement?
Thanks,
Greg M
@ Greg M – First off it partially depends on where you live. However, I would insulate it regardless if it were my home. Secondly, Tyvek will actually allow water vapor to move through it in one direction so technically the water vapor “could” move from the foundation to the framing depending on the side that is towards the framing. Frankly even a “dry” looking foundation was is extremely damp and full of moisture.
Todd great article, just ordered my rigid foam and materials to frame the basement out. I live in Northwestern Indiana and will be finishing my basement as to your article. As an extra form of protection we used Epoxy on all the joints and used Zinsser waterproofing paint LX. We will be using 1 1/2″ foam. I am unclear about a few things: How much adhesive should be used per 4×8 sheet of pink foam? Also for the pink foam which side goes towards the concrete?
Lastly we have had a moisture problem on the Rim Joists where air seems to be getting trapped between the Batt Insulation and the Rim Joist creating dampness. Would this work well for the Rim Joist? We are looking for the best solution before we get to the drywall portion of the job. Happy New Year!
@ Alex – Thank for the compliment.
The amount of adhesive really isn’t all that important. We typically install a bead every 12″ or so. Apply it to the foam, let it stand for 5 mins until it skims over then apply to the wall. Foam board works great on rim joists. Use 2″ minimum and seal it in place with spray foam. Good luck.
Todd,
I have glued 2″ Foamular 250 to my concrete walls and taped the seams with Tyvek. I have built the 2×4 walls with 1/2″ to 1″ gap between the studs and foam. My plan is to use the encapsulate fiberglass insulation.(I prefer working with it). Is there a problem in using totally encapsulated fiberglass?
Thanks,
Nick
@ Nick – We’ve never used it so I can’t give an opinion. I think it should work fine after what you’ve already done. Best of luck.
I have read all of your articles on foam board and vapor movement, but do not understand how the foam board approach solves the problem of trapped vapor. If the foam board is glued tightly to the wall (avoiding the air gap), the water vapor still needs to go somewhere. Why would it not just penetrate the foam board and cause the same problem as insulation? It seems to me that the foam board is as much of a vapor barrier as foil-backed insulation, which everyone agrees is a problem.
Can you help clarify? (I have a below-grade basement (100-year-old house) that is freezing cold in the winter, so I am trying to insulate in some way. I also have some minor seepage that comes through the wall during heavy rains.)
@ Paul – Properly installed foam board insulation can create a very effective vapor barrier. Foam board also has the benefit of not promoting mold growth like fiberglass. There are two issues that you’re trying to deal with. First of all the foundation walls are FULL of water and we want to keep that from getting to the framing and wallboard. Secondly we want to keep any moisture from the finished space from passing through the wall and hitting a cold surface where it could condense into liquid form and saturate the framing and wall finishes. Closed cell foam insulation products provide a great barrier to vapor movement. I hope this helps.
Todd,
I have 40 year old pored concrete walls that have never had a water problem in turns of seepage, though have scaled off the original paint job considerably in some areas. Should they be repainted before gluing the foam board to them?
Also, is a combination of foam board and batt insulation the way to go in insulating the areas above the sill plate? I can’t tell you how many different opinions I’ve read on this.
Thanks,
Bob
@ Bob – In both situations it’s all about a cost issue. Ideally we’d all insulate basements with spray foam if money were no issue. The idea of using both foam board and fiberglass is a more economical hybrid. Having said that I like to see a minimum of 2″ of foam board on the rim joist, spray foamed in place….followed by additional fiberglass to supplement. Best of luck.
I have been searching endlessly and i believe @todd explained this finally for me. Here is what i am doing, I’m sorry if this scenario has been explained somewhere else.
I have a 4 year old house (southern Ontario) it has a delta membrane on the outside foundation… builder has put up R12 fiberglass batts about 4-5 ft down on the concrete wall. I want to install durafoam EPS not XPS directly (PL Premium)against lower half of concrete wall. Tuck tape into existing upper half. Then put dricore down, add metal framing on top. I want to use XPS or EPS directly on the rim joists and seal around with canned spray foam then add roxul insulation behind everything. Then no more vapour barrier just drywall it up.
I know this is not code, but can you foresee there being problems with this hybrid insulation method? thanks
Paul – First off I would never use EPS in a basement, it’s an open cell foam and it can/will collect/hold water. Secondly, I would remove the existing fiberglass insulation. You need foam from the top to bottom on the walls.
I am using EPS rigid 2″ durafoam with the foil backer (it is a closed cell foam) has an R value of 7.5
http://www.plastifab.com/homeowners/buildinghome/plastispan_duro/plastispan_durofoam.html
Paul,
EPS is NOT a closed cell foam board….it’s made with closed cell foam balls…not the same thing.
http://www.homeconstructionimprovement.com/foam-board-insulation-values/
I would NOT recommend that in a basement.
Hi Paul
I was following your post as I need to insulate my basement (block foundation) and was thinking of using Durofoam 1.5 inch (R 5.6), and I was wondering if Durofoam is what you ended up using for your basement. I’m located in the Ottawa, ON area.
Tanya
Tanya – I responded to your email. Durofoam is an XPS foam, which I do not recommend in basements. It consists of closed cell balls of foam that are compressed together, but the “matrix” of balls is not truly closed cell.
Good luck.
Hi Todd,
I have an interesting question. We’re all worried about moisture in the basement and getting into the insulation. I was thinking of putting a layer of rubber tar on the inside of the basement foundation and then putting the foam board up. It comes in 5 gallon buckets and you just roll it on. Theoretically that should keep all vapor from coming into the inside of my house. I have a layer of tar on the outside of my foundation for waterproofing when we built the house. The only thing I’m worried about is does the concrete have to breath, and maybe all that tar might make it too water/airtight. What do you think. I thought it would be a good idea. – Erik
@ Erik – In theory it might work but most all tar based foundation products are damp-proofing and not really water-proofing. What that means is it helps keep most of the water out but it won’t keep it all out. Plus, if it cracks, it won’t likely stretch enough over that crack and it will crack itself. The other thing you might consider is the VOC’s and off gassing. That stuff typically smells horrible and might not be a great solution inside. Just my thoughts…..
Todd,
Framing poured basement walls in a new house in Delaware. I too am concerned about creating a mold situation. I stapled 15 mil plastic wrap on the inside of the 2 x 4 walls prior to putting the walls in place. Then plan on using R13 basement Insulation then cover with 1/2 sheet rock. I have a floating slab which doesn’t contact the walls and it all drains into the sump pump. Held the 2×4 walls 1″ off the Basement wall. My question is should I cut the Plastic off and discard it? Will I trap moisture between the plastic and the insulation? Should I just let the walls breath?
Joe – The plastic is a problem along with the approach. The concrete wall will be cold and damp. If you place the plastic and any water vapor gets into the wall cavity it’s going to condensate against the cold plastic surface. If you remove the plastic, water vapor can really go nuts in two directions, drying of the concrete in the summer can move water towards the fiberglass and in the winter it will go the other direction. You REALLY should consider using foam.
Hey Todd, great article. I have a dilemma–just moved into a newly-constructed home and we want to finish the basement. The basement walls are fully insulated with the foil-faced fiberglass blanket insulation. I’m unsure whether to just frame my wall in front and cover w/ .5″ drywall, or rip it all down in favor of the foam board system above–it seems that buildingscience dot com would recommend the latter option, but wanted to see your thoughts-we’re in MD if that matters.
thanks
john
@ John – Thanks! I hate to say it but if it were my home I wouldn’t leave it that way. Just too risky with mold problems.
Todd,
Thanks for the advice on 12/31 about glueing the foamboard to the basement wall and screwing furring strips over the top of the board. A much better approach for sealing the wall. For southern Missouri do I need 1 1/2 inch board or will 3/4 inch serve the purpose of moisture barrier and temperature control? I’m covering the foamboard wiht paneling.
thanks again, Gary
@ Gary – Most literature that I’ve read says that 1-1/2 to 2 inches is the minimum to create an effective vapor barrier. Being in Southern Missouri I’m not really sure how cold your weather gets. You might be able to use foam plus a vapor barrier…but if that foam get’s cool on the finished side it might promote condensation of any moisture that get’s past the paneling. I guess what I’m saying is I’m just not sure. Good luck.
I called the manufacture of DURA FOAM (Plasti Fab in Ont. Ca.) they recomended that I use there 2″ foam board that has a green and a foil side. They said that the foil side should face toward the room to reflect the heat back into the room and the green side against the concrete wall.
do I have to use foam board that is covered with foil or plastic or can I just use standard 2″ foam board (ei. not coated) ?
@ Paul – If you use 2″ of foam it is thick enough to create a vapor barrier. However, if you use a product with foil or plastic the vapor barrier is even better! As with anything….you get what you pay for :)
Todd – I have not found the two inch foam insulation with foil at any of the local suppliers (Lowes, Home Depot, Menards). Where can I find it? What company makes it?
It’s a DOW product and it’s typically sold at more traditional building supply / lumber yards that deal with commercial construction as well as residential.
Hi Todd:
To begin with, many thanks for offering your time and expertise to help those of us who lack the necessary training. I have some questions concerning insulating the interior surface of exterior concrete walls that have the same problem as basement walls.
I am purchasing a small, 600 sf, top floor, corner unit apartment in a concrete building that is presently under construction (top floor!!!??? I know, I know, but I cherish a quiet living environment). The apartment is located in the south-east corner of the building with other apartments to the north and west sides. The apartment has radiant heat flooring. Sorry, I don’t have the specs, but my understanding is that it is intended to maintain an interior temperature of 16 degrees C (61 F), but at what outside temperature, I don’t know yet. The outside temperature can vary from 40 degrees C (104 F)(normally 30 to 35 degrees C) in the summer to -40 degrees C (-40 F) (normally -8 to -20 degrees C) in the winter. There may be some insulation on the outside surface of the exterior walls and flat ceiling, but I’m not sure. I am not permitted to alter the outside surfaces of the exterior walls and flat ceiling. None of this would be a problem if it weren’t for the fact that I prefer a constant 25 degrees C (77 F) interior temperature. Thus, it could be said that my problem is self-inflicted.
It was when I read your article that I discovered the problem with condensation on cold interior surfaces and the ensuing mold problem. It seems to me, as you say (I think) that the solution is to add insulation to the interior surface of the concrete walls and flat ceiling so as to create a monolithic wall with a dew point somewhere in the interior of the concrete wall while ensuring that there are no air gaps between the concrete wall and insulation or between multiple layers of insulation. After creating such a monolithic wall, I would then construct a frame wall and install additional insulation. Assuming that my assumption regarding the nature of the problem and its solution is correct, I have some questions:
Question #1: Do I correctly understand the problem?
Question #2: Do I correctly understand the solution?
Question #3: You mentioned that you install an adhesive bead about every 12 inches on rigid foam insulation to bond it to a concrete wall. Is if permissible to cover the entire surface of the rigid foam insulation with adhesive in order to ensure that there are no air gaps between the concrete wall and the rigid foam insulation?
Question #4: Would it be best to bond multiple layers of rigid foam insulation to each other using an adhesive in order to avoid any air gaps?
Question #5: Will using “RadonSeal Deep-Penetrating Concrete Sealer” (http://www.radonseal.com) to seal the concrete in conjunction with using rigid foam insulation solve the moisture problem? To what level of certainty? (It is my understanding that painting a concrete wall with a water-proof paint will not work.)
Question #6: Will the solution for the concrete walls also work for the ceiling? It seems that it would, but hey, I am way out of my league here.
Question #7: You said that spray-in-place foam insulation is one of the best ways in which to insulate a basement wall, but it can be expensive. I’m thinking that since my apartment is only 600 sf, and I only have two exterior walls and a flat ceiling, perhaps the cost wouldn’t be prohibitive. I would greatly appreciate it if you would provide the construction details on the use of spary-in-place foam insulation to solve this problem.
If you need any additional information, please let me know. In March, I will have a chance to meet with the engineer who designed the building. I want to ask him for information regarding the capacity of the radiant heat flooring and the construction details of the exterior walls and flat ceiling.
Many thanks for your help.
Sincerely,
Dan
It’s hard to imagine anything passing through HD (high density)foam!If I use the foil covered and seal it well toward the foundation wall(concrete), will I require a vapour barrier after my studed and fibre insulate wall prior to installiing my dry wall? (pink or blue foam? in case I don’t go with the foil covered) Thank You!
@ Paul – There are two issues…moisture from the concrete….but also moisture from the finished space moving towards the wall and condensating on the surface of the foam.
Does this order for a well insulated the basement sound correct: Foundation wall, HD foam (covered with foil, plastic or not) , 1″ air gap, 2×4 fibre glass insulated studed wall, dry wall, primier and paint, living space! Thank you!
@ Paul – Depends on where you live..if you live in a really cold area….you really should consider 2 inches of foam.
Hi Tom,
I’ll soon be moving into an old farmhouse with a stone wall basement up to ground level, and then a concrete sill sitting on top of the stone wall (an addition in the 1920s after the original house burned down and the latest one was built). The floor is dirt.
Knowing that there will be gaps between the stone wall and the foam board, do you recommend I still trying to insulate this way? Mary
@ Mary – I would recommend spray foam for a stone foundation such as yours.
Hi Todd,
Great article.
I live in a house about 10 years old in MI. It has 90% below grade poured foundation without any water problems. It does have some sort of product sprayed on all the foundation walls by the builder that looks like a stuco of some sort, but I’m not sure.
Anyways, I was hoping to use 1″ rigid foam glued to the foundation for the moisture barrier, then 2×4 frame with fiberglass insulation, then vapour barrier and drywall. There is a drastic difference in cost with the thicker rigid foam.
Do you think my direction will work or should I spend the extra few hundred dollars for the 1.5″ and still use the vapour barrier?
Thanks again,
Rob
@ Rob H – I highly recommend you use the 1.5 inch foam.
how would you insulate a walkout basement that is block wall and has sides partially under grade,
thanks
]
mike
@ Mike Jones – Just the same way we’ve shown in our other articles. Block wall is really the same thing as a concrete wall.
Hello Todd… We live in Ontario, Canada. I am doing our basement over…have put 2″ foamboard and taped and sprayfoamed all gaps. Have studded the walls and because of sewer line have allowed for 5 1/2 inch insulation against the foam board. This bat insulation is from the pt baseboard and full height. My question is do I need to leave an airspace between the foam board and the bat insulation? Should we have a vapor barrier due to our cold winters? Thanks Marvin
@ Marvin – No air space is required. Because you’ve used 2 inches of foam i would skip any kind of vapor barrier.
The one inch gap is between the foam and studs but not necessary between the foam and fiberglass? Is that correct?
@ Vern – You are correct.
Hello Todd. House was built in 1957. Has poured walls. Bought the house about 5 years ago. Looks like they had a water problem at one time because there is metal flashing somewhat newly concreted into the edge of part of the basement floor along the basement wall. Also, similiar concrete without flashing along other edges. there are afew cracks in the wall that they have covered up with flashing and that plastic wallboard you see in bathrooms sometimes. We have never had any water in the basement. I wonder if the foam board style vapor barrier would work? And if so, do you think I can nail the composite decking into the edge?
Thanks
@ Dave – The foam board should work great. Not sure I know what your question is about the decking though? Can you be more specific?
Todd:
I live in Michigan and have started my basement project. I,ve applied 2″ foamboard to the poured walls, sealed it with sprayfoam on the tops and bottoms and either spray foamed or taped all seams depending on gaps. My rim joist is insulated with R-13 fiberglass. My intention is to install a floor system that allows an airgap between the slab and finished floor, and to build the walls on top of that leaving a 1/2 inch airgap between the studs and the foam. I’ll drywall the cieling too.
Do I need to insulate the stud walls? What about a vapor barrier between the stud walls and the foam? Any thing else I’m missing?
Many Thanks!
@ Rich – Sounds like you’re doing well so far. Couple things, one I really recommend you change that R13 and install foam on the rimjoist. Fiberglass doesn’t do well in that application and I bet it’s likely you’ve got moisture behind if you check. With 2 Inches of foam properly sealed there’s no need for a vapor barrier. The only issue is whether you want more than the R10 the 2 inches has given you.
Good luck.
Todd,
Good information here. We have an 8yr old home with unfinished basement. Walls are poured concrete ranging from 9’tall stepping down to a walkout. I understand your approach for insulating the complete walls but areas of the basement only have 4′ and 2′ concrete walls with the remaining height being wood framed. The builder of the home used unfaced fiberglass bat insulation within the stud cavity with an additional poly vapor barrier stapled over the framing and insulation. Question…Do we attach the 2″ foam to the concrete portion of the walls and leave the existing wood framed portion with insulation and vapor barrier as is? Obviously the wood framed exterior walls are above grade. I’m assuming the poly vapor barrier on the exterior framed walls needs to be somewhat air tight?…Tape the seams, etc….What mil poly do you just as being adequate for acting as a vapor barrier?
@ Bryan – Thanks for the compliment. Your house is built like many new homes today. Your assumptions are correct. Just be sure that you seal the foam to the poly vapor barrier well with tape. Also, just to be sure that your existing condition is ok, cut a small hole in the poly and check to be sure the fiberglass is dry. If it is, tape up the hole and proceed as you’ve indicated. Typically 6 mill poly is sufficient.
I have the same setup at my basement but was wondering about the framing. Instead of a stepped frame/drywall directly against the above grade portion, I wanted to go straight up from the floor. There will be a few inches of gap from the finished drywall to the poly & insulation on the above grade section. Is that an issue, or should I remove and re-tape the poly between the new drywall and framing?
Thanks,
Eric
Should be fine, having air behind that drywall is always a good thing :)
Thanks Todd. I’ll change out the R13 in favor of 2 inches of foam sealed with spray foam. Should I worry about moisture from inside the living space going out into the air gap?
What about the cieling? Basiclly when done I’ll have an air gap around the whole basement. Will that create any issues in the cieling cavity where the air can flow between the floor joists above? Should I insulate it or will that create other issues?
Thanks again for your expertise.
@ Rich – I wouldn’t worry about living space air getting into the air space. Frankly, a well primed layer of drywall acts as a vapor inhibitor which drastically slows the movement of water vapor but lets it breath at the same time. Unless you have a high moisture level after finishing the walls I wouldn’t worry about the ceiling area. If the moisture levels are high then you’ll want to use a dehumidifier.
Todd,
Clarify what you mean by seal the foam to the poly vapor barrier with tape? Do you mean at the point where the top portion of the concrete wall covered with the 2″ foam meets the poly vapor barrier covering the wood framed exterior wall? I assume the 2″ foam is only needed on the concrete portion of the basement walls.
Thanks
@ Bryan – You are correct.
Greetings Todd
Great info on doing basement walls. Could you answer a question i have? how do insulate the pockets were the floor joists meet the toe plate above the sill plate? or do you just leave it? I think the toe plate is resting on the top of the cement wall and the sill plate as well which is flush to the inside of the basement wall.
Thanks Doug
@ Doug – There are several approaches.
1. Spray Foam – Best solution but most expensive.
2. Foam Board – Great solution not as expensive, cut the pieces to fit loosely and then spray foam (Great Stuff) to seal.
3. Fiberglass Insulation – This is the bear minimum.
Todd,Thank you for your answers,One more question if you could? I do have some fiberglass between the joist already but there is no vapour barrier? i assume that this is not correct. Thanks Again, Doug
@ Doug – Have you taken a piece down and checked for moisture. Typically we see lots of moisture, frost and mold between fiberglass insulation and the rim joist. Without a vapor barrier the warmer, moist air get’s behind the fiberglass and condenses on the cold rim joist. That’s why we like using foam board.
Hi again Todd
I live in South Ontario, Ajax close to the lake. I have a poured concrete foundation (25 years old). I have decided to spray foam (2″ R-13) from above the sill plate in between the joist down to the concrete basement floor. The next step will be erecting a 2×4 studded wall parallel to the foam and insulating it with Rocsul Bats an R-15 (TOTAL R-13 + R-15 = R-28).
Two questions: Should I stud my wall first 2″ away from the concrete foundation then have the foam srayed in allowing no air gap between the back of the studs and the foundation ( which will also tie in the top plate of the stud wall to the joist-sill plate area) or spray foam first then build my stud wall ? both application will leave the stud cavity viod so that I can install a R-15 Rocsul insulation.(total R-28)
Second question: Either way do I require a Vapour barrier on the front of the studs toward (facing) the warm zone? Thank You in advance!
@ Paul – Question #1, I don’t think it matters either way. Question #2 no need for a vapor barrier in your application.
Todd
In your opinion in question #1 what would you do since nothing exist at this time but a bare wall?
@ Paul – Not sure I understand your question. I don’t think it matters if you frame before or after. I think your approach is solid and will create a very nice R value.
Sorry Todd I should have been more clear ! I want your opinion on whether you would spray foam the bare wall first then build your stud wall or would you build your styd wall then spray foam? Thank You!
@ Paul – That’s what I meant when I said it doesn’t really matter. Frankly your spray foam guys will probably be glad if you frame afterwards. Good luck.
Todd
Thank you for your time and advice. I was think the same thing about how difficult it would be applying foam around the studded wall, not to mention the header plate with all the cold/warm air ducting.
Just to recap, the finished wall will look like this:
Foundation wall, foam sprayed 2″ R-13, studded wall with cavity fill with Rocsul R-15, dry wall sheeting, primer & paint, which will equal a warm health basement . If this is correct work starts Friday!!!
@ Paul – Good luck! Send us some pictures and we’ll show everyone!!
Hey Todd we did the 1.5″ thick Rigid Foam on the walls and all concrete, we sealed off the seams. It made a HUGE difference in the temperature. We live in Northwest Indiana about 2 miles from Lake Michigan and its very cold out right now. We are going to have the Rim Joists spray Foamed with closed cell spray foam. We noticed since we put the Rigid Foam and increased our temp our Cold Water pipes are starting to condensate, and drip. We started framing, and also are putting in zones so we can control the heat/ac separate downstairs. We will have about 1300 of finished SQ. footage all drywalled. How do you suggest we handle the water pipes? Should we insulate them? Should we do anything different for the cold / hot water pipes? They are the blue and red plastic pipes, not copper.
@ Alex – Glad to hear you had good results from the insulation. You’ll want to wrap those pipes, both hot and cold. It will help in the summer and winter.
Hi Todd,
We just got water in our basement which required us to twear down the finished portion. As sort of expected we found the vapor barrier againste the drywall and the wood studs pressed flush with the bare concrete blcoks. Of course this meant wet insulation and mold behind the wall. Once we solve the water issue (which may be a quick landscaping fix) is it just as prudent and relatively not that much more costly to just tear down the framing and start from scratch or can we use the existing framing and improve on the moisture barrier situation that existed previously? I think I know the answer but anothe ropinion always helps.
@ Peter – Sorry to hear about your water problem.
Depending on the severity of the mold problem you may be able to save some of the framing. I would recommend you move the wall away from the concrete block, install foam insulation, then finish the wall. If the wood is soft, really molded, etc then I’ll throw it out.
Thanks Todd,
I dont thisn k it is all too bad. Ther emay be a corner whenre the water damage seems to have orginated form that needs to be replaced but having got behind the wall, it appears that there is minimal wood damage. Now that we have addressed the mold, I will be tackling the insulation and walls next. Glad I had a chance to read this article and forum.
Todd,
1. I have purchased the 2″ XPS and I am ready to adhere it to the walls. My question is “Do the walls have to be perfectly flat for the foam to do its job as a moisture barriar?” It is a poured foundation, but in some places where the concrete forms joined there is a bit of mismatch which could leave an air gap behind the sheet in certain areas as it over laps these. Or is the tyvek tape and spray foam seal top and bottom going to take care of this problem?
2. Does the XPS sheet have to stop at the top of the concrete or can it go all the way up the top of the top plate? (top plate is flush with the top of the foundation wall, not set back)
Thanks,
Rob
@ Rob –
1. No worries….there are very few if any perfectly smooth walls. Just be sure to seal everything well.
2. The key is to stop it where you can continue it back to the sill plate insulation so that you have a continuous envelope.
Thanks Todd,
2. My PT sill plate and gasket are wider then usual and they come to the edge of the concrete foundation. So you can’t or don’t need to continue back. My question is do I have to stop the XPS at the top of the foundation and seal it to the sill gasket or can I go up higher (like an inch) and seal it directly to the sill plate?
Thanks again,
Rob
I would run it up to the top of the plate. Then I would also cut small pieces to sit on top of the plate all the way back till it hits the rim joist insulation, sealing each joint.
I’m in Southeastern Pennsylvania and plan on using a method like this if my inspector will allow it (big if). I plan on installing 2 inch foam board against the concrete, .5-1 inch gap and then steel stud 2×4 wall with rockwool instulation (roxul AFB or similar) with no other vapor barrier. I have a ‘floating slab’ so I plan to run the 2″ foam board down into that. It isn’t truly part of the sump system and is already partially filled with closed cell back rod (radon system). I plan on removing the fiberglass currently at my rim joist and installing foam board installed with spray foam. My township will require fire blocking (drywall) on the underside of the joist behind the new 2×4 walls. I will be using the Delta FL floor product, so I play on running that under the new 2×4 walls and sealed to the fiber board.
Any issues with this plan overall?
Couple of questions. If the foam board has foil does it go against the concrete (I have read different stories on that)? What should be done on areas where you can’t get to the concrete (i.e. sewer lines run horizontal against them? Is it OK to just run the foam as close to the PVC as possible and then spray foam?
Dave – You are on the right track…even with the sewer lines. I would put the foil towards the finished site…it’s a good radiant barrier.
Thanks. Is there any advantage/disadvantage of using a “waterproofer” (i.e. Drylok, Xypex, etc) on the foundation interior prior to attaching the foam board? Do you recommend a particular product?
Fsbr – Let’s put it this way, it can’t hurt….I’m not sure it will do much if you’re going install the foam board.
What would happen if you only use an interior cement sealing paint without the foam board attached to the foundation wall for a vapor barrier?
Then stud your walls(float,with an air gap)and use a vapor barrier- paper faced insulation to fill the stud wall.
Then after dry walling, seal that wall top to bottom with caulk( to keep moisture from inside the basement getting behind that wall and also protect that wall from leaks that may occur in the future from washers or toilets in the basement)?
Also with the glue on paint,I’m guessing at this one, your glue on paint is only as strong as the paint job itself,if the paint that is stuck to the wall is not all that great with bonding then your glue may not bond that well either. So if the paint will somehow peel off the wall so will your glue that is stuck to the paint. I’ve accidentally gotten spray foam on my cement painted walls(using cement paint) then took that foam off after it dried,easily, with the paint attached to it leaving my wall bare in that spot.
Al – That method won’t really work. One problem will still exist. The concrete will still be cold and allow water vapor to condensate on the surface. I just don’t recommend the approach.
Hey Todd,
Peter G. here, how have you been? Question for you. Building out a finished basement. I did one in Beverly and about year ago, we moved to Marblehead, and now I am doing another.
I’ve built my framing/walls about 8 to 10 inches off the foundation to give room to get behind all the walls. This being the case, do I need to put a vapor barrier between the foundation and isulation when I have about 10 inches of space now between?
Thanks, keep in touch
PJG
Peter – How the heck are you man? Small world! You really do need a vapor barrier. Basements are really tricky due to moisture movement from two directions, finished side and foundation walls. Foam insulation is really the best/most appropriate application in the basement. I’ll send you an email and we can discuss more if you like.
Todd,
I am planning to finish my basement in NJ. I have concrete walls and my contractor plans to use polyethylene sheeting on the wall then frame it using pressure treated lumber and then insulate with R13. I have had some leaks on walls in the past and will have a French drain installed. Is this plan ok or should I insist on first having him install 1 ½ foam board insulation and skip the sheeting.
Thanks
RJ – That plan won’t work and it will lead to mold growth. You’ve got to get foam against the concrete first.
Todd,
If the plastic sheeting is covering the entire wall running straight into the french drain and the framing is not touching the plastic would this still create a problem? I failed to mention he plans to use mold and moisture resistent wall board.
RJ – It still won’t work, the concrete wall will be cold, the plastic will therefore be cold, if/when moisture get’s into the wall cavity and hits the cold plastic it will condensate, once it does that the water will be absorbed in the fiberglass and it’s only a matter of time before mold starts.
Thanks
If we use 2″ of foam board I believe I read it had a R value of 13, 1 1/2″ was about 9. Do I still need to have him use insulation in addition to the foam board or is that enough.
RJ – Just depends on what your local energy code requires.
I’m researching a basement remodel also. I believe that building sciences recommends unfaced foam against the foundation. I haven’t seen an R13 unfaced product but maybe it is out there.
Dave – Facing on the foam isn’t all that important as most of it is either plastic or foil. If the foam has a paper type facing then that’s a problem. Unfaced fiberglass is available at all building supply locations.
Thanks. I was just responding to RJ’s comment about R13 foam. I was referring to unfaced foam not fiberglass. I believe Building Sciences recommends, “2” XPS rigid foam insulation(unfaced) tape all joints”. I can’t say if it makes a difference or not as I haven’t every done it. I believe the R12/R13 foam I have seen is considered faced. Perhaps it doesn’t matter.
Todd
Just a quick follow up
Assuming the local code is ok with the R12 or R13 that I’ll get from the foam board would you recommend addding more or is that enough? I am in NJ.
I also noted that at the bottom of the foam board that hits the floor you recommend to seal it with foam insulation. The bottom of my wall will be a french drain, so do I just cut the foam board even with the floor (and then how do I seal that) or do we need to run the board into the french drain an inch or two?
thanks
RJ – The R value really depends on value/versus comfort after you deal with code. It’s like anything else, you get what you pay for. I would imagine R13 in a NJ basement will be quite comfortable.
As far as your drain, I think I’d leave yours open at the bottom so water can get to the drain if necessary.
Todd… Great article. Thanks for the info. I’ve read through the comments and have a better idea of what I need to do but here’s what I’ve got. I live in Michigan so we have some harsh winters. My house is 60 years. To my knowledge there has never been a water leakage or dampness issue and I have lived here over 2 years. The previous owners finished half of the basement walls with brick, floor to 2″ below the first floor joists. There is a 1″ gap between the brick and concrete wall. I’ve torn down a wall that was dividing the finished side with utility side and now want to finish the rest. I intend on using your methods described here instead of brick, however… The brick stops 3/4 across one of the walls. Do I butt the foam right up to the brick (which would close off the 1″ gap behind the brick) or leave a gap? Must I leave a 1″ air gap between the foam and studs if I use 1.5″ or 2″ foam? Do you have any suggestions for insulating beind the brick or is it even necessary? I was thinking I just need to fill in the 2″ gap above the brick to seal in the air gap. Or do you think that will just trap moisture? I hope you can picture all this. I can send pictures if necessary. Thanks!
Dan – can you send me some photos? todd at frontstepsmedia dot com
Todd,
I’ve been thinking about finishing my basement and my research led me to this website. I have a couple of questions for you.
I plan on putting Drylok on the concrete walls, install INSULPINK on the walls, frame with 2×4 ( with 1″ between INSULPINK and studs), spray foam insulation, mold/moisture resistant drywall, then prime and paint.
1. Will the Drylok help or cause harm to the walls? Someone said to allow the walls to breath and the Drylok was going to harm the walls.
2. Is there a better more cost effective product I can use in place of INSULPINK?
3. Will the spray in foam pay off in the near future and does it help with the prevention of mold and moisture?
Thanks in advance
Robert – Thanks for vising the site. Below are some responses to your questions.
1. Frankly I’m not sure Drylok will benefit you at all considering you’re going to use foam insulation. Drylok will not hurt the concrete regardless of the decision you make.
2. Not sure why you’re using both Insulpink and spray foam?
3. Spray foam will pay off, however, its not likely to pay for itself in just thermal performance quickly. However, the real benefit comes from the fact that foam will not lead to a nasty mold problem.
Todd,
Thanks for the reply.
The idea of using both the insulpink and spray in foam was to strengthen the mold and vapor protection.
Does spray foam insulation get moldy when it comes into contact with water? In other words, if my basement get’s flooded, will I have to pull all the spray foam out and re-insulate like I would with regular insulation?
Thank you
Robert – Foam shouldn’t however i caution you that you should use a closed cell foam that will not absorb water.
Todd,
Thanks for the great article.
The previous owner of my house put up wall frame in the basement in front of the concrete, leaving 1-2in” gap.
And he put pink fiberglass insulation between the stud and cover it with plastic sheet vapor barrier.
After reading your article earlier this year, I went down and checked, water was trapped behind the fiberglass, and many of the bottom plate has rotten.
I was planning to replace the bottom plate and redo the whole insulation this spring with rigid foam glue to the wall as you suggested.
Last week, we got 2 feet of water flooded into the basement! I removed all the fiberglass insulation as they are all wet.
If I glue the rigid foam insulation to the concrete wall, and if I get another 2 feet of water, will there be a problem? Will moisture trap between concrete and rigid foam insulation? Do I have to tear out the insulation to dry it?
I am also worry about moisture coming up from the ground.
If I put up dry wall on the wooden frame, the will be a cavity between the foam insulation and the drywall, and since moisture can come up from the floor, wouldn’t the moisture be trap in the cavity and rotten the wooden frame structure?
Thank you,
Tim
Tim – For starters I wouldn’t recommend finishing a basement that has the chance of 2 feet of flood water. Frankly your money would be better spent trying to fix the flooding issue.
The foam would be fine after a flood. however, the drywall, framing and other products would not fair so well. Sorry for the bad “recommendation”.
Todd,
Thanks, I will not finish the basement now, even the neighbor said they were never flooded for the past 15 yrs.
Instead of completely finish the basement, I just want to glue the wall with rigid foam now. The whole house become very cold now with any insulation in the basement.
The code here require a fire barrier to cover the foam, as the foam will release toxic gas in case of fire, thus, I need the wood frame to put up gypsum board. Any suggestion on how I may do that without wood frame?? Or any other material choice?
I was hoping to semi-finish it: just put up some wall, and rubber mat on the floor like the gym, so the kids can run around and play down in the basement. When I get flood again, I can just bring the mat to outside, and dry the floor and wall with a blower.
Thanks,
Tim
Thanks,
Tim
Tim – A flood every 15 yrs isn’t all that bad I suppose. In that case you could probably frame it and insulate with foam, then install the drywall.
Hi there, thanks for all the great info! I’m insulating the basement as you’ve advised (rigid foam on walls, 2×4 walls, and then batt insulation). My question is regarding the floors….I want to put the rigid foam insulation on the floors as well. (we live in very cold manitoba). Do I insulate the floors first, leave a 1/4″ gap around where the floor meets the wall, then insulate the walls, and then spray foam where the wall meets the floor? And then put a plywood subfloor on top of the floor??
Does that sound right to you??
thanks!
Kendra – That will work fine, you may need to add a Tapcon screw or two to keep the floor tight.
Good Day Todd,
I am very glad I found this website as it has pretty much confirmed what I wanted to do. Of course with any basement there are variations and mine is no different.
I live in Southern Ontario in a 6 year old home that I have been in since it was built. The basement is completely below grade with the exception of the top 12″ or so.
The builder insulated the upper 4ft of the basement wall with a pink batt style insulation which is held to the wall with a vapor barrier. The vapor barrier is sealed to the concrete wall at the bottom with some sort of seal and nailed directly to the concrete. The insulation and barrier extend right up into the joists where they are heavy duty stapled to the joists and flooring on the main level.
My question is can I leave that in place and install the XPS foam on the lower 4 feet of the concrete wall and seal it to the insulation with a thin section of vapor barrier and tuck tape.
I have gone ahead and unstapled the currently installed insulation vapor barrier in a few sections and found no moisture or mold in the insulation behind (either at the top or bottom). In fact the insulation feels brand new. The installer also did an excellent job as all the seals around the joists are excellent.
I understand that the best best choice would be to rip it all down and do XPS all over, but given the addition cost and labor to do so would I be taking a big risk to leave that insulation as is?
Thanks in advance for your advice.
Stuart
Stuart – Sounds like your builder did a great job. If you’re satisfied with the job then I’d leave it. Good luck.
Thanks Todd!
I was hoping you would say that.. It will save me a lot of grief..
This is exactly the same scenario and execution I am planning on doing… And searching for an answer whether this will be acceptable. I am in southern Ontario and most new homes are insulated this way.
This is an amazing reference website and thread. Thanks Todd
Hi Todd!
Thank you for your service. I was so glad to find your website and get definitive direction on properly insulating a basement.
I live in Michigan and am having my previously semi-finished basement redone. I have had some water leakage (cracks and rod holes) that will be sealed before insulating. Here are my questions:
1. Is spray on foam superior to rigid foam (i.e., is it worth the extra cost)?
2. How important is it to place the frame an inch away from the wall, and does the answer differ if I use spray versus rigid foam?
3. About 2/3 of my basement is already framed tight against the wall. Should I remove the frame (especially since I have had water leakage and the bottom plate is not pressure treated nor placed on composite decking material)?
4. I was not planning to drywall the foundation wall of my utility room and narrow storage room. How do I properly insulate these areas? I assume I should not leave them bare even though the outside walls of these rooms will be insulated?
5. Do I need to treat the walls or floor for any possible mold growth before insulating?
6. If I am installing carpet on the floor, how do I properly insulate the floor?
Sorry for so many questions, but I really appreciate your help!
Richard – Thanks for all the compliments. First off I would suggest fixing the leaks and waiting some time to be sure the repairs were effective especially seeing you want to use carpet.
1. Spray foam is definitely superior, it’s just a matter of cost.
2. The gap isn’t all that important when foam is involved, in fact, you can place the framed wall about a 1/2 from the concrete if you want and spray foam the wall in place.
3. This won’t matter if you choose spray foam. Be sure to check the plate for any rot.
4. If the outside walls are insulated you could leave them un-insulated.
5. You should check for mold before you start. If you find it the surfaces should be cleaned.
6. Check out my article on basement floors, http://www.homeconstructionimprovement.com/how-to-insulate-a-concrete-floor/
Good luck.
I am in the beginning stages of finishing a completely unfinishined/bare cement basement in Southwest Michigan. I read your articles on insulation and appreciate the tips, however I haven’t read anything on floors. Can you give me any suggestions on how or if I should go about insulating my cement floor.
Justin – Check out this: http://www.homeconstructionimprovement.com/how-to-insulate-a-concrete-floor/
I am a little confused. You state to install atleast 1.5 inch foam and seal alll joints to create an effective vapor barrier. How does the concrete wall dry up then?
Tariq – Concrete actually will never fully “dry”. In fact, you really don’t want it to. Concrete is created by a chemical reaction between water, cement (calcium and other chemicals), sand and stone. Water gets trapped in the micro-structure of the concrete and continue to react with cement particles for years. Water inside the concrete is actually a good thing! All we’re trying to do is keep the water away from the wall framing materials. I hope that helps.
Thanks for the great information. i’m starting my basement finishing project and am wondering if the fiberglass insulation you recommend installing in the wall cavity is supposed to be kraft faced or not? thanks for any advice.
Tike – It depends. The easiest answer is to read through the comments for several questions/answers that address that question depending on the insulation that you use.
Question,
You say to use spray foam and tape, is there something wrong with using some kind of caulk in the the tongue and grove as well as where the foam meets the floor?
Thanks,
Fred
Fred – Most caulkings don’t interact well with foam. Spray foam from a can works best.
You have lots of great info, hopefully I will explain my situation good enough so you can tell me what I shoul do.
Just bough a house in NY about 1 hr north of NYC,its got a finished basement no water on floor but, the sheetrock gets wet only at bottom.
Behind sheetrock is a foil like material with paper backing, behind that is plastic sheeting, the moisture is on the plastic and the painted concrete blocks, it runs down plastic and gets absorbed into bottom of sheetrock.
Should I remove plastic? If so I need to remove all sheetrock to get to it. If not where should all that trapped moisture go?
Thanks in advance
Lou
Lou – This is a classic example of what happens when moist air hits a cold foundation wall. The best solution is to remove everything and insulate the walls properly with foam (spray or board). You need both an insulation and vapor barrier to stop this problem. You could remove the lower couple inches of drywall but frankly the water/moisture is going to cause other problems. You’re better off fixing this situation properly.
We’re finishing our basement, and we have a vapor barrier installed against the concrete walls as advised. However, we’re using a foil-based radiant barrier instead of foam.
Does it matter then if we use faced or unfaced insulation between the studs?
Alex – In my opinion you’re asking for trouble and here’s why.
1. That foil faced radiant barrier is only a radiant barrier. It will still transfer the cold temperatures of the concrete.
2. If any moist, damp air passes through the fiberglass and contacts the cold foil it will condensate.
I would not use this method.
Hi,
Very interesting page.
We just moved into a house this winter. Now, with this weather, I start smelling something like water vapor(this what I think).This smell It is only in living and kitchen. This house it is not new. The basement it is finished but in an old stile like ’70 or ’80 with wood panels and carpet and no insulation against the walls. It is also the coldest place in the house.
What shall I do to get rid off this smell in the living and kitchen?
Do you have an idea what the cause could be?
Thank you!
Florin – Not sure what you’re smelling. Water vapor can’t really have a smell. Maybe you’re smelling mildew? Could be old carpets, mold, mildew or a number of things.
Hello, I am in need of some help. My wife & I live in a new home(2yrs) in Spruce Pine, NC. Because of the moisture problems of building a below grade basement, we built an above grade block basement with 8 inch hollow block walls, so our house actually looks like a split level. I have sealed the walls with a water-proofer & have no problems with water intrusion, the only problem we had this winter was that if the basement temperature was allowed to drop to 55 degrees the walls would start sweating and was actually causing some problems. The reason I have come to gather that it is sweating is because after we applied heat to this space, about 62 degrees the sweating stopped & the walls were dry. So now my question is what can I use to insulate these walls to make a living space & then not have to worry about the walls sweating?
Thanks for your help & God Bless
Jason – I would suggest insulating the walls with 1-1/2″ to 2″ of closed cell foam board, seams taped, then framing a wall in front of them. We have several articles on this site about that topic. The insulation will keep the walls from getting cold on the inside which is why you’re having sweating problems. The nice thing about foam board is it’s a very friendly DIY product. Good luck.
I am about to start my basement and have been going back and forth on whether to use a 4mil – 6mil vapor barrier plastic on the walls or use something from HD that is a 3/8″ pink insulation board from Dow. I was then going to frame and insulate the walls with faced insulation.
As a follow up to my posting, I read on the Building Science site that using 3/4 xps on the foundation walls along with 3.5″ fiberglass batt insulation would work well as long as humidity was kept low during the summer.
Does that include faced and unfaced batts?
Would 3/8 xps work?
Can I leave a gap between the xps and the studed wall?
Julius – Thanks for visiting the site. 3/8 xps really won’t cut it and frankly 3/4″ is marginal in my opinion. The foam board serves two purposes, first off if it’s thick enough (and most people argue about this but i say 1-1/2″ minimum) it will act as a vapor barrier so long as it’s truly closed cell foam, secondly the thickness creates a thermal break so that any damp air from the “warm” side that migrates towards the concrete will not hit a cold surface and condensate. Make sense?
I live in Pgh and purchased a home with a finished basement. Noticed some leaks under baseboard and had interior french drains installed. The basement is heated by furnace vent and gas stove and Air Conditioned along with dehumidifier. I want to reinstall the wood paneling that was removed to have french drains installed. Do I need to do the vapor barrier and insulation? I’d like to eliminate those to avoid future moisture problems. Thanks.
Carolyn – Where abouts do you live? Where is Pgh? If you live in a cold climate I would highly recommend that you properly insulate the walls. I suggest you consider using foam board (which we’ve written about quite a bit on this site) as an alternative that’s DIY friendly.
Thanks Todd – Pgh is Pittsburgh PA. I was leaning towards using the foam board, until the interior french drains were installed and the drain contractor said to attach 6 mil plastic to hang over concrete block wall 1/2″ into drain “trench.” My thinking was that since the basement is heated and cooled that condensation would be eliminated and the air flow between the block wall (without vapor barrier) and wood paneling (or drywall) would be beneficial.
Carolyn – The problem is this. If you heat the space in the winter, you have warm, damp air floating around. That air will get behind the paneling and come in contact with a very cold foundation wall. That wall will be well enough below the dew point for the warm damp air to condensate. I would highly recommend installing a minimum of 1-1/2 inches of closed cell foam on those walls prior to installing the paneling.
Thanks Todd. That does make sense. After much review, my question now is which is better, extruded polystyrene or polyisocyanurate for basement walls?
Julius – I like using xps, it’s cheaper and does what it needs to do. Polyiso is better suited for exterior wall applications where you can also take advantage of the foil faced covering for radiant.
Hello Todd, Just wondering if it makes any difference if the concrete foundation walls are exposed to the air outside or if the foundation is below grade. My house in Missouri has both, with the back wall of the house being a walkout basement with framed walls but the other three walls being concrete. The side walls have the grade traveling up the wall until it is fully below grade, and the front wall being completely below grade. I want to use foam board but am not sure if the exposure makes any difference as to the thickness of foam required. Thank You.
Mark – It doesn’t really matter that much. I always size the foam based on worst case, the exposed concrete. I say pick a thickness and use it everywhere.
Todd,
Thanks for the basement insulation info. I am in the planning stages of finishing my basement and wanted to know your thoughts on the following:
I originally had planned to put a 3 mil vapor barrier directly against the basement walls (painted concrete) and then frame while leaving a gap between the frame and basement wall and insulate with fiberglass batts. The rationale was the 3 mil vapor barrier would serve to protect the framing from any water intrusion (i.e such as the vapor given off from the walls as in your first figure). After reading your website I realized that this approach isn’t the best.
It seems that the key here is to separate the “interior” (i.e. the conditioned air in the finished basement) from the “exterior” (i.e. the basement walls and their associated moisture vapor) as much as possible.
That separation needs to be done both physically (vapor barrier) and thermally, something the vapor barrier alone doesn’t do. Without a thermal barrier there will be condensation on the interior side of the vapor barrier which can lead to problems.
Would it be advisable to put a vapor barrier directly against the basement wall, then put foam board against the vapor barrier and then frame and insulate as described? Would a second vapor barrier over the fiberglass and behind the sheetrock be a good idea?
Thanks in advance for your thoughts!
Jason N
S.E. Michigan
Jason – Glad you read it and understand it!! It’s a complicated thing to wrap your head around and you seem to have picked up on it.
Frankly the vapor barrier on the wall prior to foam won’t buy you much unless you’re going to use a layer of foam less than 1-1/2″. If you properly install a layer of at least 1-1/2″ of closed cell foam, tape all the seems, seal the edges with foam (spray foam in a can) then you’ve created a thermal and vapor barrier.
I prefer to then use a kraft faced insulation as it tends to breath better than poly. Also, if you can afford it, you can just use 2″ or more of foam and skip the fiberglass all together.
Todd i have a basement with cinder block walls. these walls are damp about 2 to 3 blocks up in some places. Also in the corners it goes higher in 2 corners 3 to 5 blocks high.Also i think i have an old french drain system.I say this because i found clay pipe about 4in below the footing.This was found while digging around the sewer outlet pipe. This house was built in 1956.I am going to have a new french drain installed with 2 new sump pumps.I am then going to finish the basement.My question is can i install riged foam about 2in from the block walls then frame it out?I figure this will let some air movement between the block and foam and keep it somewhat dry and stop mold.
Mark – Water won’t hurt the cinder blocks a bit. All concrete (which is the main material in blocks) contains water in the pore structure for years so the water is not a problem. Water also won’t cause a problem with the foam. That’s why we attach the foam to concrete and block walls. The foam will keep moisture from entering the finished space and keep it against the block/concrete wall.
It’s pretty hard to come up with a way to attach the foam 2 inches off the wall and keep it in place.
Todd,
I have a trench around the perimeter of my basement leading to a sump pump. I’ve lived in the house for two years and have never had any water problems thus far. How should I go about insulating around the trench?
Matt – I would just bring the insulation down to the top of it. Are you going to frame a wall?
Todd- Yes I plan on framing the walls. So with 1.5 inches of foam should I space the wall an additional 1.5 inches away from the foam? I believe the trench is approximately 3 inches wide.
Matt – Couple of options. You could do just that or you could install a piece of composite decking down first over the 1-1/2 of remaining drain, then frame on top of that.
Hi
I live in a colder northern part of Canada and I have a cinder block foundation that had many leaks and problems. To this point I have done the following. Dug up the outside of the whole foundation and repaired damages areas. Applied 2 coats of sealer around the footing and up 36 inches. I than installed Delta MS house wrap around the whole foundation right down to the footing. On the inside I have installed 1″ foam board and taped with tuck tape. I have the 2×4 framing up around 1″ from the foam board. My quetion is should I also put 6ML vapour barrier or just install the fiberglass insulation, than drywall.
Also any comments on what I have done to this point, weather it should be enough etc. would be appreciated.
Carl – Sounds like you’ve done a great job so far! Congratulations for fixing the outside problems first!
1″ of foam isn’t really enough to act as an effective vapor barrier on the concrete side. What that means is during the warm summer months moisture in the foundation could possibly permeate through the foam and enter the stud bay with the fiberglass. Because of that you’re going to want to use a vapor retarder and not a vapor barrier. 6 MIL poly will not let it breath enough. There are quite a few vapor retarder products on the market now that should work well. Ask you local building supplier.
The rest of it looks great.
Good luck.
I am currently in the middle of refinishing a finished basement. The house was built in the 50’s. It is located in central new jersey so summers are hot and winters are cold. The problem I have is that the wall studs were built up on the cement basement wall. I can not get behind the studs. First thing I was going to do is drylock the walls, then buy R-15 (used in this area), and install the insulation backwards, so the plastic vapor barrier is touching the drylocked cement wall. Then finishing with Drywall.
There is no signs of water damage. I do not think water is getting into the basement, however the floor does sweat when the air difference is great between the basement and the rest of the house. I am trying to for the cheapest solution to sweating floors.
Thank you in advance for your answer.
Ryan
Ryan – Your solution only solves half the problem. It will keep moisture from the concrete wall from getting to the insulation. However, it won’t stop moisture from the finished basement from entering the stud cavity, passing through the insulation, hitting the cold plastic and condensating inside the wall. What you need is both a vapor barrier and insulation at the concrete interface to stop both processes.
Todd,
Thank you…one last question (maybe)
I am not worried about the temperature of the basement. It is cool in the summers and warm in the winters. I am only worried about stopping the tile sweating. I would like to put a carpet down. Will insulating the walls help with the floor sweating. If not, I might just make the it easier and not insulate at all. Will Drylocking the walls, and running a dehumidifier, with the AC/Heat on upstairs stop the sweating enough that I do not need to worry about mold going under the carpet?
Ryan – It’s very hard to say. Sweating is based on dew point. While you might not be concerned about the walls what I’m pointing out is likely to happen. Warm in the winter inside the finished space can and will cause a problem as you described. Warm, moist air from the finished space, passes past the insulation and hits the cool/cold plastic that sits against the concrete causing condensation.
In the summer the opposite happens.
Insulating the walls will make a drastic change in your basement. Are you sure the floor is sweating or is moisture coming up through the slab? If a vapor barrier was not used that is a real possibility.
Drylocking walls won’t necessarily stop the situation on your floor. Dehumidifiers will help some but i’d be very cautious about carpet in a basement that clearly has damp/moist air problems.
Todd,
I’m planning on using 2″ square edge Dow foam (T&G was twice the price) insulation adhered to the block wall with adhesive and taped along the seams. I plan to leave at least a 1-1/2″ gap between the foam and the wall. I have extensive 3″ DWV pipe running along the walls.
1. Should I cut a channel for the 3″ DWV and fill that channel with spray foam?
2.
a. Since I’ll be paying only $18 a panel for the 2″ foam, should I place the rigid foam in the 3.5″ stud cavity, i.e.,
block wall–> 2″ XPS foam–> 1-1/2″+ gap–> 2×4 framing (rigid foam within the stud cavity with the foam pushed against the drywall, and a 1-1/2″ gap to the rear edge of the framing)?
b. Instead of placing rigid foam in the stud cavity, could I glue some 2″ and 1″ together against the wall with the seams staggered?
Thanks,
Ben
Allow me to clarify 2b
Can I glue 2″ and 1″ rigid foam panels together on the block wall and leave, leaving the stud cavity empty?
Ben – Square edge is fine, the T&G just makes it a bit easier during installation but it’s not necessary.
1. Not sure exactly what you mean. Are the pipes tight against the block wall? and therefore you’ve planning on leaving a gap at pipes and sealing along the edges?
2a. Depending on where you live 2″ of XPS is a pretty good insulation layer and you may not need additional insulation for the stud cavity. Having said that using another layer in the stud cavity is sure better than using fiberglass in there.
2b. This method would also work nicely and create an even better vapor barrier.
Thanks, Todd!
The pipes in some places are pretty tight to the wall. I was going to use a hot knife or something to shape the panels to fit around the pipes. What do you think about this technique? Should I spray some expanding foam behind them?
I still have to run 3″ drain pipe along one wall, but I would really like to keep that pipe pretty close to the wall. Would cutting the panels and sealing the gap between the block and the pipe with foam significantly compromise the barrier properties of the foam panels?
One more question: how critical is the gap between the foam and the framing members in the wall?
Thanks again!
Ben – If you can fit the foam tight and foam the edges that should work pretty well to lock out water vapor. The gap isn’t critical if you don’t plan on using fiberglass.
Todd do i have to use blue foam on my damp basement walls,or can i use another type then stud up aginst it and then use batt with a vapor barrer.I have seen pink,green,foil backed both sides and white,and the type they put behind siding,but no blue.Also i was told i could tar the inside wall then put plastic on the tar?.
Mark – The color doesn’t matter, pink and blue are typically XPS, closed cell foam. Foil faced is typically polyiso insulation, that works too. Be careful of white as it’s typically open cell foam board. I’d avoid putting tar inside your home. Good luck.
Todd,
Thanks for providing a wealth of info here. Back in March for the first time, I had some water seep into my basement which I refinished 15 years ago when I purchased the house in Queens, NY. The water entered at the bottom of the poured concrete wall where it meets the slab in a small area after a 3″ rain storm. I removed the drywall, 6 mil vapor barrier and insulation from between the studs which does not have any mold. However, some of the paint / moisture proofer applied to the concrete has spalled off in some areas near the bottom of the wall and the bottom plate, which I removed had some mold. The studs are about 1/4″ from the concrete which were in place with wood paneling from previous owner. I was going to cut 1′ off the bottom of the studs, install trex deck as you recommended, install pressure treated plate on top of it and splice in studs. Is it necessary to remove everything and install 1.5″ foam unto concrete wall and reframe and insulate? Do you have any recommendations to treat the seam to prevent water from penetrating again?
Thanks, Peter
Peter – Sounds like you’ve been quite fortunate with a relatively dry basement. 15 years is a good run!
First off the water issue. Sounds like this was caused by a very rare large rain event. I’d say the best approach is to evaluate the outside of the house, gutters working? grade sloped away? any cracks in the foundation? settling? etc. Deal with any issues you may have outside.
Sealing inside at the base of the wall is probably a futile attempt but I suppose it doesn’t hurt to try and seal that joint with a good quality masonry patching materials.
Why are you removing the lower foot? Rot? Mold? Damage? If there’s no damage that may not be necessary. The bigger issue is whether to leave the walls in their current position or to move them. You could install foam board between studs in lieu of fiberglass. This won’t create a tight barrier but it seems as though your moisture problem isn’t too bad.
Or you could cut free the walls, move them forward, add a layer of foam and go from there.
Hope this helps.
Todd what is the thinest rigid foam i can use over my damp walls since i am also going to add batt.
Mark – you really need a minimum of 1-1/2 to create a vapor barrier.
Todd,
Thank you for the great articles. I’ve read both this and your basement floor finishing article in preparation for my basement repair (in southern New England.)
We have had a few intrusions of runoff during bad storms recently, and as a result I need to repair/replace at least the bottom, below grade half of our finished basement walls. I would like to avoid whole-wall replacement due to lots of soffits and trim up at our basement ceiling which would add complication/cost to the project. We have never seen runoff damage or condensation higher than about 12″ off the floor, and I’ve verified there is no seepage on the bottom 4′ of wall with the aluminum foil test.
The interior walls are currently just drywall attached to 1×3 firring strips, which are attached directly to the concrete block wall. No insulation, no vapor barrier. Since I am not planning on replacing the whole wall, what I’m hoping to do is take down the bottom course of drywall, and cut the damaged firring strips off. When replacing these parts, I was thinking of first adhering a 6 mil poly barrier to the concrete, then installing new pressure-treated 1×3 firring strips, and putting 3/4″ XPS foam in between these strips.
I realize this is not really insulating the wall since I’m leaving the top half, which is all above-grade, untouched, but I figure something is better than the current nothing. Also, the poly against the concrete, covered by foam, will make me feel better about condensation, which we had on the bottom 2 courses of block in the summertime before we started using a dehumidifier. Maybe help that dehumidifier not run so much? :)
Could I have your thoughts on this approach?
Thanks,
Mike
Mike – Thanks for the compliments. Honestly I think that you’d be wasting the foam board. Frankly having 3/4″ part way up the wall and fit between firing will likely do little good and it may just trap water against the strapping and drywall. I think you’d be better off trying to stop the water problems especially if they can be corrected outside. Can you remove the wall from the soffit down? That’s maybe a better idea and get a good layer of insulation in there?
Thanks, Todd. Yes, I probably should have mentioned that we are taking big exterior measures, including regrading the soil near the foundation, adding a French drain to divert some runoff that comes down a hill towards the home, and tying our downspouts into a drywell/pipe system that should pull the water past the house rather than allowing it to pile up alongside. I’d also like to dig around and waterproof the exterior, but the budget won’t allow it – it would involve getting under a crawlspace to the true foundation footer in one area of water intrusion and moving a small back deck in another area.
Is just insulating from the soffit down that much better than my original halfway-up idea? I’d still be leaving an area of the above-grade wall uninsulated. I guess I see that it would be a smaller portion and the extra “stuff” around the soffit would give me some more insulation, but if it’s not significantly more than my first idea I’d probably rather save the materials cost and time.
I would love to just pull everything down and start from clean concrete, doing the 1 1/2″ of foam, etc. but in addition to the soffits and stuff at the top there’s also an 8 foot baseboard heater I’d have to work around. And I don’t feel like draining the system to move the pipes out from the wall. Unless I could recess the heater slightly in the finished wall? I’ve never seen that done – do you think that’s possible?
Mike – Sounds like it would be a rather big job to take it all down and start over. Then again, might be worth it. What if you do the exterior repairs and wait a year, see if water comes back. If water doesn’t come back it might be worth spending the time and money to move it all. Having a plumber come in and move that 8′ section wouldn’t cost too much.
Thanks again, Todd. Sound advice. I very much appreciate you taking the time to respond to all your readers’ comments.
-Mike
Todd:
I have a new constructed home with poured concrete basement walls. Basement is rough plumbed for one full bath. I will be insulating the full basement including walls and floor. I plan to insulate the floor with 1″ thick T&G foam panels with OSB overlay (like you have explained in another article, or maybe even use the “Barricade” brand subfloor system). Then I will insulate the walls in a method you have recommended with 2″ thick foam board. My only real question is related to the basement wall surface: It was formed with a faux “brick” surface. Will this be a problem with the obvious gaps between the faux “brick” concrete wall and the foam board?
Jay – Was it just a form liner? Meaning is it concrete that just has a surface that looks like brick? If so that’s fine, I’d only worry if it was a material that might mold.
Todd,
I am finishing my basement in Iowa. The builder had framed the entire basement leaving less then a 1/4″ gap against the concrete. They then put r13 unfaced fiberglass between the studs and covered with a vapor barrier. Everyone (including the wife) says to just leave that and put up the drywall. Spray foam for the entire basement would be pretty expensive. I was thinking about putting 2″ xps between the studs and spraying the gaps. That would give me R10. That would also leave a 1.5″ gap between the xps and drywall. The hardest part will be behind the tub surround which is already installed and has the fiberglass/vapor behind it. Should I rip that out if I can get to it?
Jeff – If you leave the fiberglass I can pretty much guarantee you will get mold. It’s been well documented and proven time and time again.
I would say you have 3 options.
1. Remove fiberglass and poly. Have the stud cavities spray foamed. (Most expensive but best solution)
2. Remove fiberglass and poly, cut loose walls, move walls forward a couple inches, install 1-1/2 to 2 inches of foam board, seal, re-attach walls, then sheet rock.
3. Do as you’ve indicated above, fill stud bays with foam. This solution will work fairly well but it doesn’t create the best vapor barrier. It’s not an approach I would do in my home but it’s certainly better than fiberglass.
Good luck.
Todd, thanks for all the great articles. My mind is swimming with a problem I am trying to fix…I have a 20 year old home. The basement is 3/4 finished with 6 mil plastic vapor barrier, then studs with fiberglass insulation. We have been here 7 years with no moisture or mold problems. Last year I finished a room. I did not use plastic (I was told that was a bad idea). I coated the exterior cement block walls with DryLock. I have the studs up against the walls (some spots there is a 1/4″ gap but that is due to irregular shape of the cement block walls). I put R-13 faced insulation between with the face on the exterior wall (oops!!!). I started smelling mold/mildew and pulled off some drywall. There was evidence of condensation and some mold. I pulled off ALL the drywall and insulation and cleaned the walls (spotty mold, not too bad). Now here is my dilemma. How can I FIX this with what I have in place? Can I put 1″ foam board between the studs and use great stuff or caulk in the cracks (I can squeeze it in the gaps behind the studs too), then use R-11 or R-13 (I’ll only have 2.5″ left after the foam)? If so, should I use faced or unfaced (with the paper toward the warm side!?!)? I have also already finished the ceiling with drywall and don’t want to pull it down. I used fiberglass in the rim joist gaps (I should have read your stuff first). Can I have holes drilled and foam or cellulose blown into the gaps?? Ultimately, we have had no problems at all and it was all done the “old way” with the plastic and fiberglass…was my main problem that I put the facing the wrong way?? I have seen no reason inside or out that the walls in questions should be any different than the rest of the basement. Please help!
Tom – Sorry to hear about your problem. In order to fully answer this it would be very helpful to know what part of the Country you live in. I’m a bit surprised that the old method worked as well as it did, but that may in part be due to where you live. Let me know where you live and I can better assist you.
As a followup, I still have 1/4 of the basement unfinished. It is untreated, unpainted cement block. Do I need to put anything on that or can I insulate the interior walls that separate it from the rest of the basement and just write that off as a ‘colder” space (it is just storage)?
I live in SE Michigan, so I too am surprised we have had no problems with what had been done already…
My question now is, since the condensation was on the “cold” side of the facing paper (against the cement wall), then if I put foam up against that, or plastic, won’t I have the same problem, just mold between the wall and the foam??? Will it be different if I put the facing toward the inside (to prevent warm moist air from coming into the wall space)?
Tom – Based on how your existing walls are insulated I would conclude that most of the moisture is coming from the cool/damp concrete wall. So, having said that, if you were to install foam (I’d recommend 1-1/2 to 2 inches) board in the stud cavities, foam/seal the edges, you should be able to stop the moisture from getting to the back side of the drywall and causing mold. In your situation I’d skip the fiberglass and just install a good layer of foam board.
Good luck.
Thanks. I talked with an installer today and he suggested the even foam board would allow a small air cavity where mold could grow. Is that true? If so, I will spend the $$ and have spray foam (closed cell) applied as that will adhere to the walls, fill gaps behind studs, and prevent any moisture. I was told that TigerFoam sells a kit online for about $300 that will allow me to do it myself if I want…Any advice?
Tom – First off mold needs food. If you seal the foam then there’s basically concrete (mold can’t eat concrete), foam (mold can’t eat foam) and then small strips of the back of studs. Mold could eat that. The reality is if you install a thick enough layer of foam it will stop moisture from getting into the stud cavity where the mold would be a problem on the back of drywall, etc.
Just to clarify, the mold was on the facing paper that touched the concrete, not the back of the drywall. Does that change anything?
Doesn’t really change things.
I read a post about my question, just didn’t see answer.I have a poured wall with a brick coarse on the inside,(very Rough) how do you apply foam to that surface? I understand that by using 2″ foam i will not need to add any plastic as a vapor barrier is that correct? Thanks
Todd – You can use Great Stuff Pro – It’s a spray foam adhesive in a can and it works very well. You are correct…no need for poly. Just seal all the joints very well.
I live in minnesota I have 2 and on half inches of spray foam on the outside of some of my foundation it looks ugly can I scrap it off and put something over it and if I can what?
Mike – Now that’s a first, haven’t really seen that before. Is it insulation or some type of water proofing membrane?
it is insulation you can tell it was sprayed on but has bulges all over so it looks ugly only on the heated basement walls any sugestions the house next door has the same thing
Mike – I suppose you could try and scrape it off and install foam board. If you do that it can be stuccoed over for a nicer appearance.
thanks one more question do I need that on the out side wall.
the basement is finished and heated ?
thanks for you quick response
Mike – Really depends on how much insulation is on the inside and if you’re willing to give up such a good layer of insulation that currently contributes to a warmer basement.
Todd,
I have a walkout basement made from block. Currently there is a window and door on the back of the basement (walk out) area that was framed out in 2x4s with batt and plastic over top. I plan on putting 1.5 inch foam around the perimeter of the basement with a 2inch gap between the foam and the wall frame, then insulate with faced batt, possibly R13. I was wondering what to do around the window and door that already have the insulation and vapor barrier? Do I not put the foam over top of this, but then have the R13 in the frame? Would this be a double vapor barrier? Thank you.
Derek – You have a couple options.
1. Leave it as is.
2. Remove the poly, install the foam over the fiberglass, install extension jambs on the doors and windows.
I’d go for option 2.
Todd,
I live in SE Michigan have a 7 year old home with a poured concrete basement and no moisture problems… yet. I am beginning to finish it. I was planning on leaving the ceiling open and spraying it black. I’ve studded the walls, but not secured them in place yet. Based on your comments and articles, it’s clear to me I need to use 1.5″ to 2″ of foam insulation against the concrete and no additional vapor barriers. Then leave a 1″ gap to the back of the studs. My questions:
1) Where the wall meets the ceiling do I need to do anything special to seal the backside of the wall from the rest of the room? Or is it advantageous to have the additional airflow allowed by not closing it with a ceiling? (seems like the latter would be true)
2) I have a storage closet (8sqft) & a storage room (200sqft) that I didn’t plan on insulating. Is there a good way to transition from the insulated concrete to the uninsulated concrete?
3) The walls are already studded w/o a composite board on the bottom to stop wicking. Would a strip of 4mil plastic beneath the PT2x4 provide the same benefit? Or not necessary?
4) Is polyiso worth the extra money for its higher R value per thickness? If I went with polyiso could I use a thinner layer attached to the concrete and achieve the same thermal/vapor barrier? Or is the 1.5″ thickness a guide for vapor permeability mainly, and polyiso maybe isn’t better at vapor, only thermal??
5) To keep from a 7″ thick wall (2″foam+1″gap+3.5″stud+.5″DW) I was considering only putting foam insulation between the studs, sealing between the wood/foam gaps and adhering the foam to the concrete. However, does having an open top to the wall (unfinished ceiling) expose the backside of the studs to mold? Or are the studs less susceptible than the drywall?
Sorry for so many questions, and thank you for your clear answers.
Ben. Thanks for stopping by and posting your questions. Below are a few thoughts on your situation.
1. I would be sure you insulation up the entire height of the concrete wall, over the top edge of concrete and then up the entire height of your rim joist. What you want to avoid is gaps in your insulation/vapor barrier. It’s important that all seems are sealed well.
2. Again the idea is to create a good continuous barrier around the entire basement as best you can. Sometimes this is difficult to do at utilities and stairs but the more you do the better. If you’re going to skip those rooms I would be sure that the interior walls of them adjacent to insulated concrete walls are also insulated.
3. The composite board “trick” is a nice thing to do but not 100% necessary. You could also use a role of Vycor (or similar) and adhere that to the slab under the bottom plate.
4. In some situations polyiso is actually cheaper. I would go with which ever you can afford but stick with the minimum 1-1/2 inches.
5. The 1 inch gap is 100% necessary, again, it’s a nice to have feature. You can install the framing up tight to the foam especially if you’re not going to insulate the cavities with fiberglass. I prefer not to do the “between” studs method unless it’s the only solution available, just not as good of a system and prone to air leaks and vapor movement.
Good luck!
Todd,
Thank you very much for all the information you have supplied. I live in Central New Jersey and I am trying to finish off my basement. To help with flooding, I had 2 sump pumps installed. They also broke up the floor around the edges and installed a drainage system where the channel is approximately 3/4″ away from the wall and 1-1/2″ high. I am trying to finish off the basement and just started researching the framing and sealing. I have painted the walls with drylock but I am still concerned with mold forming behind the walls after they are up.
1. You recommend using Spray foam insulation as your top choice. Will it prevent mold from forming? Also how do I accommodate the channel with the foam? Do I cover it and spray over it or just go directly to the channel and make sure not to get any in the channel?
2. If I go rigid foam, can I put it on top of the channel or do you recommend cutting out an edge on the bottom of the foam so it forms around the channel and goes directly to the floor to create a solid seal? Does this prevent mold from forming between the cement block and the rigid foam since there is limited air flow?
Ken – Do you have any photos of the channel? Photos might make it easier to evaluate. My first thought/question really is how much water does your basement get? If there is a continuous amount of water seeping into the walls then you might want to pass on finishing your basement. Or is the water entering at the base of the wall? The answers to your questions really depend on where the water is entering and how much of it there is.
With either product I’d try to avoid blocking off the new drain.
The water is not continuous. On heavy rain storms I have the sump pumps going off sporadically. I had the Watergaurd solution installed. This is the website of the product. http://www.basementsystems.com. They drilled a hole in the bottom of the cinder block to prevent them from filling with water. How would you proceed? The other part of my basement is a floating slab with a 3/4″ gap. There is no water problems on that side.
Ken – I think for your situation I would go with foam board. This way you can install the foam board and let it over hang the newly constructed channel. Then frame your wall out from that as well. This way if water does get behind the foam it can drain away. The beauty of the foam is it won’t support mold growth. You want to keep that water behind the foam and next to the concrete/block wall.
Todd,
Thanks for this helpful site.
I live in the St. Louis area. I am starting to finish my basement. I’ll be using you rigid foam method.
1. There is a 1/4 ” gap between my basement floor and the wall. I know it’s open to the soil below, because bugs get in, and a little moisture, but not much. What should I seal this with. Great Stuff? Or that rubbery concrete sealer that comes in a tube like caulk? Or what else?
2. There is a crack in one wall and a fair amount of water gets in there when it rains hard. On the other side of the wall is below my kitchen. There is no basement under the kitchen. So it would be very difficult to seal the crack from the outside. There are companies that advertise that they can seal this type of crack from the inside. Any good? What system would you recommend?
Thanks in advance for your reply.
Tom – First off thanks for the compliment. I hope you sign up for our newsletter.
1. I would leave the crack alone in case you do get water so it can drain. Just let the foam board come down on top and rest above it.
2. Sealing a crack from the inside is very difficult and sometimes impossible. First I recommend you concentrate on isolating the water outside, is there a feature that’s causing excess water to pool in that area? Can you add gutters or regrade the site to move water away? After that there are some epoxy injected systems that work fairly well but they can be hit and miss.
Good luck!
Hey Todd,
Can you spray foam over XPS foam board and should I foam the entire sill/band joists? Is rockwool a good alternative?
You should foam the entire rim joist. I’m not sure if you can spray over xps, however, most one part sprays in a can work fine. Rockwool wouldn’t be my first choice but it’s better than fiberglass.
Hi Todd,
I began a basement remodel and then happened to see this site. I live in SE Michigan. I first drylocked my basement walls to control humidity, then applied 1/2″ of rigid foam insulation to the concrete walls. I left a 1″ air space and have my studs in place. After reading and noticing your 1 1/2″ min. recommendation on the rigid foam insulation, I am wondering what your suggestions would be to remedy and finish what I already started. Also, after placing my rigid foam insulation, do you recommend that I spray foam the 1/4″ gap betwwen the bottom of the rigid foam insulation and the basement floor? Additionally, I was not going to add any batt insulation beween the studs, is this a good idea?
Thanks, in-Advance.
Ali – I think what I would recommend for your situation is this.
I would install an additional 1 to 1-1/2 inches of foam between the studs. I would completely skip fiberglass and stick with just foam.
I would not seal that bottom as it’s a good way for water to get out if you get any behind the foam.
Good luck.
Todd-Thanks for your response.
I have one more quick question. Does it make a difference which way I install my rigid foam board against the concrete? The foam board has a foil backing on one side and it is blue with the company logo on the other. I installed it with the foil facing toward the concrete beacause of a a source at the hardware store. This foil seems to have a paper-type backing and is easy to tear. I am now concerned that this paper-type foil will have a tendency to mildew against the concrete over time.
Now I am hearing that I should have applied the foil facing toward the air space and the blue side with the company logo toward the concrete because it has more of a plastic material. Should I just completely remove this material from the concrete wall and just stick with the insulation between the studs?
Thanks again.
Ali – The foil typically faces the conditioned side (finished side) as it acts like a radiant barrier. I would check the manufactures web site for some insight as to whether your installation will lead to a problem. My guess is it might be ok unless there is a high “paper” content to that material.
Todd –
My house was built 10 years ago and I have a walkout level ‘basement garage’ beneath my 3 stall garage. I live in Minnesots.
The basement garage has pre-cast concrete planks that form the upper garage floor and the basement garage ceiling. The outside perimiter has been professionally waterproofed with drain-tile installed. The floor is heated in winter with a hydronic system. The inside of the basment garage area does not have any signs of leakage from outside, but in the summer does feel damp due to condensation. I expect much of this might be due to limited airflow with concrete block walls, concrete floor and a concrete ceiling.
My question is whether you have any specific advice for finishing this space. I would like to add some insulation, frame it, sheetrock it and use as a workshop. Do you have any recommendations on how or whether to use a vapor barrier on the concrete ceiling? Also, I was wondering if you ever recommend using a product like DryLok, or if it causes more problems by inhibiting the concrete wall’s ability to ‘breath’?
Thank You
Mike
Mike – Your situation is a bit unique but the same principals apply. I would definitely consider installing foam board insulation on the walls followed by framing. Check out some of our articles on insulating basement walls in that fashion.
I would also use the same approach with the ceiling if you can figure out the connection details otherwise leave the ceiling alone.
The biggest key for that space is air exchanges but I have a feeling you can deal with that with your dust collection.
Thanks for the quick response. Just one more quick follow-up. Regarding the concrete ceiling… I may just do as you suggest and “leave it alone.” Would you have any concern with painting it? I think white paint would do wonders for making it brighter.
Thanks
Mike
Mike – Painting it is fine, just be sure to use an appropriate paint and primer so that it lasts.
Todd,
Thanks for taking the time to maintain this site!!! What a wealth of good knowledge here. My project for today was to finalize my design for how to insulate my basement. I think I have found the right place!!!
Looks like it will be later today or tomorrow before I can get you some pictures for everyone to look at…but I will start with some history.
I live in the Fargo, ND area…so keeping the cold out is my focus. Basement has been completely redone structurally due to flood damage 2 yrs ago.
Basement is a walkout on one side, one side has grade sloping up and the other two sides are completely below grade.
Walls are poured concrete. Exterior was excavated and walls sealed, drain tile installed and class 5 put back against the walls.
Waited a year to begin finishing basement because I wanted to make sure we didn’t have any leaks or other booboos. Looks like we are tight.
Basement slab was removed and replaced due to cracking. Interior drain tile and two sump pumps were installed along with lots more class 5 and pea rock to make sure there is good drainage under the slab.
Hydronic heat is under the slab. Eventually think we will have ceramic tile on most of the floor.
1. The unique feature that I am trying to incorporate in my wall design are 6 inch steel ibeams that were installed vertically on either side of wall openings and. Good thing is that I have a nice 6 inch cavity to fill with insulation.
After reading your blog I’m pretty set on 2 inch rigid foam. Question is does it make sense to double up and get 4 inches???? I will make sure all seams are sealed good.
Will have to get you some pictures of the ibeams later…but be thinking if I should spray foam the edges of the ibeams. Not possible to get behind the ibeams.
I have one set of stairs that are going to be hard to insulate and finish. I’m thinking about biting the bullet and sprayfoaming those areas to maximize my insulating power and minimize thickness.
2. I have seen one or two people ask about do it yourself spray foam kits but don’t think I have seen you respond. Any thoughts on those??
3. It seems like you have indicated that adding fiberglass insulation in the 2×4 wall cavities after properly putting in rigid foam board is a waste of money. Just want to confirm this is you are saying.
Thanks
Allen
Allen – Thanks for the compliment.
Sounds like you’re on the right path. 2 inches of foam is great, 4 inches is twice as good. As you’ve pointed out the steel beams are the real trick. They will be very cold and any moisture that hits them will want to condensate. Any chance you could box around them so you can continue the 2 inch foam around them?
2. Most of the DIY spray foam kits have started disappearing from the market due to all the crazy rules and regulations around VOC’s. I think they are great for small little areas but it’s something that you really need to be prepared and spend some time researching how to do it.
3. Not necessarily. Adding fiberglass can be a good financial alternative if the first layer of foam is thick enough (minimum 1-1/2″) and sealed properly, and no risk of flooding.
Hello Todd, I have a century old house built on a stone foundation with a dirt floor. Sometime the top three or four feet of the rock wall was taken down and replaced with block. Would it prevent heat loss if I insulated the top three to four feet of the wall.
MIke
Mike – Any insulation you had will certainly help, especially if that upper portion is exposed above grade.
hi todd. you’re site has been a guide for me. i gutted my basement and basically followed your instructions. i’m in salt lake city, utah so the winters are pretty cold. i’m installing a shower in my basement. i’ve done the rigid foam on the walls and for all the framing i’ve installed fiberglass bats. now i’m just working on the bathroom. should i put a vapor barrier on the exterior wall of the bathroom? should i put it just on the walls of the shower? the humidity is low but i purchased the house a year ago and the previous owner had plumbing leaks and foundation leaks so i had some mold which i got rid of when i gutted the thing. i’m just nervous not having a vapor barrier for the bathroom. vapor barrier in the bathroom or no vapor barrier in the bathroom?
what say you, insulation guru?
thanks
mark davis
Mark – I wouldn’t use fiberglass in the walls of the bathroom, I’d stick to just foam board and call it quits.
I live in Minnesota and about to install 1 1/2 inch rigid foam on the concrete blocks of my basement.
First question: is there a significant difference between 1 1/2″ and 2″ rigid foam board that I should reconsider using 1 1/2″ and use 2″? I plan on framing my wall 1″ from the foam board.
Second question is: what is the best way to seam the vertical seams and the top/bottom of the foam board.
Would you recommend leaving a 1/4″ gap on each side of the foam board and filling the gap with expandable foam as opposed to using tape that could fail over time?
I noticed in a previous post that you recommended against using expandable foam on the bottom, does that advice also apply to the top of the foam board? If I didn’t seal the bottom of the foam board wouldn’t that allow moisture to enter enter the wall cavity and possible cause mold growth?
Thank you in advance
Mark
Mark – 2″ foam board is definitely better and I say use it if you can afford it. It’s a better insulator obviously but also a much better vapor barrier.
I really like using Tyvek Tape. You’ll be very impressed on how well it seals to foam board.
As far as the top and bottom it’s really up to you. I’ve mentioned to some people that leaving the bottom isn’t a bad idea if there’s any chance of water getting behind there to allow it to escape and also let you know there’s a leak. If your basement is fairly “dry” then it won’t hurt to seal the bottom.
Todd: The builders installed my electrical panel to a piece of particle board attached to the concrete wall. Can you install the foam board over the particle board and around the electrical panel? Or should I have an electrician uninstall my electrical panel, I install the foam board, and finally have the electrical panel reinstalled on top of the foam board? I live in Eastern Pennsylvania and the climate is cold in the winter.
Second, I am framing around the furnace room (contains furnace, hot water tank, and an 8 x 8 foot storage area). Can I leave this area unfinished (poured concrete floor and poured concrete/block walls) and use fiberglass insulation between the wall studs?
Brian – Couple thoughts.
1. The electrical panel is something that most builders never consider and I wish they would all start putting 2 inches of foam board up before the darn plywood panel. At any rate you have a couple options. A – Do nothing and just insulate up to the OSB and leave that small area un-insulated. B – Most new panels have all the wiring coming in to the top and sides. So you could technically remove the screws in the back of the panel, pull it forward, slip a piece of insulation behind it, and re-install with longer screws. If you’re not VERY familiar and VERY comfortable working inside a panel box I’d suggest having an electrician do it. Even if you get a piece of 1 inch behind it that would be better than nothing. Frankly I think I’d just leave it alone and think of it as similar to a window. Windows have a very low R value and we live with them..just a thought.
2. That will work ok. Just remember, the furnace is likely to give off some heat so it’s difficult to say exactly which side is the warm/cold for vapor barrier issues. If you’re going to do this approach I’d use kraft faced fiberglass.
Good luck.
I find your articles very helpfull on basement finishing. I plan on finishing our new home basement in NE Pa soon. I do have a pretty good understanding from what I have read so far, and plan on installing 2″ foam to the block walls and studding the walls out for future drywall. However I do have a few questions. (1) I plan on installing rubber belting material under the treated two x four at the floor to prevent any moisture from absorbing into the wood (are you for or against this ?).(2) Also still not sure if I need to leave a space between the foam and wood framing with fiberglass insulation? (3) not sure if a plastic moisture barrior before the sheetrock is best or fased or non faced insulation? Also planning a drop ceiling. Are there any types advatages for non absorbing for this application?
Thanks ahead of time.
Mike – Thanks for the kind words.
1. Rubber belting is an interesting idea. I’m sure it will work fine. We use composite decking simply because it’s easy to work with.
2. If you’re using 2″ foam then there’s really no reason for a gap and frankly you may not need fiberglass. Have you checked to see if your energy code requires a certainly level of insulation? If there’s no need for more R value then I’d skip the fiberglass.
3. I would NOT use poly in a basement. If you do end up with fiberglass then use kraft faced or unfaced.
A couple of other ideas poped into mind for your comments. I haven,t read any opinions on the use of metal studds and moistue resistand sheetrock. Please comment on the use of these in a basement application. Thanks again
Mike – Metal Studs are an option if you’re got plenty of insulation behind them. If not you’ll have a serious condensation problem. Moisture resistant drywall is obviously a good choice, just a matter of cost.
Hi Todd — great site; very informative!
Do you recommend Drylocking a concrete block wall before installing the foam board, framing, etc?
My basement has had some obvious moisture issues over the years (bottom third of wall has efflorescence and the hot water baseboard radiators (attached directly to the block walls) have rusted through in spots).
I think most of this was due to the extensive shubbery and poor grading of the yard, which I have since fixed, so I don’t think that the basement should have any major future moisture issues — but I want to do everything I can so I don’t have any problems down the road.
The walls already have a thin coat of cement (or something) that give them a smooth appearance, but I was wondering if using waterproof paint before insulating and framing would help or hurt (or do nothing).
Let me know what you think —
Thanks!
Tom
Tom – I typically say skip the Drylock but in a situation like yours it certainly can’t hurt. While I don’t particularly subscribe to sealers as I think it’s nearly impossible to stop water pressure at depths of foundations I think it can be a good belt and suspender approach.
I wish there were more web sites as informative as this one! I live in Northern Michigan and plan on finishing half of our basement this spring. Basement walls are block, walkout on the west end, a small portion of the south wall also above grade. What is your opinion of filling the void space within the blocks themselves with spray foam or granular product? Would this be beneficial to do in addition to the method you recommend? During the coldest part of winter, I get ice crystals in the southwest corner (the only corner that is exposed, above grade) and am unsure that 2 inches of foam will do the job. Any thoughts?
One more question: Is the foam board fastened to the block wall using construction adhesive only, or should it be screwed or nailed to ensure that it stays in place? Thanks for such a great site!
Greg – Thank you so much for the kind words.
I’m not sure that you’d be able to easily fill those voids and frankly the effort might not be worth the results.
If you’re not sure 2 inches is sufficient (which it may not be by code) then you can either add another layer or you could use fiberglass in the wall framing after the 2 inches.
We just use adhesive (Great Stuff Pro works wonderfully).
Best of luck!
Thank you for the informative site.
I live in central Michigan and have recently begun finishing my basement–beginning with an additional room which is now complete.
The basement is, as usual in this area, rather high in humidity year round. Recently we installed an interior drain system that has seemingly resolved the previous standing water issue (which was not severe) due to the constant hydrostatic water in the general area.
Given the moisture concern, the contractor who assisted with the project suggested and installed the following:
1. 3/4″ 1″x2″ furring strips were installed 16″ OC directly on poured concrete wall using Tapcons.
2. 3/4″ thich foil faced XPS was cut and snugged in between the furring strips. (Foil side facing towards the interior)
3. 6 mil clear plastic sheeting was then applied over the board and XPS.
4. 5/16″ thick cabin grade T&G pine boards was then installed over it all (we were going for the rustic look…and it turned out visually exactly as we desired)
The purpose of using the foil face and the sheeting was to establish a vapor barrier. However, having read your article..I now wonder if this was a bad idea. I’m unclear as your article suggested that if one were using less than a 1 1/2″ rigid insulation, then a vapor barrier may be the next best choice.
Also, what are your thoughts on the foil faced? Will this combination result in vapor lock and create havoc?
I need to finish off the rest of the basement and planning on the same scenario unless otherwise advised.
Thank you in advance. (You won’t hurt my feelings if you tell me that this was a big mistake…I just don’t want to make it twice if that’s the case)
Steve – Thank for the nice compliment.
Your situation is a bit unique for one main reason – You’re Not Installing DRYWALL!. While I’m not sure your approach is the best given the area you live in I’m not sure it will lead to any severe problems. Here are my thoughts just talking out loud.
1. Your system doesn’t provide very much insulating value. Foil faced polyiso (if that’s what you have) has an R value of 7 to 8 per inch (see this article for more info, http://www.homeconstructionimprovement.com/foam-board-insulation-values/ ). So effectively you have an r value of about 5 to 6 (if it were continuous and yours is not, strapping in between).
Most new energy codes require significantly more R value than that. While I’m not sure what is required in MI I would imagine it’s more.
2. The way that you’ve built it I highly doubt much water vapor could get from the foundation to the T&G wood siding. That’s a good thing. I also doubt much water vapor from the finished space will end up trapped behind the T&G as it will breath pretty good.
3. If it were my basement, you could use a similar approach on the next section with some better details.
For instance, why not install at least 1-1/2″ of continuous foam (2″ would be better). Then if you don’t want to frame a wall install the same wood strapping OVER the foam with longer nails. This provides a continuous layer of insulation. Then install your wood.
I hope this advice helps. Good luck!
Todd
Great insight on basement insulation. I’m getting ready to finish my basement (live in NW Ohio) and want to make sure I understand you correctly:
1. Use a minimum of 1 1/2″ thick Dow blue board glued directly to the poured walls.
2. Tyvak tape the seams (the local lumber yard told me Dow suggests NOT to use a tapeon seams?)
3. Install studs in front of the blue board using a composite board below the treated lumber board for the base (is plastic necessary between?)
4. Insulate the stud cavity after the wiring is complete and before drywall is installed.
If I were to only use 3/4″ Dow blue board would you advise plastic sheeting between the blue board and the studs? If so what mil?
Thanks in advance for your advice.
Bryan –
1. Use 1-1/2″ minimum closed cell XPS foam (blue, pink, doesn’t matter the brand).
2. There are some people that say Tyvek tape shouldn’t be used, we’ve never had trouble with it. There are several similar house tapes available, some are read, but they are all pretty similar and they stick VERY well to foam board. The idea is to seal it well.
3. No plastic.
4. This is optional, the best approach is a thicker layer of foam and no fiberglass. The fiberglass is an attempt to keep costs down.
5. I would NOT recommend 3/4″ as it doesn’t provide a vapor barrier AND if you use only 3/4″ it may still be “cool” enough to allow the sheet of poly to be near the dew point. If water vapor hits that poly it will condense. So I would NEVER recommend that detail.
Good luck!
Getting ready to finish my basement in southwest michigan. I have a walkout that has 2″ x 6″ framing that are still open no insulation or drywall. I need to insulation these walls and I plan to lay brick on these walls what is my best options for this. Also I have block foundation and i want to lay brick on these as well what is the best bet for insulation. Thanks
Tim – Is the brick interior or exterior? Probably foam will be your best bet.
I have a friend who said to just use a 2×4 frame, fiberglass bats and no vapor barrier. This way the moisture can freely move in and our through the walls. This has worked without issue for about 20+ years now at their house.
I am seriously considering using your method, but am a bit afraid if I miss a little spot then I could have a huge mold mess down the road. Valid concern?
Also, just to get it straight in my head. The foam board will obviously be in contact with moisture. Mold won’t grow here or if it does it isn’t an issue because it’s sealed off from the inside?
Jason – There are definitely basements like that without problem. However, there are lots of reasons why older buildings worked and today’s newer one’s won’t. At the very least that “old” method is very risky.
Foam board won’t “feed” mold growth and once you seal it all up it’s not a very good environment on the back side (foundation) to promote mold growth.
If you are really concerned then I recommend skipping the fiberglass and going with just foam board (thicker).
Good luck.
Great, Thank you Todd! Would you say 2″ would be enough (up in Vermont)?
Do you leave a gap between the rigid foam boards for spray foam insulation? Gap between the floor as well?
Jason – The thickness really depends on the R value you want to achieve. Up here in New England I’d recommend a minimum of R21. Gaps are not necessary.
I’m insulating/framing a basement in a 80 year-old house. I can only use 1/2″ foam because of the placement of existing gas & sewer pipe. I can put 1″ in some areas. You recommend a minimum of 1.5″ to get away from potential condensation issues. Here’s my question(s):
If I seal the foamboard well, and then frame 2×4 and use fiberglass and then a vapor barrier, how great is the chance for failure? What things should I pay particular attention to? And last, is there a better fiberglass insulation than others?
Thanks for your help!
Tom
Tom – I don’t recommend you do this approach at all. The 1.5″ of foam is to stop moisture from the foundation wall and top be sure the foam is warm enough on the framing side that any moisture in the cavity does not condense on the foam surface. If you build as you suggest you’ll get moisture from the foundation wall through the foam and trapped with that outer vapor barrier.
You’d be better off boxing around the pipes and using the recommended thickness of foam.
Make sense?
i was going to renovate a basement and was surprised to find that the entire basement was covered in an aluminum faced fiberglass blanket. the insulation was installed directly onto the concrete (untapped seams). i wrote the local code enforcer to see if this application passed code and he said that it was a fsk insulation jacket and that it would pass inspection. after reading lots of articles on vapor retarders im still weary about covering this stuff behind a wall. am i being paranoid?
Eric – Do you know how old it is? Did you cut a whole in it and see if it’s dry?
the house is 2 years old. it was dry. we are planning on throwing some more heat into the space too
Is there a product name on it?
An excellent article. We live in East Tennessee in a fifty year old house. Lower level walls are filled cinderblock masonry with paneling over studs and fiberglass batts. No drywall or vaport barrier was used. I am planning to take down the paneling and now I see I must take down the studs to put foam board behind it and reinstall the studs. Your explaination makes sense.
Problem is, the local lowes only has blue XPS board (DOW) up to .75″. They say they have no demand for thicker.
1) Is it because I am in a more temperate climate and will that work? (I am betting the answer is no.)
I can get 2″ pink Foamular F-150 (Owens Corning) at Home Depot and I think it’s an XPS. I see them refer to extruded but they don’t seem to like to say polystyrene.
2) If the 1.5″ minimum really is critical, can you recommend a supplier of XPS or is the Foamular identical with an extra 0.5″?
Louis – Thanks for the nice words.
1. I’m sure there is far less demand where you live and that is driving some of it. The real answer probably has a lot more to do with what Lowe’s feels is the best use of their space! The Owens Corning Foamular F-150 is an XPS product and will work just as well.
2. Same stuff. You could also do two layers of 3/4″, taped sames in between.
Good luck!
I live in in southwest Michigan and I am working on finishing my basement. I have been doin a lot reading on line lately about different options to insulate my basement walls but I have been unable to really come up with some good answers for my situation. I recently found this websit and I believe that it is one of the best and more intelligent websites on this matter.
To start with let me discribe my basement. It is a walkout basement with the south wall totally underground, the north wall is totally above ground and the east and west walls are only about 20 to 30 percent below ground. Now my home also has a two car garage that is attached to the home with a walkout basement under the gararge. There has a poured wall that seperates the basement under the garage and the basement under the house. Finally the walls are poured walls on most of the house with a small section that is framed. The poured walls though have a brick “texture” imprinted on them making them rough.
Now here are my questions:
1. I am going to need some form of vapor barrier for the poured walls. After reading your posts I have decided to use foam board, them 2×4 studs and unfaces insulation. But what I am wondering is will this actually give me a vapor barrier due to the fact that if I put the foam board directly on the wall I will still have air gaps from the texturing?
2. The next problem that I have is that I plan to have the framed wall spray foamed. How do I effectively insulate and create a vapor barrier in the area where the poured walls meet the framed walls?
3. The third problem that I have is that one corner of the basement I wasn’t planning on finishing because this is where the furnace, the well, the water softner and other things are. will it creat a potential mold problem here, where the wall is left exposed?
Keith – Thanks for the nice compliments.
1. The key here is using a minimum of 1-1/2″ of closed cell foam (XPS). You could eliminate the fiberglass entirely if you use a thicker foam board. In order to create the vapor barrier you need to seal all the foam very well. The air spaces behind will not cause a problem.
2. I would be sure you do the concrete wall with foam board, then frame those walls. When the framed walkout wall is spray foamed I’d have them spray foam the two walls “together” for a bay or so to create a good transition.
3. I would just be sure to insulate the walls that separate the two spaces well.
Good luck.
I live in the middle of Indiana. I am getting ready to finish my basement. On the exterior of my basement walls I put 3/4 foam insulation I stuck that to the tar sealer on the exterior. The concete is 8″ thick and 10″ on one wall with the walkout. I have heard from the guy who built my house to put an air gap between the concrete wall and the framing and no foam since mine is on the exterior. If this is not true here some questions
1. Should I still go with 1.5 foam insulation or can I go with less thickness.
2. The framed wall inside thickness 2*4 or 2*2.
3. Will green mold resistant dry wall be worth it to put in the basement on exterior walls or would that be waisting money.
David – While the 3/4″ exterior foam is certainly going to help with R value it will do little to help with a vapor barrier. The 8″ and 10″ concrete wall is just like a HUGE sponge full of water throughout the life of the concrete. So, what you really need is a vapor barrier on the inside to stop and water vapor from leaving the concrete and getting to your walls. so….
1. I’d still stick with 1-1/2″ minimum thickness.
2. Wall framing doesn’t matter, seeing you have 3/4″ on the outside, you’ll have a really good R Value.
3. I’m not sure it does all that good. Then again, it can’t hurt. Most people skip the green MR board.
Good luck.
I live in Northern California where the winters are around the freezing mark and the summers are hot and dry. My house is made of hollow concrete block from the 40’s. All our exterior walls are painted and not furred or sheet rocked. The house is also all above grade. We moved our bed against an exterior wall and noticed condensation between the bed and the wall after the temps dipped below freezing. I want to try your method but really cant afford to lose that much space. Can I use 1×2’s over the XPS and then insulate between the studs with another 3/4″ foam or fiberglass board?
Jonah – I think that would work. I assume you’d install 1-1/2″ of foam before the 1×2’s correct?
I am reading about how you have advised to insulate basement walls. I had to straighten some of my walls and have steel beams to work around. Any extra procautions I need to take. Thanks
Scott – Steel beams are not by themselves an issue. However, they do hold heat and cold longer than surrounding materials. Because of that they can sweat. I would ONLY use foam around steel.
Thanks Todd. Yes that would be on top of the 1.5″ of foam. Any suggestion for the 3/4 inch layer or does it matter because its so thin.
Doesn’t really matter.
Todd,
Following your recommended installation, should the fiberglass insulation be faced or unfaced?
Would that change if the XPS was only 1” thick instead of 1.5”?
Thanks.
Matt – I’ve gone over that question quite a few times in the comments. First off I NEVER recommend 1″ of foam as it’s not sufficient to stop water vapor from leaving the concrete and passing through the foam. The faced vs unfaced question is quite difficult. It really depends on how dry that basement is.
Todd,
This entire discussion has been some amazing in site on this situation and has almost finally helped me with how I am going to insulate my basement. I’m from Thunder Bay, Ontario and it can get extremely cold. I was originally going to get an R22 out of 2×6 studding the wall and putting Roxul batt insulation but I was fearing that if I got any moisture coming through the wall that it would get trapped within the space. I was going to use 6 mil poly on the inside of the wall(drywall side) and a friend said to run poly against the concrete side up to grade level. It just didn’t sound right to me. Is he not going to trap moisture in the bottom of his insulation and create problems not allowing it to escape unless it can all come out through the exterior of his foundation which doesn’t give it much to get out from? I want to go with the 2″ XPS, but if I get an actual water leak through the wall, will the insulation help stop it from coming through? If not, will it ruin the insulation by absorbing any of the water or as the rest of the water runs down towards the floor? I plan to paint all my walls and also plan to dig up around my entire house and put a rubber membrane and insulate it from the outside as well. I plan on studding and putting 2×4 roxul batt insulation for extra r-value afterwords as well, running my electrical, etc, drywall.
Dan – The beauty of XPS is the fact that it’s a closed cell foam. Closed cell foam will not absorb water, it doesn’t promote mold growth and it won’t get damaged by water. Once you tape and seal all the joints it works very well as a vapor barrier and insulator. You can then frame in front of it and insulate.
If you do that method just be sure that the bottom plate sits up off the slab (we use a piece of composite decking below the PT plate) so that water can’t get up into that insulation (Roxul).
Putting poly against the concrete is just asking for trouble. The poly surface will be cold and any damp air that hits it will turn into water condensate.
Good luck and thanks for visiting the site.
Thanks for the speedy reply, last quick questions.
I noticed you got R-9 out of 1 1/2″ foam. What brand are you using to get that?
I am looking at buying a 2″ XPS which gives me an R10 for $18.88 from Home Depot or Menards. I am down for the weekend and this stuff is like less than half price compared to our stores…robbery up in Canada!
Is my painting of the walls overkill? The reason why I am painting is because I discovered about 6 leaks when it rains hard on 2 of the 4 walls. All my walls are about 80% below grade. I’m not using paint as my solution for the leaks but as a back up/preventative and to seal in the moisture as good as I can. I plan to dig up around 2 sides of the house, possibly all 4 if it makes sense to just do everything if I’m already doing 2, what’s your opinion on that?
I plan on using blueseal against the concrete and gluing more foam against it to protect the blueseal when backfilling and give it more insulation. If I achieve R10(XPS) and an R14(2×4 stud with Roxul, totalling R24) on the inside, would an R5 1″ XPS suffice on the outside? The foam would act more of a protector when backfilling rather than benefitting from more R value. Or should I go with 2″ R10 for that extra insulation factor if cost difference isn’t too much of an issue? That XPS on the inside would never sweat with R10 on the inside and some on the outisde!
My foundation(above grade on the outside) is currently painted really well and if I plan to cover it with an R5 it will really then not be able to breate anywhere! Where will any of the moisture trapped in the concrete wall go to? I understand could some of it transfer into the footing and then possibly into my slab floor on the inside?
I also plan on insulating the floor as well, should I do this with XPS or should I use a DRIcore type product? My biggest fear is having a leak coming through the concrete, running down the wall and coming out onto the basement floor, or having it trapped underneath whatever my floor will be, I am planning on having anything from tile in the bathroom and laundry room to carpet in the main living areas. Last thing I would want to do is rip off any flooring work I did and then be cutting out the XPS I laid down! Can you shed some light on this?
Thanks and sorry for the unorganized sets of questions in advance, I know I like to ramble on.
Dan – The R values vary quite a bit from brand to brand. I’d say stick with what you can afford.
In your situation the paint is probably worth the effort. Typically I’m not sure it is.
I wouldn’t worry about the foundation breathing. Concrete holds water for the entire life so it’s not going to matter.
Before finishing that floor I’d do the outside stuff and wait a year. Finishing a floor before you know the water is taken care of is pretty risky.
Forgive me if this question has been asked before, but how do you frame in the vertical firestops when using rigid foam?
My local code requires either 2x lumber or a piece of plywood attached to the framing that sits up against the bare concrete from top to bottom. I would expect that this firestop would wick up the moisture from the concrete and need to be contained. It seems that even if I put up rigid foam, I’ll still need to use a vapor barrier.
Thanks.
Jim – Not sure exactly what your question is. For the projects that I deal with the fire stop is actually the sub-floor above and the exterior rim joist. If they are requiring something additional then I’m not sure what provision would trigger it.
Todd,
Good info, thanks.
Sorry if this has been asked before, I didn’t see it posted.
Any ideas for a split foyer? I have block about 4′ up, 2×4 framed on top of that, fiberglass insulated. Should I use foam all the way up to the joists or stop at the top of the block wall and seal it? I don’t care about using 1.5″ foamboard at the bottom, but what would you do about the 2×4 wall above? I want the wall to be straight on the inside. I have some ideas, but looking for other solutions?
Thanks from Des Moines, IA!
Clint – I would use foam on the lower portion and probably attach 1×3 strapping through that into the block wall. Then fir out the upper wall so that it’s the same thickness. For the upper wall you can use any conventional insulating materials you desire.
Todd,
I am so pleased to have discovered your site before I started my project. I am very concerned about moisture/mold and your info is finally making sense to me. Thanks for clearing up much of the mystery about this topic.
My foundation is poured concrete with sealer, 2″ foam, and a membrane wrap on the exterior. After reading your responses to other inquiries, my plan now for the interior of these walls is to glue on 2″ foam and not cover it with a vapor barrier. Instead of furring or framing over the foam, I’m thinking about gluing the drywall directly to the foam. Am I inviting trouble with this approach? Wiring on these particular walls is not an issue.
Thanks from Minnesota
Jim – Thanks for stopping by….I hope you visit often!
There’s nothing wrong with the approach other than it’s nearly impossible to get a decent looking wall. It will be hard to get a smooth looking, tight fit. Typically the foam fits “ok” but there are uneven surfaces and the glue really just holds it in place, not nearly strong enough to hold drywall in place (in my opinion). I’ve never tried it but I really don’t think it will work. Then again you never know unless you try!
Good luck.
Hi Todd,
I have a wood construction basement/foundation – no concrete (built in 1990).
We noticed condensation building up on the plastic vapour barrier so we ripped it down & noticed that there was more condensation/moisture behind the fiberglass insulation. No mould found. Due to age of house, the vapour barrier is not 100% intacked/sealed. We want to fix this moisture problem but have been told many different solutions. What do you suggest?
Should we be treating our situation different since it is a wood basement & not a concrete basement? Our walls are fully studded (2×6’s)& we can’t take these down to put any sort of blue board fully against the wood walls. What do you suggest we do?
Thanks in advance!
Emily
Emily – can you give me more information about how your basement is constructed? I’m not familiar with wood only foundations. Are you saying there is absolutely no concrete?
Instead of having a poured concrete foundation – everything is built with pressure treated wood. Instead of having concrete walls, they are wood. The floor is raised wood floor with a crawl space underneath that has our concrete footings and gravel sloping down to a sump pit.
Just less then 1/2 the basement is above grade.
Currently, the home has fiber glass insulation & then a plastic vapour barrier that has been sealed (some seals have broken due to age)- basement has never been finished.
After pulling down more of the batting, we have noticed that there is some condensation/water between the insulation & wood in some areas at ground level. Everything below grade is dry.
Should we just re-do how it was oringinally insulated but do a better job? We have been told to put the ridgid board insulation between the studs and then fiber glass batting on top & then the plastic vapour barrier. Is this a better solution? What do you think?
Above should read: there is condensation on the wood at & above grade (some areas are worse then others, some areas are 100% dry), below grade is pretty good with no moisture/dry***
Emily – You certainly have a unique foundation type (at least for me!). The first thing worth discussing is the fact that pressure treated lumber typically has a very high moisture content (at least when it’s new). However, your home is now 20 years old so most of that concern is probably not an issue.
From the little I know about this I would say this.
– The reason you see moisture at and above grade (not below) is water vapor is getting into the leaks in the vapor barrier and coming in contact with the cold above grade wood surface. Once that vapor heavy air hits the cold surface it will condensate.
– I think it would be reasonable to remove any wet insulation and dispose of it. Dry out the wood as best you can. Install new fiberglass then a vapor barrier.
– If you want to improve on the system I would recommend 1-1/2″ of foam board against the exterior wood, then fiberglass. This way if moist air gets in there it will hit the foam and not the cold wood.
Make sense?
Thanks Todd!
What types and brands fiberglass do you prefer for basement environments? I live in Chicago and its winters can get quite cold. I will be using 2″ foam board for the vapor barrior. What additonal R value would I want with the fiberglass?
Also does it matter what type/brand of drywall to use for a basement? And what thickness is recommended?
Jeff – It really doesn’t matter much on brand. Typically I prefer kraft faced in this type of application.
The R value really depends on the local energy code. The energy codes have become so complicated that it’s typically not a matter or R value. Most energy codes require a system approach, so you look at not only insulation levels but window performance, door performance and even the heating and cooling equipment.
So…..it depends :) I would shoot for R13 to R21.
Drywall doesn’t matter.
Hey Todd,
The foam contractor is stating that 1″ should be enough for the basement. Then getting the basement framed and then going with fiberglass to increase the R value. 2” spray foam seems like its going to be fairly expensive. I am not sure what to do/
Thanks
Rick
Rick – One inch is not enough to provide the necessary vapor barrier. You have to install at least 1-1/2″ of XPS or closed cell foam.
Todd Hi
thanks for your helpful forum
i have a basement i have gutted, i have put 1 1/2 inch pink foam then 1 inch foil lined foam in the rim, then 1 1/2 pink on top of block wall in rim area. now for the walls in minnesota i plan on 1 1/2 pink close cell foam sheets in steel Z – studs ? i no the best advice seems to be foam on its own then frame a walll the sheetrock ect. but the z studs will save a step or 2. what do you think ?
Tony – We use that approach on commercial buildings so it will work. The tough thing is sealing things really well so that moisture that may condensate on the z studs doesn’t penetrate the finished wall.
Todd,
I live in a new house in northern Ohio, and I am going to start finishing my basement. My thoughts were to forget the moisture barrier on the basement walls and just leave a space between the concrete wall and the insulation in a studded wall. The insulation would be unfaced. I was hoping this would allow everything to breathe without causing condensation. The outside of the basement walls are covered with a product called Rub-R-Wall. Just wondering if this would be okay or do I need to rethink this idea?
Ben – You really need to rethink the idea. Without the vapor barrier your foundation will dry to the inside. Then vapor will be trapped in the cavity. Today when finished walls are painted they create a semi-permeable vapor barrier just from paint, you would end up locking that moisture in and causing serious problems. Once the vapor was trapped it would eventually condensate on the cold foundation wall creating a cycle of wetting and drying.
Great website.
I have a question re. what is the preferable option re. attaching 2 inch XPS/Foamular rigid foam insulation to an exterior below grade brick basement wall. I want to avoid having mold problems down the road. The basement is a little humid but not very humid. Twice during the last 6 years we had slight flooding in the basement because neighbors irrigation pipes busted (we live in a row house). I installed a “french drain” along the wall where the flooding occurred. I’d like to find out your opinion re. which option is better, whether one is a bad idea or whether both options are OK.
OPTION 1: Attach the rigid foam directly to the wall with 1/4 inch or so furring strips facing the inside of the basement. I attach drywall to furring strips (with a strip of waterproof cement board for the first foot of drywall in case it floods again).
OPTION 2: Nail the 1/4 inch furring strips to the brick wall, then attach the rigid foam to the furring strips. This leaves a small gap between the exterior basement wall and the foam. I attach the drywall to the foam with 2.5 inch screws that screw thru the foam and into the furring strips.
Rob – Thanks for stopping by.
First off as you know the biggest issue is trying to prevent future flooding. A french drain is good and a sump pump would be even better.
If you have the room I prefer using the solution that is outlined here: http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
If not then I would say option 1. You want to have the XPS foam against the foundation before any wood, or material that might promote mold.
Thanks for the information provided, your a big help. I plan on doing my basement N/E cold poured wall always dry. Will do the foam, the 1″ gap and fiberglass insulation. My problem, when house was built my electrical panel and all the cable and phone hook ups were placed on a large piece of plywood which was secured to 2 2×6’s vertically floor to wall and lagged. is there an easy way to seal, insulate that area without having to remove the whole mess from the concrete wall.
thanks
Ralph – Just do the best you can. I’d put foam up close to it and seal with Great Stuff. Thanks for visiting the site.
Todd,
I’m a contractor based in Rochester, NY. I met with a potential customer this weekend for a basement estimate. They gave me your site; I have read your information. It is their take that you are saying a thick barrier of rigid foam will stop any moisture from occurring at all. If this is what you’re saying I am not certain I agree. More-over if moisture (water) develops between the foam and the wall gravity will bring it to the floor. This is generally not an issue with a floating slab but this particular house was built mid 20’s and has only a few drains in the center of the structure. The floor is poured tight to the walls. Any water getting behind would stop and pool at your composite “dam”. Please tell me why my thinking is wrong or what method I should propose to these people regarding this point. It has long been my practice to avoid complete finishing of basements that are of this age because of this situation and their heavily sloped floors. Your response would be appreciated especially since they are using your information as their bible. An email to me would be great. Thanks, Mike.
Mike – I think they are slightly mis-understanding the issues here. As you and I both know basements are extremely complicated and they need to read several articles on this site along with hundreds of comments to truly understand what I’m promoting.
Foam board does a great job stopping water vapor from entering the framed walls. However, foam board does nothing to stop water (physical water) that might leak through cracks. As I’ve said on this site many times water drainage issues MUST be fixed first and foremost before finishing any basement. Older homes are especially susceptible to this problem and are far less likely to meet my standard for finishing.
I frankly don’t think basements should be finished if there’s any chance of flowing/free water infiltration as it’s asking for trouble. If there’s a very rare issue of water then I recommend using some sort of floating floor system that will allow the water to get to drains.
What I’m trying to educate home owners on is the overwhelming problem of people insulating basements with fiberglass insulation up against poly directly over the foundation wall. I’m sick and tired of seeing contractors and home owners insulate their basements in that fashion and then wondering why on earth they have a mold problem.
In your situation I would use the foam on the walls and then use one of the floating sub-floor systems (lots out there) that has the plastic “feet” that will leave an air space below for drainage.
Does this sound better?
Todd,
This sounds great. One of my most difficult tasks over the past few years has been working at sales when the customers have heard or seen something via TV or internet. The methods we used before are constantly being improved but a small point being misunderstood by either party can sour a relationship before it gets a chance to develop. This particular house will not be getting a finished floor so I’m pretty sure I can give these people a very good result using your method. I do have a question of my own; would double sided tape work instead of glue? Thanks for your prompt and professional response. Mike
Mike – You’re very welcome. All of us in the construction industry have to help educate ourselves and help promote better building practices. Every day it seems there are better products and better approaches that we can all learn from. I’m amazed at all the new techniques that my crews continue to learn and advance.
I’m not sure tape would work all that well. Frankly in many situations we don’t use any glue at all especially if we are framing the walls at the same time. The nice thing about XPS foam is it won’t absorb water, so we typically fit it tight, top and bottom and then only worry about taping and sealing the joints.
We’ve been using this type of approach for several years with very good results. In fact, I’ve seen several basements where we went back to do additional work and we removed some of the old foam and everything is nice and dry, no most on framing, all looked like new.
Best of luck and I hope this year is better for everyone in the industry.
Todd, I have started gluing the foam board to the walls and have read where you suggest sealing the boards. Is a layer of Tyvek tape all thats needed or do I need something in addition to that. Thanks for all the time you put into answering all these questions, its a great help to alot of people. Thanks, Dave Taylor
Dave – Yes you can seal all the joint with either Tyvek Tape or DOW construction tape.
BTW…you’re very welcome.
Todd, Whats your process for keeping the foam board tight against the wall while the adhesive dries.
It depends on what you use for adhesive, some of them, if you put the adhesive on, then wait a few minutes for it to tack up, they then stick better. Sometimes we use scrap lumber leaned up against it.
I had to order the Great Stuff Pro adhesive so in the meantime I was using the Loctite PL300 foamboard adhesive but it takes forever to setup. I will try letting it set for a few minutes to see if that helps. My concrete walls are relly ruff and uneven so its hard to make it stick good. Would it hurt to use a couple of 2″ concrete nails to hold it in place?
Thanks, Dave
Dave – Are you cutting the sheets so they fit tight top and bottom?
No Im going from the floor to the bottom of the sill plate. The sill plate has a piece of 1/4 foam between it and the concrete foundation. Im going to have a company come in and spray foam all of my rim joists when Im finished with the walls. My thought was to have the foam cover the point where the foam board meets the sill plate. Since Im doing that theres a gap the thickness of the sill plate between the top of the board and my floor joists.
You could also grab a can of regular great stuff. It takes a bit longer to set up but it will hold it. On most of these products the trick is getting it to tack up first.
I am in the process of finishing off my basement. I have a wall that is half concrete, half 2×6 studs. Its in a bathroom and have adjusted the half concrete wall from 2×4’s to 2×2’s for more space for a shower to go into, in order to get 60 inches.
What I currently have is 1″ foam insulation (with plastic on either side of the foam) on a drylocked concrete wall, then a 2×2 wall about 4 ft high. Can I put more 1″ foam between the 2×2’s with great stuff and then sheet rock over that? Is there any problems with this construction? Do i need a vapor barrier there or is this sufficient?
On the other side of the basement is also a 4 ft concrete wall with the remainder of the wall 2×6 above. What I currently have is drylock, 1″ foam (with plastic), 1 inch gap, and 2×4 stud wall. I will fiber glass the bays for the stud wall. Do i need a vapor barrier in front or behind the stud wall? And then eventually sheet rock.
Thanks for your time!
Tim – Unfortunately 1″ foam board doesn’t provide two things that you need.
1. It doesn’t provide sufficient vapor barrier to keep water vapor from leaving the foundation wall and penetrating the framing, insulation, drywall, thus a potential mold risk.
2. It doesn’t provide sufficient insulating value to keep any water vapor from the finished space from contacting the foam surface and condensating. If warm air gets into the wall cavity and hits the foam that might be cool enough to hit the dew point, it could condense.
You might want to read: http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
That will show you what I recommend.
Thank you for your reply back. Okay, that is dreadful news, now that I need to redo it all. But I understand why it would not be sufficient.
Am I able to double up on the 1 inch foam or do I need to take it all down and put 2 inch foam up there?
Also another question, Do I need to put up a plastic vapor barrier up in front of the stud wall after we are done with the fiber glass insulation?
Thank you, Tim
Tim – You can probably add another inch just realize that it’s not perfect and it could have problems in the future. I would NOT use plastic, you might want to use kraft faced paper.
Good luck.
Todd, in places where there are gaps around the foam board like on uneven floors or at the top of the board where glue holds it off the wall a quarter inch or so , do you suggest using cans of spray foam to seal those gaps? Is it a good idea to seal these up completely so that no air can get behind? Thanks Dave
I would seal them up. What you’re trying to stop is moist air from getting to your framing materials.
Todd, As far as vapor barriers in basements are concerned, I have a poured concrete basement. The one room left unfinished is a walk out under my garage. It is literally a concrete cave. 1 1/2 walls is totally exposed to the environment, 1 1/2 walls is underground, and the other is back to back with an already finished basement but is solid concrete. I want to finish it so I can use it in the winter. What should I do? As is it is freezing in winter and sweats a lot in summer.
I’d recommend using 2″ XPS foam board on the walls followed by framed walls. Something similar to the walls in this article: http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
Todd,
I’ve used 1 1/2″ XPS around all my basement walls except in the bathroom. When we had the house build the builder roughed-in the basement bathroom only leaving me 1/2″ from poured concrete wall to stud wall. My original thought was to use spray foam for the 1/2″ cavity but after researching spray foam kits I’m not sure I want to take on that task. (Supposedly, spray foam gets everywhere and it takes a lot of prep work. I’m also worried about the vapors.) My question to you is, should I not insulate the bathroom walls or should I rip down XPS and fit in between the stud cavities and GreatStuff spray between the stud and concrete wall?
Thanks! Your web site has been a great resource!
DIYer – Travis
Thanks for the nice compliment.
Question – Were you planning on framing with 2×4? If you use 2×3 on that wall you could get 1-1/2″ foam in.
Could also potentially frame that wall with the 2×4 flat on the wall, then Tapcon it.
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I already framed the wall with 2×4’s and the plumbers have already plumbed for the vanity and urinal. I ended up being able to use 1″ foam board behind the wall. I had to cut them and piece them in place. I used tape for the accessible seems and great stuff in the tighter places.
I know you recommend 1 1/2″ or greater foam board. Should I use an additional vapor barrier? Also, I’ve read not to use fiberglass batting in a basement bathroom. Is this your recommendation too?
Thanks!
In your situation I would not use fiberglass. I’d add more foam in the cavities.
Todd-
Thank you for the time you have dedicated to answering questions on this subject matter. Your comments are extremely informative.
While I think you’ve touched on my question, I don’t believe it has been specifically addressed. I have a 6 year-old walkout ranch style house in Nebraska with no history of water in the basement. The house has poured concrete basement walls (except for the studded walkout wall)with sealed foam board (foil style showing) on all concrete walls except for the wall that is shared with the garage above. This wall has nothing on it and bare concrete is showing. I assume foam board is not required on this wall per code in my area (due to the fact that it is above the garage). I have framed this wall using 2×4’s turned on their side attached directly to this concrete wall (shared with garage above) secured with Tapcon screws. I have insulated by cutting and piecing 1.5” foam board in the stud cavities. My question is: I am planning on putting a bathroom on this wall. I have already set the tub and put a vapor barrier (6 mil poly) over the top of the studs/foam board behind the tub. In reading your comments I am under the impression this is not a good idea. Would it be best to tape/spray foam all seams surrounding the foam board I have access to and do away with the vapor barrier? Also, the other walls of this particular bathroom will be interior walls shared with a great room. For the purpose of sound reduction, I need to insulate these interior walls bathroom walls. Can I use fiberglass, faced R-13 batting for this? If so, which way should the facing go (bathroom side/great room side?)? If you do not recommend fiberglass insulation on interior walls in this bathroom what would you recommend for sound reduction?
Any information you could provide would be greatly appreciated.
Thanks in advance, Todd.
Brett – Glad you find the site useful, I hope you’ll consider signing up for my FREE Weekly Newsletter.
Your situation is a bit different but not completely. Unless your garage is heated that wall should still be treated as an exterior wall with respect to insulation. If I were you I’d have installed another layer of foam over the existing foam and studs so that you’ve created a proper vapor barrier. While the poly will work to some extent it will still be touching “cold” studs. Any moisture that hits that poly will condense and possibly lead to mold/rotting problems.
Sounds like the tub is already in so it’s hard to say exactly what I’d do. I guess I’d probably leave the poly as is, it’s not ideal but I don’t see any solution short of re-framing your bathroom walls.
You can use fiberglass on the interior, I’d stick with un-faced fiberglass.
Good luck.
I should clarify that the wall in question is in the basement and is a shared wall with the garage above it. My previous comment was stated incorrectly as follows: “due to the fact that it is above the garage”. Instead, it should read “due to the fact that it (the wall) is below the garage”.
Sorry for the confusion…
Thank you Todd
Since I still have wall space that is not behind the tub/shower (and I have access to)but that still has 1.5″ foam board pieced in the stud cavity, should I do as you suggested by putting additional foam board in front of the existing studs/foam board or can I tape/spray foam in the unsealed areas? If it is best to use foam board over the existing studs/foam board, what thickness (of foam board) needs to be used? Also, how would you hang drywall over the top of this application?
Thanks Todd
I’m looking forward to the Newsletter
If it were my home, I’d install an additional 1-1/2″ over the studs. First of all the additional foam is only going to make things better. Secondly, You really need that to stop vapor movement. You can definitely drywall over that so long as the sheets are up tight and secure to the 2×4’s. Good luck!
Todd–
Thank you for the great information. We have an old basement (50s) with a new basement addition (last year) with kitchen above. We added drain tile to the inside of the old basement and are completely redoing the old basement using your advice (2″ foam & rim joists etc).
My question is about the new basement. It has drain tile inside and out and was insulated on the outside with polystyrene foam and was wrapped with Tyvec. On the inside, the builder framed it and insulated with fiberglass, but we did not get it finished. We will be putting up the drywall ourselves. Should we take out the fiberglass and use foam board?? Or with the foam and wrap on the outside, is the fiberglass on the inside OK?
thanks!!
Rose – Thanks for the nice compliment. While the insulation on the outside is certainly nice it won’t stop moisture that exists in the foundation walls from getting into the fiberglass insulation and possibly leading to a mold problem. If you haven’t read it yet I’d check out: How To Insulate Basement Walls for additional information.
The ideal situation would be moving the framed walls out away from the foundation enough to slide foam board in behind the framing. If you can’t do that then definitely remove the fiberglass and use foam between studs. However, be aware that you could have issues with the framing down the road as the wood will be in contact with moisture.
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Todd!!
Thank you so much for your response. You provide wonderful information. I neglected to mention that the concrete was waterproofed on the outside with a black membrane first, then foam insulated and tyvek wrapped. The studs are about 1 1/2″ away from the concrete wall. The fiberglass insulation is R-13. After checking with the builder, I was told it was done this way so the walls can breathe and dry to the inside and I should not use foam insulation or a poly vapor barrier.
I realize concrete is a porous material full of moisture. I want to use my time, energy & the meager financial resources I have wisely. I have read all your great articles, all the posts on your site, the Cornell study materials, dept. of energy info and more, but I am at a loss.
thanks so much for your help — Rose
You’re very welcome.
For starters go read this: http://www.buildingscience.com/documents/reports/rr-0202-basement-insulation-systems
It’s one of the most widely accepted articles on the issue.
Being a person who has studied concrete material science in graduate school I can tell you this. Concrete doesn’t need to breath. In fact, the more water it holds the stronger it gets as the chemical reaction that happens inside concrete will continue to happen for years. So…no real need to let it “dry” out to the inside. Most people now agree that it’s best to seal it off and keep that moisture out of your home.
That 1-1/2″ space behind the studs is probably enough that you can get a layer of foam behind the wall without tearing the wall down. That’s the approach I would take.
I think your builder is saying that to cover his own behind and also it’s likely he just doesn’t know. There are thousands and thousands of cases like yours all the time. We just need to keep educating these folks until they get it right.
Hey Tod,
Fantastic article and a point of departure for dealing with a wall which vents moisture into a large room. The wall has about 1.7m of soil behind it as the row of properties go up a hill. There is only soil behind this wall, the side walls are completely clear of soil (a yard on one side and the street on the other).
The problem is that the brick wall is over 100 years old quite uneven (old French property). I am considering first rendering the wall up to 2m to make the surface smooth. Then to apply the foam boards onto the render and finish the project the way you describe in this article.
Do you think I can skip the rendering step or is it crucial?
Any alternatives?
I think you can skip that step. What’s important is creating a good seal on the foam board layer.
Todd, nice blog. We too keep the wall cavity dry using foam and agree with 99.9% of your article.
The question I have is with this part:
We also like to install the PT bottom plate on top of a piece of composite decking material to prevent any wicking of moisture into the framing.
The composite decking…. as far as I know it’s not rated to bear weight. I’m not saying it won’t but can you give a link for a approved study saying it can? It might come in handy for us, ya never know.
Thanks, Paul B.
In the details that I’m showing the decking is ONLY under a NON-LOAD bearing wall. That detail can NEVER be used on a bearing wall.
OK, that’s what was my concern.
Hi Todd.
Finishing my basement by creating 2 bedrooms, I have block walls that I sealed (painted) with a latex based waterproofing product and planing on 2×4 stud walls with fiberglass. What I’m wondering is with the sealer on do i still need to use a foamboard? Also, would using a plastic barrier against the block in between the framing be sufficient? All but one block is below grade.
Thanks, Josh V
Josh – If you use just fiberglass you WILL have a mold problem at some point. You should also read:
http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
Wow, I think I may have finally found the right person to answer my questions.
I’m planning on insulating our basement using your method described in your “How To Insulate Basement Walls” link, but using 2″ pink insulation board with 2×2 furring strips over it instead of a 2×4 studs. The problem is with my concrete walls.
We live in Minneapolis, MN, where temps can get bitterly cold in the winter. Our house is a bungalow from 1921 with a poured concrete foundation that needs some work, but the question is, how much? The walls appear to be structurally sound. There are cracks here and there, but there is no bowing, no gaps over 1/16″, and none of these cracks have ever leaked. In fact, we’ve never actually had so much as a dribble of water seep onto our floor. However, the concrete is spalled and crumbly in several areas going from the bottom of the foundation to about 3′-4′ up. Also, there are damp spots near the bottom foot or two that seem pretty consistently damp, at least a little bit.
There used to be a 1/4″-1″ cement coating that had been parged over the surface, but I removed almost all of it because it had separated from the foundation. I now have an uneven surface with a few pits up to 1.5″ deep. Do I need to re-parge an even surface over the foundation so that I can adhere the insulation board properly? Or should I use Drylok to abate the moisture in the damp/crumbly areas and just use an extra thick layer of construction adhesive in the more deeply spalled areas? I’ve done everything I can barring wrapping the foundation on the exterior to mitigate water problems from the outside (sloped the soil and directed downspouts away from the foundation) but I think I’ll always have some level of dampness. I’m also wondering, if I do re-parge the walls, how long I’d need to wait for it to cure until I put up the insulation board, framing and drywall.
My other question is, since we are only finishing 1/2 of the basement, will the unfinished/uninsulated half of the basement basically negate the insulation in the finished space? In addition to insulation board along the foundation, the finished space will have an insulated framed wall with one door dividing it and the unfinished half of the basement, an insulated ceiling (fiberglass batting) and has two forced air vents in the ceiling blowing heat downward. I’ve done some research on heat bridging, and it seems that unless I totally insulate the whole basement, the unfinished areas will just suck out a lot of the heat.
Of course, we’ve been using the room we’re finishing in its uninsulated state for 7 years without freezing our butts off, but I know we at least need the insulation board as a vapor barrier to protect the drywall from eventually getting damp and moldy.
Thank you so much for your help!
From the sounds of it you’ve done some great research already.
Couple questions:
1. Why not frame a wall? if you do that you won’t have to worry about parging the surface. All the adhesive has to do then is hold it in place until the framing goes up. The framing will also allow you to install some additional fiberglass insulation for more R value if you want.
2. You might want to use DryLock on the damp areas although I’m not 100% certain it will work that great unless you can dry it out ahead of time.
3. Can you separate the two spaces with an insulated wall? If not you’re likely to not reap all the benefits of doing the one side.
Good luck!!
Todd whats your opinion on using steel studs vs. regular lumber for basement walls?
It depends on how you insulate. If you use a layer of closed cell foam like i do in this article then I think they are fine. I think they are also fine if you spray foam around them. However, if you use fiberglass (which I don’t really recommend in basements) then it’s likely to make a real mess with condensation.
todd , i am currently remodeling my basement the house was built in the 50s.it is located in new york approx.1hr north of nyc.my question is i have already framed out the walls approx.1 from the concrete block foundation walls. my plan was to have it spray foamed with 2inches of the closed cellinsulation.my concern is will it be an effective vapor barrier behind the studs since they are in some spots only 1 inch from the concrete block wall?? the sray foam is expensive will i be wasting my money? thanks todd!
I think you will be fine. With 2″ of spray foam it will be a good vapor barrier. I’d also install some fiberglass over that.
Good luck.
In a new construction house we plan to spray foam the basement walls on top of barricade. My question is how far away from the wall do I build the 2×4 wall (building the wall b4 the spray) and how thick should the spray foam to get the proper vapor barrior and R value (NW Ohio)? I would like to leave a gap between the foam and the drywall if I would ever want to run wiring in the future, can I leave an air gap or should I fill with fiberglass or something?
Most of the time walls are framed an inch or two away from the concrete so the spray foam can get behind the studs. The thickness of foam will depends on the type of foam and the R value that you need. My biggest recommendation is to NOT use open cell foam. Be sure to ONLY USE CLosed Cell Foam. There are tons of guys pushing open cell as it’s much cheaper, don’t fall for that.
Depending on the R value you need for your local code you may be able to leave a space.
Our basement ceiling has the fiber insulation facing down (paper to the under floor) and we added mil plastic to the ceiling to prevent the loose filaments failing down. We then covered the ceiling with sheetrock and now i’m wondering if moisture could be trapped between the insulation and mil plastic. I have a dehumidifier and the basement is heated.
Well I can tell you that having a vapor barrier on both sides is typically a big NO NO. I guess my first question is whether you heat/condition the basement or if it’s just a cold space?
The basement is heated via baseboard (circulating hot water) from the oil burner. What are my options to remedy the situation?
Thanks for the quick reply.
How long has it been like this? I’d probably cut a small hole and inspect the insulation. Seeing that you’re heating both sides it might be ok as is.
I would say about 2 weeks and we are about to start the tape and mud stage. I just want to make sure that i’m not creating a moisture/mold problem because the basement will be a playing area for the kids.
I can’t say for certain. What I do know is the industry standard is to NOT have double vapor barriers as you have done. Basically you have two options as I see it.
1. Take down the drywall and remove the plastic.
2. Live with it….your situation is one that might be ok as you plan on heating both up and downstairs.
I’d be tempted to leave it….but check on it after a year. Wish I had better guidance on the issue.
We’ve decided to remove the plastic barrier, but we’ll leave one room covered to see what happens one year from now. Do we have to change the insulation to face upwards?
We really appreciate all the advice you have given us so far. :-)
You can leave the insulation the way it is. I’m glad you made the decision to change things, it’s always best to air on the side of caution. Good luck!!
Todd
First I live in Chicago, trying to finish the basement. I was helped by a family member that has done numerous basements before and he has always put up the walls and insulate. So right now where I am at is the 2×4 walls are up about inch away from the walls no foam or vapor barrier. I started to look online baecause a couple of co-workers said they thought I should have a vapor barrier. I really do not want to take the walls down I ran all the electrical alreay. I was wondering if you have any suggestions. I looked on-line and with the room I have behind the 2×4 studs i might be able to get 6 MIL plastic behind their after that I don’t know what other options I have. Spray foam is out of the budget.
Thanks In Advance.
Honestly the only thing I’d recommend at this point is spray foam. Any other solution (minus taking things down) is susceptible to mold problems. Sure there are lots of folks that have built basement walls that way in the past, but from my experience and countless other experts the likelihood of trouble is far too risky. Wish I had a better solution for you.
Good luck.
Hi Todd, I am in MA. My basement is a poured concrete basement. It was built in 1950. The concrete is not good enough. I can see lots of efflorescence on these walls. There is an addition which was built in 1980s, I guess. Those walls there are good. There is no efflorescence. If I cleanup those efflorescence, they will come back very quickly (few weeks or months). That means moisture is keeping moving from the soil into my basement. There is no water issue. So the basement is kind of “dry” but damp (during the summer).
I am planning finish my basement by using 2″ rigid foam (XPS) and then frame and then dry wall, basically as the way you suggested.
But I am thinking add one vapor barrier between the concrete wall and the foam. The purpose of that vapor barrier is to trap moisture in between the concrete wall and the barrier. So it will reduce the possible migration from the soil (differential is smaller then) and toward basement space (barrier to stop the movement). The trapped moisture will be absorbed by the concrete wall during the winter, i think. Because there is a 2″ foam insulation, the condensation on both sides of the vapor barrier should be not a problem, i assume. What’s your option about this extra vapor barrier? thanks, James
It won’t hurt anything. Then again I’m not sure it will do much for you. The 2″ of XPS foam will stop moisture as well.
Hi Todd, I live in upstate NY and partially finishing my basement. House is 7 years old. Builder used 1 1/2″ foam board on exterior of poured foundation walls. Basement has floating floor with french drains inside and out and sump pump. Basement is “dry” but air does feel a little “damp”. I plan on heating and cooling the finished space. Planned to stud walls 2″ from foundation walls. Do I still need to cover inside of walls with foam board since builder did it on outside? Thanks Rob
The answer is yes. If you don’t those concrete walls will dry to the inside and moisture will get trapped in the framing behind the finished wall surface.
Hi Todd,
We have lots of effloresces in our old poured concrete basement and they are actively growing and very quick. Few weeks or few months later you will see them again after a simple clean. That means we do have serious moisture issue from the soil because of the bad poured concrete. We can see the huge differences between the original 50s’ concrete wall and the 80s’ or 70s’ addition concrete wall. One is flat and smooth with enough cement and water when it was poured; another one is uneven and shows too many gravels and sand were used when it was poured. So I plan to put a layer of fine cement to fill in those small holes to reduce the moisture passages, use something like Quikrete Non-Shrinking Precision Grout. Do you have any better material to recommend for this purpose?
I have two photos here to show you my old concrete wall: http://www.flickr.com/photos/oldyoungguy88/5167526392/in/photostream/
We have done two big projects started from last summer: exterior grading and French drain (not down to the foundation) to make sure surface water will have no chance to close to our foundation; interior French drain to make sure no water will come from ground. Now it’s time to reduce moisture issue.
thanks,
James
Your situation is not uncommon with older foundations. While the surface of the older concrete looks like the problem I’d be more focused on the water in front of that wall. All concrete is porous and able to absorb and release water. In your situation it’s likely that the concrete was fairly low strength which means it has even more porosity.
So trying to ‘patch’ concrete from the inside to stop water is like trying to put your finger in a hole in the bottom of a tall dam. The pressure is too much and the patch typically doesn’t hold. So patching from the inside is seldom successful.
The best way to fix this is having a water proof membrane installed on the outside along with a proper footing drain.
Without doing the outside work it’s likely you’ll be dealing with this issue for years to come. You might also want to read my Basement Insulation article that discusses some of these issues.
Todd,
I live in Birmingham, Alabama. My poured concrete walls have been in place for 6 years without even a hint of moisture problems. The were water proofed on the exterior to just below grade with Tuff-n-dry.
As a test for condensation, I taped squares of aluminum foil on the concrete walls, and no moisture was evident on either side after remoival.
I have started to finish my basement and the walls, electricity and plumbing are finished. Dpepending on the location of the wall, the 2×4 studs are 1/2 – 1 1/2 inches from the concrete wall. I see that most of your questions about insulation are from colder climates, but what would you recommend regarding insulation? I started to install fiberglass batts, but I decided to put 1/4 inch dow XPS behind the studs to keep the batts from contacting the concrete.
I know this is way off your recommendation for 1 1/2 XPS, but if there is any chance of mold, I’m wondering if I need to use any fiberglass batts. My unfinished basement stays at 70-72 degrees in the summer, and around 60 degrees in the winter. What are your thoughts?
Thanks,
Steve
Steve – The bigger question is relative humidity. Here’s the risk especially in your part of the Country. Basement walls stay in the 50 to 60 degree temperature range all year long (at least the portions in contact with the ground). If you have hot, humid air come in contact with that cool surface it’s going to condensate. That’s the first problem, the second problem is regardless of your foil “test” concrete has a very high moisture content for years….100+ years…so there’s always a risk of moisture leaving the concrete and getting trapped behind a wall in insulation, drywall, framing, etc.
Honestly my experience is heavily weighted to cold climates where I’m used to the best approach. All I can say is those two concerns above are enough for me to still think 1-1/2″ is the best minimum approach.
Todd
Great site with INCREDIBLE information. But I can’t find anything on this.
I have access to recycled 2″ ISO board with a fiberglass facing (from roofing). Can this be used in place of the foil faced board? Is a vapor barrier then needed? And do you know if it can be used under a future radiant heated concrete floor? If so, should this have a vapor barrier below the foam?
Thanks,
Jim
Jim – Thanks for the kind words. I certainly hope you bookmark the site or LIKE us on Facebook so you can keep up with all our great articles.
ISO board is the typical name for PolyIso Roofing Insulation. Polyisocyanurate insulation is a closed cell insulation which means it shouldn’t absorb water. So I think it will certainly work well as a basement insulation layer and if you use at least 1-1/2″ of it you’ll likely have sufficient vapor barrier protection.
The idea of installing it below a radiant concrete floor is certainly interesting. It’s used on roofs all the time so I have no doubt it would be strong enough. I’ve never seen it done but I can’t think of a reason why it wouldn’t work.
Good luck!!
Thanks, Todd
I like the green-ness of using reusing a product, and when it makes sense from a cost standpoint, it seems to be even better.
Would you put a vapor barrier below this product beneath the concrete?
Jim – It certainly wouldn’t hurt. Keeping moisture at bay under slabs is always a good thing.
todd ,
i am currently starting to finish my basement the house was built in the 80s, and uses the poured wall foundation. .it is located in Illinois . my question is i have went ahead and dry loc painted the walls as a precautionary measure. i have never had a water problem tho. The rim joists are already insulated with fiberglass as is the ceiling, should i take that out a use foam board or just leave it, or put foam board up with it ?
And will i have any problems gluing the 2″ foam board to the dryloc painted walls ?
Thanks for all your advice it is greatly appreciated !!!
Bryan
I would check the old fiberglass and be sure there’s no problems with it, moisture, mold etc. The foam will stick just fine to it.
Hello Todd,
Thanks for your reply, however on the rim joist pockets i am still a little confused.
The fiberglass stuffed in those joist pockets, if there is no sign of moisture and mold can i leave that up there then cut some 2″ foam board to stick over it ? then great stuff spray around it or should i take the fiberglass stuff out? then put up the 2″ foam board ?
Onc again , thanks for your reply.
Bryan
The best approach would be to pull the fiberglass, install the foam, then put the fiberglass back. Obviously that’s more work. If there’s no sign of water or mold then the other method will likely work. One bit of caution, if water does get in there after, the foam will lock that moisture in and it won’t be able to get out.
Another unique situation…I guess…(not an expert here, so the terminology may be lacking!)
I live in Minot, N.D., cold, cold, and more cold. I have a 20×50 outbuilding that I plan on converting into a 20×30 woodworking shop plus 20×20 cold storage area.
Unfinished basement (compacted dirt floor) under the main floor, block walls (on 3 sides, 4th wall will be a framed up wall dividing up the building, “standard” roof (wood, rafters, shingles, etc), main floor is plain plywood over the floor joists.
My garage is setup basically the same way without the basement and when I run the “torpedo” heater in there in the winter, the inside walls get pretty frosty, so I can only assume that when I do the same in the new workshop, I’ll have the same problem with massive amounts of moisture being generated everywhere…frosting on the block walls, “wicking” up thru the plywood floor, etc.
My original plan was to line the inside of everything (walls, floor, ceiling) with a layer of house wrap, inside of that, rigid foam board (the blue type I think? or will pink work?), and seal all the edges/seams with tape.
The open area in the roof has soffit vents every few feet already, and assuming I’ll accidentally block some of those when I put the fiberglass batts up there, I’m going to add vents in each end of the roof. The ceiling is going to get as thick of fiberglass batts as I can put in there without crushing it with 7/16″ OSB under it. For the walls, I had planned on building basic framed walls, 16″ (24″ if I think I can get away with it) on center studs with 3 1/2″ fiberglass in between and 7/16″ OSB on the walls (I don’t plan on hanging anything on the walls directly anyways). The floor will get a framework of 2×4’s laid on the sides and 1 1/2″ of pink (or blue?) and the same 7/16″ OSB on top of that with maybe some cheap laminate later on.
I’m sure there’s 100 things wrong with this scenario. What’s the #1 problem with this amateur plan?
I would use the foam board on the walls. You can attach it to the studs then put plywood right over that with long screws. No need for house wrap as it should really go on the outside.
The floor you could just put down high density foam on the current floor then another layer of plywood. Fiberglass for the ceiling would work just fine.
Thanks for the advice. I think I forgot to mention that I’m going to install a small furnace and A/C unit into this shop.
The outside of the building is un-sided plain white painted block wall, and the house wrap on the outside would look a bit silly since I don’t plan on siding it any time soon.
On the walls, are you suggesting to line the inside of the block walls with the foam board then put the stud walls on the inside of the foam with additional insulation between the studs? Or place the stud walls directly up against the block wall with insulation between the studs?
Probably wouldn’t hurt to run a decent sized dehumdifier all year either…
I would just install foam on block walls. Then you can stud walls or install strapping over foam using Tapcon screws then your plywood.
I gotcha now. Keep the studs away from the walls (and hence the bulk of the moisture). Going out tomorrow morning to pick up as much insulation as my truck will hold…and a framing nailer. Only put together one chunk of a wall tonight getting ready to raise it tomorrow and my forearms feel like Popeye already…
Thanks for the info/verification/etc.
Hi Todd,
And thanks for all the great info…I have a 40 year old house in the DC area and the basement is a walk out, so the walls are only partially below grade, and the basement is finished and used everyday and heated etc.
I’ve taken the old thin wood paneling off and will be putting drywall on, and have several questions…it’s a concrete block wall with 3/4 inch furring strips on the wall. (there is not enough room to build a brand new studded wall)
1. Do I seal/paint the block walls first?
2. Do I install the foam board in between the furring strips, or on top of them.
3. Do I install a vapor barrier, and if so, where.
4. Should there be an air space between the drywall and the foam board?
5. The lower section of the block walls appear to have been “slightly damp” during this last hurricane which was the worst rainfall and flooding on record–and I will be installing new french drains around the house, just for insurance.
Thanks for your insight and guidance!!
Joe
I’d recommend removing the old strapping. Install the 1-1/2″ min XPS foam directly to the wall. Install new 3/4″ strapping over the foam board and attach with Tapcon Screws or a Hilti type powder actuated fastener. Be sure all the seams are taped. Then you can install drywall over the strapping.
Good luck.
Todd,
I am in the process of insulating my basement, and am using the approach you have explained and illustrated here… if the foundation walls dry, from the part of the foundation, that’s above grade, outside of the house, wouldn’t moisture also be able to get on the underside of the sill plate, especially if there is no sill plate gasket?
Thank You
It is possible but it really shouldn’t be a long term problem unless your sill plate isn’t pressure treated.
My house is 60 years old, and it is not pressure treated.
I still don’t think it’s a big problem.
Thanks for the excellent information!
I am in the process of finishing the basement using the methodology you mention. The only catch is that although the basement was 95% unfinished, it did have stairs obviously and a cedar closet under the stairs.
I noticed that the stairs and cedar closet were simply built on the cement with no vapour barrier or insulation. Do I finish the basement up until those items and leave them as is or do I rip it all our the properly seal everything. Note that I have never had water in the basement and it is pretty dry.
I am in Monteal (cold winter, hot summer) if that makes a difference.
Thanks so much!
Most people just leave it as is. Obviously doing it right is better but frankly on an existing job like yours it doesn’t make financial sense. It really comes down to dollars and cents.
Todd, I have an interior french drain system that works, but moisture/mold is an issue. The slab is not touching the wall, it’s about an inch or two off of it. If I were to glue the foam panel to the wall, would I have it sit right on top of the “trough”, touching the concrete floor or should I glue it so it is just above the trough/floor?
I would run it down and touch the top of the “trough”. Any water behind the foam will still seep into the trough.
Thanks Todd. I really appreciate the fact that this article is almost 3 years old and you still respond to questions! thank you, thank you!
My pleasure. I hope you’ll consider signing up for my FREE weekly Newsletter.
Todd,
I am currently in the process of trying to find a good “replacement” insulation method for my basement in Fargo North Dakota. My house was just constructed and the normal method of framing a 2X4 wall and filing it with fiberglass batts was used. A vapor barrier was also applied. I recently looked behind the insulation and found a large amount of condensation (I wasn’t surprised).
I think I have a few options for a “replacement”.
1. Take out fiberglass insulation and wall. Apply 1.5″ of extruded polystyrene to the concrete wall, Tape seems etc. Put up 2X4 wall and insulate with fiberglass batt insulation again. My concern is that will the 1.5” of extruded polystyrene be enough to prevent the condensation on the surface of the polystyrene.
2. Spray foam with 1″ of closed cell insulation with 2X4 wall in place and then batt. (Flash and Batt) My concern is that 1” will not provide enough R value to prevent the condensation on the spay foam.
3. Spray foam with 2″ of closed cell.
I realize that the 2″ of closed cell would be the easiest but also the most expensive. Do you think my concern about option 1 or 2 is valid?
The current industry “standard” (I use that term loosely) calls for a minimum of 1-1/2″ of XPS foam board to create a vapor barrier. My experience that it’s sufficient to prevent the problems you are concerned with. I wouldn’t demo those walls, just cut them free, slide them out of the way, install foam, then slide them back in place.
Good luck.
Todd,
Thanks for the response. Any feedback on option number 2 or 3?
I wouldn’t recommend option #2 and option #3 will be quite costly.
Hi Todd, I have an “upstairs” question for you regarding insulation. I am in SD, have my basement all done like you said with 1.5″ EPS. I have 2×6 walls upstairs, have 2″ EPS with R-11 3.5″ fiberglass batts over that. Should I put a poly vapor barrier over this? My lumber yard guy says I should, would like your opinion. Thanks for you help, Jim
Yes I would recommend a vapor barrier. Good luck!
Hi Todd,
I have a quick question about the preparation of my poured concrete walls before I put up the blue/pink foam. My wall have what seems like verticle seems running down the wall every 4-6 feet, as well as little circles every 2 or 3 ft, I assume that this was created during the pouring of the concrete. Both are raised at most 1/2 of an inch from the rest of the concrete wall… my question is:
– Should I chisel away the raised seems and circles to ensure the rigid foam goes directly against the concrete?
– Is it prefered to use 8ft by 2 ft foam over 8ft by 4 ft?
– Do you have an article on insulation/preparing basement floors?
I guess I had 3 questions… thanks for your help!
Those lines are just the seams in the concrete forms and the circles are where the form ties are. Chipping it away is one option or you can leave as is if you have enough room with the finished wall layout.
I like 4×8 sheets because there are less joints to seal.
http://www.homeconstructionimprovement.com/how-to-insulate-a-concrete-floor/
Good luck.
Thanks…
What do you mean by :
“if you have enough room with the finished wall layout.”
From other comments that you’ve responded to it sounds like a lot of the issue is ensuring their are no air gaps from foam going into the basement… space between foam and concrete is ok. is that correct?
I was going to use PL 300 to glue the foam to the wall, to each other. and then I was going to use acoustic foam to seal the foam on the foam on the basement side of the foam pieces (the vertical points where the foams meets) and then tape over top… is this ok?
Thanks again for your help… very much appreciated.
Gaps behind the foam are of NO concern. The issue is sealing the entire layer of foam to keep moisture out. Lots of times we don’t even glue the foam to the wall if we frame the walls at the same time. The glue just holds things in place long enough to get the walls up.
Great thanks again for your help. I won’t worry about chiseling the concrete.. I’ll just make sure to seal everything very well. I took another look at tbe seems and they are only a 1/4″ thick maybe less.
Good luck! Let me know how it works out!
Todd,
I am trying to determine with my builder how to finish a walk out basement in a cabin in northern Minnesota. The background is below:
Basement: The basement was built in 1989 and was capped with a flat roof with all utilities added at that time. It is 12” block, with 9 rod and core fills to its footings. The dimensions are 28’ x 30’. It is built in clay soil, on a gradual hill. It is drain tiled beside the footings on three sides and the drains exit to the front,and has a 2 foot overhangs. There is 3 1/2 inches of faced (facing to inside) insulation still on the basement ceiling. The flat roof did leak the first year but I used bleach to get rid of any stains or removed any wet fiberglass. The exterior block was asphalted at the bottom 2 feet and 2 inch Dow XPS pink foam sheets placed outside, but joints were not taped nor sealed, the “4×8” panels were glued to the block and then backfilled with rock, sand and soil. The foam is covered on all 4 sides with spruce siding screwed in with Tapcon screws above ground level. Inside basement walls have a waterproofing latex paint on each wall. The concrete floor was poured on a compacted base and has no cracks but no vapor barrier or foam was laid down before the floor was poured. The inside joint between the wall and floor is sealed with 50 year silicone. I have tested the walls with 6 mil plastic sealed with duct tape to the walls and floor and never had condensate. I have never had a leak in the walls or floor. One room, a bathroom, has 1” XPS foam, 5/8’ moisture proof sheet rock and has no signs of water, mold. The 3/4 “furring strips are concrete nailed to that north side wall. The basement humidity runs above 60-70 percent in the summer and I run a dehumidifier at that time, humidity in the winter 20-30 percent but do not humidify. When the structural engineer built the plans we agreed the space would be heated to at least 45 degrees year round. The walkout basement is completely below grade on the north side, has a sloping grade diagonally up the west and east sides and fully exposed on the south side. The stairs going up butt against the wall and assume the landing should be removed (has to be changed to put in the flooring required anyway) and then finished.
House:
The top two stories and side porch (covered with T&G plastic decking) and front porch (roof covered) added in 1992 and has 2” x6” walls and a 12 x 12 pitch roof. My builder put a drip edge cap against the foam and then covered the foam with fir siding. The exterior is plywood, with Tyvek underneath and 5/8th redwood siding as a finish. The roof and side porch were replaced this year and no issues with rot, mold.
Question:
My builder wants to cover the basement walls with dense foam, Fiberglass, 2 x 4’s, no vapor barrier. But I would like (wish) to save 1/2 foot on each side since I already have dense foam on the outside. Are there any options?
From what I learned in reviewing the last 392 comments it looks like:
–Carpet the floor? (Answer no-have to tile it.)
–1½ foam on walls, 1 inch of space, 2×4 (Answer: Yes, but I lose 6 ¼’ plus 5/8” fire stop wall board)
–Remove the ceiling insulation, and spray foam the ceiling (noise) and the rim joint which now only has 3 ½ inches of fiberglass. (Answer; Costly option but gets cold here and the living and dining room upstairs are covered with doug fir and transmit noise like a drum.)
Todd what is the answer?
Thanks for you work and after reading all the comments you have helped lots of people correct past practices. Few can come close to saying they have changed what other people do!
Best Regards,
Gary
Gary,
Thanks for the kind words. I sure hope you’ll consider signing up for my FREE weekly Newsletter as well!
It seems you’ve done your homework and that’s a good thing. While the insulation on the exterior will certainly help keep things warmer it won’t stop the natural moisture that’s in all concrete from migrating to the finished framing and surfaces in the basement. I prefer having the 1-1/2″ (minimum) foam board then the wall. Because you have insulation on the outside you might be able to use strapping over the foam, then finished wall surface, this would save you several inches.
The floor can be several things, carpet, tile and even some of the laminate floors.
The ceiling above could be sound proofed with resilient channel.
Good luck..hope I didn’t miss anything….crazy busy day!
Todd, the builder is planning to got out and start the work on the walkout next weel and we discussed several ideas this morning. (I sent him your url) In order to save some space-(stairway landing into basement) rather than use 2×4’s use 2×3’s against the 1 1/2 foam, insulate with some EPS Dow 3″ foam? Thoughts? Thanks, Gary
That will work just fine. Good luck and enjoy the project.
Hey Todd –
I’m working on my basement wall and have a 3″ drainpipe running down the wall that will prohibit me from putting the styrofoam board behind it.
My plan is to just have the styrofoam “bump” out around the 2×4 framing on either side of the pipe. Does that pose a problem since the board won’t be flush against the wall?
The other issue I haven’t seen addressed above is what to do about a window in one of my walls. It’s flush with the outside wall and has @ a 6″ ledge. How do I seal/insulate that?
Thanks for this excellent discussion. I’ll definitely subscribe to your newsletter.
You can simply create a foam box around the pipe, just be sure you seal all the seams well.
The window is fairly easy to deal with. Extend the foam to within 3/4″ of the inside edge of the window jamb. Then when you frame your walls you can install a 3/4″ thick, extension jamb, from the window out to the face of the wall finish. Once you get the window all trimmed out it will look really nice.
Good luck and thanks for the kind words.
Wow – FANTASTIC stuff! Thanks so much for answering all of these questions!
I have read through about half the comments and have seen a few similar situations to mine, but nothing exact. I have two questions:
1. My basement is unfinished as of right now, but I am in the process of starting to finish it. One of the walls (the one facing the front of the house) is half concrete and half wood (I believe). The concrete portion is bare, obviously, but the wood portion is insulated with faced batt fiberglass. Should I leave this? If so, when I put the foam board up on the concrete portion, do I just leave the two types of insulation seperated, or do I need to join them somehow?
2. I am leaving about half of my basement unfinished for storage. A small section of the wall, which will be located about 5 feet from any of the finished portion of the basement, lets a small amount of water in during HEAVY rains. Do you think this is an issue? We had the heaviest rains I can remember this August/September, and in total it let in about 5 gallons of water over a 1 month period, so it is a very slow leak.
Thanks so much!
Jeff – Glad you are finding the site useful. I hope you’ll consider signing up for our FREE Weekly Newsletter as well!
1. If the fiberglass is in good shape (no moisture or mildew) then you can leave it. Be SURE it has a proper underlayment placed under it. If you leave the fiberglass just be sure that the two propucts have a decent seal between them.
2. Is there a crack or hall causing the leak? 5 gallons seems like a fairly large amount of water so try to find the cause and repair it.
Hi Todd,
Signed up for the newsletter – good stuff!
The water is coming in from behind the wood that my circuit breaker is mounted on, so it is impossible to see if there is a crack, or if the water is just following the opening for the wires. Do you think this is a serious enough issue to have someone come out and fix it? I don’t really feel too comfortable messing around with a circuit breaker, to be completely honest.
Thanks again!
Sounds like it’s likely a leak at the conduit for the power. Does your power enter the house underground or overhead?
Underground. I live in a townhouse, and there isn’t much room outside directly above where the electric comes into the house. It’s very difficult to tell how the water is entering the area.
Sometimes water gets into the conduit and then drips into the basement. This is very hard to stop in most cases. I think you’ll be ok but there are certainly no guarantees. Good luck.
Todd,
Great blog, I am glad I found it before starting my basement redo in the morning.
I live in Southeastern MA, and our basement is poured concrete walls, but is also a one car garage in 1/4 of the basement. I plan on finishing half of the basement, and leaving the other half as garage/workshop/storage.
The walls are all currently covered (incorrectly!) with wood studs up against the concrete, with bat insulation and plywood walls. there is obvious mold along the bottom of all the walls.
I plan on using the system described above, with the 1.5 to 2 inch foam insulation. On the floor I will put 6mil poly then dricore flooring system, then some kind of floor covering, maybe rug.
The questions I have are:
1: Should the poly on the floor come up and be taped to the foam insulation boards?
2: I plan on using a drop ceiling, do I need vapor barriers for the ceiling?
3: What about the walls that are in the middle of the basement, do they also need the foam or regular insulation with a vapor barrier?
The room will have 2 exits into the other part of the basement as well as the staircase going upstairs.
My main concern is mold more than anything, I want this to be a safe room for kids to play/exercise in.
Thanks so much for this great page, I look forward to your advise!
Brandon
Brandon – I’m glad you found the site useful. I hope you’ll consider signing up for our FREE Weekly Newsletter where I share great home improvement tips, tools and products.
Yes it’s a good idea to bring the poly up and attach it to the foam. Tyvek type tape works very well.
No vapor barrier in ceiling required.
The interior wall separating the spaces is a tough one. If it were my house I’d insulate that will foam as well.
Good luck!
Todd,
I too am glad to find the blog. I recently started working on a basement bathroom. The walls are 2×4’s and had 1/2 paneling attached.
I removed the paneling and would like to insulate the existing walls.
I’m in need of guidance in regards to insulating a basement wall, I removed the 1/2″ paneling from the walls and found no insulation so I would like to insulate. The walls are currently studded out with 2×4’s and are 1″ away from the foundation. Some places less with concrete chunks. I have been told by a big box store that all I needed to do was add 3 1/2″ faced insulation but than I came upon this site. I was wondering what is the best way to insulate without removing the walls. I may be able to slide a 1/2″ or maybe a 3/4″ foam board behind the studs and than add 3 1/2″ faced fiberglass in between the studs. I was going to tape and calk around the 2/4’s and foam.
Frank – First off please, please, please try to avoid asking for advice at those stores. No offense but many of the folks working there just don’t have the proper experience and this is one of those situations. The worst thing you can do is insulate your basement that way.
Honestly, you need at least 1-1/2″ of closed cell foam against the concrete BEFORE any fiberglass is used. I would recommend that you install a layer of 1/2″ against the concrete, tape the seams well. Then install 1″ between the studs and pushed in tight to the first layer of 1/2″. Then use your fiberglass.
Unfortunately this isn’t perfect. I’d rather see the 1-1/2″ behind the studs.
Good luck.
Todd, Will 1 1/2″ Expanded Polystyrene Foam added in between the studs pushed to the concrete.Than adding great stuff to fill behind the 2×4 studs followed by fiberglass work?
It’s a solution that’s better than some. It’s hard to say how well that foam behind the studs is going to seal. It’s likely moisture will still get to the studs and cause problems down the road.
Todd; I’ve been (slowly) finishing my basement space in my ‘free time’ over the past 3 years, and am just at the point of putting up the drywall – – – but I am agonizing over the ‘do I put up a 6 mil poly vapour barrier, or do I not?’.
I live in the Toronto, ON CAN area and have insulated in the following way:
– 1 inch blue foam board fully adhered top to bottom to concrete block wall (read your article after recommending min. 1-1/2″);
– fully sealed all joints with combo of ‘red tape’ and spray foam sealant;
– interior framed 2×4 wall inside blue foamboard, with bottom sill in ‘Bluewood’;
– used Roxul R-14 insulation inside the framing (found this to be a great alternative to Fibreglass – both easy to work with and supposed to be water repelant.
So – – – the question is; Should I consider using a 6 mil poly vapour barrier, and is there any downside to using one? I’ve got a left over roll from an earlier reno, so it certainly isnt an added cost at this point. I just dont want to put it up if there could be a reason NOT to!
One more bit of info – the house has has local leaks in the walls in the past, but all have been well addressed with re-grading, excavating and waterproofing, and eases/downspout repair.
Your input is appreciated! (Best article source I’ve been able to find on-line).
JB
Well I’d prefer that you had more foam first. So…..I’d skip the vapor barrier. The last thing you want is to trap moisture between the two.
Hi Todd,
Thanks for the article. We have a new construction home in upstate NY. There is a 3 in channel around the perimeter of the basement (drainage, I think) – there has never been water in the drain during the 2 years that we have lived here. How would you go about framing/insulating in that situation? (We will be using 2″ foam board against the poured concrete walls and fiberglass insulation between the studs.) Where would you place the wall in location to the drainage area? Would you recomend filling the drain? Any suggestions would be great… we haven’t been able to find any information about this online.
Thanks!
Go ahead an install the 2″ foam board as I show in my other articles. The foam can sit right on top of your 3″ trench. If any water gets behind the foam it can fun down the wall and into that trench. Next I would hold the wall out 1″ so the back of the framing is at least flush or further from the front edge of the trench.I would cut a 1″ wide piece of foam and lay it on top of the trench in that gap. Seal that well. This will keep moisture from leaving the trench and working up into that space.
Good luck!
Great information you have here! I am currently redoing my basement. The basement has only leaked 4 times in the 14 years I have owned it, and only through the floor cracks after very extended periods of rain (water table I gather). I put on drylok 10 years ago to the poured concrete walls to keep it clean looking and smelling better. I never finished the basement because of the water appearing once every few years from the floor.
Currently I am finally having drains put under the floors, tied back to a proper sump pit. I plan on following your advice and I am going to glue up 1 1/2″ rigid foam to the walls but with them pre-notched for 1×3 furing strips(to be tapconned), then I will attach dry wall to furring strips. I’ve read almost every post and article but still I am unclear on a couple things.
1. The old drylock has a few efflorescence spots that have bubbled through showing white powdered areas, not bad but noticable in some areas (no water, ever). Do I scrap down and re-drylok these before I glue up the rigid foam? or go right over it?
2. I don’t have much height clearance and want to put down a laminate floor, can I put down 1/2″ rigid foam directly on the floor, tape the seams, foam seal to walls and then put down a sturdy laminate? (sorta like barricade)
3. Since I know I now will have the proper drainage under the floor, should I chisel out and patch every sprawling crack and patch with hydraulic cement? or can I put the 1/2″ rigid right over it?
4. Also about the rigid foam on the walls, if you cut it to fit tight between the floor and joists, what do you do about the small concrete ledge on top of the wall? Cut a small strip and glue/tape it in?
5. Lastly, when you put the 2″ insulation in the rim joist and seal it, do you line it up with the bottom sill plate, leaving an air gap between the insulation and outside board? Do you fill that area with foam? or press and seal the insulation right against the outside board.
thanks so much!
-John
John – Welcome to the site. I’m glad you find it useful. Below are a few thoughts/responses to your questions.
1. Efflorescence is a sign of water infiltration through the concrete. It’s creating by water pushing through the concrete and depositing lime on the surface. While your case doesn’t sound too bad you really should be certain that all your drainage around the exterior of the house is installed and working properly.
2. You can try that approach but it wont’ stop moisture and water. You’ll need some sort of vapor barrier in addition to the foam.
3. I would seal any large cracks. Hairline cracks are not an issue.
4. Yes
5. You want the insulation tight to the rim joist. You also want to fill that gap at the bottom. You a continuous insulation layer from slab to sub-floor.
Good luck.
Todd, I have one wall that the stairway is against. I really can’t build that section of the wall out at all, since my stairs would be too narrow. I believe my only option is to put up poly and then moisture resistant sheetrock in that one area. what size or thickness of poly has to be used so it’s a true vapor barrier? Also would this be the same for under the laminate floor, to preserve the ceiling height? thanks
John – I wouldn’t recommend that at all. That will keep moisture from the concrete from getting at the sheetrock, but it won’t stop warm moist air from the finished side getting behind the sheetrock, hitting cold plastic and then condensing. If I was in that situation I might choose some type of wood wall panel. Far more forgiving with moisture.
Hi Todd,
I truly appreciate the work you’ve put in to this blog. The information, research and experience that’s being shared is “price-less”. I’ve been considering doing my basement for quite some time now. I’ve done extensive research online and feel that what I’ve read here makes the most sense. Ok, enough Fluff for now…lol
After reading all 420 comments over the last few days, I think I understand. My plan is to put up (whether on it’s own or glued), 2″ Closed-Cell Foam Board directly to the concrete poured walls…then, 2X4 walls (no vapor barrier other than what the Foam Board has provided), and depending on whether I decide to fiber-glass (insulate) the 2X4 walls for an added R-value (still undecided at this point), I will add an inch of separation if I do, no separation if I do not, correct?(1)
Based on your experience, I can use any grade sheet rock with this application correct?(2)
I want to maximize the height of my basement. I plan on installing a drop ceiling and will leave the current insulation that is suspended in between the floor above. (Within the I-Joists). The paper is facing up toward the floor with the fiber-glass facing the basement. This is so condensation does not get trapped in between the paper-side and the floor above correct? (3)
I still haven’t decided how I’m going to finish the floor. I’d like to lay down something that looks like hardwood flooring. While trying to stay on a limited budget, what products do you recommend? I see that some come with a vapor-barrier incorporated into its construction but am unfamiliar with how cost-effective it is and how reliable it is. If it does come with its own vapor barrier, how does that tie-into where it meets the walls? Simply leave it be, or should I still lay a vapor barrier underneath whatever I end up using on the floor? (4)
Lastly, how do feel about products like the “Insofast” system? It is 2″ of Closed Cell Foam with plastic studs built into it. I’m guessing you’ve heard of it but I haven’t read any comments on it on this blog. If you do recommend that type of product, please give the pro’s and cons. Based on estimates that I’ve obtained, its not that far off in cost. What are your thoughts?
Thanks again for all you do, and my apologies for the mini-novel.
Gilly
Gilly – My pleasure, thanks for the kind words. I hope you’ll consider signing up for our FREE Weekly Newsletter so you can continue to get all kinds of great tips, product reviews and the latest home improvement advice.
1. You are correct. The gap is one of those things thats not necessary, it’s just nice to have air spaces if you can afford the space, sort of belt and suspenders approach.
2. Yes. However, if you want to be really conservative many people like to use Moisture Resistant or Mold Resistant drywall in their basements.
3. The paper is facing up because the floor above used to be the “warm” side if your basement was unheated. You can leave it as it is as you won’t really have a cold vs hot side now.
4. If head height is a concern and you want a wood appearance I’d go with a good quality laminate floor. They are made to sit directly on concrete. Depending on the manufacturer you may be able to install a vapor barrier (plastic) before it’s installed, then tape that to the foam on the walls.
5. I haven’t used Insofast. However, a quick look at their site reveals a hidden detail that I would be leery of. They use EPS foam which is closed cell foam balls that are adhered to each other. Why is that important? EPS is not a true vapor barrier in my opinion. The voids between balls are really small areas for water vapor to penetrate through much easier than in EPS foam. You can learn more about foam types here: http://www.homeconstructionimprovement.com/foam-board-insulation-values/
Good luck!! thanks for stopping by.
Hi Todd, and thanks again for the quick response.
In regards to (5.) – Thanks, it’s the small details that a novice doesn’t know about that could lead him in the wrong direction. Not that it’s a bad product, but it too has it’s flaws.
In regards to (4.) I should lay the vapor barrier directly on the concrete (on it’s own with no adhesive), and then lay the laminate flooring directly on the vapor barrier. Is that correct, or should I be putting something between the vapor barrier and laminate flooring? Someone mentioned to add a buffer of sorts for comfort, some time of 1/2″ foam. What are your thoughts?
Thanks again, and I did sign up for the FREE newsletter. Your Miter bench looks great. I have my miter saw set up on a rolling aluminum cart for mobility, but I obviously can’t do great lengths without setting up supports. With the cart being aluminum, it’s easily transported when needed. I also plan on winning the Dewalt Saw, so thanks in advance (grinning
Gilly
My pleasure!
#4 – I would check with the laminate flooring specification. Many of them use a foam under them, some have it attached already. You want to be sure you follow their specifications so you don’t encounter any warranty issues if the product happens to be faulty.
Hi Todd
I’ve been reading the posts for hours now, and it just seems like there is no for sure way to complete a basement. After dozens of websites I am still as confused as before I started researching.
“the walls”
I recently had a contractor come in and install a interrior french drain in the basement with about 4 inches of the dimpled plastic sticking up the wall. My basement has been dry ever since. I am leaning towards the foam board glued and taped against the wall, but of course im just another person that would like to save a few dollers where i can. My contractor told me I should just get 6mm plastic put it on the walls and tuck it down in behind the dimpled plastic that leads under the concrete to the interrior french drain. He said after I complete that to just go ahead and frame out my walls. He also added to not tap-con my base plate of my walls he told me to use liquid nails in fear of the tap con holes could draw moisture, will liquid nail hold … After the walls are up im going to use fiberglass insulation to add more r-value to the basement. So i guess my biggest question with that paragraph is what should i do 6mm plastic then frame up, or foam board glue and tape it up and frame.
*Another question that I have is if I go the route of the foam board i would probably use 1 inch thick. I would then frame, and then add fiberglass insulation in between the studs probably an r-11. The 1 inch foarm board is i believe rated at an r-5 totalling a my wall having an r-value of 16 do you think that is to much insulation that I could be over insulating my walls making them not being able to breath causeing them to sweat? FYI i live in central PA
“The floor”
Of course I’d love to have carpet down for a warm cozy feel, but my biggest fear is for the interrior french drain to clog up or fail ruining the carpet and wasting alot of money. So as of right now im leaning towarding caramic tiles. I know it will be a cold floor but I’ll just throw down some area rugs and wear slippers. And if it gets wet it wont be ruined…I hope…
I would really like to go with carpet on the floor and if I would go that route i would start by putting down a moisture barrier (6mm plastic or foam board dont know whats better) then i would put down a layer of plywood and tap con it into the floor. Then capet padding then carpet. What do you think about carpet or tile?
“The ceiling”
As of right now I have a couple different options but might i add that i removed all the insulation out of my ceiling and dont plan on replacing it. I have a coal stove in my basement and am going to let the heat rise from the basement through vents in the ceiling of the basement and vent in the first floor of my house. I plan to make some sort of box to match between the vents so heat is not wasted in between the rafters…back to ceiling options. Just like anyone else I have water lines, plumbing lines, and electrical lines ran in between the rafters. I’m leaning towards drywall, tonge and groved pineboards, or fake wood like a laminate flooring. All three of those options are obviously pretty much perminent after the are put up. Taking away acess if i needed to fix somthing like a water leak or anything. I know a drop ceiling would be ideal but i was never a big fan of them due to the fact of I would be loosing head room, but i might have to go that route incase of a leak. I guess my question in this paragraph is do u have any other suggestions for ceiling options that might look nicer than a drop ceiling
(sorry for the bad spelling and grammer I typed this up in a hurry)
Ryan – Thanks for stopping by. I’ll give you my 2 cents but I think you already know what I’ll say.
1. Walls – If you take any advice from me this is the one you really should listen to or you’ll be VERY sorry down the road. DO NOT LISTEN to your contractor. 6 mill poly on the wall will only fix the moisture problem from the concrete, it will not fix moisture from the finished space. That moisture will hit the cold plastic and condense. You MUST use 1-1/2″ minimum thickness XPS foam or you’re wasting your time and money. Find other areas to save money….you’ll be very glad you invested in the foam.
2. Floors – Tiles are the safest and you can still put area rugs down. I would use Schluter-Ditra between the concrete and tile.
3. The other option I’ve seen at the trade shows the last couple of years are drop ceiling tiles that are actually wood. They look amazing and they still offer the access that you’ll most certainly need.
Good luck!!
Todd
Thanks for the advice. I do have a few more questions.
* Can I use liquid nails between my base plate of my framed walls and the concrete? Will liquid nails keep my wall in place? I’m nervous to tap con them through the new concrete that was poured over top of my interrior french drain because the concrete isnt that thick. My worry is that the tap con holes could draw moisture.
* My next question is 1.5 inches of foam board against the block wall, and r-11 insulation between the studs to much insulation that I could possibly be over insulating my walls causeing them to sweat?
Thanks for the speedy response
Liquid nails should do just fine. That’s how we install walls when there are radiant tubes below.
That’s not too much insulation. We often install even more than that.
Todd,
I’m in the process of re-doing a partially finished basement (done at least 35 years ago). When the 2 x 3 stud walls were put up, they put clear plastic on the side facing the concrete block (with about an inch air gap). The basement is partially at grade and partially below grade. I live at the top of a hill and have never had any moisture problems. There was no insullation at all behind the wood paneling (4 x 8 sheets). My questions are:
1. Should I remove or leave the plastic before I put in rigid foam?
2. If I remove the plastic, should I put a water resistant paint on the wall (to seal it), then put up the rigid foam?
3. Should I leave an air gap behind the rigid insullation and just wedge it between the studs?
Thanks
Paul
You can leave the poly. The bigger issue is only installing foam between the studs. It’s not ideal but it’s really your only option without tearing out the framing. An air gap would be nice incase you get condensation between the poly and studs.
Todd you are a angel for answering and helping all these folks, I bought a new home and the basement walls came prewraped in a “tyvek” type wrap, about 2 inces thick, and prenailed in place, I was told I could put framing over this and the builder said i dont need any insulation between studs.. he told me to slit the plastic randomly so moisture wont be traped between sheetrock and wall.. what do you think of this? secondquestion,, I saw a neat prodct called “drycore, 2 by 2 foot squares you place on concrete floor and it allows air to flow and then you put your sill and framing on top of it,, I was going to use Bluwood for sills and all framing to be sure of no rot,, this was sills never touch the concrete? what do think of this,, oh I was going to use anti rot drywall too,, I have zero moisture issues so far, but I would rater overkill and be safe? thanks Todd,, Chris
Drycore is great for the floor. I’m not sure what you have on the walls. Is there some sort of name on it?
Todd, I have a unfinished basement and only the builders poly wrapped insulation, top to bottom,, what do you think of using “drycore” 2foot by two foot panels all the way up to wall and then putting Bluwood on top of floor,,? that way no moisture will hit sills? tks Chris
Are you suggesting putting drycore on the walls?
Todd,
There is a colossal amount of information on the general subject of basement moisture control and prevention available on the internet, and I have spent more time than I want my wife to know about studying your comments, the BuildingScience.com site and the GardenWeb sites, just to name three.
It seems to me that nearly every situation is unique, due to climate, details of construction, site orientation, ultimate purpose, personal habits, personal preference, etc., etc.
I have tried to parse out the significant suggestions to suit my situation here in Canton, GA (35 miles north of Atlanta), and I would greatly appreciate your input as I try to decide how to finish the floors in my 1800 SF daylight basement.
Our house is about 8 years old, with a poured slab and poured walls (7.5″) on the uphill sides. The daylight walls are 6″ studs with fiberglass insulation. It has always been bone dry, with no efflorescence on the concrete walls. It has always been pleasantly cool in the summer and warm in the winter without any HVAC in the basement.
I have recently finished the walls pretty much as recommended by BuildingScience.com, and have had a high efficiency heat pump installed. I haven’t used the HVAC yet, but it’s programmable, so I think I can set the fan to run often since I don’t want stagnant air.
My current thinking is as follows:
Bathroom – Ceramic tile on thinset directly on the concrete
Laundry – Same as bath
Storage – Latex floor paint
Sewing Room – Carpet on Roberts Airguard underlayment
TV Room – Carpet on Roberts Airguard underlayment
Remainder (700 SF) – Snap-lock laminated flooring, 10mm on Roberts airguard
I am very concerned about the moisture barrier subject. All the local big box stores preach the moisture barrier approach, but many of the really thoughtful articles I have read lead me to believe that a moisture barrier simply provides a place for mold to grow beneath it.
Is it not better to allow the concrete to breathe so that moisture can be evaporated by the HVAC system? Should I use 1/8″ cork instead of the Roberts Airguard?
Thanks in advance for your comments.
Ron – Sounds like you’ve done your homework. You are certainly far more prepared than most!
The vapor barrier on the slab is an interesting topic. First let me say that it would be nearly impossible for mold to grow beneath a vapor barrier on the slab unless there is a food source. If the vapor barrier is some type of plastic or foam that simply won’t happen.
In commercial construction we install carpet, tile, and laminate flooring directly over concrete slabs all the time. My best advice is to strictly follow the manufacturers recommendations for on slab installation. It’s quite likely that you have a vapor barrier under your slab which helps prevent additional moisture from coming up through the slab. So you really only have to deal with the vapor that’s trapped in the concrete and will be trapped in the concrete forever.
In your situation a vapor barrier certainly wouldn’t hurt under the laminate and possibly the carpet. The carpet is tricky because I assume that the underlayment get’s glued down right? That can be trouble if it’s a water based adhesive.
Thanks for the response.
Yes, there is a vapor barrier beneath my slab, so maybe I’m lucky there.
The question of gluing down the carpet underlayment was the reason for my question about cork as an underlayment. Since it is semi-rigid, would I get away with no glue?
Really not sure Ron…..those are technical questions best left to the flooring folks. I would ask them for suggestions and note your concern about water based adhesives.
Todd i have an interesting situation my home is not even a year old and i had been getting moisture in the corners of the basement and by the windows. The insulation goes half way down the wall the builder came and told me that it was normal being a new house that there was alot of moisture and he said frost on rim joist was normal as well. Well i live in Iowa its been freezing the only way im able to get humidity below 60% is if i run a dehumidifier non stop basically everyday. Now that its been raining for about the last week i pulled away the square pieces of insulation covering the rim joyvce now there is black mold all over rim joist but only on North side of the house.
Basically i want to know is this normal or is the Builder feeding me a line and what could i do ?
Jason – Sorry to hear about your situation. Here are my thoughts.
– Your builder is correct that there is HUGE amounts of moisture in the home the first year or more. Run your dehumidifier as much as you can afford to.
– We seldom insulate rim joist with firberglass today for this VERY reason. Fiberglass pretty much sucks in most cases. There’s no easy way to seal it with a vapor barrier. That’s why I highly recommend using foam similar to this article: http://www.homeconstructionimprovement.com/rim-joist-insulation-insulating-options/
– Mold is not acceptable. He used the cheap easy way of insulating your rim joist and he likely knows this. Obviously foam would have been much better but also significantly more expensive. My recommendation is sealing things properly with foam.
Good luck.
I guess a follow up question to that is what kind of foam closed cell or open cell and whats the diffrence? The things ive seen have been kind of confusing as far as correct application.
Jason – Closed foam is the only product that I recommend in residential construction. Open cell foam can hold water like a sponge. If you have a leak the foam will hold water and cause serious problems.
Ok thats what i wondered ive heard mixed reviews. Ive seen alot people say the exact thing you’ve said then also say that the closed foam wont allow moisture to escape and it can also cause rot or damage to wood so ive been confused. I only intend to use this in the rim joistto prevent moisture/molding/frost.
Open cell foam is the kiss of death in a house…it shouldn’t be used…EVER.
Hey todd. Awesome site.
I have a few questions. I started doing my basement. And applied 1 1/2 foam on the walls and didn’t glue it to concrete waLls just made it tight top to bottom. Is this okay?
And also I plan on framing with 2×4 and then insulate it with r13. Will faced insulation be good?.
Levi – Your approach is fine. With only 1-1/2″ foam it’s a toss up. Unfaced is the safest.
Hi Todd:
I am finishing my basement and there is an interior french drain so there is about a 1/2 inch space for it between the floor and the wall in the ground. I would like to use your method but if the foam board insulation is glued to the concrete foundation wall, any water that flows down the concrete wall will have no way of getting to the french drain and evacuated via the sump pump. What solution would you propose for this dilemma??
Thanks!
Clara – Either put beads of glue vertically to create channels for water to get down to the drain or cut the foam so it’s tight top and bottom and omit the glue.
Good luck.
Thanks Todd. What do you think of furring out the wall with a hat channel and attaching the foam board to the hat channels?
You can certainly do that. That will help with air flow. If there is moisture the hat channel will corrode over time.
Hi Todd:
Remodeling a room in the basement. It originally had carpet on the floors and paneling on the walls. 2 of the walls are exterior walls. They just had 1″ X 3″ furring strips attached the concrete blocks with no insulation on the exterior walls. I really don’t want to tear it out and put 2″ X 4″ stud walls in. What do you recommend to keep moisture down to a minimum? I’m replacing the carpet with laminate flooring so I was going to put a vapor barrier down on the floor. Should I run the vapor barrier partially up the walls also?
Thanks!
Scott C
Central Illinois
Scott – Thanks for visiting our site. I hope you’ll considering signing up for our FREE Weekly Newsletter. It’s full of free tips, product reviews and even giveaways.
I certainly understand the hesitation to not want to take the extra steps. However, in the long run, having a properly insulated basement will pay off. If room is an issue I’d use 1-1/2″ thick foam directly on the foundation wall (remove the 1×3 strapping). Then install 2×4’s flat on the wall and TapCon them to the wall. This takes up 3″ but you’ll have a great insulation layer that will keep out moisture.
The vapor barrier from the slab should run up the wall 6 inches or so. You might want to read more on this topic here: http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
Good luck.
Hi,thank you for this site. I am looking to build in Phoenix AZ. a basement home for my self. How does the concrete cure in ICF walls that are 8 feet in height.
Richard – Concrete cures from a chemical reaction and NOT by drying out as some people might think. Concrete is often placed in mass pours sometimes over a hundred feet deep in foundations. Curing in an ICF wall is not a problem.
Good luck.
Hi i wanted to ask you a couple questions regarding the basement vapor barrier. We are about to have our basement finished the contractor states he would put vapor barrier directly against basement wall then framing. Is this the best way to do this? Thank you!
Jason – Depends on how you define vapor barrier. The vapor barrier must be either closed cell spray foam or a minimum of 1-1/2″ (2″ preferred) of XPS foam board. I have several other articles on the topic that discuss this in even more detail. However, a simple poly vapor barrier is NOT adequate and will lead to serious mold problems down the road.
I will have to get specifics and let you know. I have a new home and basement has had humidity issues all winter/summer. I beleive he was going to seal the wall with some kind of sheeting and seal the floors with some kind of moisture seal.
Ok what he says they use is 6mila plastic sheeting on basement walls.
Jason,
That’s exactly what I thought he’d say. Please listen to this advice. DO NOT use that approach. You MUST have either closed cell spray foam installed or a layer of 1-1/2″ thick XPS foam board taped and sealed. Check out this article for more information: http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
If you use his method…you will have mold in your basement eventually.
Great topic and many answered questions. I am starting a basement project in Wisconsin and will use the 2 close foam board and studs placed on the 2 inch foam. My question is I will be creating a wall that will enclose the sump pump and a nook (est. 10×8) which will be a wine celler in the future. I need to insulate the interior wall keeping the sump pump and nook area of the basement cooler. Do I use the 2inch foam board in the studs and use hardie board instead of drywall for my finished board. I want to stay away from paper. The so called green board is starting to mold in my shower after 10 years upstairs. Does this sound like correct in finishing this part of the basement until I fix up the wine celler? Or can I leave this section cold which stays at 61to 65 degrees all year. I have 9 foot ceilings and a black tar or plastic on the outside with 1 1/2 inch pink board on exterior poured walls.
Again thanks for your advice.
Paul – Great question. I’d use some sort of wood to cover those walls as it will be more forgiving. Ultimately it comes down to a code issue and protecting the foam. Typically (you’ll have to check your code) the code will require a 20 min barrier….i.e. 1/2″ sheetrock, or some sort of wood paneling. For a room like that you might want to use some type of plywood for now. Good luck.
Hi Todd,
I have an old stone basement technically in a flood zone. Althought this part of town floods only every hundred years or so, the area I live in is very humid. I am about to start rejointing the stone walls in the house and am not sure what to do about the basement. I’m told if I rejoint (lime + sand) without a moisture barrier, my rejointing won’t hold up very long. I do not plan to centrally heat the basement, but would like to have a small bathroom in it, so I will need to insulate and heat that. What do you suggest?
Repointing the stone shouldn’t matter at all with regard to a vapor barrier. Plenty of basements have pointed stone work without any vapor barrier.
I’d be cautious how much money you sink into a bathroom down there. A room in a stone foundation basement, located in a flood zone, is ripe for a flood. Even though the floods are on a 100 year cycle that doesn’t prevent them from happening next year, or even a couple years in a row.
If you must have a basement down there, I’d suggest framing walls and spray foaming the walls adjacent to the old stone. That will help stabilize the wall and also lock out moisture. Be sure to use closed cell foam.
Good luck.
Am having trouble finding anything or anyone who knows anything about closed cell polyuethane foam insulation in France (where I live). I am being to suspect it doesn’t exist here. Assuming I’m right about this, do you have any next best choice ideas? what about a double wall, insultated on the interior, with the whole thing at a (breathable) distance from the stone wall?
Thanks for your help!
That will certainly help, but it won’t stop “open cell” foam from soaking up moisture and holding it like a sponge.
Todd…
Absolutely fantastic site!
I have already done everything as you described, but came across your site after searching on whether or not to use foamboard WITH the batts. The reason I was curious is that after I put the foamboard up, I used a infrared thermometer to check temps. The temperature between an interior stud (near steps) and the foamboard was less than one degree. The difference between the same foamboard and the block wall adjacent to it (wasn’t foamed up yet) was six degrees. If the foamboard alone was doing the job, why would I add the batts? Am I missing something?
I have the batts already, but I am now wondering if they are worth the cost and the work for less than one degree.
For reference, I live in Pittsburgh, it was last Winter, and it was 38 degrees outside.
Thanks again for the site and in advance for the response!
Daniel
Daniel – It just comes down to comfort and performance. In fact, in many locations like here in NH we have an Energy Code that requires a certain level of insulation to meet the code. So some people will use an additional layer of fiberglass to get extra R value.
Todd, just stumbled upon the site after days and days of researching insulating basements. Fantastic resource! Thank you so much! I have read a ton of the comments but there are so many that my questions might be answered somewhere already…but I can’t find anything.
I have a 1 year old home in southern Ontario. The builder has fiberglass insulation covered in vapor barrier the full length of the wall. I have been told by several contractors that they will just frame over this to build my walls. Is this ok?
I have been researching xps rigid foam boards and prefer that method however it is rather expensive. If I should go this route, I read that glueing the foam to the walls may not be a good idea as the glue is food for mould and bacteria etc. any truth to this? I was thinking that I would put 2″ foam on the walls, seal it with spray foam top and bottom and tape the seams, then frame right up against the foam, no space. Then re use the builders fiberglass insulation between the studs, then drywall (no plastic sheet req I’ve read) All this sound like a good plan?
Thanks again!
Martin – Glad you found our information useful, I hope you’ll sign up for our FREE Newsletter or LIKE us on Facebook.
I would certainly remove the fiberglass (another good resource for Canadians is Holmes on Homes, he does a great job with foundations up north). I’m not sure there’s much validity to that concern, and even if there was, it’s on the wrong side to even matter.
However, many times we are able to stand up the foam, tight fit it top and bottom (occasionally put a dab of spray foam on the back to get the panel to stick), the tape seams. Many times that’s all you have to do. Re-using the fiberglass in the wall bays is a great re-use.
Good luck.
Thanks Todd for the fast response! This tread has been going for quite a while, didnt know ig you would. I’ve signed up for the newsletter too!
I have another question. You said make sure the foam board is tight at the top and bottom. At the top the concrete runs paralel with the joists and there is a gap that the house sits on, on the top part of the concrete wall. How do I get it tight to that? Do I put foam board on the top flat part of the concrete then fit the wall foam under that? Sort of making an upside down “L” Then a board down the wall, then sprayfoam the bottom of the wall and foam?
My pleasure.
The idea here is to cover all the concrete. So….yes place some on top of the wall up tight to the wall plates. Then go down the wall, either tape and/or foam the joints to be sure you have a good seal.
Good luck.
Seal the bottom too? I’m planning to not put foam on the floor but dricore instead. Didn’t know if sealing the bottom of the foam wall would trap water vapor from going up the wal from under the dricore, or stop water from escaping from the wall… Sorry last question :)
it’s not super crucial, for your setup, I’d install the dricore, then put the wall foam on top of that, maybe a bead of caulking between the two, other than that nothing special is needed.
Hello!
My basement walls are painted with UGL waterproofer. This was done to control humidity in the summer. I live in north NJ. The basement is usually 60-75 degrees year round with no water issues.
I am gutting and replacing a 1/2 bath in the basement.
As for vapor barriers will the UGL cause any problems or just be a bonus. I plan to put the blue board on the block, recess studs 1/2 to 1 “, install R11 kraft faced fiberglass, then green board and partially tile it. And also install an exhaust fan.
Too many vapor barriers or am I good to go?
THANKS A LOT for your time and knowledge.
Ray
Ray – You’ll be good. Thanks for visiting our site.
Hello,
I am about to finish insulating my basement wall with foam board 1 1/2 in foamular board from Owens Corning. I only have two walls to insulate as the other two are interior walls. I have a few question have..
1. Should I seal where the foam meets the basement floor(which is concrete) and if so should I seal with great stuff foam or adhesive tape?
2. I plan on using a T-111 type board for finishing the walls, is it okay to us PL Foam Adehsive Caulk to secure the T-111 board to the foam board instead of using furring strips. I am afraid if I drill into concrete that in the future I could have water coming through the holes. It is concrete block wall.
THANK YOU!
Jay – Good questions.
1. Really depends on your basement. In most situations I would just let the foam be a tight fit. If you have a VERY dry basement you can seal it, but that won’t allow water to get out if you ever have a flood.
2. Adhesive alone won’t keep the foam and T-111 in place. Install strapping over the foam and behind the T-111. You can shoot the strapping on with a concrete nailer, that won’t be a big deal.
Hi Todd. Great info man, thank you. I would like to insulate and heat my NY basement but after reading through the site i’m concerned about how my walls will “dry.” The top 2′- 3’of wall is above grade but has been painted/drylocked all the way up (exterior). I’m suddenly thinking this will be an issue and wondering if you can make any suggestions. Thanks again.
Jay
Jay – It really isn’t an issue. Even though it’s been painted the moisture will use the path of least resistance which is still likely the drylock. I wouldn’t hesitate to insulate the basement.
Todd,
Awesome information…I have read a lot of these articles, and most of the comments. I am getting confused because, like stated above by another commenter, I was told by a contractor to install a 6 mil vapor barrier directly against the concrete wall, followed by framing, insulation, and then rough cut lumber (my walls will simply be vertical pieces of rough cut lumber). I was going to use 1x3s for framing, and use a 1x4x8 Polystyrene Insulated Sheathing.
So my question is, should there be no air gap at all between my insulation and concrete walls? On the inside if the insulation I would have rough cut, so this would not be air tight, and none would be needed, correct?
As of right now, I have a dry basement system installed, with drainage in the lower corners or all walls to my sump pump. I am getting a minor amount of moisture coming through the walls, after drylock has been put on. This is only spotting, not running, but noticeable.
Thank you for any assistance!
Dan
Dan – Thanks for the nice compliment. First off let me tell you that a vast majority of contractors insulate basements wrong. Forget about plastic anywhere in the basement as it’s just bad news.
You should use 1-1/2″ minimum, 2″ preferred closed cell foam board installed against the concrete. The foam just be sealed well at seams to prevent moistures from the concrete from getting to the framing and insulation. The thickness is such that the interior surface of foam won’t be cool enough to condense and moisture that hits it from the interior side. Don’t worry about the concrete side, mold needs food to grow, concrete and foam are not food for mold.
Next place your framing up against the foam board. Then you can install additional insulation in the stud cavities if you need more R value. Either use un-faced or kraft faced insulation. Do NOT use plastic.
Todd,
When creating a vapor barrier with XPS spanning from the floor all the way up to the rim joist when do you need to be concerned about “drying to the exterior”? The block foundation of my house only has about an inch or two exposed to the outside. The rest of it is underground. The sill plate is not pressure treated and just sits directly on top of the block foundation (no break). My fear is that by preventing moisture to dry to the inside it will overtime start to rot the sill plate because the moisture has nowhere to go.
Oddly enough in places there is fiberglass insulation that sits between the sill plate and block. Of course this seems to be a great place for mold to grow. Especially if drying can’t occur to the inside. Any thoughts?
Thanks for your time! Just a great site for people looking to do the right thing.
Josh – First off I hope that the exterior grade at your home isn’t really an inch away from the siding and framing. That’s a bad deal to start with. You should have 6″ to 8″ min for good building practice. At any rate, unless your home is new, I wouldn’t really stress over the 1″ for drying to the exterior as we’re talking a pretty minimal amount.
Just my 2 cents…good luck.
Todd, great site.
Live in Mid-Michigan, newer construction, poured walls.
I know you’ve mentioned no plastic in the basement, but…
I’m going to put up the 2″ XPS. Then a studwall with insulation. I’ve seen mention of plastic between the drywall and studs, but what about putting the plastic on the back side of the stud wall? What problem would you have with this?
Second question – if the XPS foam board barrier is forcing the moisture up, what’s to stop an issue of too much moisture at the floor joists above?
Thank you in advance.
Plastic is bad because it traps moisture and it makes a great surface for damp air to condense on if the dew point is correct. So it’s best to avoid it all together if you can. The 2″ foam board will act as your vapor barrier, nothing else is needed.
The exterior top of foundation wall will be exposed, it has the greatest area exposed to air, and will provide the path of least resistance for the escaping vapor.
Good luck.
Hi Todd:
I asked a question about the space between the foamboard and the framing in another forum.
Now I’m reading about the vapor barrier.
This is what I plan to do, and what I already have purchased.
My basement has had very little to no water issues. I have had a professional seal where the bottom slab meets the foundation wall with DRYLOK Fast Plug, and with 4 coats of DRYLOK latex waterproofer extreme. – It was a mess and alot of work, but that is done.
I have since followed your advice on fixing drainage issues, I’ve installed new drains outside. I have sump pumps, that are rarely used. – So history of this basement is, little to no water.
===================================================================
my plan is to foamboard the basement walls with 1 1/2 foamular 150. Doing that now. – then frame with 2×4 studs, and deckboard/PT lumber on bottom – as per your advice – then install R15 fiberglass with the kraft facing – “already purchased before I read your link”
and 5/8 sheetrock.
So question is, can i use kraft faced insulation, or do I have to pull it all off? – I can’t return this kraft faced material, i’ve had it for over a year now – to get unfaced insulation.
It would be a big hassle for me to get unfaced at this point.
Do you think I’ll be fine? – Between the foam board and the R15 – I’ll have R22.5 for a great insulated basement.
Since I had the pro install the drylock stuff, we have had huge downpours, tons of rain and snow, and no more water leaks.
I had this down, because some water came in once, and it was due to improper drainage, the water came thru the slit between the wall and slab. –
Do you think doing the drylok thing was worth it? It should have had a seal anyway – it wasn’t there before.
thanks for listening, and giving me advice on my project.
Greg
Minot, ND
Greg – I think you’re fine. The kraft face vs un-faced issue is a tough one to answer. Considering the fact that you have sealed the wall first, then used 1-1/2 foam, I think you’re more than ok.
Good luck. You’ll have a very nice basement space when you’re finished.
Hello Todd,
I just found your site and have to say how impressive it is that you dedicate as much time as you do to it and your thoughtful responses you give. I also have to say it probably would have been good to find your site a couple months ago but this is where I find myself now. I live in South Central Pennsylvania in a new house that was completed about one and a half years ago. The back wall is totally exposed 2×6 framing. The remaining walls are poured concrete. I have run a dehumidifier constantly for the entire time we have been in the house to help remove the “new construction” humidity. I also have had no moisture or water on any basement wall or in the sump pump pit. I removed the fiberglass insulation wrap that the builder had attached to the foundation walls and applied 1″ rigid XPS foamboard directly to the foundation walls. After reading your comments I understand I should have gone thicker but it is too late. My 2×4 walls are already framed up and electrical run. I am plnning on puttin R-13 fiberglass insulation in the walls but was trying to search out “faced” vs “un-faced” recommendations when I came across your site. What recommendation do you give me at this point? Do I want the faced insulation to avoid humidity from entering the wall cavity and collecting on the foamboard? I do plan on continuing to run the dehumidifier to keep the humidity level low in the basement.
Thanks in advance for your help,
Mark
Mark – Thanks for your kind words. It’s my pleasure to help homeowners out and I hope that you’ll share this site with friends and family and even consider signing up for our FREE newsletter.
Frankly my bigger concern using only 1 inch of foam is moisture from the concrete penetrating the 1″ blue board and then getting trapped in the fiberglass. So in situations like that I tend to recommend omitting the vapor barrier because you don’t want to trap that water vapor. So if it were my home, I’d skip the vapor barrier in your situation.
Hi Todd:
My parents house flooded from Sandy and now they are looking to re-do it. I would like to help them do it right and am wondering if xps is necessary if there is only about 3 feet underground and the foundation is brick. Is XPS only necessary then on the 3 feet that is actually below grade if it is necessary?
Thanks again!
Clara – I recommend foam for any insulation that’s used to insulate a space below grade and/or crawl spaces. Does that help?
My question to you is: I’ve installed dry-core flooring in my basement, wall to wall. My above grade walls are spray foamed but below grade is a blanket insulation with vapor barrier attached and is 6 inches above the floor. How do I enclose the lower portion to the sub floor, should I insulate and vapor barrier the lower 6 inches and tuck the vapor barrier under the flooring? Or diy spray foam the lower to seal the gap?
Any help is welcome…
BJ – I’m not a huge fan of blanket insulation in basements. If that blanket gets even the slightest hole it will fill with mold over time. My suggestion would be to install foam board insulation on all the below grade walls instead of the blanket insulation. You can run that right down to the new floor. I suppose you could do the same thing with the last 6 inches but I’d really avoid the blankets all together.
Good luck.
Hi Todd,
Great article! I have an existing finished basement in the great state of Maine. The 2×4 studs were installed on the flat,naied to the concrete with no insulation and a suspened ceiling attached to the 1/2″ dry wall. I was thinking i would take remove the dry wall and place 1.5″ foam insulation between the studs. I have a tight budget, what do you think, any other ideas? Thanks for any input.
Thanks for the nice compliment. That solution is a marginal one because it leaves cold spots at every stud and it also leaves a space for moisture to leave the concrete and get into the wall cavity.
I would highly suggest you remove the old drywall and the old studs. Install foam board, seal it, then install studs either as before or with traditional framing.
Best of luck.
Hi Todd,
I have taken your advise and removed the existing walls and I glued 1″ foiled faced foam board to the walls and taped all of the seams. MY building center did not have 1.5″ and the 2″ was too pricey. From here I will leave an inch space between the foam board and the studs. Will i be okay with fiberglass and with the foil faced foam should I install another vapor barrior? Would cellulose be better?
Thanks,
Stephen from Maine
Stephen – First off, I never recommend “foil” faced in direct contact with concrete (I only recommend foil faced against rim joists). It will react over time and the foil will corrode from a chemical reaction with the chlorides in the concrete. However, not all is lost as it won’t hurt the foam itself. Having said that, the foil won’t provide any real protection against water vapor. You really need another layer of closed cell foam. Instead of leaving that 1″ space, I’d go buy another layer of 1″ Blue or Pink foam board, install that, then the studs. At that point you’ll have sufficient vapor barrier. THen you can install fiberglass in the stud bays to get the R value you need.
Hi and thank you. I think i may have mis-lead you. The foil facing faces into the room not the concrete. Does that change your advise? Also,my rigid foam is tight to the floor; should I chaulk the seam between the floor and the foam, there does seem to be enough space to spray “great Stuff” foam? And, last question; are you saying to glue the rigid foam on top og the concrete wall up to the sill plate?
Thanks again!
That’s certainly better…but you still need more foam. At the very least you need to add another 1/2″ but an inch would be better. Tight fit at bottom is fine.
Again…I said it wrong; i do NOT have enough space between the floor and the rigid foam to spray “Great Stuff”.
Hey Todd,
What a well done site. Very helpful information. I live in NY just outside of NYC. I am finishing part of my basement that is poured walls with about 16 inches around the top exposed to the outside and 2 small windows. Like many of your followers I wish I had found your sight earlier. I have already framed the walls using 2×4 and have put up r-13 fyberglass insulation with kraft paper backing. My basement is not damp at all and there are no water marks on the foundation or sump well. Should i add a plastic water vapor on top of the insulation before I sheet rock? Also I have not laid the subfloor yet. i was going to put a plastic vapor barrier on the floor and then plywood on top if it. After reading some your responses to your other followers I realize this is not the ideal way to go about it, however I am already far along. What would you recommend I do from this point?
Thanks
Bobby
Bobby – Thanks for the kind words. Unfortunately the only thing I can recommend is removing the fiberglass and fixing it. The fiberglass as installed will eventually get mold. As I see if you have several options:
1. Leave as is (no plastic, that will only make it worse). This will likely result in mold.
2. Remove the fiberglass and install spray foam (only use cosed foam).
3 REmove fiberglass, cut free wall framing, slide framing forward, install foam board, slide framing back and finish.
With regard to the floor, I’d follow our article on that topic: http://www.homeconstructionimprovement.com/how-to-insulate-a-concrete-floor/
THanks for your quick response Todd. If i go the route to cut the wall free and slide it out and put up the foam board, after that is done and i slide the wall back should I then reinstall the fiberglass insulation?
yes sir.
Thanks again Todd. Sorry for all the questions, this is the last one if I go the spray foam route, after the spray foam is applied should I put the fiberglass insulation on top of that?
Thanks again for you help
It really depends on the R value you want. You can have 1.5″ of closed cell sprayed (this is your vapor barrier…that’s the vapor barrier….then possibly the fiberglass if you need more R value.
My house is 24×42 with a full 8’concrete foundation around the entire house. The house is built on a hill, and as a result i have one length of my house 42′ with an exposed 8′ wall of concrete. I live in New Brunswick Canada and it gets pretty cold here, would you give my some advise on how to finish the exposed concrete wall. The basement is cold making the heat bills high and the whole house cold. The basement currently has 2×4 with fiberglass insulation and a vapor barrier. :(
Steven – If it were my home…I’d remove that 2×4 wall. Insulate with at least 2″ of closed cell foam board, then re-frame (or re-use the previous wall if you want tilt it down and then lift it back up). Then I’d install additional foam or fiberglass in the stud cavities.
Good luck.
Hey Todd thanks for the great info. I live in central NY and am in the process of buying a block house on a slab. Its back wall is built into a hill with about half the wall exposed. There is no evidence of moisture damage now but first thing will be to install new drainage tile,Mel-Rol, and Mel-drain. Then new roof and gutters.I would like to vinyl side it in the future too. Does your hybrid insulation method work with above grade block insulation too? Also should tyvek be used outside before attaching furring strips? Or would this trap moisture?Will vinyl allow moisture out? Don’t want to cause a problem,the block is about 40 years old and in great shape with only paint. Thanks for your help!
Dan – Sounds like a fun fixer-upper. The method works great for any block wall, above or below grade. I would NOT install Tyvek on the outside. Just install the furring and siding. Vinyl siding actually is VERY breathable.
Good luck.
Thanks for the information. How about foam insulation between furring strips on the outside? Will this help or just trap moisture? Thanks again!
Outside? you mean exterior of house?
yes on the exterior between the 3/4″ furring strips under vinyl siding.Thanks
Unless it’s continuous it’s not a great detail. i.e. between strapping.
Hey Todd,
Great site. I have been reading through this and cant believe how long you been answering questions on this topic. Great read and I apologize if this has been asked before.
I have a basement that is mostly 75% above grade (lookout) and back wall maybe 90% above. The builders insulated the framed wall. I think the foam board might be a bit much for my purpose. This is what home depot suggested, I would like your input. I live in cold ontario btw.
exterior wall (which is wrapped outside) > remove builders vapour barrier > add tar paper (top to bottom. over frame wall and poured wall underneath) > new frame wall with Roxul > vapour barrier > drywall
thanks in advance Todd.
Gary – Thanks for the kind words. With all due respect the folks at HD clearly don’t have a clue. If you install tar paper over that existing framed wall I can almost certainly guarantee a mold problem. That tar paper will trap moisture into the framed wall.
The foam board approach should be used on all concrete surfaces. Framed surfaces can be insulated with traditional methods, however, in a basement, I prefer they are insulated with spray foam or foam board. I just can’t recommend that approach with good conscience. Good luck.
thanks for the response Todd,
So, just so Im clear.
I should take off existing vapour barrier from insulated wall > install blue board as you have shown from ceiling to floor (over poured concrete wall and framed builder wall with insulation) and seal it tight. > frame new wall > insulate (if needed) > drywall (no vapour barrier)
correct?
Gary – You lost me on the last comment. The concept should be:
– Traditional framed wall with fiberglass insulation and vapor barrier.
– Framed wall on top of concrete, new wall to be built in front of it. This should have unfaced insulation in the cavity, then the new wall should have either fiberglass with a vapor barrier or foam.
Just avoid having two vapor barriers in that “sandwich”.
Hi Todd,
I am redoing an old stone house deep in French countryside. The basement walls are partially underground (mostly on one short wall and less than 50% on the side walls, totally above ground on the remaining wall, but that wall doesn’t enter into my question).
I want to put a bathroom/utility on the side of the basement with the partially underground walls. I am unable to find anyone who knows anything about closed cell spray-on insulation and have been told that even if I could find someone, they would not come for such a small area. Here is what has been proposed by 2 different contractors -contractor #1: will leave air space between the stone wall and BA13 (I think this is about 1/2″) water resistant plaster board. He will then insulate on the inside of this plasterboard (not next to stone, but towards the interior of the basement) with fiberglass insulation, then cover that with another water resistant plaster board which will form the interior wall of the bathroom (FYI – they never use wood studs here, always metal framing) -contractor #2: also will leave air space, but instead of plaster board, he will construct a brick wall. He will then plaster (not plaster board) the inside of the brick wall.
Both claim that their system will work like a charm as far as the moisture is concerned.
I am thrilled to be able to ask someone a question in English for a change! But I admit that even in my native tongue, I’m a bit challenged by “construction talk”. Please assume virtually no prior familiarity with terminology in responding to me!
Thanks so much
Christine
Christine – Well obviously there are always differences when it comes to methodologies in different Countries. Here in the US we would never build a wall in a basement with either of those methods.
I have to imagine that foam board is sold in France. It’s an international product sold by DOW and Owens Corning. Maybe you can search those two companies in your Country and see if they show sources for it.
Good luck!
Great article Todd.
I’m somewhat unsure if the best approach after installing 2″ DOW on the basement walls is to stud against the DOW foam board, or leave a 1″ air gap between the studded wall and DOW foam board.
Seems to be conflicting answers.
Thank you,
Keith
Keith – It’s not really that big of a detail. If you can afford the space then the space is another layer of defense. If you can’t, It’s not likely to make a huge difference.
Todd:
I live in Ohio in a condo which is about 8 yrs old with a full basement which I’m trying to finish. Out of the four walls I’m studding, one is just a room divider. Two of the other walls are actually inner walls, meaning other condo’s are on the other side. The fourth wall is the one I need your help with. It is an outside wall with a small window at the top. I wire brushed the wall and painted it with two coats of Driloc. It was dry pryor to painting and the basement has heating and a/c ducts in the ceiling and it is comfortable all year around. Do I have to install any vapor barrier or insulation of any kind or can I just erect the studded wall with drywall? Any information would be greatly appreciated since I keep reading different opinions on the internet.
Bill – You ABSOLUTELY need to insulate and create a vapor barrier. If you do not, water vapor from the concrete will get trapped behind the new wall and cause mold and mildew. While that wall may look dry the reality is concrete has LOTS of water trapped in it. The Drilock alone will not stop it from drying into the space behind the wall.
I recommend you install 2 inches of closed cell foam board (DOW Blue or Owens Pink). Seal the joints, then frame your wall. If you skip this important step you’ll eventually have a problem.
Good luck.
Thank you for your reply, it helps me a lot. I hate to sound stupid but when it comes to keeping my basement dry I’m lost on these issues. I take it that I glue those foam pieces to the blocks and do I need plastic afterwards before the studds? Also I’m trying to keep the room as large as possible so do I still use 2 x 4’s for the wall for a full 5 1/2 inches? That being 2 inches of foam and 3 1/2 inches of wood. Thank you once again
Bill – If you follow the methods I describe here: http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
You won’t need plastic. The walls can be framed with 2×4’s, 2×3’s, or even strapping over the foam.
Hi Todd,
I have a summer cottage 24×32 i built in 2006, it has 2×6 insulated R12 walls with vapor barrier and paneling over the vapor barrier. The camp is on sona tubes and the floor is not insulated (yet), the ceiling is insulated with R20. the cottage is not heated through the winter, We have electric heat and a wood stove, we were up and stayed over night and i noticed on the inside along the bottom of the walls there were water droplets. I am very concerned about potential mold issues, as i hope to retire here. I would like to hear your thoughts on why this happened and a possible solution.
Thanks Steven
Were you using the fireplace? Sounds like high humidity levels…..which ended up condensating on the lower walls that are nearest the cold un-insulated floor.
yes,we had the wood stove on and the electric heat on. Do you think it may be too air tight which is causing the high humidity? does that mean i would need to install a system to circulate the air? Any suggestions, or should i not worry too much about it?
First off you really need to insulate the floor below. That will help keep the surfaces from being cool which promotes the condensation. Secondly you would benefit greatly from using a de-humidier when using the wood stove. Burning wood creates LOTS of moisture in the air.
Hi Todd. Great site, lots of good info! Wish I’d checked this site out weeks ago! Read many of the posts, but not all, so I apologize if this has already been covered. I’m wondering about insulating what are now “inside” concrete walls. Walk out basement, lower Michigan home originally built in ’89 w/ a major renovation in 2002 that bumped out on 3 sides. Luckily, no water problems, sandy soil, good drainage. Now finishing basement with studs and drywall, and wondering what needs to be done to these walls. 3 situations, 1 will be finished on both sides, 1 will only be finished on 1 side (other side is a utility room), the 3rd to finish has a 4′ deep crawl space (with concrete floor) on upper half that is accessible, but crawl will not be finished off. Trying to keep expenses down, what do I need to do to these? I’ve been getting mixed suggestions…Thanks in advance for your input. Anne
Anne – Thanks for visiting our site. All three walls are fairly similar. The issue is you’ll be building a wall that “encapsulates” the concrete wall. The concrete wall is full of water and will be forever (I’m talking at the microscopic level here, never the less, enough water to be of concern). So I still recommend that the wall be covered in foam first, then framed around. This prevents the water from getting to the framing and potentially causing a mold problem.
Good luck.
Todd,
We are finishing our basement (was partially finished before we moved in , owners started the finish but had to move due to job change and didnt continuie the work). Essentially the framing was completed. What the original contractor did was put up 1 inchy rigid foam insulation on all the outerwalls and than framed in front of that. I notice that the rigid foam isnt secure to the wall in all areas either due to not enough glue being used or just having put up the rigid foam and using the wall to hold in place. The result it it isnt tight to the wall. Is that a problem? Also assuming it is not, we were going to additionally use R13 fiberglass insulation in the stud cavities. Can this be faced but leaving out a plastic sheeting vapor barrier before sheet rocking?
David – If you read through my other articles on how to insulate basement walls you’ll find that I recommend a minimum of 1-1/2″ of foam but preferably 2″. Ideally you’d move the framed wall forward (even lay it down) and install another inch of foam. The foam does not need to be tight to the wall. However, the seams, joints, etc must be sealed tight to each other.
If you don’t install more foam then I’d suggest installing another layer between studs, then additional fiberglass.
In all three situations so not use plastic.
Good luck.
Well, moving the wall isnt a great option since the framing is already in place nailed etc. I also managed to catch up with an old friend of mine who is a contractor. he also said that 2.0 inch would have been preferred but short of moving the walls as you said, also suggested either more foam or using batts of fiberglass insulation (faced or unfaced) but absolutely no plastic (said plastic is the worst recommendation ever). He told me the actual permability specs for 1 inch and 1.5 inch foam are virtually identical such that going from 1 inch top 1.5 inch really doesnt matter, it the jump to 2 inch that makes it virtually impenetrable and provides a more significant value.
Thanks for the feedback!
Moving the wall isn’t that hard :) You don’t tear it apart, you cut it free top and bottom, tip it down…..insulate…stand it back up. Just my 2 cents :)
Good luck….glad to hear your friend understands the situation…most contractors today have no clue on basements.
Great site! Have lived in new construction home for two years. no water problems in the unfinished basement, but have noticed frost in between fiberglass insulation and plywood – I do notice some mold (behind the furnace/tankless water heater). We were planning on finishing the basement soon. Not sure what we can do, worried about the mold. Any advice would be great, thanks for your time.
Mike – Your situation is not unusual. Let me guess…fiberglass insulation on the walls (plywood) in the basement without a vapor barrier? thats where the mold is?
You really need to read the following articles:
http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
http://www.homeconstructionimprovement.com/prevent-mold-growth-under-fiberglass-insulation/
Hi Todd, I appreciate this site, and have learned alot. I have a unfinished basement 3 walls mostly below grade. I framed stud walls over 1/2″ Dow pink board 12 years ago and went no farther. I have had some water vapor problems, no a/c or air circulation down there. I use Dehumidifiers with pretty good results. I want to finish the basement now with a/c added. I plan to follow your advice and remove the framed walls, replace with 1&1/2″ blueboard. tape&seal. The exterior wall( below grade) were sprayed with thick tar like substance & wrapped with a dimpled black vinyl waterproofing material…. By using 1&1/2″ blue board on interior walls, will this cause any water vapor problems inside? I just want to be sure I can use your application before I proceed. Also would it benefit me to paint Drylock first? Thank you, Al
Go ahead and add the 1-1/2″ over the original 1/2″. This will give you 2″ which is really good. This will help cut down on humidity substantially. Drylock is like suspenders…..can’t hurt ;)
Todd, What is the name of adhesive used to apply blue board to cinder block wall? Al
There are numerous products that work. I prefer the construction adhesives that list foam board.
Hi Todd,
I am having some issues in my basement. Had a big rain and the carpet got wet. I opened up a hole in the wall to make sure everything was ok. The wall was good. I also opened up a hole in the rigid foam. It was damp behind the foam board.
Any Recommendations? This is the first time this has happened.
thanks
Ron
Ron – Sorry to hear about the problems. First off it sounds like things are not that bad. Obviously you’ll need to dry the carpet and/or replace it. As long as the wall is dry, the foamboard doesn’t matter. Foam board is designed to be exposed to moisture, but it won’t absorb it or promote mold growth.
Good luck.
Thanks,
What are your thought on BARRICADE flooring. I had some condensation build up under the carpet that was placed on top of the old asbestos tile.
I am kind of limited with height. I need something to limit the condensation on the floor. I researched some things but I am all over the place looking for a solution. I don’t want mold again. And i don’t want to have to rip things up again.
Barricade is a great product.
Thanks,
I am going to insulate my floor. My walls are already installed. i have owens corning sill seal then my PT 2X4. I noticed some moisture under the PT 2×4. Will this be a problem now that I am insulating the floor?
Should I leave a gap or take the XPS insulation right up to the wall?
Also if I go 1/4 inch XPS should I install poly then the xps then the 1/2 inch OSB?
Ron
Ron – I HIGHLY recommend you read several of my posts before you get started. Start with this one: http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
If you start to insulate your walls as you’re hinting you’ll be VERY sorry. If I were you…I’d tip those walls down so you can insulate them properly, then stand them back up.
Sorry to keep bothering you.
My walls are insulated with 1.5 inch XPS all the way down to the floor.
PT 2×4 sits on the sill seal.The walls are already complete(last year). My floor is not insulated yet.
I am planning on insulating the floor with XPS. just wondering if i should run the floor XPS all the way up to the wall or leave a gap.
I should have insulate the floor first but i didn’t think it was going to be a problem.
Ahh…..I understand now :) sorry for the confusion. It’s fine to run it tight to the other insulation. Good luck!
Hi Todd,
You have a great forum here. My block walls are insulated with 1″ XPS with foam spray in all gaps top to bottom with seams taped. My basement is a walk out with 2/3 of the walls not touching soil. Half of the other 1/3 of basement will be unfinished storage. Keep in mind my lower level is completely dry all the time, no rain problems whatsoever. Now that the foam is up I am considered leaving a 1″ gap then framing in 2 x 4 wall with r-13. My question is –“Do you think this will be satisfactory? and will I be ok if I use faced r-13 since I am leaving a 1″ gap? I have read on your site that if you have less than 1.5” of XPS if you leave a gap you could use the kraft faced fiberglass. ?? Also my rim joists were spray foamed when we built.
Thanks for all your help.
Jeff – Thanks for visiting. Current “science” tells us that you need a minimum of 1-1/2″ of foam in order to stop water vapor. So you’ll run a slight risk that water vapor can move from the block wall, through the foam, in into the wall cavity where the fiberglass is located. It’s possible that you’ll never have an issue. It’s really a matter of cost vs risk. If it were my home, considering that fuel is always rising in costs, I’d put more foam up before framing. Good luck.
Thanks Todd. If I put up 1/2″ more foam, can I still use kraft faced fiberglass? Is that the preferred method?
-Jeff
After you install another 1/2″ you can use either faced or unfaced. If you use kraft faced, then I recommend cutting some holes in it just to be sure you don’t trap any moisture (double vapor barrier). Good luck.
Thanks Todd. One final question. If I do decide to just keep the 1″ foamboard without any additional foamboard, can I use the r-13 faced without cutting some holes or would I cut the holes as well using the 1″ foam? Thanks.
You’d want to use un-faced. Just need to be aware that you run the risk of a moisture problem that could lead to a mold issue.
Hi Todd:
I have just finished putting Dow Styrofoam up in the Joist Cavities and already find a HUGE difference in heat retention in my basement. I will be doing the walls soon as money and time permit. A rather bizarre problem I have encountered is there is now a VERY noticeable draught upstairs in our small den. I double-checked and there is no cold air escaping from the joist areas. I am wondering if the cold air we are now experiencing upstairs could be coming under the aluminum siding and am considering either putting “Great Stuff” or caulking just under the bottom of the aluminum siding. Sorry for the long post, but I am at my wits end. Thank You.
Don McKinnon
Don – It’s pretty common that air infiltration can increase in one area when you “tighten” up another area. Having said that I wouldn’t recommend trying to foam/seal under the bottom edge of the siding. Vinyl siding moves so much with changes in temperature that it won’t stay sealed and it will likely only make a mess.
I would start by carefully checking the windows, doors, electrical outlets, etc for drafts and seeing if you can weather seal them better. Often times something as small as an electrical outlet can really cause some serious infiltration and cooling.
Another option is to do some testing with a thermal testing gun. THere are lots of options from something as cheap as this: http://www.homeconstructionimprovement.com/black-decker-thermal-leak-detector-review/ to something a bit more precise like this: http://www.youtube.com/watch?v=wzvqbWaSVYg
Those tools can really help you pinpoint the problem.
Todd,
First of all, thank you so much for your advice, professionalism and patience in answering the questions of all of us DIY’ers. I have received to much important information from this site and feel so empowered as a female to do as much myself to be able to afford so much more when I do need a contractor. I am just finishing my attic after finding I only had 1″ of insulation, no barrier, no rafter vents and my attic vents clogged with nests. Needless to say, what I thought would be 1 weekend turned into 3 weeks and counting. Almost done, need to roll out the R-30’s in opposite direction to complete.(I live In New England) Ok so, I have also upgraded my heating system and gutted my basement (dry, no water issues even after much rain) and now I want to finish my basement to become living space and possible rentable space as I age. My question, I get what I need to do for the walls, you have covered that to great extents and those who ask questions are thorough enough I am good with it, however, What should be done first, the walls or the floor? I will probably need to use Barricade subfloor tiles unless you recommend another way. I chose this due to floor to ceiling height. I plan on adding heat to the basement, already have a zone set up. Any advice is greatly appreciated.
Judy – Thanks for the kind words. My goal is to share knowledge and offer a resource that can be trusted. I hope you’ll help spread the word by using social media or programs like Google+ and Pintrest.
Sounds like you’ve been very busy! Your question is one I get fairly often so maybe I need to write an article on that as well :)
In my opinion, it really doesn’t matter which you do first. Typically my preference is the walls first. Having said that there’s really no benefit either way. I think it’s easier to frame the walls on the concrete first, stand them up, then deal with the floor, especially with a system like Barricade.
Best of luck! Don’t hesitate to stop by and ask more questions.
Thanks so much, Todd. I think doing the walls first is easier to start with, so as long as it doesn’t matter, that’s the way I will go. I have researched and came up with 2 products that I feel could do the job for the basement floor and I was wondering if you had any experience with either and if you feel one is better than the other as far as insulation value, durability, longevity, and weight capacity, the two systems are: Barricaide and Dricore. Remember, I am doing this myself also, so I guess ease of use would be a big factor too.
Thanks again for all your help.
BTW, The absolute best product out there is Great Stuff!!! I should have bought a case of it.
Judy
I have used both on projects and both are very good. One is a bit more insulation, one is a bit better at creating an airspace. Honestly, I’d go on price and availability most likely.
Good luck!
Great information. I would like to know what would be the best vapor barrier for me to finish my basement. I have an basement where the concrete wall is half to 3/4 of the 9-foot walls, the remaining of course is wood framing with insulation. On the outside of the concrete walls is 1.5″ rigid foam and on the inside of the concrete walls, sealed with sealant. Since I already have foam insullation on the outside and the wall sealed, that a plastic or thin foam vapor barrier would be sufficiant. What are your thoughts? Incidently, there is radiant floor heating in the concrete floor also. Thank you.
Pat – Thanks for the kind words.
Unfortunately even though you have insulation on the outside, you’ll really need to do the same on the inside. Why? Well that 1.5″ isn’t enough to keep the concrete warm, or at least warm enough that it doesn’t give interior moisture a place to condense. If you install a plastic barrier against the concrete, that plastic will take on the temperature of the concrete, likely around 50F at best, so when warmer, moist air hits that, it will condense. Then you’ve got actual water running down the plastic and trapped behind your wall framing.
Best to just tackle this head on and do what I’ve outlined here: http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
Good luck
I have a split ranch facing eas, above ground. South west rear is partly below grade (1-2 feet). It is concrete block (stucco) with studs, fiberglass and paneling. I removed an interior sheetrock wall to move it back 4 ft andfound black mold on a couple of studs and bythe ceiling plate of this wall. The thermal condition is such that the first level stays cold while we live on the second level. Keep the lower at 60 and live upstairs with 68-72. Then when we go down we turn up the heat. I want to remove the paneling, sheetrock, insulate, sound proof and solve the thermal barrier that seems to be the reason for the mold on the interior wall. There are 2 heating FHA zones 1 up and down and 1 ac up.Downsairs is comfortable in he summer. Thoughts? Products – this initially was a vapor barrier issue andi think has become a heating issue.
If it were my home or a client I’d recommend using the following approach: http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
The big issue is sealing any water vapor from the concrete and also insulating that surface. The best approach is using closed cell foam.
Good luck.
Hi Todd:
This website of yours is one of the most informative sites I have ever visited. Many thanks for such helpful advice. My question is that I have installed my 1.5 inches of Dow Styrofoam and am now in the process of building out my walls. I have just come to the laundry area copper pipes and am wondering if it is wise to leave them (the pipes) between the Styrofoam and the new walls that will have Roxul R14 Insulation between the studs, or is there a chance that they could freeze and burst? Many Thanks – Don.
Don – Thanks for the kind words. Let me see if I understand your question. You have the concrete wall, then 1.5 inches of foam, then the copper pipes, then framing with insulation? If that’s the case it should be fine. As another safety I’d just install some inexpensive pipe insulation. The reality is the pipes should be more than ok even without the additional insulation. Good luck.
I appreciate your good advice. I plan on adding insulation to my rim joist. In the cavity between the floor joists, I’ll use Dow’s Tuff-R, which is 2″ thick, an R-13. I’ll under cut these pieces about 1″ and fill the gap around the perimeter with expandable foam (Great Stuff).
The Dow Tuff-R (blue) is cheaper than the Owens Corning (pink) foamular, has a foil coating and greater R value. It’s about $30 for a 2″ x 4′ x 8′ sheet.
Tuff-R foam has a foil coating on both sides. However, one side is blue and the other side is reflective. I’ll use the reflective side toward the living space.
On top of the foam, I’ll add 3 1/2″ of Roxul, which is an R-15. This will be a thermal barrier for the foam and covers the remainder of the sill plate. So, the final insulation value will be R-28. Roxul is non-combustible, fire-resistant up to 2150 F and water-resistant. I find it easy to cut and install. IMO, it’s better than fiber glass in a basement.
Provided this goes well, I’ll use the same 2″ foam on the interior basement walls. I’ll foam any gaps and tape all the joints with Tyvek tape.
I hope I’ve correctly explained this and it meets your approval.
You’ve got a great insulation package planned. Roxul is an EXCELLENT choice in basements.
Good luck :)
Todd, I have a brand new house with poured concrete foundations And I plan to finish the basement. I live in the north east specifically, Long Island New York. I initially planned my approach in this manner: 2″ Owens Corning Foamular 250 rigid sheathing or Johns Manville/DOW Super tuff/Thermax foiled faced sheathing. Then will place studs over the bards then place fiberglass faced batts (Owens Corning 3 1/5 fiberglass for basements with paper faced) then cover the whole wall with 6 mill vapor barrier plastic then drywall over to finish. What do you think of this approach in my situation? What should I use as the foam board the Owens Corning Foamular (pink) or the Johns Manville/DOW Super tuff/ Thermax foil-faced sheets and why? Then should I use the paper faced fiberglass or unfaced? Should I place 6 mill plastic over the stds and fiber before dry walling? Also, I have drylock paint sealer should I use it or not before I place he foam boards? Any benefits or waste of time? Also on the bottom of the boards do i have to seal the gap between the board and the floor with foam spray?Your opinion would really help me with my fickle mind.
Thanks, Ernie
Ernie,
I like the Owens Corning or DOW products. Foil facings should not be in contact with concrete. I’d recommend using the fiberglass with paper face (in this application I usually cut some holes in the paper to let it breath is necessary). DO NOT use poly in the basement as it will create a double vapor barrier with the foam. It’s not necessary to seal the bottom unless there are large gaps. Drylock is like belt and suspenders if you ask me, can’t hurt, but not sure it does much good. Good luck.
Todd,
Thank you for your thoughts on this. What you are doing is really great for all the DIYers out there! I will follow your advice regarding the wall insulation. Probably, I will not use Drylock anymore and not use a vapor barrier under drywall and poke holes on the fiberglass face. Now, I am also going to do my basement floor as well. Do you know about Products such as Certainteed Platon, DMX Step 1 and Delta-FL subfloor system that uses HDPE dimpled membrane plastic as the subfloor? Do you know which one in your opinion is superior amongst them? Because, I think they are the same and just going to the cheapest ones can get which is the Platon system at 0.49 sq/ft. But if you differ, I would like to know. This might be another “yo get what you pay for” thing. And they said you don’t need to place OSB/plywood over them if I am creating a floating floor system which I will be using wood laminate flooring. If I choose any which one of these products, do you think i dont need to put OSB/plywood over them? and if you suggest i do, how thick at minimum should i use for wood laminate floors.Now, any of these products mentioned, how would you compare them with the Dricore system other than its convenient for the size of 2′ x 2′ and already has the OSB on it? That system costs $5.97 pet 2×2 panel. I have 1041 sq/ft to cover. What system would you prefer, the pastic HDPE above or Dricore? And if I chose the Dricore system, should i build the walls before the subloor or should i do the dricore subloor then build the wall frame on top of it? Also, other than the underlayment advised to use for the floor laminate like Roberts 2 in 1, can I use the Owens Corning Foamular R1 1/4″ Fanfold XPS rigid foam insulation used for wall sidings instead for a floor application? For the same price it’s thicker. It’s not mentioned for floor application but the other I underlayment is also foam. Let me know what you think on each of those scenarios. I saw your basement topic link and wanted to know other options. Thank you very much and I love your topics on your website.
Ernie – My pleasure. Please consider LIKE’ng our page on Facebook, or sharing on other Social site, it really helps grow our site. Ok…enough of my selfish plug :)
Sub-floor panels are all pretty good but there are some differences. Dricore (and other systems with a wood top) offer a more rigid, stable base to install flooring on. In a perfect world, you insulate the floor (or use some sort of air flow/barrier system), then install a layer of floor sheathing to create a rigid, quiet floor.
Sure, you can put a floating floor on Platon and it will work. However, it’s likely going to be really noisy and feel as though it moves a lot. So if you use Platon, then install sheathing, the cost will likely turn out similar to the Dricore. As you said, you get what you pay for.
Fanfold foam is really just meant for wall applications and most likely won’t sit well under the flooring and also doesn’t have as high of a compressive strength which means it will likely crush under loading. XPS sheets typically have a higher compressive strength. In some situations it makes sense to buy the high strength to really combat compressing.
Most of the time I prefer to build the wall first, then install the floating floor. In some situations the sub-floor does down first, then framing, but honestly it doesn’t matter.
Hope that helps…good luck.
Todd, thanks for the advice again! It’s so much comfortable to know I can ask freely about my project. I liked your Facebook page!
Anyway, I will follow your advice for the floor and wall DYI. I just have a few more if you don’t mind.
For the basement wall, I am contemplating if I should get e regular Sheetrock $8 or the Mould Tough Sheetrock $12. Is there any benefit going to the mould tough Sheetrock? I saw these at Home Depot.
Also, do you think I can use Vinyl wallpaper over the basement wall? I’m thinking of doing an accent wall on one of the four walls.
Also, would it help a lot if I put in a ductless AC/Heat mini split system for the humidity and the condition of the air or its not needed since the basement is usually cold and aftr all the insulation I will doing its not at all needed? And I have 2 dehumidifies being currently used in my 1061 sq/ft open basement.And if you do recommend a mini split system, how many BTU,s is Ok and what brand you recommend? I’ve seen a lot of unknown brands to my knowledge like YMGI, Gree, Klimaire, Senville and such or should I go to betters know brands such as LG, Samsung, Mitsubishi, Fujitsu and such? I am thinking to buy online and have a professional install that. Might be too much for me as a DYIer.
Todd, thank you agan for sharing your expertise! I’m so excited doing this project all by myself.
Ernie
Ernie – Glad I can be of assistance.
The debate about regular vs mold resistant drywall is always tough. There are studies that make conclusions in favor and against it’s use. Typically I would not use it in a large, well ventilated room. On the other hand, I do typically use it in bathrooms or rooms that might not have good ventilation. Some people say it’s a small price to pay for some added insurance against a very costly problem (mold).
The AC/Heat question is a good one. First I’d start off asking do you have any other heat source / cooling source for that space? If there’s none, this might be a great choice. If you already have heating/cooling then I’m not sure this is a cost effective way to manage moisture. Also, mini-splits are fairly easy to add after the fact, so you might want to wait and see how the space works before making the investment.
I’ve had really good luck with LG and Mitsubishi mini-splits on projects. For something as expensive and complicated as these systems are, I’d stick with a name brand. Also, you may find it’s the same price to just let the installer supply the unit, that way if there’s any issues they can deal with it vs you having to deal with returns, warranty, etc.
Good luck.
Todd, how are you? Ernie again here. I have a few questions as I in the process of doing the insulation in the base,net already. I put on the polysio DOW Tuff-R 2″ and tried to adhere them to the wall using the foam board adhesive. Apparently, the foam isn’t adhering to the wall. What should I do? Also on a few of them there are little gabs between the edges of the foam boards. Should I foam spray it before covering with Tyvek tape? Also, does it help if taping both sides of the board or just the interior part where the foil is facing interiorly is suffice?
Also, when I start dry walling, which should I hang first, the ceiling or the wall? Should I also place the drywall before laying dricor on the poor or do the Dricore first against the studs then drywall next?
Also when doing the wall framing/studs, the there are two walls where I can’t hang the preformed studs since its parallel to the joist. What would you advise on that?
Todd, again, thank you again.
Ernie
Ernie – Most times we install the foam board and frame the wall at the same time. The wall holds the foam in place. Any large gaps should be filled with spray foam. Tape just the interior. Hang the ceiling first. Then leave a 3/4″ to 1″ gap at the floor so water can’t wick up into the drywall. Dricore doesn’t matter, however you want to proceed. Not sure I understand your last question about the studs.
Hi Todd
i have poured basement house is in Pennsylvania (no water leakage) 3/4 in ground. I was thinking to seal inside walls (with drylock or some other sealer or epoxy) then install 2″ xps, frame out with 2×4 install r15 fiberglass right against foam then drywall. – would this be ok for walls
on the floor i was thinking: to seal the floor then create 24×24 grid out of 1×2 PT strips in between xps then cover it with 3/4 plywood – would this work for my basement floor
thanks
Both sound just fine. The sealers are not really worth the time and effort in my opinion, on the other hand, they can’t hurt. Good luck.
I’m convinced that insulating my poured concrete walls in my basement with 2″ XPS is the only way to go. However, we have a building inspector that is difficult and will not allow this method as it is not approved by the Internatioanl Code Council. He recommended I either install it the way the code calls for with a vapor barrier or he said he allows for no insulation as in his words” its not needed in a basement, the earth insulates better than any man made insulation”. I find it frusterating that he will deviate from the code to allow me to forgo insulating my basement, but he will not deviate to allow me to go with a proven method. Does anyone know if there are any formal approvings of installing XPS to interior basement walls by the ICC? Any help would be greatly appreciated, otherwise I my have to forgo obtaining a building permit so that I can have a insulated basement without promoting mold growth. Thanks in advance for you help.
Jake – I can tell you that I’ve insulated dozens of homes here in New Hampshire where we follow the International Building Code and I’ve NEVER heard of this. What part is he saying this method does not meet? Now if he’s saying it needs to be properly protected with a wall covering like drywall then he would be correct. However, if he’s saying this method doesn’t provide a sufficient vapor barrier then I’d start by showing him references from Building Science. If that doesn’t work then if I were you I’d call the state and ask who has supervision over the local authority (here in NH it’s the State Fire Marshals office). I wouldn’t give up just yet!
Todd,
I’m getting ready to finish my basement and am going to use 2 inch rigid foam board to insulate. Do I have insulate walls in what will be an unfinished are of the basement? I also have a sewer pipe running the length of a wall in the back that is not really moveable. What is the best way to insulate around this?
Wade – The amount or level of insulation depends on the code and how well you want it insulated. So every situation is different.Typically the best way to deal with a sewer pipe is to box around it with insulation.
Hi Todd:
I have completed insulating the walls with Dow Styrofoam and have the wall insulated with Roxul 3 1/2″ Batts on 16″ centres. The walls are about 2″ away from the Styrofoam leaving an airspace.
I can but my hand down between the Styrofoam and the studs. Should this space be closed with insulation all along the top of this space or is that what you mean by “dead air space”.
I am stumped on this situation. I will not install the drywall until I have your expert opinion. By the way, I am not planning on dry walling the ceiling, since I have decided to paint the joists and in between them.
Many thanks in advance, Don
Don – I think I understand your situation. The Roxul should continue up until it hits the floor deck above to be the most effective. The air space is a good detail as it acts as an insulation layer as well as providing ventilation.
Hi Todd,
I am in the middle of a basment remodel project and did not think what the builder was doing looked correct so I hope you can add some insight!
I live in WI, the rim joist was spray foamed. The builder put up 1″ Foamular 250 against the concrete foundation walls using concrete nails and a plastic washer. He did not use many so the sheets of foam float against the concrete walls. He taped all the seams with the clear tyvec tape. He then built a 2×4 wall in front of the foam about 1/4″ to 1/2″ away using green treated for the bottom plate, he then used can spray faom to seal the foam board to the floor between the foam board and the treated bottom plate We have a few days prior to electrical so I can do some corrctions. From reading your information he should have used the blue foam board 1-1/2″ and glue. I cant take it all down and start over so what would you recommend.
Thanks for providing the valuable information!!
Joe
Joe – All is not lost. Frankly you’re in better shape than most that come on here looking for advice after the fact. The 1-1/2″ minimum is the recommended level to prevent moisture from penetrating the foam from the concrete. Obviously 1″ doesn’t quite meet that requirement but you’re close. If it were my place, I’d cut the wall free and slide it forward and install another layer of foam. For more people that’s not all that feasible or might be too expensive. If you can’t do that, then I’d install another inch of foam board between the studs and seal it to the studs with spray foam. This isn’t perfect, but it’s better than not doing anything. Good luck.
Thanks Todd,
Do you think the foam only not being tight against the concrete will be a problem?
Joe
Not an issue, all that matters is it being properly sealed. Good luck.
I want to insulate my basement concrete walls but don’t want to finish my basement. I have a sump pump and I’m worried about power going out and flooding is the reason I don’t want to finish the basement. What would you suggest is the best way to go about doing this? Also would 2 layers of 3/4″ xps with staggered joints be better then 1 layer of 1 1/2″?
Dan – There’s no real difference between two layers and one. However, not all foam products can be left exposed due to fire code regulations. There are some products now approved for exposure so be sure you check with your local building code official and the product literature. Good luck.
Dan,
Put a backup sumppump system in. Any DIY guy can do it.
I prefer the watchdog battery. The main reason – the ease of installation as compared to hooking into your home’s plumbing system.
Hey Todd
Awesome resource – thanks
My basement has insulation and vapor barrier in the upper wooden half and 1.5 inches blue sm insulation fully taped on the concrete half. I am about to install the studded inner wall. My questions:
Since the sm is the vapor barrier is it still ok or beneficial for me to fully insulate the studded wall to increase the r value?
Would it be ok to have a plastic vapor barrier on the outside of the studded wall or is this overkill, troublesome or conpletely unnecessary?
Glenn – In many locations, additional R value is required in order to meet the energy code. Often times this is done with fiberglass in the stud wall that’s built in front of the foam board. I do not recommend a plastic vapor barrier in this situation, use unfaced or kraft faced with holes cut in the paper. Good luck.
Thanks Todd
To confirm, vapor leaving the room tgrough the drywall and passing through the new fiberglass insulation will not be an issue since the sm will not be cold on the inside?? I still find it confusing since my instruction was always that the vapor barrier is supposed to be as far to the inside of the wall as possible. Am I right here?
Glen, there are several things at play here. First, most quality latex paints create a semi-permeable vapor barrier which is your first line of defense. Also, you want to avoid the dreaded double vapor barrier situation.
Todd,
I live in Missouri and bought a house a few years ago with a finished basement. Shortly after I moved in the basement flooded from storm water coming in the sewer line. I installed a backflow to prevent that, but not before the basement was trashed. I gutted it down to the framing and there was 0 insulation previously, but the walls are painted in some sort of dark grey paint.
I don’t really want to tear down all the framing to install foam boards, how can I create a vapor barrier without re-doing all the framing.
Nelson – The only option I’d recommend in your situation is spraying foam. Cheaper to move the walls and install the foam board.
Todd,
Thanks for sharing your knowledge and experience. It’s really appreciated.
I have a situation similiar to Frank’s about 50 posts back. I have a poured concrete wall with a 2×4″ stud wall in front of it with a space of 1/4-1/2″ between and no way to move the wall forward. I was going to snug and seal 3″ of foam board (2 boards of 1 1/2″ each) between the studs.
Question #1: I’m assuming moisture will not penetrate 3″ of foam board, but will there still be moisture movement through 3 1/2″ of wood, the studs themselves, even if all the gaps and joints have been sealed properly?
Question #2: The wall in question is a short, 6’long bathroom wall and it would be possible to slip a sheet of poly between the stud wall and the concrete. Would you recommend putting plastic behind the wall (against the concrete), in front of the wall (behind the drywall), both, or none at all?
If you have time to answer yet another question, I’ll be very appreciative.
Mike – No way to move it or don’t want to? Moving it is the best approach and I highly recommend it. If you can’t possibly move it then I’d first consider spray foam unless you just can’t afford it.
If you must do as you propose, understand that the moisture can and will penetrate the framing and likely mold/mildew over time. Also, it’s likely that water vapor will get around the foam even if you seal it very well.
Poly won’t do anything, but give a cool surface for water vapor to condensate on.
Wish I had better advice, but basements can be a huge problem if they are not done correctly.
Good luck.
Todd,
I can’t move the wall because of plumbing that has already been put in. Believe me, I would move it if I could. I’ve been calling around about getting the wall spray foamed with about 3″ of closed-cell foam. It is costly, but if it’s the best option, I’ll do it. However, I have a question about that. I’m told the spray foam sets up very hard, as hard as concrete, according to one contractor. And so, in my mind that begs the question, does the cold from the concrete wall transfer to the foam making it a cool surface for water vapor to condensate on? Seems like it would, if the foam is that hard and in direct contact with the concrete.
Thanks for your help.
Mike
Mike – Spray foam is applied directly to concrete all the time and it works amazing. First of all it does an amazing job of sealing against moisture and secondly it has a great R value. It’s no different than the foam board which is quite stiff, yet placed directly against the concrete. It’s really the best long term solution for your situation. Good luck.
Probably should mention that I live in Iowa.
Hi Todd,
Thanks for the site. I’ve studied it over many times as I’m looking at doing some finishing work on my basement. I think my plan is pretty solid based on your comments and explanations…but I’m a little paranoid, so just to make sure would you mind giving me a thumbs up here. I’m in Northern VA, my house is on a pretty steep hill so water drainage is king here. I plan to lay 2″ close cell foam boards (~R10 which is suggested for my area)on all poured concrete surfaces, tape and close all gaps, frame it out laying the 2x4s against the insulating boards…or 1/4 inch out if you think that would be better, then just drywalling it up. I don’t think I’ll need fiberglass batts since the R10 is enough for my area. Does that sound about how you’ve explained it here. I like your methods and would like to get them right. Thanks.
Cortland – Sounds like a solid plan. The key for you frankly is the exterior drainage :) Good luck.
Hi Todd,I’m thinking of using ach foam control plus on my interior block walls 2 inch r 10 type 2 Eps. Is that a bad decision? I know you recommend xps. Blue or pink board. If I do would you recommend a vapor barrier over the foam? I’m also going to put a 2 by 4 wall with r-11 faced insulation.
Thanks
Allan
I appologize if this was covered. My husband and I already have framed the basement, electrical is in, along with plumbing and HVAC is coming to do vents soon. We were under the impression that we should be insulating lastly before drywall. Now after reading your articles and watching video I see we may have made a mistake, but can’t go back. What do you suggest we do in order to help prevent the moisture from entering our home and creating a mold issue? We live in WI where we have hot summers and cold winters and poured basement walls. (we did have moisture in the basement a few times due to a sump pump going out and our egress window didn’t have proper dirt filled around it) These problems have been addressed and no longer have had moisture issues. Can you give me advice as to what the best approach is for us? Thank you!!
ELizabeth – From my perspective there’s only one solution at this juncture and that’s having a spray foam contractor come in an spray it. I would not recommend fiberglass under any circumstances. Best of luck.
Todd
Hi Todd,
So I have a follow up question. If we have insulation in the exterior of the basement walls is it still necessary to do spray foam insulation? (Outside) Thank you again for the info!
Thank you!! So.. We did more looking into the structure of our home and found that the exterior of our home has insulation, on the perimeter of the walls. Does your suggestion stay the same? Is it even necessary to insulate in the inside if there is on the outside? Thank you so much for your feedback!!
Elizabeth
Yes…..having insulation on the outside is good, but it’s not nearly enough and it doesn’t stop the moisture problem. Good luck.
Tod, thanks for all the great info you’ve posted. Super useful! I’m planning to do the framing, insulation and drywalling of my basement. My house is a new construction and the builder wrapped the basement walls with the fiberglass batt insulation (not pink but, creamy/white-ish and has some kind of paper facing that looks like aluminum). They nailed to the foundation walls using concrete nails pretty hard to remove. For some reason they left the bottom of the walls (5 inches or so) uncovered.
What are your recommendations in my case? Remove it and install the rigid insulation against the wall and reusing the fiberglass between studs, or leaving the fiberglass there and frame against it?
Hector – Use the contact form and send me an email, I’ll respond…I’d like to see some pictures so I can better advise you.
Hi Todd,
Great articles on basement insulation and great web site. Thanks. I have a quick question about the top of my cinder block walls.
My walkout basement is dry with no water issues. I would like to glue 2″ XPS board insulation all around the interior of my basement walls. But the cinder blocks are tapered in at the top, then continue up a couple of inches, and then the sill plate is there.
If I glue the XPS boards to the wall all the way up to the floor joists, then the “tapered-in” part of the block wall will not have any insulation or vapor barrier. Is that a problem? I can send you a couple of pictures if you like. Thanks a lot for you help and advice.
Mike – The gap doesn’t matter, what matters is sealing off the gap at the top. Good luck.
Hi Todd,
Thank you for your great articles on basement insulation – and amazing help in the comments section!
I do have one question of my own – I live in Toronto, in a 100 yr old semi detached house and am considering finishing the basement. The basement walls are 80% below grade and made of brick. The basement is currently heated, but otherwise unfinished. In the 4 years we have lived here there have been no moisture or leak problems.
Am I crazy for wanting to finish the basement without insulation?
My current plan is to polish the concrete floor and paint the brick. I’d like to do it this way for a couple reasons:
1. To save square footage (basement is 35′ x 13′) and keep costs low.
2. To be able to see any moisture and mold problems if they occur.
The basement will essentially be one large room and one bathroom once finished. Does the moisture from the bathroom present any additional concerns if I plan on not insulating? Thanks so much for you help!
Joe – Thanks for the kind words. I wouldn’t say you’re crazy but there are a few things to consider. Here in the US when you finish a basement for spaced to be used as living space, the work must follow the code. Where I live (and in most places in the US) there’s also an energy code that applies. So strictly speaking the basement needs to be insulated to meet code. Beyond that, insulating a basement is a good investment as it will significantly impact long term heating costs not only for that level, but also the upper levels of the home.
The bathroom will most certainly have an impact. Bathrooms generate a ton of water vapor especially if there’s a shower. That water vapor will leave that room and find it’s way to a cold surface and condensate. That can lead to only one thing….mold and mildew.
If it were my home…I’d insulate it properly and be done with it. Good luck.
Hey Todd,
I live in Southeastern Massachusetts. M house was built in 1910 and is a granite foundation. How do I go about building and insulating the walls? Not being smooth and flat like poured concrete has me scratching my head as how I am going to properly do this. Thanks!
Most likely you’ll need to consider spray foam. Stone foundations are really best dealt with that way.
Todd, Great information and site. I have a new home in MI and the outside basement walls were sealed with tar and 2 ” foam board. The basement is dry and heated with no water issues. The walls (poured) are 65 degrees below grade and above grade around 56 degrees. If I use spray foam how far away from the wall should the studs be? If I don’t use spray foam will OwensCorning 3/4″ t&g foam board be sufficient? Then finish with pink r13 inside the cavity. Home Depot sells 3/4″ RMAX 3( r5)with foil on both sides but not sure of this product. Not sure what to use before I start framing. Please confer. Thanks,
Joe – If you use spray foam I’d only leave the studs about an inch or two from the foundation, then let the spray foam fill the gap. If you use foam board, it needs to be closed cell foam board and a minimum of 1-1/2″ thick. You can learn more about why that’s so important here: http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
Todd
I am looking at buying an old springhouse in PA that is two stories. The basement has a running spring in it and a stone foundation with no heat.
I would like to finish the upstairs as living space and want to insulate the basement ceiling to keep the first floor warm and dry.
I was thinking a closed cell sprayfoam on the basement side joists and decking and then covering with pressure treated plywood.
Should i just sprayfoam and leave it uncovered?
Thanks
Tom
Tom – That’s a decent approach especially considering the foam should be protected from flame. Plywood in most cases does count as protection from flame spread (not a true fire barrier…but protection from flames igniting the foam).
Hi Todd, Thanks for so many helpful ideas! I am trying to finish off a small area in the basement, under my split level where my sump pump & water softener hang out. I live near Ottawa (cold and colder).
My plan is to use 1 1/2″ foam board and attach to concrete using Great Stuff adhesive and then seal all with tape & foam the top & bottom for a great seal.
My question is, this only does the concrete wall…can I use the same insulation on the walls or under the stairs to create an insulated small room?
Sorry if this sounds like I am a DIY beginner, it is because that is what I am. Thanks for your great insight.
Yes you can, but I must caution you, in many places this material must be protected from fire with either drywall, or some codes allow wood.
Hi Todd,
First thing very good information on your site been doing my home work on insulating and finishing my basement band it is some of the best I’ve seen.
I have 3 questions for you:
1) I have glued 2 inch ridge foam to the walls of my basement which are block walls and they are also dryloked. I also tyvek taped the seams, spray foamed the gaps my question is I have read people leaving at least a 1/2″ gap between studs and foam. Can I place the studs right up against the foam?
2) Between the studs I wanna insulate with Roxul R-15 can this go right up against the foam as well, and with this all being said do I need to do a vapor barrier?
3) I spray foamed around the whole area where the house sits on the foundation to stop any air flow, can I use roxul R-23 for insulating the rim joist or do u still recommend the 2″ foam with the spray around it? They reason why I wanna do the R-23 roxul is I have so much left over from insulating my attic I want to use it up. Or if u recommend the foam can I put the roxul behind it?
4) I also want to insulate the floor with 1″ foam, tape the seams and spray foam around as well and put 3/4 plywood over it what are your thoughts on that.
I thank you in advance for your time and in sight on my project.
I’m not sure where to see your reply, can you reply to the email above if possible?
Jared – THanks for the kind words.
1. You can frame directly in contact if you want, typically we do that when it’s a fairly dry basement.
2. Yes tight, no vapor barrier.
3. Roxul is a good 2nd choice. Foam seals MUCH better, but the Roxul is certainly better than fiberglass.
4. That works very well. You’ll likely need to Tapcon (or other anchors) it down in order to get it flat.
Great website, fantastic information.
I moved into a house that has 1″ XPS on basement walls and cold storage ceiling. I would like to increase the thickness to 2″. I purchased 1″ XPS sheets (2 x 8 pink foamular boards) and PL300 foam adhesive tubes but then read that it is not for gluing foam to foam (one surface needs to be porous). Will it still “work”? Or is there a better product to glue XPS to XPS? Perhaps PL Premium or PL Premium Advanced? I’m confused by the technical sheets and I don’t want to melt the foam!
Thanks in advance!
Chris – Look for foam board adhesive, might have to look at a building supply house. There are some products out there. THey might be in the caulking isle, might be with spray foam. My experience hasn’t been great foaming the boards, usually just to hold it in place till we frame a wall that more permanently holds it in place.
Todd – As I’m working with my builder, it’s come up that I could save some labor by insulating the basement on my own. After reading your article I think I have a good base to start.
My plan is to do at least the minimum 1-1/2″ foam insulation against the concrete and then frame in front of it and use fiber insulation. However, at this time we’re not wanting to put up drywall. I believe I’m required to have some sort of barrier over the fiber insulation and I’m looking for the right way to go.
Thanks,
Robert
Robert – In most jurisdictions, both foam and fiberglass insulation need to be protected from flames. This typically involves either wood or drywall, or a material that has a flame spread rating approved by the code. I’d work with your local building code official to come up with a plan that’s acceptable to him or her.
Good luck.
Hi Todd,
We live in southern NH. We recently had a rodent problem in our split level basement, so we took out all the basement insulation (walls+ceiling) and we are thinking of using 3″ foam board on the walls, seal it and put dry wall directly against it without leaving any room. Would that be a good idea? Also not sure if we need to use faced or unfaced insulation in the ceiling. We keep the temperature around 55 in the basement during winter time. What would you recommend?
Thanks a lot.
JoAnne – First question is what type of foam board? It needs to be closed cell foam. Secondly, applying drywall is fine in theory, nearly impossible to do in reality. You’ll need some strapping or framing to attach the drywall. Kraft faced insulation, with the paper UP against the floor.
Good luck.
Hello Todd,
Please help with advice please, I have a 1900 old home (semi) with stone foundation, mostly below grade with about 2 1/2 feet above. I have tore out all the old insulation (fiberglass with plastic grrrr) obviously this was a horrible idea for past owners as it was saturated. We have fixed prepped the basement with spray foam insulation at the top of foundation and where the house meets to stop any drafts and other stuff as such.
Question is how should I insulate on these walls?
also
DuraFoam VS blue 2″ Foam ?
friend of mine says to use 2″ foam sealed with tuck tape and foamed in corners to help adhere. Can I frame it up after all that is done? or is any other insulation or vapor barrier required? My friend was saying to frame up with 2x2s as its not a load baring wall and just used for drywall. Please email if you can or post here… not sure what to do.
Bob? Is that you?
Todd,
I lot of great information. I live in NH as well. The house was built 10 years ago. The builder framed the basement with the studs with very little space between the foundation and the studs (actually touching is some places. Currently he placed 3.5″ of fiberglass in the walls.
I was thinking of removing the fiberglass and having the walls spray foamed with closed cell. I would be a big project to take the walls down an move them.
What are your thoughts.
John – If you have it spray foamed that will likely do ok. My preference is a space so that moisture doesn’t get into the back of the studs. If you can manage to slide any of the walls away from the concrete even a small amount prior to spray foam it will help. Good luck!
Hi, I am trying to decide how to insulate my basement walls and the insulator does not use foam board…. He said the batt would be fine, but I have read too many articles that disagree with that. I live in the midwest. He mentioned the use of certainteed dry right as an option. Any thoughts on that?
Find a new contractor…..seriously you need to find someone that understands the science. Good luck.
Hello Todd,
Question on my situation. My framer framed up my basement walls and unfortunately only left about 1″ gap from wall. I was or he was planning on installing r 13 batt insulation but I had concerns because it could essentially touch the wall and I don’t want moisture to hit the fiberglass.
so my thought was to put 1/2 inch owens corning 150 behind the studs, glue to wall and then put in the batt insulation in the cavities. The owens 150 1/2 is film faced. I have read so many articles that have conflicted each other I am really getting confused.
Mike – That really won’t work. 1/2″ foam will be as cold as the concrete surface, any moisture that hits the foam will condensate, and be just as bad as the situation you’re worried about. You need a minimum of 1-1/2″, preferably 2″ of closed cell foam before you install any fiberglass.
The basement in my home was constructed with pre-cast concrete panels, they are top notch and the basement stays dry. I want to finish the space out and am in a dilemma as to how to insulate. The foam boards definitely seem a great way to go but my precast walls have 6″ deep cavities, it has the look of like 18″ on center concrete studs, that’s the precast mould. Should I use the foam panels glued on each of these so called studs (which would leave a 6″ deep air cavity in every cavity), or should I cut 6″ foam strips and follow the concrete?? I hope you can picture what I’m describing. I could email you a pic if needed.
Robert – I’m familiar with this type of foundation. I would likely run foam board horizontally over the concrete ribs, then frame the wall tight to the foam to be sure it doesn’t move. The air space is fine.
Good luck.
Hi Todd, great article. I would like to insulate my basement in this same manner but with one difference: Instead of finishing off the interior side of the framed wall with drywall, I would like to install t&g pine paneling. However, with regards the foam sheet insulation, IBC says this:
2603.4 Thermal barrier.
Except as provided for in Sections 2603.4.1 and 2603.10, foam plastic shall be separated from the interior of a building by an approved thermal barrier of 1/2-inch (12.7 mm) gypsum wallboard or a material that is tested in accordance with and meets the acceptance criteria of both the Temperature Transmission Fire Test and the Integrity Fire Test of NFPA 275. Combustible concealed spaces shall comply with Section 718.
This seems to imply that whatever I use as my inside surface must be fire-retardant, which pine paneling is obviously not.. Do you have any suggestions? Aside from doing drywall then putting paneling on top of that, I’m at a loss as to what to do. Any code-compliant ideas would be much appreciated. Note* I live in Montana, if that makes any difference. Thanks
Kevin – That part of the code is fairly vague. I can tell you that we built an auto dealership several years ago, at the time the code official allowed us to use 1/2″ OSB on a wall to cover insulation in lieu of drywall. I think if you were to look at the specs on certain wood sheet goods you’d find they meet the flame spread criteria. If they do, you could install that first, then the T&G. It’s also quite possible that T&G might meet the criteria…it really has more to do with slowing the “fast” development of flame spread. Just my 2 cents…
Great article. We have a 40 year old o rental home in the Seattle WA area that had a finished basement until a pipe burst in conjunction with a grow-op resulting in a basement full of mold. I have stripped the sheetrock to discover both 3′ and 5′ high foundation walls with faced fiberglass insulation above the foundation on the exterior walls. Exterior walls are framed on the outer edge of the approx 9″ thick foundation while interior walls were framed from floor to ceiling with 2×4’s set flat against the foundation resulting in a 1.5″ – 2″ depth to foundation and an additional 5-1/2″ beyond that to the inside of the outer wall. Given the ceiling is all still in tact and it is a rental home I am reluctant to change the existing structure of the interior walls. So . . .
My plan was to replace fiberglass insulation as required on the exterior walls but should I just sheetrock over the 2×4’s and forget about insulation against the foundation given I suspect the insulating value would be negligible? Or would I be better off gluing some foam board between 2×4’s on the foundation to protect the sheetrock from moisture?
Lee – My bet…there was mold there under that drywall even before the flood. Either way…I wouldn’t recommend either approach..the only one I can recommend is installing a minimum of 1-1/2″ to 2″ of continuous closed cell foam between the foundation and the framing. Wish I had better advice.
Good luck.
Todd
Why did I know you were going to say that? :) Thanks Todd, I appreciate your feedback and as much as I may not want to, I do agree with you. Sadly things just got worse. I just discovered the base of a center load bearing wall and presumably all perimeter nailing walls have their primary 2×4’s 2″ below the surface of the concrete. Presumably someone in their infinite wisdom thought that building a concrete moat around the base of the walls was a brilliant idea.
Lee – Sorry to hear this. Stinks that a few bad builders leave such a sour taste in our mouths. I wish you luck!
This article finally answers my questions about the proper way to insulate basement walls and frame/drywall. I am in the middle of my project and unfortunately I already installed 3/4″ XPS (glued to concrete) and framed my walls with 2x4s before reading this article. In all your posts you recommend a minimum of 1 1/2″. I live in southern Michigan. What should I do at this point? Should I use faced fiberglass insulation with the moisture barrier against the drywall? I’m worried the foam board isn’t thick enough and it will be too cold compared to the warm/conditioned space inside my basement and cause moisture/mold. Any thoughts?
Ryan – Here are a couple options:
1. Move the wall framing (in most cases it’s not that hard to cut the plates free, tip the wall down and away so you can install another layer of foam, tip the walls back up. In this scenario I’d install at least 3/4″, preferably another 1″.
2. Add foam between studs. This isn’t ideal, but its WAY better than what you proposed. If you’re going to go this route, install as thick as you can afford.
3. Spray foam the stud bays, this is expensive, but a good option as well.
Hope this helps. Good luck.
Thank you Todd for tips on my options, this is very helpful. I don’t think #1 will work since I am pretty far along with electrical. I like option #2 since I should be able to slide more foam behind my electrical in-between the studs. If I go with another 1″ will I need to use fiberglass or will the 3/4″(R4) and 1″(R5) be enough? Sorry – last question – should I glue the new foam board to the existing foam board or just use tape/spray foam to create a good seal? Thanks for your help.
The difference between #1 and #2 is you get the required thickness continuous behind the framing. In option #2 you do have the risk of moisture getting through the first layer and contacting the studs. I can’t tell you how much of a risk, and you won’t be the first person to use this approach.
The total R value depends on local energy codes and also the desired insulation value you want. I tell people install as much insulation as you can afford…it’s a one time investment that pays for years to come.
No need to glue it, but be sure you seal each of the 2nd pieces with can foam at all edges of the framing. Good luck
todd,
i was all set to pull the trigger on having 3″ of closed cell foam sprayed in my basement, but then ran across this article:
http://www.greenspirationhome.com/sprayed-foam-insulation-why-homeowners-must-proceed-with-caution/
could you comment on some of these concerns? i’m tempted to go back to just doing rigid foam insulation & great stuff. not as ideal, but doable.
Mike – Sorry I’m so late to this….been a crazy few weeks here.
– These are valid concerns and why it’s critical to hire someone that has a long, proven track record with spray foam. I’ve been using one installer for over 7 yrs now with not a single issue. They are on top of the industry, keep me informed of products, techniques, etc.
– Find an installer that can give you references and check them. Best if you can find builders that can give feedback.
If you can afford it, if you can find a good installer, this is the best approach. Good luck
Thanks for all the information. I have a newer construction and did spray foam on the exterior foundation walls. I was planning on still insulating the interiors walls by installing 1 in R.5 foam sheets that will be glued to the concrete walls.
Will I be running into a problems doing the walls in this manner.
Thanks
Jon
Jon – No….in fact I think this is good…otherwise water vapor will try to dry to the inside of the home.
I am building a new house. The basement is poured walls with a walkout in the back. I used delta wrap on the outside of the basement to help keep the water of the outside of the wall. The basement has been dry and since the heat was turned on for dry walling it has been perfect. The building inspector passed the insulation inspection but told me I would have to insulate the basement walls before the final inspection. I was going to finish the basement at a later date but, now I have to do it. The inspector said I don’t need Styrofoam and the just stud it out and use in-faced fiberglass because I used the delta wrap and I don’t need a moisture barrier with the delta wrap on the outside. I already ordered the foam to put on the basement walls to make sure the wood studs and fiberglass do not get wet with moisture. Your thoughts on this would be greatly appreciated. He told me I could use the foam but, it would be a waste and not enough insulation as code requires R-15 for basements. I want to use foam and R-13 in the cavities. So my question is does the delta wrap on the outside of the basement wall work as an moisture barrier enough, that I will not need one on the inside of the concrete walls.
Thanks,
Mike
Mike – The inspector really doesn’t understand the issues with concrete and insulating a basement. The membrane will surely help keep water away from the foundation and it’s a great safety measure. But concrete itself is loaded with water for it’s entire life. If you look at concrete under a microscope you’d see the pores filled with water. This water can migrate out of the wall and get into the insulation. That’s why it’s so important to install the foam and seal it well. Then you can supplement the R value with fiberglass, Roxul, or another cheaper product.
Hi Todd. I will be using 1.5-2″ over concrete block. I have a french drain already installed. @ questions:
1. Should I build the wall out before the french drain is (approx 10″ from the wall) or am I ok starting the wall right on top of the concrete covering the french drain pipe?
2. My french drain has the plastic channel about 3″ up the wall so that leaks (haven’t seen any though) can drain down the wall and go into the french drain area. How do I install the XPS over this? Can I run the XPS floor to ceiling in front of the plastic channel and seal/caulk? I’m unsure because moisture will get behind the XPS between the XPS and the concrete block. Thanks.
Robert – Without seeing photos it’s hard to say exactly how I’d deal with this situation. Typically, I’d install the foam against the wall, if you use adhesive then apply it vertically so any water can drain down to the French Drain. It will run out below the foam and into the drain. The only other issue is what to do with flooring. A floating floor system is best, to allow water into that drain, and also air to dry things out.
New construction in MN to be built. There will be 2″ of foam board on the exterior of the poured wall. For a split entry style, how does installing 1 1/2″ rigid foam board work on the 4’of poured walls and 2×6 framing above that(& fiberglass in that part of the wall)? We want to finish the basement and were planning on building a 2×4 wall in front of the foam. Where does the vapor barrier go? What is the best method? We will also have a non-vented crawl space under the foyer entry, accessible from the closet under the staircase. What to do with that?
You can find more info here: http://www.homeconstructionimprovement.com/category/home-improvement/structure/insulation/
Hi Todd,
Good article on basement remodels. I am doing a basement remodel where we have 4′-0″in height of exposed foundation wall and then a 3′-6″ framed walled above. We furred out our interior walls with a 1-inch air space. I was planning on putting rigid insulation for the first 4 feet, then batt insulation, without a vapor barrier for the top part of the wall. Does that seem like the correct approach?
I live in Seattle btw.
Thanks, John
You’ll need a vapor barrier…even better if you can do the upper portion with foam as well.
Why you suggest the frame bottom plate to be pressure treated if you are installing a composite decking material underneath? Wouldn’t the PT bottom plate be enough protection against potential wicking of moisture into the framing?
The composite material doesn’t wick water like wood framing. However, it’s still possible that the composite decking can be damp, so the PT is just extra insurance against rotting.
Hello, I am finishing my basement in an OH home. The home is 8 years old and the basement is in great condition. My builder used foil back insulation on the top half (extends below the ground/soil level) of the walls and the bottom half is exposed. The foil insulation covers a studded wall which sits on top of the concrete slab. I guess this is a typical setup.
Can I place poly sheets on the exposed concrete slab and leave the foil insulation? In other words, the top half of the wall would be foil insulation and the bottom half would be poly sheets. I have no current issues with temperature, my concern is water issues. Appreciate your help!
Steve
Hi Todd, I hope you don’t get a duplicate of this question….not sure if the last one went through or not.
I live in OH and my house is 8 years old. The basement walls are in good condition and the climate is good too. My basement has the foil backed insulation on the top half of the walls and the lower half is exposed poured concrete. Behind the insulation is the exterior wall studs. Will I encounter problems if I apply 2″ polystyrene foam board below the foil insulation? In other words, the top half of the wall stays “as is” with the foil insulation and the bottom half is covered with the foam board. I would also fill any gaps between the two barriers. I would then frame and drywall as normal.
Also, if I can do this, is it ok to add additional insulation (without facing/vapor barrier) in between the studs?
VR
Steve
I have an older house in western new york that has minor water seepage after major rain fall/during the spring. I have one wall yet to paint with drylock. I’ve decided to finish a closed off room in the basement. The two walls in that room experience some minor seepage as indicated, but nothing major. Does this need to be corrected before applying the 1.5″ rigid foam board, or is that the purpose of the board. Will I change getting mold build up if the seepage continues behind ght rigid foam board? I am limited in my ability to redirect any more water on the outside of my house.
Definitely need to stop the water if at all possible.
Hi, hoping you can advise. I live in Western PA zone 5. We have a new house with poured concrete (subterranean). It is waterproofed on the outside tar and 1 inch styrofoam on the exterior (done by builder). What I am trying to determine is whether or not to insulate and if so how. I have seen articles recommending foam board to vapor seal and others saying that will create a bad situation combined with the exterior waterproofing and trap moisture that will then turn into condensation. So if I don’t foam board, I could use rolled pink stuff or bats but I am worried about everything I have seen that says if there is no vapor seal I could end up with mold. I had a contractor out yesterday and he does basements and he said he doesn’t even insulate in our neighborhood because our basements stay warmer in the winter and colder in the summer already and there is heat.
I’d ONLY recommend insulating the inside….the outside will have no effect…concrete is always wet…on a molecular level….use the interior foam.
Todd, I’m looking for some advice. I have a basement that was poured in 1962 in Connecticut. I finished the basement in 1993. When I finished it, I put 6 mil poly against the basement wall. Then we used steel studs for all the walls. We then used fiberglass insulation with another vapor barrier facing inside. At the time that was the way the builder and the town building inspector wanted it done. Over the years I have had some water come in the basement (once was a broken washing machine hose). As a result I have some mold on sheetrock in different places in the basement. I am planning on fixing everything and putting down a new floor. My question is do you think there could be mold in the insulation or paper backing? I’m not sure if I should just bite the bullet and re-sheetrock and re-insulate everything. Thanks
You have several problems, the biggest being a double vapor barrier. Wish I had good news…but not much is going to fix your problem short of tearing out the drywall, removing the insulation, then the only option I’d recommend is spray foaming each bay.
Hello…I’m in the Midwest (SD) and recently purchased a new home. The outside basement walls are framed with insulation and a plastic barrier. In the past month, we could see moisture forming on the concrete floor and along the bottoms of the 2x4s. After removing the plastic in some areas, the walls were wet and/or moist in a lot of areas (soaking the insulation at the bottom and creating the moisture we could see). We were told by the builder that the humidity in our home was too high and it was creating condensation between the cold walls and insulation/plastic barrier. My question is this – once we have the walls dry, should we put up a different kind of insulation (XPS?) directly on the concrete wall (then put the insulation and plastic barrier back up)? As I mentioned, the framing is already in place and there is a slight gap between the wood and the wall. My husband doesn’t think we’d be able to get a form board between the framing and the wall and we should just paint the walls? Any advice would be greatly appreciated.
Certainly the XPS installed first is a better option, just not ideal with the framing that close to the foundation.
Hi Todd, great site! I’m finishing 3/4 of my basement. On the walls that butt up to the unfinished space (not against the concrete) I was going to use rockwool for the insulation with 1/2 purple sheetrock on both sides. The unfinished area has a water pump / boiler / water filter and gets damp in that area. Should I add a vapor barrier anywhere in the mix for these walls?
Thanks,
Derek
No vapor barrier
Hello.
I live in central Pennsylvania. Home was built in 1988 with a cinder/concrete block foundation. I’ve just torn out the previous owners handy work which consisted of 1x framing directly to the foundation with 3/4″ foam in between each “framing” member. Needless to say there were problems aside from the hydrostatic water issue present when we purchased the home. We’ve has a french drain installed on the entire perimeter and are looking for the proper method of insulating this space. The french drain has a dimpled plastic “tile” that folds up onto the wall 3″ to 4″ to allow any water that may intrude through the wall to run into the french drain. Reading all of your answers above, XPS of 1/5″ or thicker is the way to go. My question is…how do I deal with the foamboard as it relates to the 3″ to 4″ inches of dimpled plastic element of the french drain referenced above?
I would install the foam down over the dimples (you may have to notch the back).