Foam Board Insulation R Values
Foam Board Insulation Types
I’ve written several posts about how to insulation basement walls in which I promote the use of foam board insulation as the first line of defense against moisture and mold. Because of this I often get questions about which type of foam board insulation to use and what R values these products provide.
There are three basic foam insulation board products on the market produced under several different manufacturer names. The basic types of foam board insulation include: polystyrene, polyurethane or polyisocyanurate.
They include expanded polystyrene, extruded polystyrene, and polyisocyanurate unfaced or foil faced. DOW products has lots of information on their site about different foam board products here. I also recommend you read a recent article about Open Cell Vs Closed Cell Foam products to understand the differences between the two product types.
Expanded Polystyrene Foam
Expanded polystyrene foam (EPS) is the cheapest and least used foam board product on the market. This product typically has an R value of 3.6 to 4.0 per inch of thickness. Expanded polystyrene insulation is similar to the foam used for packing “peanuts” and it’s typically used for insulated concrete forms also knows as ICF’s. It is also sometimes used on commercial buildings for roof and wall panel insulation which is typically sandwiched between light gauge metal.
Cost = Cheapest of the foam insulation boards.
Extruded Polystyrene Foam
Extruded polystyrene foam (XPS) also known as blue board or pink board comes in many different thicknesses and edge profiles. This insulation board is probably one of the most widely used foam board insulation products in the residential construction industry. XPS has an R value of 4.5 to 5.0 per inch of thickness.
This is the product that I typically use to insulate basement walls. It’s reasonably priced, light weight and easy to use. This product is also used to insulate the outside of foundation walls and even under slabs.
Cost = This product is the middle of the road for these types of foam board insulation products.
Polyisocyanurate and Polyurethane
Polyisocyanurate also known as polyiso is seen in all kinds of commercial building applications and more recently with residential building projects. Polyiso is typically used with a foil facing and it has an R value of 7.0 to 8.0 per inch of thickness. The reflective foil facing makes it an excellent insulation board when radiant heat is involved. The foil facing also makes it very easy to seal with good quality foil faced tapes.
Cost = Polyiso is the most expensive of the foam board insulation products however it’s the highest R value.
Polyurethane and polyisocyanurate are both closed-cell foams. They contain low-conductivity gases in the cells (usually one of the HCFC or CFC gases.) The higher R-Values (R 7.0 to 8.0) are the result of thermal resistance of the gases in the cells. This can lead to a couple of disadvantages including: off gassing of HCFC or CFC gases, and reduced R Value over time as the gas escapes.
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Also Polyiso is the least moisture resistant. Not only is it subject to breakdown from extended exposure, it also loses significant insulation value when wet.
Use expanded or extruded in any potentially damp locations.
Mr. Wells is incorrect; the foil facing makes the Polyiso the MOST moisture-resistant of the products discussed.
Andy Engel from FHB did an article on this and EPS is the way to go. It allows misture to move back and forth through the board but protects 2×4’s from contact with damp concrete. Of course, you should eliminate any leaks first but vapor WILL pass through concrete no matter what you do – therefore – let it breathe in order to avoid rot.
Chris – I respectfully disagree. The problem is it will hold water like a sponge. So it’s no different than using open cell foam and I’ve seen disastrous problems with open cell foam. I’m of the same opinion as the folks from Building Science who also steer clear of EPS foam.
I have to agree with Todd on this one. The EPS products are one of the culprits in the synthetic stucco debacle. I have personally seen attic condensation on EPS that produced visible water flow and serious problems. Wherever EPS touches Wood you will eventually have mold, mildew, and rot.
As to ISO and water absorption, that will depend on the type of ISO. Open cell will absorb water like a sponge and soft open cell ISO is used to make sponges. Closed Cell ISO is inherently the most moisture resistant.
External applications should always use Closed Cell ISO. It is the most water resistant of the three but there is one caveat. External application of ISO must be protected from UV as UV radiation will cause it to break down. Hold a thin piece of ISO up to the light and think about all those cell walls breaking down from UV damage. Now you have open cell foam.
What about a coating that says it is UV resistant? It depends on whether or not it means the product will weather UV or block UV. Two very different things. Look for coatings that are both UV “Blocking” and Resistant. The Foil is a blocking on the faces only but a silicone coat may not be UV blocking at all.
All good info. Add to that the ability to purchase recycled/once-used rigid foam insulation boards of all types and sizes and you have a eco friendly solution.
Thanks,
Mike
I am going to build a new home on the Brad’Or Lake in Cape Breton Island Nova scotia. It will be a two story with a furnished walkout basement (built on a hill facing the water). The lower walls will be poured 8 inch reenforced concrete. On the inner side I intend to use one inch of rigid foamboard then 2″X 4″ 16 in OC framed wall. Fiberglass batton insulation and 1/2 inch gypsumboard. My question is, is this a good idea, what type of rigid board should I use? My understanding is that the polyiso foamboard does not hold up to any type of moisture but has a higher r factor per inch than the extruded but the extruded holds up better to moisture. If the polyiso is foil faced does that protect it against moisture and act as a vapor barrier. And in either case what is the best to use for a vapor barrier and where??
@ Robert Rein – Building a house that far north I would opt for a minimum of 2 inches of DOW extruded tongue and grove (other brands are fine as well), joints taped and sealed. Then go ahead and frame with 2×4 with R11 fiberglass insulation. No need for a vapor barrier if you install 2 inches of foam and seal all the joints really well. Best of luck!
Hi Todd,
Your suggestions as very helpful re foam board insulation.
Here’s my question: I’ve added about 12ft by 10 to a garage extension in northern NY and want to heat it so I can work in it during the cold winter months. The roof line is lower than the garage roof. I have 7/16 sheathing on a slight slope roof and want to insulate it with 2″ foam board – and then button it up with an additional 7/16 sheathing on top to “sandwich” the form board. I then want to shingle the top sheathing so it matches the existing garage roof.
Would this work? Any specific suggestions?
Thanks!
Angelo
In theory it should work. I have a couple thoughts.
1. 7/16″ plywood isn’t really sufficient on a roof in a snowy climate. In this situation you could argue that it’s ok.
2. 2 inches of foam on a roof isn’t nearly enough in my opinion.
Hello , i would recommend an Air Barrier anywhere but floors , and preferably closest to living space as possible , lets not confuse Air barrier with vapor barrier … We need to protect the structure from all the humidity generated inside a home …ie each molecule of air in a home normally has 45% to 55% water .
@ Robert Rein:
I’m presently insulationg my basement with 2″ foil-faced polyisocyanurate glued directly to the blocks. Then I’ll screw resilient channel through the rigid, to the foundation wall using 3″ tapcons. Then drywall. 2″= R12, minimum.
I’m curious how this project turned out. Its completely wrong and will most likely result in wavy walls and moisture trapped in between the concrete and the polyiso. don’t do what this guy did.
Ryan – Trapped moisture behind the polyiso isn’t of concern in my opinion. It doesn’t matter if you spray foam, rigid foam, etc., you’ll trap moisture behind the foam. What I don’t like is the foil faced against concrete. The aluminum facing will react with the concrete and deteriorate.
Hi We are insulating and attic to make it another bedroom.Can we use 1″ isoboard and leave a 1″ gap between the second sheet isoboard?
Thank you
:)
Not sure I understand your question. An attic that’s turned into a room typically needs quite a bit of insulation. Gaps are fine with foam insulation.
We were wondering if we could layer 2 1″ sheets of polyiso to get a better r value.The insulation has foil on both sides.
Thank you again
Sure…but that’s only about R14….not really up to today’s minimum insulation standards.
So if you left a gap between the 2 sheets of isoboard would that give you a higher r value we were told it would then we read that there would be condensation between the 2 sheets.This is my last question.Thank you :)
That really isn’t going to increase the R value. It does potentially create an area for condensation as well.
Yes, the foil is moisture-resistant, but according to Dow, none of their rigid insulation is a barrier for water vapor.
John – It’s proven that closed cell foam is actually a good vapor barrier when it’s installed at a minimum thickness of 1.5 to 2 inches.
Why not use ICF foundation construction. Far superior method than insulating from the inside and trying to seal out moisture.
This method of construction is becoming more popular as the price of heat continues to climb. Very cost effective over the long haul. Don’t look at the inital cost of construction without doing the math on the energy savings ove time.
It’s certainly a very good option. ICF does have some minor issues that need to be considered. You must cover the foam for fire protection from the very beginning unlike concrete where you can wait until you want to finish the basement. ICF is much harder to deal with electrical and plumbing (although certainly not impossible). And obviously there are cost issues. Certainly worth looking into though.
While ICF’s certainly have the issue of having to protect from sun and elements, I am not sure I agree regarding electrical and plumbing.
On a conventional wall, you would typically stud it out and run your electrical and plumbing. You can do the same thing with ICFs, but you do not have to run conduit because the wiring is not exposed to concrete. You will not need to insulate the cavity either. So, the electrical in a studded cavity along an ICF wall is less expensive than along a conventional poured or block wall.
If you choose, and this is where it can become more work, you can embed plastic conduit into the ICF wall while constructing. If you do it this way, I agree with Todd, because you are going to incur a higher cost of labor. But you gain square footage of living area because their is not any studded wall cavity. I would not recommend running plumbing this way though. This method will kill you on costs if you are not doing it yourself, as you may need to have the electrician working with the ICF installers.
Personally, I would do what I am going to do when I build my next house. Use a thermo mass foundation – four inches of rigid foam sandwiched between two 4″ reinforced concrete walls. I don’t want to worry about off-gassing. The basement, if I finish it will be framed with 2×4 with the cavities filled with Roxsul. Vapor will move as it will.
In this house there is 4″ of rigid foam on the OUTSIDE and the interior walls of the 8″ reinforced CIP walls are coated with two coats of Ultra DryLok followed by two coats of SW highly reflective paint. The floor is painted two coats SW concrete paint. Nice and dry and almost totally dust free. It is also warm.
With not much room to build a 2×4 wall frame and insulate along the side of our basement stairs, we have opted for polyiso sheets with foil and plastic face. Now on the inside of the wall, which face (the plastic or the foil), goes against the block wall and do I still need a vapour barrier between it and the drywall?
@ Debbie – I would place the plastic side against the concrete. No need for vapor barrier if you seal all the joints well. For foil faced polyiso i suggest you get a good quality foil tape (used for duct work…..but NOT duct tape).
As long as you’re building new and have the luxury of doing it right the FIRST time, why not put the insulation, and the waterproofing on the OUTSIDE of the concrete?
You get the advantage of the thermal mass inside, to moderate temperature changes, and it doesn’t cost you any more.
Also, instead of conventional insulation, do superinsulation and cut your heating bill by 80%- you can save most of the cost of the insulation by installing a TINY (and much less expensive) heating system, and pay $300 a year to heat instead of $3000 (most of your heating would come from waste heat inside the building). A savings of $2400/year would pay for about $48,000 greater expense in construction.
@ PeterL – Insulating the outside is certainly one option. However, it’s not as simple as that. The big issue with insulating outside is the detail where the foundation comes above grade. Making the transition from below grade to above grade and transitioning to the interior insulation without a break it difficult to do properly. Furthermore, many people in the industry agree that exterior insulation still doesn’t’ address the severe moisture problem that exists throughout the life of concrete products.
Your point is well taken on spending up front to save in the long run. We’ve built several homes in the last two years that use less than 50% of the energy that previous homes use. Thanks for your input.
Todd – I’m in the planning stages of building an earth bermed single story home. The basis for mine is the Earthwood home built by Rob Roy in New York. He’s had great success building (to all intents and purposes) underground homes with external extruded foam insulation, and also using bituthene membrane applied directly to the outside of his surface bonded concrete block walls. Of course, he also has the luxury of building from scratch, and he puts great emphasis on drainage rather than waterproofing, but his house was built in the mid 80s and is still dry. I intended making the transition from below grade to above grade (the south facing walls/windows will be exposed to maximize passive solar heating) by staying with exterior insulation and going with a natural or manufactured stone veneer. Any thoughts?
Sounds like an interesting project. What will be the “structure” above grade? Below grade I assume these homes rely on the earth as the major structural component but you will not have that once you’re above grade.
I am planning to insulate a large basement, over 200 ft of outside block wall. It is damp in basement but no water problems.There are mildew problems, especially in summer. We run two dehumidifiers constantly, which uses alot of electricity. The floor is concrete. I am wondering how much good it will do to put two inches of extruded or iso sheet on exterior walls, if I don’t cover floor with anything.
@ Charlie – You’d be amazed at the difference 2 inches of foam on the walls can make.
I’m going to use the XPS on basement walls, but i’m not sure what to do about the space above the concrete walls between the floor joists. Currently batt insulation is placed there. Do I need to do something special in this space? I don’t want to spend the time and money on the XPS only to have the moisture barrier benefits negated because I didn’t address this space. Thanks!
@ Mike – I recommend you replace the fiberglass with XPS. You can cut pieces to fit between the joists. Use spray can foam (Great Stuff or similar) to seal each piece in place.
todd….We are in need of any of your advice. We have a walkout basement, three framed walls,the other wall concrete. the framed walls have a paperfaced R 19.the basement is unfinished and has no drywall.The slab was poured over 2″ foamboard and plastic on top as a vapor barrier. In the winter, the framed walls have moisture and black mold behind the insulation. the dehumidifiers keep the basement @ 30% humidity. There is also a pellet stove which keeps the 1200 sq. basement @ 70 degrees. The exterior consists of vynil siding and Tvec. My husband dug the cellar hole,he stated, the ground is pervious, with no ground water. Any help or advice you could lend would be greatly appreciated. Thank you, Dawn Dicarlo
@ Frank – From the sounds of it the kraft faced insulation was not properly sealed and moisture has been trapped between the fiberglass and sheathing. If the basement will not be finished I recommend a poly vapor barrier, properly taped and sealed. At this point it sounds like you need to remove the damaged fiberglass, clean the mold, and start over.
We live in the northern minnesota. The house I worked on has plaster walls, Kraft-faced R-ll insulation, shiplap exterior sheathing, and 3 layers of tar paper. We put 1 inch foil-faced polyiso insulation on the exterior of the house to get the most insulation for the price. With no poly vapor barrier, is this installation correct?
@ tnt – Sounds like a good detail. You do have kraft faced insulation on the warm side so it’s all good.
I live in Alaska and I am having a new build done this summer. The winters have gotten down to -70 in the past. I want the best insulation available. The slab will be radiant heated. I’ve seen previous posts about foam insulation on the outside of the concrete slab, how beneficial is it? What is the best possible insulation for the exterior wall? I’ve heard R-5 blue board on exterior of stick frame walls with vapor barrier and R-11 fiberglass on the inside. What would you do if it was your place and you were looking forward to that extreme of cold?
@ Brent – I’d look at two options.
1. Spray foam entire house inside stud wall cavities, I might even consider a 2×8 wall section for maximum insulation depth.
2. Spray applied dense pack cellulose in the wall and a layer (1″ to 2″) of blue board on the exterior of the house.
If I lived in Alaska I’d spend every dollar I could on insulation versus other nice to have things like nice countertops, etc.
As far as the slab goes you’ll want to install foam board insulation on the outside of your slab/walls, down at least 4 to 6 feet.
Greetings, I’d like to get your advice on insulating my basement. We live in MA in a middle townhouse with a walkout basement. One wall is completely below grade, two side walls are shared with neighbor’s basement and back wall is completely above grade studded with fg/vapor barrier/door/windows. Area is approx 800 square feet. The concrete walls are poured. I’d like to:
– glue 1″ XPS to all concrete walls, then stud
– NOT use bat insulation on shared walls, only front below grade wall/possibly back above grade wall (unfaced)
– lay 1″ XPS over slab, then carpet
Questions: Should I:
– Remove insulation/vapor barrier from above grade wall and use XPS
– Fill in studs on shared walls w/ bat unfaced insulation
– DryLoc walls before insulating. Is this necessary for the walls above grade/shared walls?
We plan to tie into HVAC for heat and air return and run dehumidifier when necessary. I did the moisture test with the taped foil on the walls, no moisture on either side.
Thank you, John
@ John –
1. I would leave the old grade wall insulation. However, check it and make sure there is no moisture or mold in it.
2. Just foam is fine on those walls..however…i recommend 1-1/2″ min. foam board.
3. DyLoc is just added protection…not sure how much it buys you in the grand scheme of things.
I would generally agree with you with these exceptions. If you have a shared studded basement wall, I would be sure the insulation is Roxsul (mineral wool) which does not burn or retain moisture. On the concrete walls, I would use the Ultra DryLok. Yes, it is extra protection but it also controls the smell of bare concrete and the dust.
Can I use 2″ of foamboard (Polyiso) under my metal roof. foil facing up?
James – Sure can!
Hi. I building a new home in Ontario and will be installing hydronics in the basement floor. I will install 2″ of rigid foam insulation under the slab. Question is which rigid foam insulation is best “Pink or Blue”? I’ve noticed “pink” carries a premium price to the blue. Both have the same R value and the same compressive strength. Is there something I’m missing? Thanks D.
David – No difference….free markets driving price….nothing more.
I live in Geneva, Switzerland. Temperatures range between 25 and 35 in the winter. I am insolating my basement but the Swiss tend to over-engineer their walls so I want to provide some guidance to my wall-guy. I don’t have a lot of space and would like to forgo framing and batting. Is it possible to use 2″ Extruded Polystyrene, attach furring strips and then gypson board? By screwing the furring strips through the blue board into the cement, does that not let in the moisture that seems to be the trouble with basements?
Thank you in advance.
Christine
Christine – That method actually works quite well. You want to be sure you’re using galvanized or stainless steel screws and be sure the screw heads are sealed well afterwards before the gypsom board.
Todd, your article says polyiso is more expensive than XPS but is higher R-value per inch. Is polyiso also more expensive on a per R-value basis? OR is cost-per-R-value close enough that one or the other product may be less expensive per R-value in any given market?
I currently only specify polyiso when the insulation is exposed, as in an unfinished basement or closed crawlspace. The foil face satisfies code officials. Unfortunately, I never get to see the costs.
David – Good question, frankly I’ve never compared cost per inch. Next time I purchase some I’ll have to run those numbers. Good point!
I’m currently finishing out my basement. I’m going to use 1 1/2″ extruded polystyrene on the concrete walls and frame and drywall against them. What tape is recommended to seal the joints? I read somewhere about tyvek tape, but I’ve never seen that in my area. Also, I’m considering drywalling the ceilings, mainly due to costs of drop ceilings. Are drop ceilings a better idea to encourage air flow? Will a drywall ceiling create a basement that is too airtight?
Jacob – You can find Tyvek tape as most big box stores and lumber yards.
http://www2.dupont.com/Tyvek_Weatherization/en_US/products/residential/resi_seam_tape.html
You can also use this stuff, it’s similar, http://www.amazon.com/exec/obidos/ASIN/B002KM1APU/homeconstimpr-20
Drop ceiling are better just for future access. Drywall ceilings will perform just fine.
Todd, I did find a tape equivalent to the tyvek product, and I’m going to go w/ that. Thanks for the reply.
We have a two-thirds finished basement, and have stripped the finished side down to the studs. Currently there is no insulation nor vapor barriers. We would like to add some insulation to the finished side to help normalize the basement temperature to the rest of the house.
1. Does it make sense to insulate the finished side, if we are leaving the unfinished side alone?
2. Can we put foam board between the studs, since we don’t want to remove the studs and install the boards against the concrete walls?
2a. Would this configuration still require some type of vapor barrier?
We live in Ohio, if that helps, and have had no moisture problems in past.
Frank – Thanks for stopping by the site.
1. It certainly doesn’t hurt! You’ll probably find that the rooms above the finished/insulated area will feel more comfortable afterwards.
2. This isn’t the best option but it’s the best one if you don’t want to move the framing. Be sure to seal all the edges with spray foam from a can.
2a. If you install at least 1-1/2 inches of closed cell foam I think you’ll be ok without one.
Good luck.
Thanks for this forum and the great information! I will implement the basement wall according to your Oct 12th post. Love it!
But I have a foam board question for NON-basement walls.
Is there any advantage with using EPS insulation for “non Basement” framed wall?
Say 4 inches of solid EPS insulation stacked in a wall, then sealed with can foam (prior calking any sills and opening to prevent any air). I see no need for a vapor barrier Kraft paper. I haven’t priced it out – but since it’s “solid” though more work than then spray foam – if sealed well, it would achieve the same result – right?
As closed spray foam installers say – batt is really just a thick furnace filter, walls have convection, and even if the R values appear the same – Solid (spray) foam is warmer in use.
I’m building at 11,000 feet in Colorado. 2×6 construction and have the building weather tight but framing exposed inside.
(I should have done 2×4, saved money and did foam board layer on the outside to prevent “thermal bridging” from the wall studs)
But we are ready to start the cedar siding and the builder isn’t keen on adding layer(s) under the siding since the windows are in, tyvek is done, …) – he’s worried about moisture getting behind. So I’m pondering anything to beef up the walls
But I have very low moisture in Colorado. R21 is recommended for walls.
I likely will get the ceiling closed cell spray foamed but likely not spray foam the walls two story, plus a drive under garage is a lot of walls but not much roof.
Plus, spray foam is pricy and at the High Altitude the formulation gets even more costly (supposedly) since the microscopic air bubbles could pop.
I noticed one post above mentioned three layers of tar paper.
Could that be for R value – just for another cheap layer. Does it really help? My builder would be fine with tar paper layers.
Thanks in advance!
Joe – Using foam inside the cavities is a fine idea. However, I have a feeling it may end up costing as much as spray applied when you consider the labor to cut all the foam board, install it, seal it etc.
Not sure tar paper is going do to much of anything for you in this situation.
Hi Todd
Here is my dilemma…My finished basement got flooded…12 inches up…I cut up 12 inches of drywall & removed insulation w/vapor…I am going to go up to 4 ft because (Drywall is 4 x 8…would make it easier to replace…unless you think otherwise)… My mancave was damp to begin with which I believe is totally do to the foundation walls (totally in ground) not having any Foam xps board attached
I do not want to totally remove all drywall & studs…I will remove 4 ft of drywall from floor…This will probably be very difficult to fully tape foam boards together…but I will try my best…because I am sure XPS on the Foundation walls is better than none…Correct.
also insulation in between my studs R15 I can use a non vapor backing if I foam board my foundation walls correct?
And lastly I am installing new carpet…will the carpet pad be enough or should put down a thin foam board on the floor?
Any other ideas would be great
Thank you
Mark
Mark – First off let me say I wouldn’t go through all this trouble until you figure out why your basement flooded. If it happened once it’s likely to happen again. 12 inches of water is in my opinion a basement that shouldn’t be finished.
Having said that I also don’t think your approach will work very well. Unless you remove it all and create a good vapor barrier you’re doing to just push the wall moisture up higher and eventually into the remaining fiberglass.
Have you investigated the flooding situation?
Hi Todd
Yeah, my sump pump failed in the 2010 Greatest New England Flood of all time…Just my luck…I never had water before…
So the bottom line…I need to make sure I have a good vapor barrier…I plan on using foam board all the way up on my foundation walls some areas of basement I can make this happen easily…some other areas it will be tight but if I cut half my drywall out I may be able to reach it…How about putting foam board on my floor…or should I just use carpet pad & rug?
Thank you
Mark
Mark – The floor really depends on ceiling height, if you want to make it warmer, etc. You can read about insulating a floor here:
http://www.homeconstructionimprovement.com/how-to-insulate-a-concrete-floor/
Tood
We are going to reside with vinyl siding on an older home with 2×6 framing that has fiberglass bating insulation inside. To add insulation it seems our only option is the “blue board” installed under the siding? If so should it be house wrapped too? Thanks for any ideas. eric
Eric – The foam board should be installed first with all the joints taped. Then a house wrap should be installed over the foam prior to the new siding.
I live in Texas, the sun hits my converted garage and kitchen very hard, garage was insulated. I would like to know if I can put the polyisocyanurate over my outside wall which has stucco on it to reflect the sun rays and will it last?
Geo – I wouldn’t really recommend putting polyiso on the exterior and leaving it exposed. It really should be covered by a siding product.
I just found your site, and like the posts. I am removing my Alaskan house’s beveled cedar siding to install rigid foam insulation on the 2×4 wall’s exterior, prior to reinstalling the siding. My concern(s) are that I do not want to add furring strips for solid siding attachment, as I want to secure the siding directly through the rigid foam. I also am concerned about totally sealing off the foam, as I think it may be in my interests to allow water vapor to move from inside to out. I cannot vouch for the interior water vapor seal quality under the sheetrock. My home has been “breathing” for 40 years without mold in the walls,” so I’d better keep letting it do so.
What do you suggest as a maximum thickness for the foam, for use without furring strips? Should I really seal all foam sheet seams? I was even thinking of using house wrap on top of the foam just to provide the extra barrier for water moving into the wall. Also, what type of fasteners should I use for the foam and the siding? I admit to being new to this part of construction, and I’ve heard a different bit of advice from each person I ask.
Thank you in advance for your time.
Stan
Stan – You have lots of options and some of the options depend on the type of siding you’ll be installing. First of all I would strip the old siding, fix and damaged sheathing and then install a layer of housewrap. Next I would install a layer of rigid foam board (XPS would work fine). The thickness will depend mostly on how it affects trim details at doors and windows. Depending on the thickness you can use just nails to re-install the siding or you’ll need to use a foam product that accommodates strapping (like DOW Wallmate). However, a product like that will really only help with horizontal siding products.
Does this help?
I only mentioned once that I would reinstall the beveled cedar siding, so I do have a horizontal siding application. I’ll look at the strapping. The cedar siding was installed over celotex, which was directly attached to the studs. I’m putting OSB ontop to the celotex, except for one wall, which had the celotex removed. The XPS will be attached to the studs through the OSB. You recommend house wrap under the XPS. I was thinking over the XPS, but on second and third thought, your idea makes more sense.
Window and door trim will be dealt with by using 3/4 ply boxes inside the window RO’s, and custom furring trim on the few doors, for finish trim nailing I’m leaning towards 1″ XPS, while finding some type of fastener that will give me the stud penetration depth I would get without the foam. I can understand your inability to safely recommend details in “print” from far away.
Thanks for your time. I appreciate your thoughts on my problem.
Stan
I’d be interested to know how it worked out. I’m in this same boat as you (were), and the options seem limited. From what I’ve read, if one applies thin insulation (<=1") in climates like yours (or mine, in VT), then it encourages moisture to form at the interface between that and the siding or sheathing beneath it. Add to that the foam board being a vapor barrier, and the breathing of the existing walls to the exterior is impaired. Finally, housewraps are miraculous, but not miracles. They pass water vapor both ways, and they trap water droplets on either side EXTREMELY well. So, moisture that forms on the inside of a housewrap will be trapped as effectively as the housewrap excludes water penetration from the outside.
I've been looking/reading for days and hitting many, many, MANY blogs and advice sites trying to find a workable solution to my project that doesn't involve slapping 2 inches of rigid foam over the existing sheathing or siding.
We've got 2×6 studs w/an average of 5+ inches of fiberglass or blown in insulation (min R-19 when built). Plywood sheathing, tightly shiplapped 3/4" vertical cedar siding. House is tight and well insulated. But, the siding needs replacing and we're doing the windows while at it. So, we're looking at options to claw back some of the insulation lost to the siding while avoiding too much of a moisture or water vapor barrier.
There don't seem to be any ready solutions. If anyone has been through this and found one (for a cold climate home) I'd love to hear how it turned out for them!
Matt – You are certainly facing a situation that many home owners face. It’s hard to get the insulation value you want in old walls without causing lots of other issues. If you’re replacing the siding and windows, then you have an advantage over some homeowners. You can “absorb” most of the 2″ exterior foam by pushing the new windows out further and using larger extension jambs. That’s how I’d probably approach your situation.
Hi I’m looking to insulation my crawl space because my wood floors are cold in winter. What type should I use? I have a sump pump down there because sometimes have water.
Kyle – Without seeing the space it’s hard to recommend a system. Typically crawl spaces benefit nicely from foil faced polyiso foam board.
Todd,
I am reading the post’s and they are great! Here is my question. We have the foil backed insulation board on the bottom half of our walls in the basements. We have recently put in batting type insulation over the foil backed insulation board. We were recently told that we should remove the batting insulation as it will produce moisture between the two insulations. Is this true? What are your recomendations. (I hope this make sense)
Thank you in advance for your advice!
Dana – Thanks for the compliment.
The batts could be a problem depending on the details. First off how thick is the foam board? Are all the seams taped? If the foam goes from floor to ceiling and it’s properly sealed then it creates a great vapor barrier and it shouldn’t be a problem. Of course that depends on it’s thickness too.
Todd, we are just starting to build a new house in Michigan. I asked my builder to add 2″ of rigid foam boards to the exterior before adding brick and cement board siding and he panicked. (We have to have brick on the full front and partial sides/back.) He’s never done it before and he is concerned about several things:
1- how does it affect the foundation? He wonders if he’ll have to move the foundation wall out to accomodate another 2″ in addition to my planned 2×6 walls. (we have to have 2×6 on large side walls). of course, I need a brick ledge large enough to set brick on, so do we just move the foundation wall out or does it have to actually be thicker for my proposed 2X8 wall?
2- and he’s worried about the soffits and interfering with their depth/overhang.
3- I figured we could save money by eliminating the OSO sheathing but that worries him, too. He doesn’t know if it will pass code. Doesn’t know how to go about engineering it without sheathing.
4- He is worried if we do or don’t need a house wrap as I also suggested that we could eliminate that if we use the right foam.
5 – windows/ doors. He said he doesn’t know how to flash them with foam.
I have read your site and have investigated a little on my own but wonder if you can answer these basic questions and/or provide us with a few resources to find good solutions to build it right.
He asked me why I can’t ‘flash and fill’ inside my 2×6 wall cavity with spray foam and cellulose. From what I’ve read, and correct me if I’m wrong, here in Michigan with cold winters, I need enough spray foam to keep the dew point to the outside of the foam or risk condensation inside of my cellulose where it would get trapped. So, a little foam actually can do more harm than no foam. Exterior foam of 2″ will keep the dew point to the outside of the foam so the cellulose will stay drier and it will provide a thermal break and wind barrier over the whole wall, including the sill joists. Am I correct? Can I use both methods? ie: 1″ spray foam on interior and 1″ rigid foam on exterior? That may be more manageable for him…
Thanks, Laura
Laura – Thanks for stopping by this site. Your builder probably panicked as this is such a new concept to him. All of his concerns are valid, however, they area all manageable with proper details.
1. Typical foundation around here is 8″ minimum concrete wall. So you can actually install the pressure treated sill plate to the inside of the wall and frame above that with standard framing, 2×6, 1/2″ sheathing. Then you can install the 2″ of foam board which will bring the foam to the outside edge of the concrete wall. You could actually use a 2×8 sill, so the foam sits on the sill with a piece of flashing above the sill to keep water from migrating under the foam and back into the house. All of the joints in the foam should be sealed well.
2. By using step 1 above the face of soffit can still be in the original position.
3. I would not omit the sheathing.
4. If you tape it well the house wrap is probably over kill.
5. All this does to windows and doors is require 2″ deeper extension jambs which shouldn’t be a problem.
Installing exterior insulation is MUCH better than interior because it’s continuous. Spraying the cavities with and inch or so of foam could possibly work if you can get sufficient R value to prevent the dew point problem, but it’s hard to control. I think you’re on the right track.
Todd,
thanks for sharing your knowledge on this subject. I am a contractor preparing to renovate a 1965 house with homasote sheathing. Plan is to leave the homasote add 1 1/2 foam board, 1/2 osb or cdx and cement fiberboard clapboard siding. This will bring me to a 6 9/16 jam for the new windows. Dealing with the 2″ overhang on the foundation is under discussion. We want to avoid air and insect penetration. Proposed are metal flashing (sort of a reverse drip edge and covering the foundatiion with a manufactured stone product or using a a Weatherwatch ice/watershield and then applying an azek cornerboard as a water table. your thoughts?
Michele – Can you put an extension on the sill plate, then trim the bottom of the extension with a PVC trim board after caulking the joints? That would probably work pretty well.
yes we would need to do the extension as a nailer for the corner board idea as well. Any preference on Dow vs. Owens Corning vs Celotex?
Michele – Not really, the real issue is being sure it’s closed cell foam.
These are great comments. Here’s my situation. I have an old 1920’s home with a brick exterior and plaster interior. I am renovating it and just took down the plaster and lathe. Now all I have left is the back side of the brick with 1X3 furring strips nailed on the inside 16″ OC so I only have 3/4″ or so due to the furring strips. I plan to install sheetrock attached to the furring strips. It never had any insulation. What product do I use to get some kind of wall insulation ? Do I have to stud this out further somehow to get the thickness I need or be happy with some sort of foam insulation panel (Which type do you recommend) that gets me only a R-5 or so wall and will get this passed the building inspector and this is a permitted project. I don’t want to use spray insulation contractor and would like to do it myself. Any help would be great !!
Mark – Well it really does depend on where you live and what Energy Code if any is in effect. I’d start off by checking with your local building inspector to find out what the minimum (if any) required insulation value is. After that you can come up with a plan of attack. Most likely you’ll want to install a layer of foam board over the furring strips prior to installing the drywall.
todd I live in upstate ny I am putting a 2nd floor on my house 2×6 walls can I use foam board along with 6in faced fiberglass to get higher R value and is it better to install foam board on the interior or exterior or both and what kind of foam board do i use
Mike – Sounds like a big project. Couple of thoughts about your situation. First off are you looking to do all this work yourself or with contractors? For new construction (including an addition) I would consider having a contractor come in and fill the wall cavities with blown in dense pack cellulose insulation. I REALLY like this product for wood framed walls because it does an amazing job of air sealing and you can achieve a full R21.
If you’re looking to do all the work yourself then you’ve got a couple options. I guess I would lead towards applying the foam on the outside of the house. If you’re going to do that you need to pay special attention to all the details, depth of window and door jambs, etc. You should use a closed cell foam specially designed to be installed under siding. You’ll probably want to hold the framing back from the outside of the existing house by the thickness of the foam so that the siding all lines up.
Hello Todd. Your website is fantastic!! I read through all these posts and didn’t find my exact situation, so thought I’d post.
I live in Jacksonville, FL and due to age and water damage, I had to replace the bottom sill plate on my 1940’s garage apartment. To do this, I had to remove the shiplap tongue and groove siding. Doing this showed me that there was no insulation and I’d like to add it. Can foam board insulation be used instead of batts of fiberglass?
The lap siding was installed directly to the 2×4 studs with no sheathing. Can I use the foam board cut to fit between the studs for insulation and then re-install the lap siding directly to the studs? I could also use the spray foam (Great Stuff comes to mind) to seal the gaps between the foam and the studs. I would assume a layer of Tyvek house wrap should also be installed before the siding is replaced.
I am willing to remove and replace all the siding if I have to but if you have a better idea on how to insulate it without removing the siding, I’d love to hear it.
Thanks so much for any insight you can provide.
Kim – Foam board insulation can be used anywhere fiberglass can be used. I assume you’ve got access from the inside? Another solution would be installing foam directly over the old siding then installing new siding. This creates great insulation value but it does require some special details at doors and windows to address the added thickness. Good luck!
Thanks for the reply. We do not have access from the inside without tearing out sheetrock. And since we had to remove siding to repair the damaged sill (and also termite damage) I thought we would just insulate from the outside rather than tear out sheetrock on the inside. Sheetrock may be cheaper, but it is a lot quicker and easier to just remove all the siding rather than try to get behind tubs and kitchen counters and, and, and….. :) I don’t want to double up due to the issue you mentioned regarding doors/windows.
You didn’t comment on whether Tyvek would be needed over the insulation under the new siding. Is that required?
Thanks again!
~Kim
Kim – Your proposed method will work just fine, and yes you should use a house wrap. Best of luck.
can blue foam board insulation be used under a metal roof – I have an old cabin that has no insulation in the roof just metal roof on tongue and grove pine and need a new roof and thought this might be a way to gain some insulation
Brad – It sure can! Blue board works in almost any application. Good luck.
I started building a room in the basement. Part of the basement is above ground and was insulated with fiberglass. We moved back some of the insulation and found mold! In the process of removing and cleaning with vinegar.
So would thick xps work well with the areas that are above ground as well? Is this stuff a fire hazard if not covered with drywall? I was hoping to leave the above ground walls open in the unfinished area of the basement for easier insect and mold inspection.
Will a hepa vacuum filter work for cleaning up fiberglass particles after I’m done removing this garbage?
thanks! been asking everywhere but not getting a good response.
PS also bought a dehumidifier after finding mold.
Chris – Foam will work well there as well. Frankly foam board will be no more of a fire hazard than fiberglass. Most building inspectors would definitely require that you cover it, but lots of houses don’t. Good luck.
hI,
My contractor is installing what looks like polyiso panels 1.5 inch R10, behind new vinyl siding on 2nd floor exterior wall.
I asked about Tyvek wrap and he said not necessary, but can they really seal that well with tape
Wouldn’t it be better to put Tyvek over the foam insulation to protect the foam from water and stop airflow? He said Tyvek is expensive but I think I saw 1000 ft2 roll for $100, so maybe its labor intensive install.
Anyhow, not sure I like the idea of the siding acting as the only rain and wind membrane.
Any thoughts?
Jazz – First off the foam can be sealed very well with the right type of tape. There are many tapes on the market now that stick very well..just be sure it’s not duct tape! Secondly there are lots of folks out there that argue about Tyvek (or house wrap) over foam board insulation under siding. I will say that if you think it’s worth the cost then it’s certainly not going to hurt anything. I say make your decision based on sleeping well at night.
Thanks Todd,
1. So the Tyvek plus the tape sealed foam would not inhibit the wall’s ability to breathe.
2. Another quick question about siding selection. The contractor is offering Procanna siding for the color I want whioh seems to be OEM’ed from an Ontario siding manufacturer, thickness is .044 and 25 year fade resistance. They don’t have any detailed spec sheet touting any kind of advanced technology or features.
3. Are there big differences still in vinyl siding from different manufacturers?
Is .044 thick enough
If I could choose any brand/thickness of traditional double
panels, what are the top brands based on reputations and advanced features?
thanks
Jazz – Frankly you want to keep the water away from the framing. If you don’t tape those seems water will get in. Vinyl siding is only a facade and it’s far from a water barrier.
In my opinion there is a huge difference in siding products. We’ve tried dozens of them and my preference is Certainteed. In fact, my first preference is Certainteed’s Monogram line that has a 0.046″ panel thickness. That extra bit really makes a big difference in performance especially in climates with large temperature swings like here in the North East.
Hi Todd, I could also choose ABTCo timber creek premium plus .046 thickness rather than the OEM .044 which we chose only because the green was slightly more appealing but the more I research Procanna the more I have doubts I think it is contractor grade, no info available, they won’t tell me who makes their panels.
What do you think? IS ABTCO good?
thanks
Jazz – I’ve never heard of them but doesn’t mean the product is bad. At least it’s a thicker panel.
ABTCO is KP Building products, Home Depot carries it here.
http://www.kpproducts.com/kpbp/ca/p-norman-rockwell.htm
Jazz says:
July 11, 2010 at 10:53 pm
ABTCO is KP Building products, Home Depot carries it here.
http://www.kpproducts.com/kpbp/ca/p-norman-rockwell.htm
Do you know this manufacturer?
thanks again
Jazz – Haven’t seen them before but that doesn’t mean much. We purchase all of our building products from two large “contractor” supply companies and mostly deal with two or three large, well known siding manufactures.
I live in New Jersey and I’m currently finishing/renovating my basement and have several questions:
1. Any recommendations on how to insulate around (or behind) an existing electrical panel and wall mtd water heater? Do you actually try to get the insulation behind these items, or do you just get as tight as possible to them? Obviously, it’s a large task to get behind them.
2. When completed, my basement will have a “finished” area (that will serve as a kids play room & home gym)and an unfinished area (that will be a utility closet and tool area). The finished areas will be conditioned, and the unfinished areas will not be conditioned. In your opinion, can I get away with only insulating the “finished” portions, or would you recommend insulating all of the exterior walls? If I only did the finished portion, I was planning on insulating (w/vapor barrier)the interior dividing partitions between the finished and unfinished spaces.
3. One of my foundation walls is directly below a “family room” that is a “slab-on-grade” construction. I’d like to install a thinner insulation along this wall due to this wall will encroach on an already tight stairwell. Any thoughts on going with a 3/4 or smaller board for this section of wall? It is somewhat insulated from the outside since there is a slab on grade installed at the top of the wall.
4. For the detail at the top of the wall and into the joist cavities, do you run a horizontal piece of insulation between the top of the wall and bottom of the joist cavity so that it’s continuous, or do you just run the insulation to the top of the foundation wall, put the pieces in the joist cavity, and leave a gap?
5. With the foam board insulations, I was planning on installing 3/4″ furring strips on top of the insualtion board, and then fastening the sheetrock into the furring strips. Is there any problem with notching the insulation around electrical boxes, or would you recommend deeper strips (possibly even a full 2×4) so that the electrical boxes don’t cut into the insulation?
6. As far as adhering the insulation, do you just use construction adhesive to install the foam boards, and if so, how do you hold them tight to the foundation wall?
7. When you reference “Energy Code”, is there any website that shows the requirements for different areas?
Thanks for your time.
Pete –
1. In an existing situation most people would opt to insulate up to these type of utilities. Relocating or moving them would be a pretty costly task.
2. I would recommend insulating all of the exterior walls. Your home will be more comfortable all around and it’s easier to deal with vapor at that point.
3. In situations like this you’ve got to weight the pro’s and con’s. Using 3/4″ foam will most likely not provide a very good vapor barrier. However, that wall will likely not get very cold so if water vapor from the interior space hits the foam it may not condensate. I say do the best you can with what you’ve got.
4. You want things to be as continuous as possible. Typically we’ll run up to the top of the wall, then install a horizontal piece above that, then insulate the rim joist, then tape all the seams or seal with spray foam in a can.
5. I would just use 2×4’s or if code allows you may be able to use shallow boxes (if they will fit in the 1-1/4″ space you have. I’d try to avoid notching the foam.
6. We have recently been using DOW GREAT STUFF PRO http://building.dow.com/na/en/products/sealants/gspwallfloor.htm it works exceptionally well at adhering the foam to the wall quickly. Sometimes you do need to apply some temporary shoring but not often with this product.
7. Every state has different rules regarding energy codes. Here in NH where I live it’s governed by the Public Utilities Commission (PUC). I would call your local building officials and inquire about it.
Good luck.
Todd, What a neat website!! I’m building a home close to Houston Tx and have 2×4 walls, wrapped 100% with 1/2″ sheathing and then with 3/4″ R Max insulation boards (R-5). I’m also planning to install house wrap before putting on 3×10 log siding. While I plan to use bat insulatin in the wall cavities, is there anything else I can or should do to improve the insulation effectiveness?
I am also installing knotty pine T&G boards on the interior walls and was planning to use sheetrock as a backer on the inside to keep down any dust or airflow. Would it be better to use an insulation board and if so, what kind would you recommend?
I doing this myself, with the help of my lovely bride, and could use any help you might provide.
THANKS A LOT!!!
Earnie – Hot climates like TX are a different animal compared to here in the north. I would recommend checking out http://www.buildingscience.com they have great information on all types of insulation. You just need to be careful with where there vapor barriers are when it’s warm on the outside and cool inside (air conditioning).
I have an enclosed(aluminum) car hauler. There is about 2 inches between the roof and the bottom of the supports. I would like to insulate the roof with foam board and hold it up with some thin wood board/screws. Which would be the best kind of foam board to get and proper thickness ? Foil faced or not ? Which way should the foil face ?
Brian – is it curved? If it’s curved most of these products will be hard to curve unless you install it in several layers. Most of the foil faced products are covered with foil on both sides.
The roof is arced yes. I would say it is arced about 2ft with a length of 8.5ft. I am thinking about using 3/4″ polystyrene foam board that has foil on one side. That would leave about 1.5″ of clearance between the foam board and the metal roof.
Brian – That will probably work..might have to score the back side though.
Great site! I am planning to insulate the walls of my Illinois basement with the 2″ XPS. I’ve heard that it should be 1-3 inches off the floor to catch any condensation from behind the insulation boards. Is this true? In the past water has seeped in thru the joint (cove?) between wall and floor. Can this be sealed? How? Digging up the floor and installing drain tiles is not an option. Thanks for your advice.
Mary – Before insulating you really should address the water issues. Interior French Drains are a great way to intercept and remove water from basements. Typically that’s a job best left to professionals.
If and once you that then you can bring the insulation right down to the top of the drain, any water behind the foam will drop down into the drain. It’s VERY important that all the seams in the foam be sealed. We’ve got several articles on the site showing how to do that.
Good luck.
Hi Todd
Great website and very helpful…I have a slight variation in insulating my basement interior walls.
I was hoping you could provide some expert advise.
I had to frame out my basement walls 8″ away from the concrete walls on all sides since the house has alot of conduit and pipes. I have installed metal studs 16″ OC and the basement is moist not wet. A dehumidifier keeps the basement dry. This 8″ gap also allows me to run a fan behind the studs for good air cirulation.
Question: Can I install Extruded or polyisocyanuarate between the studs for my insulation needs then cover it up with 1/2″ sheetrock.
I’m concerned about the combustible nature of these products since the interior part of this product will be exposed (between concrete wall and metal studs)
Note: This unfinished basement without any insulation in the coldest season (NY) maintains an average temperature of 67 degrees, so I’m not that concerned
Thanks for the advise
Frank
Frank – I think I’d install a layer of foil faced polyiso OVER the metal studs then attach the drywall. I don’t have the specs handy but you could check online to see what the flame spread rating for foil faced is. I have a feeling it’s not bad at all. I wouldn’t put the foam between studs because you won’t have any thermal break.
Lots of good ideas!
I’m refurbishing a 1950’s finished basement in Seattle. It had 1/4″ plywood paneling over 3/4 furing strips on 24″ centers. I’ve removed the paneling, and was planning on gluing 3/4″ foam to the concrete between the furing strips, then another 3/4″ layer over it all. Then screw 1/2″ drywall over it all to the furing strips.
Does that sound like a reasonable plan? There’s no moisture problem, no mold found after removing the old paneling.
Brad – I’d rather see a full 1-1/2 inches of foam against the concrete. However, your system will probably work fine.
Todd,
Thanks for this informative site. The company I work for bought a large commercial building. There are many 68″x68″ openings for wall exhaust fans. My boss wants me to design some insulated covers that we can install in the winter (the previous occupants just stapled up blue tarps and they said it was still freezing inside). My boss was thinking about making steel boxes and using foam board inside. The outside temperature regularly gets into the teens and single digits during the winter. We will use a good diameter rubber tube seal between the boxes and the exterior walls. The boxes will be bolted down to compress the seal. The boxes will be stored indoors when not in use.
1. What R value of insulation do you think is right?
2. Since the boxes will be metal, does it matter what direction any liners may face?
3. Do you think open side of the box (foam side) should have a cover?
4. Would it help to have air gaps between the box’s exterior sides and the foam?
5. Do you see any problems with this idea?
Thanks for any advice you can offer (this is not really in my bailiwick).
Rich – Sounds like an interesting project. Here’s a few thoughts/questions.
– Will the box be installed on the outside or inside of the building?
– Do you know how much wall insulation the existing building has? Most commercial buildings have an R19 in the wall.
– Assuming the cover goes on the outside, I’m thinking you could install 3 inches of foil faced polyiso insulation in the “box”. I would only have steel on the outside and sides, leave the side facing the building with just exposed foil faced insulation.
– Remember that steel itself transmits cold very well, so the gasket will be key.
Make sense?
Todd,
Thanks for fast reply!
The boxes will be on the outside.
I don’t know about the insulation in existing walls, but I can probably find out. The outside walls are a decorative type masonry block.
Yes, metal tranmits cold very well, so that’s why I was wondering about having the foam actually touch the metal or not. I was thinking a little air gap would be good – ?
Hmmm, we may want to use a treated wood, or probably plastic, frame around the face of the box to mount the gasket. The insulation could extend into this volume. Does that sound good?
ps. My boss would love for these things to last a lifetime.
Rich – I think you’re on the right track. Making them slightly larger, having the foam extend slightly deeper than the box, and a gasket, should take care of it.
Thanks – I think I have a plan.
But … Thinking about it, there are four large rollup garage doors that I don’t think have much insulation. Three inches of polyiso may be a little overkill compared to three inches of blue/pink board. Well, I guess I’ll just price it out and see how the boss wants to go. Maybe we’ll see about insulating the garage doors too. In any case, this will be a lot better than blue tarps!
Rich – I suggested the foil faced as a bit of safety insurance. Foil faced insulation should have a much better flame spread number than just foam board.
Great site!
Simple question I can find nowhere on the net. I have a old dirt basement/crawlspace in my old farmhouse that is vented well. The house floor is also un-insulated so we get a lot of moisture in the house after very rainy spells. Time has come to insulate the underside of the floor and I wanted to go with spray closed cell foam for its vapor barrier and insulating qualities….Plus it will hide some ugly bits of framing, as this house was built out of what appears to be scrap wood from an earlier home.
To save money I was wondering if I could just tack 2″ foam board between each floor joist and spray the seams, joints and hard to get areas with the spray. The DIY spray foam kits run about $1.50 sf. for the foam, so this would be a huge savings if it will achieve the same effect. Is this ok to do and is a specific type of foam board more compatible with the spray foams?
Thanks
Joel L.
Franklin, NC
Jeol – Not a bad idea if you can’t afford a complete spray foam job. For this application I would recommend at least 2 inches of foam. Before installing the foam board though I would get some samples and test the spray foam on it to be sure there’s no reaction that would damage the foam board. Under a crawl space I would prefer to use foil faced polyiso myself. Good luck.
Tod,
I live in Madison, WI and I am converting a screened-in porch into a room. There is a concrete slab and the roof is held up by three 6×6 cedar posts. Because of the depths of the posts from the edge of the slab, I have framed the bottom section of the wall with 2x8s. That way the siding goes over the edge of the slab. Then, so that I can leave the posts (which are pretty and expensive) exposed, I have framed the top half of the wall (containing the windows) with 2x4s. The ceiling rafters will be furred out to 12.” And to allow for heating ducts, the floor is raised about 14′ on 2×8″ joists.
So what I’m looking for is the best and most cost effective way to insulate this monstrosity.
I was thinking of putting 6″ of foam board on the slab (the inspectors want r-30) and densepack cellulose in the ceiling. Does this make sense?
Then I was thinking of putting one inch ridged foam board over the outside of the slab and the lower 2×8 wall. Do I need house wrap for this? OVer or under the foam board?
But my big question is the walls. The upper 2×4 walls have lots of small cavities in the framing betweeen and above the window. Can you put dense pack cellulose in those? Or would spray foam be better?
What do you think?
thanks
cw – Thanks for visiting the site.
The 6 inches of foam board would work fine on the slab.
The 1 inch foam on the outside of the 2×8 is ok but you’ll need more R value (planning on more insulation in the wall cavity?).
House wrap is a good idea even with foam on the outside of the house. Over the foam.
Dense pack fiberglass or cellulose will work great in those wall.
Thanks for your help. The one inch on the outside is to insulate the studs, break the thermal transferance or whatever you call it. THere will be some kind of insullation inside the studs.
So they can blow dense pack cellulose into small cavities, say 1 1/2″ wide? Would that be better than spray in foam?
Thanks again for your help.
cw – dense pack can blow into voids that small. when the voids get down to like 1/2 inch then typically foam those while still dense packing the rest.
Hi,
Roof on Steel deck in Ottawa.
1- Is there a specific vapour barrier that goes under polyiso?
2- How to fix the polyiso on the vapour barrier? do we need to reach the deck?
3- I need one or two sheets of polyiso to get the 4 inches.
4- Can I install torch applied membrane on the insulation, is there any primer?
5- can isoply be tapered?
Thanks,
Mongi
Todd,
I live in Michigan. I installed 1 inch DOW XPS tongue and groove. I caulked and sealed the seams with tape. Then built stud 2 x 4 walls. Reading the forums, I realize I should have probably went with 1 1/2 foam. Anyway, should I go with faced or unfaced fiberglass insulation? If building inspector requires the faced would that be an issue with double vapor barrier. Thanks
Will – If it were mine, considering the stage you’re at, I would just fit additional foam between the studs and be done with it. It’s really too risky to go with fiberglass with only an inch of foam.
Help!
I scrolled through all the above stories first but cant seem to find one that fits my situation. I live in northeast Georgia (summer hits 95 some times and winter goes down to freezing temps at times) and I am looking to finish my basement (aprox. 1500 sqft) which consist of three cement walls and one outdoor exposed wall. The exposed wall is already finished but the cement walls are not even close yet. The walls are already sealed and has no noticeable moisture issues. My concerns with the project is what will make “code” vs. what is recommended. My question is…
After the walls are up w/the foam board between the boards and the cement is it still required to apply the standard insulation between the wall’s individual 2x4s? I understand that it will certainly help with the temperature control in the rooms and I know it is recommended for that point alone but, is it against building codes to not install it as well prior to drywalling?
Brian – In many parts of the Country there are now energy codes in place that govern the level of insulation in homes. I’m not really sure if you’re area in Georgia has this type of regulation. Having said that, I would imagine that down there the insulation value that might be required for a below grade basement would be substantially lower than it is up this way. Also, with your high humidity I’d be inclined to avoid the fiberglass. If it were me I’d go with 1-1/2″ of foam board and call it good unless there’s a more specific code issue.
Thanks for the response. I am very glad I found your website!
Great site, I wish I found it sooner as I am midway through my project.
I’m insulating the attic on my 1910 craftsman in Seattle. The rafters are 2X4 spaced 24″ apart. There is not a lot of headroom, and since it will be livable space, I don’t want to bring the ceiling down too far. I drilled 2 1/8″ holes in the soffits and installed a ridge vent on the peak of my roof. I installed 2″ foil faced poly panels between the rafters and kept the remaining 1.5 inches as the air channel between the soffits and ridge vent. In an effort to increase the R-value and decrease potential drywall sagging, I ran 1.5″ furring strips across the rafters spaced at 16″ and filled the cavity with 1″ foil faced poly.
1. Was there a better way to approach this without sacrificing more headroom?
2. Should the 2″ poly and 1″ poly be sandwiched together, or is it better to have an air cavity between them? (any risks with condensation/mold between them?)
3. I cut each panels to fit snuggly between rafters or furring strips however there are gaps although they are smaller than the plastic nozzle ox expanding foam cans. Do I need to seal these gaps and if so, how? is there take wide enough to span over the rafters?
4. what would estimate the R-value to be on this?
Thanks in advance for your help.
Maurice
Maurice – for the most part I think your approach is pretty good. Basically you have areas of 3″ foam, 1″ foam and 2″ foam depending on where you calculate it. In areas with 3 inches you’ll have about R21 and the 1″ areas will be about R7. I guess one slight improvement would have been installing the 1″ directly over the rafters then the strapping bu that would result in another inch lost for head room.
Small gaps are hard to deal with. You could tape at each rafter and overlap two pieces to completely seal it. Other than that I think you’ve done a pretty good job.
Can You spray foam over XPS foam Board?
We are looking to insulate our pole barn to knock off some of the cold air for winter use. Would you recommend insulation boards? I read that one of the concerns is with bugs that will want to burrow into the boards as this will also effect the insulating values plus not to mention the fact of housing for lots of bugs.
Thank you for sharing your vast knowledge on insulation.
Donna – I think some insulation products will be attractive to bugs. However, I haven’t seen much trouble with XPS or Polyiso insulation…not sure bugs would want to eat that!
Like Todd, I originally thought that bugs would hesitate to chomp on polyisocyanurate. But experience suggests otherwise! Having added polyiso between studs in an admittedly inadequate exterior gable wall (the studs were 2x4s, sideways) I was intrigued a few months later to discover a pile of white foam bits at the back of a closet. Closer investigation revealed carpenter ants emerging directly above and dropping off their cargo, chewed out from the inside of this insulation. They clearly weren’t eating it (there must have been something much tastier in that wall), but they certainly chewed it. For what it’s worth, that wall and the problems it caused have now been eliminated.
Peter – Thanks for sharing…very interesting. Sounds like they found it was a good material to nest in.
I have a project similar to “maurice from seattle” with an attic space I am finishing, and want to retain as much ceiling height as possible but I have 2×6 rafters.Can I sandwich two layers of foam board together to increase my R-value bewtween the rafters, I will leave an air space between the roof of 2-3in. Also I thought to cover over the rafters with 1/2in foam board to make it all air tight, and then install my drywall,thanks.
Rob – The approach will work. The thicker the foam you can install over the rafters the better it will perform.
I too have similar insulation questions as above with the foam boards. i have been told that I may not want to use the foam on the ceiling or rafters of a similar room due to condensation would build up between the drywall and foam and cause problems? I will only be able to put in about 5 inches of insulation and wanted to up the R value by adding 1″ of foam over the rafters then putting the drywall up.
Gary – I’m not sure that’s much of a concern. In order for that to happen moisture would have to pass through the drywall and paint. Most latex paints actually create a pretty good vapor barrier. I say use the foam! You’ll have a much better insulated ceiling than not using it.
I’m thinking of applying 1″ foil backed foam boards to my rafters to radiate the heat back out in the summer. I’m thinking that it might not be necessary to do the north side or the northeast gable due to the small amount of sun exposure they get and the fact that none of this will be air tight. Does anyone have a reason this wouldn’t be a good idea?
Anna – Are you doing this in an unfinished attic? Frankly I’d do it everywhere as the mid-day sun is strongest when the sun is directly overhead.
Yes, it’s unfinished. I have heard so many conflicting things about insulation that I’m ready to do nothing! I was gung ho on spray foam until a friend was concerned about overheating the shingles. Then I read that shingle color is more important than attic ventilation.
Can a foil really reflect the heat enough that it stays behind the rigid foam and exits the ridge vent? If I go with this idea, should I do anything to my gable wall?
Anna – You’re confused because there are many different solutions and approaches. If you install the foam on the bottom of the rafters then air can still move from down low up to the ridge. Do you have a ridge vent? Do you have soffit vents? If yes to both this approach will work well.
I’m not so sure you’ll cook the shingles any more than they already get cooked.
Obviously if you insulate the gables it will be better than not.
I have a question about Blue Board insulation in a party wall. What is the NCR rating in such a situation? Are there ways to improve the noise reduction? Does condensation occur between the properties? What if there is a bathroom on one side of the party wall?
Alison – Can you be more specific about your questions? NCR rating? Noise is best handled with independent framing. Moisture should not be a problem with party walls. Bathrooms should not matter either.
Hello there,
My bedroom over the garage is very cold. Normally it is 5-6 degree below the home temperature ie. if I set up the thermostat at 74, my room’s temperature is at 68-69. It has big window which is covered by the blind shade. I get the early morning sun. In summer this room is boiling and in winter it is frigid cold. My garage walls are insulated and so the roof by the builder. My question is if I insulate the garage roof with foam board, will it help to make the overhead bedroom warm? If so which one would be the best type (eps, xps or the foil facing?. Appreciate your answer. Thanks Bal
Bal – Living space over garages are notoriously difficult to heat and cool. Are you planning on removing the ceiling to install additional insulation? If so then I would use 2 inches of foil faced poly-iso over the bottom of the rafters so you can maintain ventilation. It would also help quite a bit if you can insulation the floor below.
Can you put foam insulation in the garage ceiling over drywall to gain better heat? We already have rolled insulation with paper backing in between the rafters, then drywalled. If so, what would you recommend? It is over a bedroom that is on the North-East side of the house.
Pat – You certainly could do that but you need to check on the fire rating of that assembly. It’s likely that you’d need to cover it again with drywall. I’d use a foil faced polyiso then another layer of drywall (size per fire code).
can i put blue board over drywall in the garage ceiling to help insult it, without putting another layer of drywall over it.
Pat
Pat – I’m fairly certain most building officials would frown on that idea. While you still have a fire barrier behind it you now have a pretty flammable material exposed in the garage….I’d drywall over that.
I am in a similar situation where the rooms above garage become freezing cold.
Adding another layer of drywall over foamboard, would mean taking out the existing garage opener, garage door railing and everything. Thaen there would be a problem of how to secure the second layer of drywall through the foamboard. That seems to be a lot of work.
Is there a better, easier and affordable way to insulate the celing ? are there any fire retardant rigid foam in the market that we can just nail/glue/fasten to the ceilings to add extra insulation?
Tariq – It may be possible to use a foil faced foam board. However, as I suggested earlier you’d have to get an opinion from your local building official if it’s ok. The real danger is whether fire would ignite it, you’ve presumably already got a proper fire wall/ceiling assembly.
The other thing is to focus on the ceiling in the space above as far more energy is lost through the ceiling compared to the floor.
I only have 3.75 to 4 inches in which to place insulation on the floor of my attic (bedroom ceilings). I was thinking of pulling up the old “pink” insulation and laying down some polyisocyanurate board between my abnormally short joists. I was thinking of polyiso because you get the most R-value for a limited space and we live in the Philly area so it does get cold. My concerns are with fire hazard, building code, and general effectiveness. This is our 1st home & it is 100 years old. Do you think the polyiso will work? I was going to get some of Dow’s Super Tuff R polyiso board and cut it into 2 foot wide strips to fit between my attic floor boards. Do you have any feedback?
Thank you,
Dylan
Dylan – Can you install it over the fiberglass or are there floor boards over the existing fiberglass? Installing the foam board in the spaces sounds easy but it’s a real pain around all the electrical and mechanical equipment. It would be far easier if you install a layer of foam over the existing plus you get more insulating value that way. As far as the fire code it really depends on the use of the space and local codes. Quite a few of the foil faced products have very favorable flame spread certification which should allow it’s use in that space. If the space has floor boards and minimal storage you might want to use foam board over the floor as it’s pretty tough stuff.
Dylan, You’re MUCH better off blowing additional loose-fill fiberglass over your existing insulation. Preferably R49 or above. It’s much more cost-effective and efficient for attic floors. If you’re able to, find a contractor that uses CertainTeed Insulsafe or some other white colored blown fiberglass. Stay away from the pink or yellow for health and indoor air quality reasons. I hope this helps.
Timm – That will work however he wants to be able to still walk on the floor, kinda hard to do with blown in fiberglass.
I have and old house with double walls built out of lath which was covered by plaster. I am thinking of using foam in between the walls. You know the type that comes in those spray cans. I wonder if that spray in foam is equal to extruded polystyrene in r value an permeability of water. Also if I use 4 by 8 polystyrene compared to the foam which is more economical?
Gerald – I’m not sure how far you’d get trying to use spray foam from a can. First of all it would be cost prohibitive and secondly it would be hard to get consistent results. 4×8 sheets of XPS foam will be FAR cheaper.
1- Per BSAF, 1#/cu.ft. eps has an r value of 3.85 AT 75 degrees F. Important for people living in the north, such as Minnesota, is that the r value at 0 degrees F is 4.55. The R Value goes up as the temperature drops.
2- The exact opposite is true for polyiso. Also it is much more expensive. The Iso starts, per the NRCA, at 5.8 at 75 degrees F and drops to 5.0 st 0 degrees F.
3- The polystyrene is recyclable and the Iso is not.
Peter – Very interesting! Thanks for sharing!
Nice site. I recently encountered a problem with foam board and the batt insulation on a below grade block wall. I had 1 inch pink board and glued it to the block wall taped it all off then put R-19 batt insulation with plastic stappled it up for a vapor barrior. All this was done in the fall and two days ago I had to access a drain pipe while doing some plumbing and the batt insualtion on the backside (what was touching the pink board) was soaking wet. I took all the batt down and the pink board looked as though it was sprayed with a garden hose. WE live in northern michigan so it does get cool it is a new home built last year… What should I do? Any help would be appriciated. THanks
Jason – Well you’ve got a couple issues happening. I’ve written several articles on this situation that will provide some insight (see list below).
Here’s the short of it.
– One inch of foam board isn’t sufficient for two reasons. 1 – You need a minimum of 1-1/2 inches (2″ preferably) of foam closed cell XPS to create a vapor barrier. That vapor barrier stops moisture from the foundation concrete from getting into the framed wall assembly.
– One inch of foam board only provides a minimal insulating value. So, the cold block wall can transfer that cool temperature through the foam. If any damp air gets into the wall cavity it now has the chance of that vapor turning into liquid condensate. At that point it gets trapped in there because of the poly you installed.
– You’ve in essence created a double vapor barrier that wants to trap water in the stud wall.
So the solution really needs to involve more foam and avoiding the plastic outer barrier. You may want to consider insulating it with just foam board to really eliminate the problem all together.
For more information see:
http://www.homeconstructionimprovement.com/basement-insulation-guide/
http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
Good luck.
Todd;
I hae just started the process of conerting an area of my unfinished basement into an office/den. I am trying to lessen the noise of people walking around on the hardwood floors upstairs while in the basement and was thinking that gluing some foam board insulation in the areas between the joists and then using Great Stuff to seal the cracks along the edges might do something to help.
Afterward I plan on doing drywall.
What do you think of this? Good idea or waste of time/money?
If it might help, what thinkness foam board would you recommend?
Also, I plan on putting recessed lights in the ceiling so they would be in pretty close proximity to the foam — I know you can get the “IC” lights, but is this still a fire hazard?
Any adice you could give would be appreciated.
Thanks
Tom
Tom – I’m not sure that method will work very well and here’s why.
– Noise is really the transmission of vibrations. If you install stiff foam board and glue it to the joists I think you’re creating a very nice “drum”. In essence I think you might amplify the sound.
– If it were me I’d do this: Install fiberglass insulation in the cavities. Then purchase some resilient channel to screw to the bottom of the joists. Only ONE leg of the channel gets screwed to the joists, the other leg is left loose. Then you screw sheetrock to that. The channel makes for a VERY good sound deadening detail.
Good luck.
ok thanks Todd — that makes sense.
Would you recommend faced or unfaced fiberglass insulation?
Tom – It’s such a toss up. This hybrid approach is a “give and take” situation. It really depends on the basement. If it’s super dry, humidity controlled, I’d use faced as it’s easier to install. If there’s any question about moisture I’d skip the faced.
I purchased a steel enclosed trailer and want to add insulation to the inside walls and roofs. I am thinking aboutblue or pink foam board. Any suggestions?
Skip – It really depends on how you’re going to use it? Does it need to be durable? How will you use it?
Todd-
I have a bedroom wall that is exposed to the attic area above my garage. I planned on just insulating with standard faced fiberglass batts. However air still will work its way through the fiberglass and to the bedroom wall. Could I add 1″ foam board on the 2×4 frame(essentially on top of fiberglass) simply to ensure that less air is hitting the fiberglass insulation? Should I be concerned with creating a double vapor barrier by doing this or is the unfaced 1″ foam board sufficient?
Jackie – I’m having a hard time understanding exactly what you want to do.
Is the wall a wall between a finished room and attic space? Do you have access to both sides of the wall? If so I think I understand the situation.
You could do the following:
From the attic side, install the foam board, tape all the seams very well.
Fill the stud bays with unfaced fiberglass.
No vapor barrier.
Drywall.
Sorry for the confusion…yes, wall between finished room and attic but only have access from attic side. Sounds like I was on the right path…I’ll fill with fiberglass first then cover with foam board (taped) Thanks!
we have a 55 year old house, brick..our bedroom is in one corner of the house and the walls are FREEZING in cold weather (no insulation to speak of I guess)..is it possible to put a foam board (which one?) on the inside walls? If not, any ideas? thanks
Mike – Have you cut a whole in the wall to see what the wall section looks like? Before proceeding I would do that. Is it a row of brick, air space, sheathing, framing, plaster? The more you know about the wall section the better of an insulation assembly you can use.
Like Skip (December 27, 2010 at 6:25 pm) I have also purchased a steel beam, enclosed cargo trailer. I’ll be using it as an RV. It will be replacing my motorhome, because I can’t fit my two 12vdc chest freezers into the motorhome.
The trailer is smaller than I wanted, so the loss of even a few inches is critical. My son can’t stand up in the trailer as it is. The meeting of the ceiling & wall is curved, so that has to be taken into account. The ceiling has a slight curve as well.
Cooling in Summer won’t be such an issue. I have solar electric panels on a rack above the roof (which will provide shade) & there will be vent fans.
I’ve thought of using packing peanuts (good way to recycle them!) I’m thinking of using Polyisocyanurate w/ foil on one side. I’m just not sure I’ll have the air space needed. I’m also not sure about what to do to deal w/ the steel supports. I’m sure I’ll ave to loose inches inside the trailer, in order to get insulation onto those beams.
Suggestions?
Evelyn – You’ve got me stumped. Using it as an RV really means you’ll also need to cover the foam so that there’s not a flame spread problem. Seems like you’d need some type of spray foam and then a custom wall covering.
I live in a 90 year old home with minimal insulation. The attic has a wooden tongue and groove floor, but no insulation. I do not want to remove the attic floor to insulate. Can I install 2″ foil backed rigid foam board on top of the wood floor? I am concerned that I may trap moisture between the rigid board and the wood floor. Since I use this area for storage, I was thinking about putting plywood over the rigid board. Your thoughts?
Stan – Frankly I’d blow in cellulose between the T&G and the ceiling below it. With that foil faced foam you want the foil on the warm surface.
Todd, another insulate the attic question. The attic I wish to insulate has minimal ventilation. It has two gable vents. If I wanted to insulate the rafters with fiberglass batts, would this create a moisture problem since there is little attic ventilation?
Stan – Are you implying that you already have ceiling insulation and then you want to insulate the rafter bays above? I wouldn’t recommend doing that at all. Ventilation is essential to a properly functioning attic.
We have a third floor condo in Chicago with Cinder block-Firring strip Wall construction. Since firring strips are used in place of 2×4 studs I believe there is 3/4″-1 1/2″ wall cavity for insulation and fiberglass bats are probably not going to be of any use What is the best product for insulating the room. Also would I need a vapor barrier when using rigid foam board?
Thanks in advance.
Ed – Are you planning on gutting the space and starting over? If so there are many different approaches. Can you explain the project further?
Hi Todd – Very good info here! I have a 90 year old home as well in NJ. The walk up attic has existing batt insulation under wood flooring (partial original tongue and groove, partial plywood. The insulation is not consistent and looks dirty in places that I can see (where the original wood is broken). The attic has a gable vent on either end; one with an exhaust fan. No insulation on the rafters and no soffit vents. The wooden door to the attic (from a bedroom) leads up an uninsulated stairway (walls are plaster with lead paint) to the attic.
My questions:
1. How can insulate the door to the attic? I’ve already weather stripped it so it seals tightly. Does the door qualify as a fire-stop, therefore allowing me to use foam board on the attic (cold) side?
2. How can I insulate the walls of the stairwell, and effectively cover the lead paint and protect it from damage (chipping) in the future. Can I use foam board without covering with drywall, since its not in livable space, and behind the door?
3. I want to retain the storage space in the attic, but want to add more insulation to the floor (so blown-in won’t work). Was thinking about building up the floor with additional rafters and adding another floor since the roof is very high.
Thanks for your help and suggestions. Mike
Mike – Thanks for visiting the site!
1. I’d use foil faced foam board on the back side of the door, the thicker the better. No real fire issues that I’m aware of (assuming you don’t have any fuel sources up there).
2. I’d use the same approach on the walls.
3. How about installing 2 inches of foam directly over the flooring, then a new layer of 1/2″ plywood screwed down with 3″ screws so it bites to the lower wood?
Good luck!
Awesome – Thanks Todd.
One follow up. Any tips for securing the foam to the painted plaster? I think I’d go with screws on the back of the door, but not sure about the stairway walls… And I have no fuel sources in the attic.
Mike – Use Great Stuff Pro, It’s a great adhesive for adhering foam panels.
All the informations are well said and helpful. We don’t have to ask questions all over again. Full of information and this will help us a lot. Thanks for posting this one. We surely learned a lot about this.
I am looking to use this XPS as a thermal break between the concrete floor in my basement and the subfloor. Is there a specific grade of XPS I should be considering for compressive strength?
Dick – The normally stocked XPS foam boards are fine unless you have a very heavy point load like a pool table. Even then it’s probably not required.
My foundation was constructed using 12″ block walls.The front wall is completely below grade and the rear wall is above grade. The sides taper front to rear. I am finishing the gameroom side of the basement. Currently the game room is studded with 2×4 walls. I planned on insulating with fiberglass batts that are Kraft faced and have an R-13 value. The home is 10 years old and has never had a moisture or humidity problem. I was extensively involved in construction and really do not anticipate any water problems in the future. I have a concern about the space between the back of the studs and the block wall. In some spots it is as much as 3/8″. Should I be concerned or do you think I will be okay as described. I wish I would have used the internet more during construction. I think I would have had more and better options before the walls were built. Thank you in advance.
Jim – Check out my article on insulating basement walls which shows how I think it should be done.
I do not recommend having fiberglass in contact with concrete or block.
I will install blue board between the studs then insulation over top. It will be to much work to take down the framed walls at this point. What about the walls that are completely above grade? Should blue board and fiberglas be installed on them as well?
Jim – You really should try to cut those walls free and slide them forward if you can. If you install blue board like that you’re going to concentrate moisture from the block wall against the studs. They will develop mold.
Are the above grade walls still block?
All the foundation walls are block. It will be nearly impossible to move the wall against grade because of a stair landing. If the stairs will slide on the landing I may try to move.
The stud walls have been there since constructed and I see no signs of mold at all.
Jim – There’s no mold because you haven’t sealed the framing in with XPS foam. Obviously there are times when it’s no practical. I’m just saying that if you use this approach you risk a very serious problem.
Todd- Thank you for your help, unfortunately the wall that concerns me the most is the one that is hardest to deal with. Hopefully I can come up with a suitable solution.
I am planning on using foam board for a slightly different approach. I want to build a portable bar (on locking wheels) and include a large enough cabinet that will hold 2 soda/homebrew 5 gallon kegs with 2 taps out of the front. The cabinet in the bar will need to be insulated to keep my already cold kegs from my basement kegerator outside while throwing a party. Is there a better foamboard to use? I will probably have some kind of tray or bucket to put ice on to help keep the kegs cold and so possble water will end up dripping on whatever foamboard I use under the floor of the cabinet. Hopefully this is not too goofy a question for this forum, but I see dual picnic taps (coolers with either coils or coldplates that have the beer lines run so ice cools the beer as it passed through the coils in the cooler) costing around $250. For that price I can pretty much build a moveable bar, though maybe a bit rustic, with an insulated cabinet and a couple of cheap beer faucets coming out the front, serve by brew cold and not worry about 100F weather heating up my kegs when having some folks over.
Ted – Great idea! If it were me I’d use some 2″ thick XPS foam (blue or pink) then line that with some fiberglass tub surround, or cheap vinyl flooring, something like that. You can glue it all together. I think it would work great. The lining will help protect the foam from chipping, denting, etc and also make cleanup easier.
Good luck!
My wife and I live in Atlanta are getting ready to break ground on a 3/2 2,700 sq ft modern house (think two 25Dx60W’rectangles on top of each other with a flat roof) with the public space at grade and the private sleeping quarters below (open to daylight). We plan on installing solar panels and want the house to be very energy efficient. The lower sleeping level will be poured 8-10″ concrete walls with 2×4 framed & finished. Since the lower level will have the bedrooms and the concrete slab will be polished and left exposed, we want the floor to be as comfortable as possible (no radiant only heatpump(s)). We plan on blowing in cellulose for the majority of the house, but would appreciate advice on insulating slab and exterior walls, plus roof (i.e. thickness, XPS, etc).
Thanks!
George – For the slab I would recommend 2″ of XPS foam under the slab.
Basement walls, I’d recommend either Closed Cell Spray foam or using XPS foam similar to the following article: http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
Flat roofs are best done with rigid foam above the structural deck and just below the membrane. Typically in this part of the Country we use 6″ of foam.
Best of luck!
I wish I would of found this site about 2 weeks ago. I have a all concrete room under my garage and I am planning on finishing this room. I have framed the walls with 2×4’s and used 2×6 for the ceiling. In order to square the walls the 2×4’s are anywhere from 1/2″ to 1 1/4″ from concrete walls and the 2×6 ceiling is about 1/2″ to 2″ from concrete ceiling. I have already cut 1″ polystyrene sheathing to fit in between the 2×6 joist for ceiling. There is no duct heating in this room and it will be closed off. What do you recomend I do to best insulate this room . This room is 15 degrees colder then my unfinished basement. The rest of the basement is going to be my next project ofter this one. Thanks for your help.
Jeremy – Thanks for visiting the site.
First off you may want to read this article: How To Insulate Basement Walls
What will this room be used for? Depending on the use there are different approaches.
I forgot to mention that were in Ky which if very humid at times. This room will be used for storage mostly but may be a office one day. Its about 400 sq ft. and will have a steel door closing it off from the rest of the basement. Thought was to keep valuables in this room in case of fire or storms. Will heat with portable electric heat if need be. This house is 5 yrs old and basement has never shown water leakage. This room only has 1 wall that is above ground. We did use treated wood on the top and bottom of the framed walls. Do you think that will be ok? I did read the article on insulating basement walls and did not use trex or simular material under treated wood.
Jeremy – I guess my concern would be the same one that I have for all basements. You really need a proper insulation/vapor barrier between the concrete and framing. If it were mine I’d recommend taking down the walls (you can most likely do that without demolishing them, just cut the top and bottom free, lay them down), insulating with proper foam board (or hiring a spray foam contractor), then putting the walls back up.
If you don’t do that you will have moisture/mold problems in the future.
Todd I appriciate your help on this. So if I had it sprayed behind and in between studs on the walls and ceiling it would be fine instead of taking down the walls? Do you know about what would it would cost to have 380 square foot sprayed?
Jeremy – Yes spraying it in place will work. Word of caution – DO NOT use Open Cell spray foam no matter what a contractor tells you. I would imagine it’s going to cost probably around $1,000 just because the mobilization, clean-up on a small job is the same….just my gut feeling.
Todd just had a contractor stop by and give me a quote on the closed cell spray insulation. He mentioned 1/2″ of closed cell and 3″ of open cell on top of that on the walls. What do you think? The price was about 500.00 cheaper if I went with that instead of just 2″ of closed cell on the walls. Also I have one wall in that room that is concrete but on the other side of that wall is my basement. Should I spray that wall also or just put 2″ of foam board inbetween the studs?
Thanks, hope I’m not bothering you to much, just want to get this right so I dont regret it in the future.
Jeremy – No worries….this site is all about helping folks out. I just hope you come back often!
I really wish contractors didn’t offer such “poor” options. At least poor from my point of view. 1/2″ of closed cell foam is NOT going to stop water and I would NOT recommend that approach. Go with the 2″ of closed cell and save yourself a lot of aggravation later.
Not sure I understand your other question. Do you have a concrete wall that has rooms on both sides?
Yes, one side of the concrete wall I’m referring to is my unfinished part of my basement and the other side is the room i’m finishing now. The room I’m finished now is under my garage where most people just backfill with dirt or make a cistern out of. I decided to make a storage room out of it instead of backfilling.
You should spray it also on the finished side.
I am planning on installing Owens Corning FOAMULAR F250 4x8x2″ sheets to concrete basement walls (is this brand ok?). Then installing 2×4 walls with a PT base. Should I still fill cavity in between studs with R-13 fiberglass insulation? faced or unfaced? House is in New England. thanks for the info!
Scott – The answer depends on your local energy code and what R value you need. Here in NH we have a pretty strict Energy Code that requires the entire building to be analyzed which determines the level of insulation.
2″ foam does a pretty good job!
Is the foamular the correct item to use or do you recommend another product?
Scott – It’s fine..there are a number of good products, DOW and OWENS both make good stuff.
I have a rustic cabin ,3 season usage, with log rafters and 3/4 shiplap cathedral ceiling ,shingled no insulation. I”m installing a metal roof ,planning on roofing felt on wood ,2×2″s parallel to ridge with foil-faced foam (1 1/2) laid between and metal roofing over. To keep the cabin look original, I want to keep the roof as a low profile (ruling out 6-8″ roof rafters). This is a northern cabin . will there be problems with foam (summer heat, direct contact with metal roof)?
John – Sounds fine, lots of roofs are insulated in that fashion. Good luck.
Todd,
What do you think about the do it yourself handi foam closed cell kit? Is it as good or the same stuff contractors use. How many board foot would I need if I was to purchase this and use for a room 20’x19’x7′? I would spray 2″ on the four walls and 2″ also on the ceiling.
Thanks
Jeremy – I haven’t used one of the kits and I hear they only work well for small areas like a rim joist. Again I haven’t tried them so I’m not sure what advice I can give you. I also hear they are getting harder and harder to acquire do to VOC laws.
Todd,
I am remodeling an old farmhouse in Pa. The exterior walls are currently double plank with 1 inch E.P.S. under the aluminum siding.
I removed the plaster and lathe from the interior and want to fir it out 1-1/2, using blue board between the studs. Would this cause moisture problems using 1-1/2 blue board or should there be an air gap. Do you have any suggestions or comments?
It shouldn’t be a problem. The 1″ exterior foam would be considered semi vapor permeable and the 1-1/2″ is also borderline.
Todd,
I’m planning my basement build out, (concrete pour, with 2/3rd below ground level). I plan on using the blue(pink) board, 2×4 walls, and fiberglass to get to the proper R value for Missouri.
My question: What is the minimum blue board thickness I can use for the vapor barrier? I have to add fiberglass for R value, is it resonable to put a 1/2 inch or 1/4 blue board without decreasing the effectiveness of the blue board?
You Rock!
Karen – You have to use a minimum of 1-1/2″ of blue board in order for it to act as a proper vapor barrier. Good luck!
I have a similar situation as Karen. I’m in central Indiana with a very dry poured wall basement. Do I still need 1-1/2 or would 1″ work? If not, can I do 1-1/2 with the studs tight to the Xps?
Thanks,
Chris
I always recommend 1-1/2″ as the minimum. If you’re confident that the basement is dry then installing studs up tight to it is not a concern. Just be sure you’ve sealed all the joints well.
Good luck.
Todd,
I live in Southern California where it ususally is warm, but my exterior walls do not have insullation in them. They are cold or hot to the touch depending on the outside weather. There is a Stucco wall outside, a 30 lb felt then drywall nailed to 2×4’s.
The house was built in the early 70’s.
I was thinking of getting some 1/2 ” blue board & nailing it directly to the drywall on the interior. NO muss no fuss for about $100 per room to add a little R value (I know it is very little, but perhaps better than nothing?).Then painting to match the room.
Would putting a 15 or 30 lb felt in between make any difference?
Your thoughts please,
Thanks,
Are you suggesting to just paint the foam board and leave it that way? If so I’d HIGHLY advise against that. It would be a huge fire hazard and frankly 1/2″ of foam isn’t going to do much of anything.
Great site. We have a basement in Baltimore that is damp in the summer. We are torn between 2″ XPS attached to the cement block wall with 1×3 furring strips covered with Mold-resistant drywall versus 1″ XPS, 2×4 wall with R13 insulation between 2x4s then covered with Mold-resistant drywall. The latter seems like it may be overkill since we don’t need to hang anything on the walls. If we go with the first option, will the gap between the foam and drywall (separated by the furring strip) be a problem for moist air? Thanks.
Harvey – You’d be far better off with option #1. You need a minimum of 1-1/2″ of XPS foam to seal out water vapor from the concrete. If you use 1″ it’s really risky. The air space is actually a good thing.
Thanks Todd. One more question, any experience/opinions on the GreenGuard XPS (Pactiv)? It seems the Dow blue or OC pink are the boards of choice but the only 2″ XPS that our local Lowes carries is GreenGuard and I was wondering if you think it would be worth special ordering 2″ blue or pink?
Seems like the same type of product. I wouldn’t special order anything. Most good lumber/building supply companies carry some type of 2″ XPS foam board. I find that Lowes and Home Depot don’t have a good selection of these type of materials.
Todd – I live in Colorado with a 1978 home. I am looking to add insulation to the above grade bedrooms on the North side of the home. The exterior has 1″ XPS covered with vinyl siding. There is some old siding board behind the XPS. The bedrooms are plenty big enough to build out an interior wall. If I remove the existing drywall (stud cavity filled with R13 fiber glass), add 2″ XPS foam and build an interior stud wall against the XPS and fill this new wall cavity with R13, then hang drywall. I know there may be alternatives, but this seems fairly straight forward way of adding R with minimal effort. Thanks.
Ed – Your method is certainly one approach. However, there are probably some easier methods and possibly some cheaper ones that will yield the same result. Here are a couple thoughts.
1. Have the wall spray foamed after you remove the drywall. This is probably the best approach and it will surely seal things up, stop vapor and air infiltration and likely be the quickest.
2. Install a layer of foam directly over the old wall, pad out windows and doors with extension jambs, drywall over the foam. This would at least eliminate the need to frame a new wall.
Good luck.
Hi Todd. Thanks for the great blog. I’ve read this whole thread, and would like to get advice.
We are converting our 21×28 garage into a family room. It is exposed on 3 sides (s,w,n) and currently only has r11. The room will have a lot of glass (great views even here in Kansas). Our contractor recommended sprayed in foam ($1000+) into the exposed 2×4 wall cavities. But I found your blog and it seems to me it would be cheaper and better in the long run if we just put r13 or r15 into the cavities and then 1″ xps board over the studs. We would end up with somewhere near r19, without having the added expense of him furring out the studs, etc.
When I suggested this to him his eyebrows raised about all sort of problems the drywaller might have with his screws popping through the paper on the drywall, or the drywall sheet not lying flush because the screws compress it into the foam. Have you heard of this happening when drywalling over foam board?
Thank you!
Dean
Dean – Thanks for the nice compliment.
First off I’d be shocked if you can get spray foam in that quantity for that price unless it’s open cell foam. I DO NOT recommend open cell foam at all. It has many problems including acting like a sponge if you ever get water in there. Having said that there are quite a few options you can look at.
1. Closed cell spray foam – works wonderfully, definitely most expensive option.
2. BIBS (blown in blanket system) – Blown in fiberglass insulation is a great product and it does an amazing job air sealing and frankly provides the same R value as most spray foams, you can read more about it here: http://www.homeconstructionimprovement.com/certainteed-bibs-insulation-system/
3. You could do the R11 fiberglass followed by an inch of XPS foam. There are a couple issues you’d need to deal with. You would need extension jambs on the windows and doors to come out the additional 1″. In my opinion there would be no issues with the screws. I say that because XPS foam has a very high compressive strength when compressed uniformly. Not sure this option will be much cheaper as XPS foam is pretty pricey and there will be more labor. If you do this approach be sure all the seams are taped with Tyvek or DOW Construction Tape.
On another note I’d love to ask a favor. Without going into a huge long dissertation I’m asking for some help from readers. You see Google has recently changed the science on how they rank sites when you do a search. This site was adversely effected by those changes which means Google things the site is just “Spam”. So in order to try and fix that I’m asking folks to share the link to the site on Facebook, Twitter, etc to help spread the word and prove those crazy engineers at Google wrong. So if you enjoyed the site any help promoting it would be “GREATLY” appreciated.
Thanks and best of luck!
Hi!
I am redoing a butler’s pantry in an old house and need insulation for the walls –I am interested in using insulation board, not batts. Advice about installation appreciated.
Details: Zone 6 climate. Triple brick construction with concrete inner walls (plaster has been removed). Space will be used as traditional butler’s pantry, i.e. cabinets and counters.
Thanks!
San
Is zone 6 a southern area?
Hi!
We’re in Pittsburgh, PA!
Thanks,
San
I think you can successfully install foam board between the studs and seal the panels all around with spray foam like Great Stuff. In that area you want to be sure you install a thickness that provides the minimum R value required by code.
Todd, in need of your help. Just want to say after reading all the posts on this excellent page I have a good idea of what the problem may be. btw I found your site using Google
I live in a 2nd floor north west coast condo and one external wall in the condo is poured concrete (i believe) and is insulated with well taped pink fiberglass and then covered with vapor barrier and then drywall. The wall has metal studs looks like 4 inch. Below my condo is a parking garage – the tiled areas of floor are generally cold. Outside winter temps norm range from 1 to 8 degrees Celsius, summer 15 to 30. Winter indoor RH is between 50-70% when occupied. The outside concrete wall is painted on the outside only.
The problem is that during the winter months in which I am resident in the condo it appears that the entire concrete wall is moist – it is so wet that the floor up to 1 ft away from the wall is also damp/wet. I have been assured by engineers that there is no water coming in any external direct source such as rain and since the problem alleviates when I am away for extended periods I assume it is a condensation problem.
I believe the moisture is coming from cooking/bathing within the unit itself or from the outside through the concrete, (if this is possible under what situations does this occur?) and is getting in the wall somehow and cannot escape due to the vapor barrier.
Can you suggest the ideal type of insulation materials / method to use here to fix the problem.
From reading other posts I think I should use 2 inch XPS foam sheets (or closed cell spray foam) directly against the concrete and then drywall with nothing else. What about using Open Cell foam to allow the concrete to breathe more or is this nonsense? A builder also recommended moving to 2×6 studs – what do you think?
Also, I turn the heat off in the condo when I leave for work and back on in the evening. Will this help or hinder in any way?
It sure sounds like condensation to me. Likely when the RH is high in the condo and the wall is cool/cold then warm damp air hits the surface and condenses. There are a couple of things that will help. First of all controlling the RH will always help in these situations. Secondly I would insulate that wall, you are correct, 2″ of closed cell foam (XPS). You can install it several ways.
1. Glue to wall – frame a wall in front of that – drywall over that, be sure to seal all seams
2. Glue to wall – Drill/shoot strapping over the foam – drywall over that.
3. Use metal Z studs which allow you to attach to the concrete and fit the foam in between them. Then drywall to the metal flange.
DO NOT use open cell foam.
Good luck.
Thanks Todd, We are running a large dehumidifer 12 hours per day in the problem area and the RH never goes below 45%.
Construction on the new insualtaion/drywall begins in 3 days so I’ll try to post with the results once it is all done. The builder wants to use 1.5 inch XPS, sealed at all the seams, I will push for 2 inches.
Saurus – 1-1/2″ XPS technically qualifies as a vapor retarder which may work fine in your situation.
Ok, I am reporting back for the benefit of others who may be having this problem.
As I wrote above this time last year we had big problems with dampness in our concrete construction condo during the winter months starting around early October when it got colder.
To remedy this during the summer our contractor replaced our fiberglass / vapor barrier insulation with 2 inch thick (at least) of XPS sheets in between metal studs and then spray foamed the gaps around the ceiling and elsewhere.
I can report that since the job was done there has been zero signs of moisture at all in our bedroom so far. I will continue to check throughout the winter.
It seems amazing the difference insulation can make in a concrete condo. There was so much moisture we had 1 building engineer conclude that it was the bathroom fan venting leaking into the wall cavity and another told us it was certainly water leaking from the outside. Both missed the insulation problem… and our condo wasted thousands on these “experts”
Thanks for reporting back and sharing your success. It is amazing to me how many people throughout the industry do not understand the science of this problem. Keep us posted!!!
Todd,
I live in the pacific NW mild/damp climate.
The roof on my home is 2×6 T&G over 4×12 beams. I plan on replacing the roofing this spring. I intend to apply vapor barrier on the exterior, then frame the roof with 2×6’s similar to a wall and fill the cavities with one 3″ layer of foil backed (both sides) polyiso foam board. Then sheet with OSB, felt paper and shingles.
I was also considering applying this foam board under the the car decking between the interior beams and covering it with 1×6 T&G to retain the appearance of the wood.
Would this be a bad idea? Your opinion would be appreciated.
PaulV – Why are you framing additional structure on top? You can just install ISO foam board insulation, then a layer of plywood with long screws. That will provide a much better overall insulation value and be cheaper.
The second part sounds fine.
GOod luck.
Todd,
I’ll check again but, I was told local codes require that I vent below the sheeting. I agree that it would be much cheaper and less labor intensive to simply attach a layer of OSB directly over the ISO with long screws. As of July 2010 our county adopted a new energy code that requires a minimum of R38 for any re-roofing applications. I figured that I would add 3″ on top of the roof and 3″ below as the ISO is rated at 19.9 for the 3″ thickness. I figure I could seal up the interior well enough to stop any air flow to the exterior using caulk and tape. I want to make sure that I do not set myself up for moisture problems down the road.
Many many commercial roofs are not unvented with 6″ of iso on top. Frankly I can’t see how they can argue the unvented roof with R38.
Got it, I will draw it up and present it to the premit center. I’ll let you know what I find out. BTW, when butting the sheets of ISO together, would you recommend an adhesive/sealant and then taping the joints? Or would a dry fit and taping do the deed?
The later is fine. Best of luck!
Todd,
The project took an unexpected turn. I found that I could remove the existing 12″ standing seam sheet metal roofing without damaging it. We removed the chimney penetrations and replace any damaged T&G. 30lb felt was used as a vapor barrier over the exterior side of the T&G. Next we created a 3 inch perimeter along the eaves and gable ends with 2 layers of 2×4’s. Sheets of 3″ polyiso was anchored with screws and covered with Feltex vapor barrier(feltex is similar to house wrap except that is rubberized on one side and is impermiable). Then we reinstalled the standing seam sheet metal panels with 3-3/4 screws. New sheetmetal facia and ridge cap was installed along with snow brakes. We also installed 4 fall protection anchors with D-rings exposed just under the ridge cap (2 on each side of the ridge). In addition we had a bit of snow brake left over so we installed three 4′ sections spaced 4 feet appart to make a permanently installed ladder on one corner of the roof to allow access to the peak. Overall, the project cost a whole lot less by reusing the existing metal panels. Had to purchase only 14 new sheets of standing seam. Only issue is that the new sheets obviously look newer than the 13 year old panels that were previously installed. Installed the newer panels (all in a row) on the side of the house that is not so observable. It resulted in an immediate impact on heating this winter. No more cold air cascading out of the loft area. The split mini heat pump heads now can handle the load.
Thanks for your advice.
Glad to hear the success! I hope you’ll become a Newsletter Subscriber and remain a member of our site. Good luck on future projects.
I have a big stack of 1/2″ eps foam boards in my basement which I was hoping to glue in three or four staggered layers against my basement walls. My winter basement temperature is 50-60 degrees and I have had small, isolated water leakage problems a couple of times over 6 years when too much water got close to the outside walls (downspout problems).
City building code requires a 1/2″ gap between the basement wall and a framed wall, with R13 in the frame. My plan was to glue at least 1 1/2″ of foam board to the concrete walls, leave 1/2″ gap, then frame a wall with R13 fiberglass and cover with drywall.
1. Is there any reason to use xps instead of eps against the concrete wall?
2. Would it be better to use xps against the wall and use the eps (rather than fiberglass) for insulating between the studs?
3. If I have another isolated water problem problem, will it simply run down between the wall and foam board, out the bottom and onto the basement floor, slowly evaporating up the 1/2 gap and through the floor boards?
Thanks for your help and your wonderful site.
Corky
1. EPS is an open cell foam product which I DO NOT recommend against concrete. It will absorb water and hold it. XPS is a closed cell foam board and a far superior choice for this application.
2. That is certainly a better choice.
3. That’s the idea. It’s also why it’s so important to seal all the joints. I’d recommend you read: http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
Best of luck and thanks for the compliment. Please consider LIKING us on Facebook at http://www.facebook.com/pages/Home-Construction-Improvement/248544769916
Thanks for setting me straight. All this time, I thought EPS was closed cell. It’s not like open cell I’ve used in other applications.
If you cut through EPS you’ll basically see lots of small balls, water can fit around those balls. Whereas XPS is a solid, closed cell foam product.
Hello,
I have question not sure if it will be a problem but…We are in a cool climate in michigan I have glued 2″ of pink foam on the concrete wall then framed the wall 1′ off the foam creating a air way between the wall and the 2″ of foam. I noticed when I was mounting the tv jack that the cooler air was being drawn out from behind the wall. I did not like the idea of using fiberglass insulation in the basement wall cavities but I am wondering now if I should have? thanks.
Sounds like you have that “air space” potentially connected to cooler air. In other words is that space completely sealed off? or does it connect to an area that’s not insulated or open to outside air?
It is completely sealed off. It can pull air from the utility room through the floor joists. The room is heated as well as the floor is infloor heat which has been off for a couple weeks now. Possibly could be a negative pressure issue? The air is not freezing cold but you can just tell it is a few degrees cooler than the inside room temp.
Definitely a negative air pressure issue…and the air in the space will most certainly be cooler.
Hi,
I am building a new house up in Maine and currently the inside is unfinished. I want to put 1″ insulation board right up against the exterior sheathing followed by regular faced insulation. I have 2×6 walls. Will this work for added insulation and will I run into any vapor problems?
Thank You.
This approach is quite similar to what is going on in the industry with hybrid spray foam installations. There are more and more folks spraying a thin layer of foam inside the cavity followed by fiberglass. This approach helps with air sealing. The key here is when you install the foam, be sure to seal it very well to the framing.
Good luck.
I am replacing my Tar & Gravel Roof on my home in sunny californa with 4″ polyiso and a roll out cool roof product to reflect the sun. With both products is the an over kill waist of money? Suggestions?
Well considering that the price of fuel continues to go up it’s my view that insulation is never a waste of money.
Todd:
Here are my plans for insulating my home during a roof tear-off here in Madison, Wisconsin. Please let me know what you think and if there is a better way of insulating and attaching the gutter and fascia in your opinion. I want to keep the ventilation space I have proposed between the polyiso and OSB if possible (and including a ridge vent) to help reduce any moisture issues. The rafters are 2x4s on this 1920’s era home and I don’t want to lower the height of the room-in-attic ceiling if at all possible.
I plan on using 2″ Polyiso insulation on top of the rafters, a layer of foil as a radiant barrier (unless I can get my hands on some foil-faced 2″ polyiso), 1″ or 1 1/2″ blocking to create an ventilation channel and at least 7/16″ OSB (maybe plywood) sheeting on top of that. I’ll also use 3 1/2″ of Polyiso between the rafters but I plan on installing that from the finished side most likely (unless we have time to do it from the top side after tearoff).
I plan on using a ventilated drip edge for my air intake between the polyiso and the OSB sheeting. Will this work? Can I go with thicker foam on the roof if I want to without running into major issues with the drip edge ventilation intake and/or fascia board and gutters? Should I include a vapor barrier on the underside of the interior foam before I insulate?
Thank you for your help and I look forward to your opinion.
Well let me start with this and I’m assuming your local building official will also evaluate. Any time you tear off a roof it’s likely you’re going to invoke some new code provisions. 2×4 rafters are extremely undersized for any roof in a snow area which you clearly live in. If you’re going to spend that kind of money on a new roof I’d address those rafters at the same time.
7/16″ OSB or plywood is again extremely undersized for modern roofs that experience snow loads. Almost all roofs that we work on today with 24″ rafter spacing includes 5/8″ T&G sheathing as a minimum. 7/16″ OSB will warp, sag and look pretty horrible within a few years of installation.
Is the attic a conditioned space? If you end up with 5″ of polyiso you’ll be around an R35. Again this is fairly low for homes in snow areas.
So before assessing your proposed details I think you need to focus on structure and insulation values as they are all on the “low” side of what normal code would require.
Thanks for the quick response Todd. Unfortunately, 2×4 rafters must have been the norm in 1919 when the house was built but you’re right, I feel that beefing up the rafters would be a good thing to do but I was trying to avoid the expense in materials and labor involved in doing so.
The attic is a conditioned space, it’s a 1.5 story home with the room-in-attic addition and I will be building gabled dormers in the middle of the roof line on each side of the house that will take up about 1/3 of the total roof area.
Do you think that I should just sister some 2×8 rafters next to the 2x4s that are currently there, install a ventilated drip-edge and keep the insulation at least an inch from the sheeting and install a ridge vent or is there a better way of doing this? I would like to avoid having to replace all of the sofit and fascia if possible but it doesn’t seem that this will be the case if I bump the rafters out that far.
Also, just as a side note, why the heck do companies that manufacture ventilated nail base use 7/16″ OSB on their produce and then feel that it’s worth $111 a sheet (for 4.5″ Polyiso) if it’s going to be garbage in snow-loaded areas?
Thanks for your input once again Todd.
The dormers create an even bigger reason to evaluate that roof structurally. Depending on how you frame the roof you’ll need MUCH larger sistered rafters on either side of the dormers. Honestly most building code officials are going to want that type of structural renovation to be designed by a professional. Have you spoken to your building code official yet? I’d start there!
Without seeing details of the existing roof it’s really hard to say how to ventilate it. The dormers are doing to complicate things even further. You might consider an unvented roof, highly insulated, to simplify things.
Thanks for your help Todd! I will let you know what approach I end up taking.
My pleasure. Good luck and try not to stress too much. It will work great.
Hi there,
I need help!! I have constructed a metal frame bldg. As you know it can get extremely hot in the south. I need to know what to use when installing styofoam insulation to keep it attached to the metal roof inside. We tried a type of glue from Lowe’s Hardware and it just would not hold. Can you give me any assistance on what to use in regards to insulating a metal roof.
Sue – Typically on metal buildings the roof insulation in done during construction with one or two approaches.
1. The most typical approach for insulating a metal roof is to install the metal deck, then install a layer of rigid foam insulation board, then the roof membrane. This is the most efficient way to insulate as it isolates the steel below the insulation and also doesn’t allow for thermal transfer.
2. Another approach which is used on projects with a tight budget is installing batt insulation on top of the structural framing and then installing the metal roof deck on top of that. This isn’t as good as the insulation gets compressed at each structural member.
Insulating after the fact is going to be MUCH harder. In that situation I’d recommend spray foam. Otherwise, efforts to adhere insulation to the bottom side of the structure will be difficult at best.
Hi all! Does anyone have any experience with the spray on cementitious foam called AirKrete? It sounds fabulous, albeit expensive and a less toxic form than other sprays that off gas.
Hello,
Just wondering what is the life time of polyiso foam board insulation. We had polyiso insulation under existing tar and gravel roof (17 years old). Recently we want to re-roof. when removing the tar and gravel roof, will the original polyiso foam be damaged? If not damaged, can we still use the original foam and will there be any problem arise to consider.(ex: will old insulation die down in the half life of new roof) Please advice.
OR is it ok to buy new insulation lay on top of old one to increase R-value.
Thanks
When properly covered from the sun and environment it should last indefinitely. You can certainly install another layer over the old after it’s inspected.
I plan to remove the existing aluminum and wood siding on an old house. The walls were blown with fiberglass insulation years ago. I plan to check that all the cavities are properly filled. I would like to use a 3/4″ or 1″ insulation board over the entire exterior before installing new steel siding and windows. My question is what is the best foam to use, do I need a housewrap, if so where sould it be placed, under or over the foam. Thanks.
A closed cell foam is best in my opinion because it will not absorb moisture. The housewrap issue is up in the air with this type of application. I would install some type of wrap whether traditional or even tar paper over the old siding before the new foam. Then I’d tape the foam insulation seams. Good luck.
Hi Todd. Great site you have I came across it and will check your tool box buzz site out also.
My garage gets really hot as it gets to 110 or more outside here in southern AZ. My attic can reach 135 deg.
My garage is a attached garage to my home and is not insulated in the attic ,but the rest of my home is. Also the garage roll up door is metal/aluminum. The garage faces the western sun.
I am not sure why it wasn’t insulated as it is a newer home ,but what can I do to insulate that garage door ? What about using blue board and is it OK to use that blow in insulation in the attic above the garage.
PS. I did put in a attic fan to help get rid of all that extra heat in my attic .
Thankx for any info……
Steve – I’m not surprised that the garage wasn’t insulated. Many builders skip that to control costs. You can certainly insulate the garage attic with blown in insulation. In hotter climates some folks insulate the roof deck with reflective radiant barrier insulation to help reflect the heat back out.
Insulating the doors might be a bit of a challenge. If you use foam then you’ll have exposed foam which is typically a code/fire violation.
Good luck.
I am building a new house and putting radiant heat in the concrete slab, which will be the finished floor. I plan to put 2″ XPS under the entire slab, but I’m debating whether to put an additional 1/2″ foil faced polyiso board on top of that. Will the foil faced give me a real advantage in reflecting the radiant heat upward towards the slab? Will the polyiso hold up under the slab? I plan to put the radiant tubing in the middle of a 4″ reinforced slab. Thanks for your input.
John – We’ve done dozens of radiant slabs and every one of them has been done differently based on ever changing recommendations from the HVAC industry. I definitely think the 2″ blue board is a very good idea. Not sure how I feel about polyiso under the slab, I’d probably just use one of the reflective bubble wrap type products if you want extra reflective properties.
The bottom line is fairly easy, heat will move in the direction of least thermal resistance. So if you put insulation under it, the heat will be forced up.
Good luck.
Hi Todd,
I just found your web site and am impressed. I have a dream of building my own semi passive solar super insulated home. My wife has early stage Limb girdle MD so our current two story no longer meets our needs. I am hoping to orient the house 60 feet east west and 40 feet North south. I want a continous insolated sunspace along the entire south side with heat rising into the attic like and then desending along the north wall into the basement with tube openings into the south semi isolated sunspace. The air with then continue the same cycle. I figured I would use earth tubes to prewarm the air before it enters into the heat exchanger. I want to put insulation between the concrete. With this kind of sipcrete wall I thought I would put up 4 inch studs on the northwall and use the empty space before the gypsum as the ductwork. This sort of makes it a sort of high thermal mass semi-envelope home. Does this make sense. I would like to make a raft with 4 inches of board insulation below both the basement and the footings. The walls are solar-crete models 7 inches of foam between 2 1/2 inch inside and outside concrete shell.
My first question is what psi would I need for the xps under the footings.
My second question is can I use polyso as the board between the shell instead of xps because it has a higher r value. I am thinking of using shotcrete with an admixture of Xypex to waterproof the walls.
Thanks for the kind words. Sounds like a very interesting house design! I’m certainly not an expert on passive solar homes so the design is something I wouldn’t be able to comment on. With regard to the compressive strength of the foam board there are several you can choose from. DOW offers compressive strengths in 25 psi, 40 psi, 60 psi and 100 psi. The required strength will depend on the foundation loading from your home design. I think the XPS is better suited for your shell application. Foil faced polyiso is a definite no as it will react with the concrete.
Todd, been reading all this information and it has been great. I am trying not to repeat much of what has been asked already. I have a similar attic project as some others, finishing a 1900’s attic for additional living space. Summary, 2×6 raters, I added or am adding ridge and soffit venting with baffles between each rafter. Would like to add 2 inches of foil faced ISO on the bottom of the rafters, then blow in cellulose in the space above the ISO, below the baffle. Now my question is, rather than strapping the ISO and adding drywall, could I add some sort of beaded board (cedar, pine, beaded plywood, etc) to cover the ISO for the ceiling rather than using drywall. I have read that a fire barrier needs to be added such as drywall. I am looking for a rustic look, and was thinking if I cannot have to strap the ceiling for drywall I could be saving some $$, space and labor. Second question, I have heard of the do-it-yourself, blow-in insulation foam options. What are your recommendations or thoughts on these? Easy to do? Better off hiring it out? Thanks for your time and I look forward to reading your response.
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Sounds like a fun project! First off let me put no my engineering hat and at least point out that if you live in an area with any snow your existing 2×6 rafters are far too small by today’s standards. If that’s the case you should consult with a structural engineer before moving forward with your project…enough of that…
2″ of foil faced polyiso on the ceiling is a great start, combined with blown in cellulose it should be a really good option. You really should check into the local building code and see if there are any energy code requirements as you might need an even higher R value. Your proposed insulation would be 5.5 inches of cellulose at 3.5 per inch + 2 inches of polyiso at 7 for a total of R33. In many locations today you need upwards of R50 for attic ceilings.
Almost every code requires a 15 minute thermal barrier. T&G can be used but 1x typically doesn’t make that requirement. I’ve heard of some 7/8″ thick material in T&G being approved. You’ll need to discuss this with your local building code official. You might want to add a layer of 7/16″ OSB then the wood which will likely make the rating pass.
DIY foam is really difficult and not something I recommend. DIY cellulose is much easier and typically something a home owner can handle.
Good luck.
Todd, I have a below grade,uninsulated,mostly dry, basement in N.H. that I would like to insulate. What do you recommend?
Check this out: http://www.homeconstructionimprovement.com/basement-insulation-guide/
There are lots of links in that article to all my other basement insulation articles.
Todd,
Thanks for the very informative website!
I am doing 2″ XPS in my basement, which has no water problems but is slightly humid. Measuring to insulate my rim joists, I have about 6″ in from the rim joist to the interior edge of the sill plate.
Would best practice be to:
a) put one layer XPS sealed directly against the rim joist (thereby creating an air pocket between the insulation and interior framing)
b) put one layer XPS sealed on the edge of the sill plate (thereby creating an air pocket between the insulation and the rim joist)
c) double or triple up on the XPS to eliminate any air pocket from rim joist all the way to the edge of the sill plate
d) none of the above
No grade for this quiz, just everlasting gratitude when I’m enjoying my nice dry basement!
John
John – Thanks for the kind words. I hope you’ll consider signing up for our FREE Weekly Newsletter!
You want the insulation to be as close to the outside as possible. Obviously you’ve got a tight space to work in but I’d get at least one layer of 2″ foam against the exterior rim joist. Then you can add more foam or supplement with fiberglass.
Best of luck!
Thanks so much! I will keep you posted as the project goes on!
We live on the main floor of a duplex and have high heating bills in part due to old (inadequate) insulation. The apartment above us heats her unit. Since insulation cannot be redone at this time, I was thinking of stapling foil faced kraft paper over our drywalled ceilings in hopes of reflecting some of the hot air back down.
Is this temporary fix a feasible solution ? And could it cause any moisture problems on the ceiling ?
Thanks for your help
Sara
First of all your proposed solution is likely not legal. Most foil faced products must be protected with a 15 minute thermal barrier. It’s far more likely that your heat loss problems are due to poor windows and wall insulation. If your neighbor above is heating the space then your not loosing as much up as you are likely out the sides.
We are currently building a new home in Indiana. It will be a 2 story home with a basement with the first floor 2200 sqft, 2nd floor- 2000 sqft. and the finished basement with 1500 sqft. They have so far poured a 10 inch thick foundation and placed tar waterproofing on the outside with some sort of non-rigid insulation on the outside. They plan on pouring 4 inch concrete over visqueen vapor barrier and granular fill after the plumbing stuff. We have a 400 sq ft sunken by 4 inches -section designed for the theater that Im concerned about especially with moisture since immediately upon digging-there was water pooling but eventually desipated but occasionally is there anywhere from 2-4 inches. We added a sump pump in that section. My question to you is what would you recommend for us to do? My builder is reluctant to use the 2 inch rigid xps below the concrete saying that he is worried that over time it would not be structurally sound with the 2nd floor weight. and claims that he has not had any condensation issues in his basements. What you would do if you lived here in Indiana and roughly how much would your recommendation cost? Our climate is not as harsh as Canada and I obviously am trying to be cost effective. He plans on insulating the walls very well upto R13 with a space between studs and the wall as a thermal break. And if you advocate insulating below the concrete does that mean above the footers too or level with footers?
Thank you so much for your time and GOD BLESS YOU!
Sounds like a great project.
1. First off I’d be sure that the area under the slab is excavated down to at least the bottom of footing elevation. Then backfilled with clean stone material with a complete perimeter drain to drain any ground water.
2. Placing 2″ of XPS foam on top of the compacted fill and directly below the slab is definitely a good idea. This will do two things; it creates a good insulation layer to help keep the slab warmer, and it also helps stop moisture from coming up through the slab.
3. I would HIGHLY recommend you read another one of my articles about properly insulating a basement. DO NOT agree to have your basement insulated as you stated above. It doesn’t work and there’s tons of good information out there to prove why. Read this: http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
I hope this helps clarify some issues for you. Investing in insulation is by far one of the best things you can spend money on in your new home. Fuel costs will only continue to rise as time goes on.
Thank you so much for your quick response. But just to clarify, does the 2 inch XPS go on top of the footers as well as the gravel or does it go on top of the gravel but level with the top of the visible footer? Last question is assuming that we will place the 2 inch XPS uder the concrete, do you still recommend something to place below the wooden studs so that it is not in contact with the cement floor? If so, what material would you use? Thank you so much again. You have no idea how much my husband and I appreciate it.
The answer to your question really depends on the slab elevation with respect to top of footing. In some situations the bottom of slab is an inch or so below the top of footing, in that situation the insulation would stop at the edge of footing. If the slab is entirely over the top of foot by more than 2 inches then you could put the insulation over the footing. Either approach is acceptable.
If you insulate below the slab then some folks don’t actually insulate above. If you install a wood sub-floor and it’s in direct contact with the concrete they you’ll want to use pressure treated lumber. I’d use pressure treated even if it rests on top of the foam.
Dear Todd,
I have a very old, partially frame farmhouse in PA. I’m presently remodeling the master bath and would like to add some insulation to the framed area. It is aluminum siding over minimal foam over wooden siding. There is an air gap, then lathe and plaster. I was thinking of adding 1/2″ polyiso foam covered with dry wall to the interior of the two ezposed walls. I read you comment about BIBS and wondered if this can be blown into the wall cavities? I’m trying to avoid ripping out the plaster and lathe.
Thank you for your help,
John
Insulation contractors have been blowing cellulose into wall cavities for years. They drill small holes in each stud bay from the outside or inside. Shouldn’t be a problem at all.
Hello,
I will be insulating my basement concrete wall. My house is split level, so half the basement is above ground (already insulated) and half below. Can I glue the foam board right to the concrete? And should the foil be facing out? ALso, will I then also need another moisture barrier like plastic sheet before drywalling? Lastly, is it ok to insulate an area (under stairs) that i will not be drywalling?
Thanks in advance! I am also in NH, gonna be getting cold soon wanna make sure I insulate properly. Thanks!!
Mike
I would not use foil faced on the concrete. I prefer XPS foam board on concrete. Yes it can be glued in place. All foam boards should have a thermal covering to protect from fire.
Thank you! I have Dow foamboard with one side foil… will this be ok? Also, what is a suitable thermal covering on a place i won’t drywall and how do i fill the foam board seams, will a tape be ok? SOrry for all the questions, i appreciate your response!! Very helpful . thanks, mike
Yes on the foam with only foil on one side. Most codes require a 20 minute thermal barrier such as 1/2″ drywall. Some wood products do meet that requirement. Products like plywood, OSB or T&G siding. You have to check with your local building code official.
Tape works great.
Will the foil act as a vapor barrier or will i need something additional? Also, I assume the top of the concrete (sill) will need to be insulated as well?
Typically we like to see at least 1-1/2″ of closed cell foam in order to have an effective vapor barrier. How the foil effects that I’m not really certain. Yes, the top of wall up to the sill plate should also be insulated.
Also, do the outlet boxes need to be filled around with foam air tight?
If you install the foam board behind your wall then there is no need. If you install the foam between studs in the same plane as electrical boxes you’ll need to seal them well.
I have a 1st level room (above grade). The wall are cement block. The 2×2 studs are nailed in the block. So I only have 1.5″ space for insulation. I was thinking of glueing 1.5″ blue or pink rigid insulation between the studs. Do I need space between the studs for expansion or can it be a snug fit? Do I need a vapor barier over the insulation or can I just use 5/8th drywall directly over it?
Also I have a garage (cold room) next to the room and a kitchen above the garage. 2″ board on the garage ceiling glued to the plywood? or 1″ board plus unfaced fiberglass insulation.I have plenty of space for insulation 18″. I want to limit air leaks between the garage and kitchen with the rigid insulation. Closed cell foam spray too expensive will open cell sprayfoam be ok?
By the way half my 2 car garage is under the deck and the other half under the kitchen. also water pipes are in the garage cieling near the garage and farther from the kitchen floor above. Worried about freezing. Kept warm with open heating duct blowing into the cavity between the drywall and kitchen floor above.
Any advise is welcome. Thank you.
First of all I would remove the 2×2 and install a continuous layer of insulation. Any other approach is prone to serious problems.
For living space over an unconditioned room like your kitchen it’s best to use either closed cell spray foam or some type of blown in cellulose with a layer of foam board. Open Cell Foam is a really bad idea in my opinion.
I am wanting to re-insulate a vertical wall which exists between a finished ‘attic’ and an unfinished attic. The finished side is actually the upper pitched end of a living room with a cathedral ceiling.
The drywall to the finished side is attached directly to a truss. The opposite side of this truss is in the unfinished attic. It currently only has faced fiberglass batts which have been installed between the voids found within the truss, which is actually 2×4’s laid flat; only 1.5″ thick.
I want to add more insulation to this triangular, center peaked wall. In a perfect world I would simply add 4″ of polyiso, seal it up and be done with it, but there are complications.
My scuttle can barely accept a 32″ piece of 3/4″ polyiso (1/3 of a 4×8 sheet). A 3 or 4″ panel would probably have to be cut even smaller.
Originally, I was planning on putting up the 3/4″ polyiso (which I can easily get at Lowes where they cut it in thirds vertically so it fits in my car..I’ve no truck). That would give me an R-5 for now (plus anything I might add in the 1.5″ void provided by the flat 2×4’s of the truss). Then I was going to later add some R-19 or R-30 batts or rolls on the side facing the unfinished attic.
The point being to seal off this area asap before it gets really cold because about 30% of the fiberglass which was there before has fallen out. So even adding the 3/4″ and sealing it would be a big improvement.
This is a 12:4 pitched roof and not much fun to work in so I want to keep the work up there as simple as possible. I am especially concerned about the increased difficulty in 1) getting the 3-4″ through the scuttle, 2) cutting it, both before I get it into the attic and also once it’s up there, 3) attaching the 3-4″ to the truss.
My gut is telling me to get the 3/4″ installed and sealed now, basically because it would be so easy to get it into the attic and especially just using not very long drywall nails to attach it. Then seal it and solve the additional R-19 or 30 later. Possibly by stacking batts or rolls against it.
The height of the truss is only 50″ at the center so it would taper down as I would work towards the ends.
Not knowing how difficult it is to cut and attach the 3-4″, my dilemma is: do I want to fight the 3-4″ in the cramped area or put on the easier 3/4″ polyiso and figure out how to add unfaced (I think) rolls to it later. I plan on blowing in quite a bit more insulation to the existing 3-4″ which is in between the trusses now, once I get the prep work done.
I do have a friend with a truck to get some 3-4″ here. I think I would need 2 or 3 4×8 panels to finish it.
Not being able to pull the trigger about which thickness of polyiso is really bugging me. Something just keeps spooking me about working with the thicker pieces.
Thanks.
I am located in an uppermost county of Zone 4, just south of Zone 5. Southwest Ohio.
I can certainly understand the cramped quarters and not wanting to spend much time up there. I have a different solution that you might want to consider. When we build this type of wall that divides conditioned and unconditioned spaces we treat it as though it were an attic floor, meaning we want at least R38 or more if we can get it. Obviously that’s not easy with foam board. So the insulation contractors typically have us create a 2′ wide void between that wall and the next adjacent truss. We do that by attaching Tyvek or Typar to the next truss and then nailing 1×3 boards over the truss members to help reinforce the building wrap. Then we blow that cavity completely full of cellulose of fiberglass. The beauty here is you don’t have to fuss with all those attachment details and you get a super insulated wall. Blown in insulation is cheap and you could even do it yourself. Make sense?
Hi Todd. Thanks for the quick reply.
I understand your idea. It’s very similar to what I was thinking of doing with rolls of R-30. The difference being your elimination of the ‘sealing’ part provided by the 3/4″ iso board, which I thought would help as I’ve noticed that some of the horizontally blown in stuff seems to have been blown around at least in one nearby corner, which is at one end of the truss I’m trying to insulate.
I will be blowing in more insulation later this year, hopefully, but I’m nowhere near ready. I need to install attic baffles (which is a pain, I’m working on trying to pre-glue and pushing them into position at the soffit ends) but that will take time. I also need to cover some voids created by dropped ceilings over the kitchen cabinets (unless it’s ok to simply fill them with the blow-in).
So I guess my question now is will the 3/4″ iso sealed board help? Would it offer a vapor retardant? Do I even need a vapor retardant?
I have been spending my morning trying to figure out a way to keep a stack of R-30 rolls in place. The stack would only be 50″ tall at the peak and shorten pretty quickly afterwards. The lowest 2 runs would take it up to 30″ (using 15″ widths) which seems to me could be held in place with wire or a similar framed rig that you mentioned. I don’t know if the rolls/batts would want to settle if only stacked 2 high, 3 at the most. The R-30 rolls would measure about 9.5 inches wide (when stacked vertically).
I think I’ve talked myself out of using the 3-4″ iso. Just too much attaching work I think.
The 3/4″ will certainly help “seal” up drafts. The reason we often do the blown in is it can really seal things up very well when pumped into a cavity like that and packed full. Even if you do the 3/4″ iso I’d still use this approach when you blow the rest of the attic.
Good advise.
At least now I have a plan of attack which can be modified along the way. I really couldn’t start anything until I had decided whether of not to try to use the thicker foam boards or not.
I’ll go ahead and put up the 3/4″ iso and see how that goes. Should help and can’t hurt. I’ll be looking for some 24″ ‘cavity designs’ in the meantime.
Great website.
Thanks.
I’m trying to insulate the completely uninsulated attic in my 1926 house, in Seattle. The ceiling is lath and plaster with 2×4 joists. Insulation would probably be blown in cellulose or fiberglass rolls. Except the area where the roof is highest, which I’d like to use for storage.
Obviously a 2×4 cavity full of cellulose with a plywood floor on top isn’t going to have an R-value anywhere near the R-38 I should be aiming at. So one suggestion I’ve gotten to is place 4″ of polyiso sheathing on top of the cellulose filled cavity, and put a bit of cheap OSB or ply on top to protect the surface of the polyiso from dents.
Is the polyiso strong enough to support the weight of someone walking on it, if there is a some kind of covering?
Will the polyiso sheathing trap moisture in the cavity under it?
The polyiso is more than strong enough. That’s what’s used on flat roofs under rubber/pvc roof linings. The polyiso does act as a bit of vapor barrier which in this case should be close to the warm surface. However, if the joints are not perfectly sealed then it’s probably ok.
Hi Todd,
I just watched your video on Youtube, Nice job.
I Have a small 900 sq ft single family house with a walk in cellar in the Boston,MA area.
It was built in the 50’s. All 4 walls of the Foundation are 7 ft poured concrete, except for cinder blocks by the doorway.
The house is heated with forced hot air.
I am wondering, since it has a walk in basement,
(the front foundation wall is back-filled, the rear is bare).
Does this affect how you insulate?
There was a family room in the cellar when I first bought the house.
The paneling had mildew stains on it, so I tore it all out.
On extremely humid days I have seen moisture spots on the concrete floor.
I am thinking of insulating the cellar so I can work down there comfortably. The furnace doesn’t seem to be able to handle heating the cellar & first floor.
At what point is moisture a problem?
Will a vapor barrier keep the moisture out or will I have to use a de-humidifier?
Do I need to insulate and seal the entire cellar & floor in order for the insulation to be useful?
Will insulating “only part” of the cellar” help?
In your video, you used 2″ foil faced polyiso at the rim joist, then you used 2″ Blue foam board on the wall.
Why did you use different insulation at the 2 locations?
Thanks, I have been enjoying reading your answers.
Brian
Brian – Glad you found the video and article helpful. Here are my thoughts on your situation.
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