How To Insulate A Concrete Floor
Insulating Concrete Floors
If you live in a cold climate then you’re no stranger to cold concrete floors in the winter. If you’re planning on finishing a basement or portion of your home that has a concrete floor then it may be a good idea to insulate it before installing basement flooring. Concrete floors are cold and full of moisture that can be a long term maintenance problem.
Methods To Insulate A Concrete Floor
There are numerous methods for insulating concrete floors and slabs. The method that you chose really depends on cost and available headroom. If you’re finishing a basement most building codes require a minimum finished head room of 7′-6″. So any choice in the insulated sub-floor must account for that minimum height including the finished ceiling construction. The following are two methods that we’ve used in the past with great success.
Insulated Sub-Floor Panels
There are numerous products being sold today that are typically a combination of rigid foam insulation and some type of sub-floor material like OSB. There are quite a few of them on the market including Barricade Subfloor Tiles. The subfloor tiles are really great for folks with little DIY experience and clearance issues as they provide one of the thinnest insulated options.
Insulated Sub-Floor
If you’ve got adequate headroom and few interferences then this is the method that we like best. This method works great if you don’t have many doors and you can deal with the higher sub-floor at the stairs. The method is quite simple consisting of a layer of foam board insulation, sleepers and a plywood sub-floor (see diagram above).
- First you need to be sure the floor is clean. Be sure to fix any problems in the concrete floor such as cracks, spalls and water problems.
- Install a layer of rigid foam board insulation such as Styrofoam Tongue and Groove or Styrofoam Brand Highload 40 (depending on the loads you have the first one provides 25 psi and the second one provides 40 psi). We recommend at least 1 inch of foam board. Use a good quality foam board adhesive to adhere the foam to the concrete. If you’re interested in learning more about foam board insulating properties then check out our article on R Values Of Foam Board Insulation.
- Seal all the seams of the foam board insulation. We recommend you tape the seams with Tyvek (or similar) tape. You can seal along the walls with spray foam from a can (Great Stuff or similar).
- Install pressure treated sleepers. We recommend using 3/4″ thick pressure treated decking. Use foam board adhesive along the bottom of the sleepers and also attach the sleepers to the concrete using masonry nails or a powder actuated nailer.
- Install a layer of 3/4 inch tongue and groove AdvanTech (or other sub-floor material). We recommend you screw the sub-floor to the sleepers using stainless steel screws and sub-floor adhesive as well. We really recommend you consider using AdvanTech because of it’s excellent properties in damp environments.
- Finally install your finish flooring. You can install any type of flooring at this point because of the sturdy sub-floor.
Final Thoughts On Insulating A Concrete Floor
The only issue to watch out for in this situation is the height. You’ll most likely end up with 1 inch of foam board, 3/4 of an inch sleepers and 3/4 of an inch for the sub-floor for a total of 2-1/2 inches. This will most likely require doors to be lifted and stairs to be reconfigured. However, you’ll have a very warm comfortable floor and a whole lot less moisture in your basement.
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Todd,
Great articles!
Couple questions for you as i’m thinking of laying carpet in my basement (there’s existing tile) but want an insulated floor:
1) I assume you recommend removing the tile first?
2) What is the downside of using 1/2″ or 3/4″ XPS instead of 1″? Any water vapor issues in that case?
3) Are the PT sleepers truly needed? Couldn’t I just tapcon/powder nail OSB or Plywood into the concrete directly through the XPS? Or are there concerns with water vapor having direct contact with the subfloor in that case?
4) Could I use 1/2″ OSB instead of a 3/4″ subfloor? Any weight concerns….not putting a pool table down there…heaviest thing would be an elliptical.
Just a little concerned with height (will need to cut bi-fold doors down), but still want to get decent insulation to have a warm floor.
Thanks for any feedback!
@ Mike – Thanks for the compliments.
1. If you’re worried about height than removing the tile will help. I’m not sure it’s absolutely necessary to remove it.
2. The only downside is less insulation value and less protection from moisture. I think you might consider a layer of poly under the foam if you go thinner.
3. The Sleepers are not necessarily needed. We’ve actually done it both ways. When you use sleepers it seems to work better connecting them to the floor then screwing the plywood down.
4. 1/2″ will work if you don’t have sleepers.
Hope this helps.
Todd, I enjoyed your article on insulating basement walls. In fact, I began my basement bathroom project, and will use your methods in addressing the concrete walls around the perimeter of the basement. Should be more than enough to handle Iowa’s winters.
I don’t quite understand how foam board has a low enough compression factor that will support furniture, etc. So am I to assume the subfloor above the foam board will take care of spreading the load across the foamboard? And any thoughts otther than price considerations for using composite decking material as sleepers?
Thank again.
@ Joe – Thanks for your compliment.
Foam board (blue board, pink board) actually have a fairly high compressive strength when they are sandwiched between two products such as the concrete below and plywood above. We’ve done this method several times and it works very well. Hadn’t really given much thought to using composite decking. I suppose that would work out pretty well aside from the price. Good luck!
Todd, thanks for the great website and information. My question is similar to the one you addressed here. I was planning on using 1″ T & G Pink Board on my basement floor and then putting 3/4″ T & G OSB on top of it and then using tapcons to screw it all directly into the concrete. I was then going to use 1 1/2″ foam board on the concrete walls and build my 2 x 4 walls with batt insulation inside the foam board on the walls and on top of the T & G OSB. However, my father in law is questioning whether the foam board on the floor can withstand the weight of the walls and OSB on top of it without getting crushed or being unstable. There will be a bedroom, family room and bathroom in the basement with typical items for these rooms (bed, dresser, couch, televsion, tub, toilet, vanity, ect) but nothing with excessive weight (pool table, ect). Are my father in laws concerns valid or will this set up be able to handle the weight? He advised using a joist system with treated lumber on the floor with the Pink board insulation between the joists.
Chris – This system is used all the time. If you look at the rated pressure for foam board insulation and you compare to code floor loading it works fine. In some cases with extra loading (pool table for example) you can purchase the stronger version but for typical room it’s not necessary. I’d do it in my own home.
Good luck.
Foam is used under your roads especially near bridges. If it can support tractor trailers I think you’ll be fine. Just be sure you use a dense foam.
Todd,since I do have an issue with height,could i use 1/2 inch foam & put a laminate floor on top,water is not a problem.Thanks for the help.
@ MikeR – What would actually hold down the foam? I’m just not sure it would be a very good system without some mechanism holding everything in place.
Todd,
Have some follow up questions for you :)
In looking at the XPS panels available to me at local stores, I saw Owens Corning Foamular 150 and 250 (high density). Noticed that the only difference is the compressive resistance of the 150 is 15psi and the 250 is 25psi. I don’t think they carry the 250 in 1″ size (or at least not in stock….however they do have 3/4″ 250 in stock). Which type do you guys use? Do you think the 150 is sufficient? Like another commenter, I assume the plywood/OSB distributes the load over the panel.
Also, if I didn’t use sleepers, and didn’t use AdvanTech, in general do you recommend plywood or OSB? I’ve seen 3/4″ T&G OSB be recommended…also have seen 3/4″ T&G Sturdi-floor plywood for ~$17. I had wanted to use 1/2″ to save height and 1/2″ square edge OSB panels are extremely cheap, but aren’t T&G. In such a setup is T&G a necessity? I assume it would cut down on the number of Tapcons needed?
Finally, if I leave my tile down and put the XPS panels over top, do you think there are any issues with the small air gaps caused by the grout lines? I had read the XPS should be tight against the wall/floor, but also have seen other products that market an air gap as a benefit…
Any recommendations either way? As you can see I analyze everything for better or worse.
Thanks again!
Mike
@ Mike – I don’t think there’s much difference between the 150 and 250 for your application. I do think you should stick to T&G as it really stiffens the floor. I also think you really should have 3/4 inch plywood over foam board. I also don’t think the gaps along the grout lines are a big issue.
I have a question regarding insulating a poured slab cellar floor with Barricade. According to instructions, an expansion space should be left around outside edges, but doesn’t leaving this gap create a non vapor barrier? I thought that in order to prevent moisture from the meeting of cold and warm air, you need to have any gaps sealed. I plan on using 1 1/2″ rigid foam panels on the walls before framing, but still am up in the air as to how to insulate the cellar floor. Height clearance is an issue, and I would like to be able to put down carpet. I live in the Western New York area where our winters are cold.
@ Betty – The floor guys don’t care much about the wall issues! Obviously there is no perfect solution. I would install the Barricade system first, leave the gap at the concrete. Then bring the 1-1/2″ foam down on top of the barricade.
Todd — great site. I am redoing my basement, ripping out hte old wall frames and fiberglass batts. There is an existing slab floor. Following your recommended methods for insulating floors and walls, should I insulate and put in the walls first, or the subfloor first? Also, did you see the article in Fine Homebuilding September 2009 about subflooring — any comments? Finally, if the basement will be heated and I use a suspended ceiling, do you think I need to install fiberglass insulation between the main floor joists? Thanks so much, Mike
@ Mike – Thanks for the compliment. I would insulate the floor first if you have the luxury to do so. I did not see the article, can you share the basic information and what your question is? No need to insulate the ceiling above unless you’re worried about getting too much heat above.
Todd — Scanned in teh FH article, but see no way to attach it to the comments. Essentially, the author recommends that when finishing a basement, adhere to the following method for the floor:
1. Install a class-I vapor retarder, specifically a 10-mil to 15-mil polyethelene sheet, taping all overlaps.
2. Install a floating subfloor using two layers of 1/2 -nch plywood. Glue or nail the second layer to the first layer, but do not penetrate the vapor barrier.
3. Use high-quality engineered wood flooring to finish.
Following up on my initial “wall or floor first” question, would the wall framing go right on top of the subfloor?
Thanks again,
Mike
Mike – You are correct, place the wall on top of the sub-floor.
How would you address sloping floors using this subfloor method? In my basement, the concrete floor slopes towards the outer walls and then towards a drain. Would shimming betwee the sleepers and the subfloor be an option, or might this create uneven load distribution on the XPS? Would something like Dricore panels be better in this situation (aside from cost and height differences)?
@ Jeffrey – This method could still work if you can manage to cut good tapered sleepers (this might be really hard to do). Does it slope much?
Hey Todd-
Thanks for the reply. Unfortunately I think it’s going to be too much for tapered shims, especially since there is a ridge more or less in the middle. The house is almost 100 years old, and it looks like the floor is designed to channel water in either direction away from the middle. Between that and the relatively low ceilings to begin with, I think I might be stuck with one of the dimpled plastic membranes and carpet on top of that. I’m not crazy about putting carpet in the basement, but I’m not confident that I can get the floor level/flat enough for tile or laminate while leaving suitable headroom.
Any suggestions?
@ Jeffrey – Short of tearing up the slab I don’t really have any ideas. Are you sure that you’ve got no water problems? Be darn sure before you install carpet.
How many tapcon screws would you recommend to hold down a 3/4″ subfloor over 1″ XPS foam?
@ Jody – It really depends on how flat the floor sits. First off I would recommend using 3/4″ tongue and groove AdvanTech sheathing. It will likely require 4 to 6 screws per sheet.
Follow up question,
I am using 1 inch foam with 23/32 T&G advantec board for my subfloor.
You recommended using 4-6 screws per Advantec board. Since it is a T&G, this means that screws need to put pn the edges or you need to put tapcons all around each board.
Please advise.
Thanks,
Tariq
Tariq – The number of screws really depends on how flat the floor sits. There’s no structural reason to use them. It’s really just a way of keeping the floor nice and tight to the concrete. You’ll need to adjust accordingly.
i am using 3/4 tongue and groove plywood (not advantech). at this point the wood seems pretty flat :)
I will try to use 6 per sheet.
Thank you.
one other question, i have a plumbing clean out access in the floor. What do you usually do with the foam and sunfloor in that area? i would like to put carpet or wood laminate flooring inthe room, but i know i will need to have access to the clean out.
@ Jody – If you go to a plumbing parts vendor you can ask them for a brass floor cleanout cover. They attach to the floor pipe and work with your finish flooring.
So here is something I have been thinking about. If I insulate the floor in my basement, I think I have two problems. The first, which may be a non-issue but to add insulboard, then sleeper, then flooring will case the last step of the stairs to be a weird height. Secondly, I am concerned about the clearance to the ceiling because I would like to install a hanging ceiling (want to be able to get to the plumbing and wiring.
What are your thoughts?
FredW
Disregard this comment. I did not read throughly.
Todd,
Great information. Can you comment on the following?
Background #1: I have a 2 year old home. The basement so far is quite dry (sandy soil and good foundation drainage). We lived there before we rebuilt the house and never had any water problems and no smell/mold with carpet over slab.
Background #2: I am looking for warmth, and I don’t want moisture issues to arise after we condition the space.
Background #3: We do plan to put a pool table in the basement.
I have been planning on putting down Delta-FL, 3/4 OSB (or other), and bamboo (click-in or nail-down). Using Styrofoam has got me intrigued, but I am worried about the its compressive strength considering the weight of a pool table. So, what do you think of each of the following subfloor options for a bamboo finish? With a fair amount of space to finish, cost is a consideration, but doing it right is a bigger one. If I use Styrofoam, what level compressive strength will I need to ensure no long term issues with the pool table?
Option #1: Delta-FL (or Platon), 3/4 OSB – $1.00-1.30/sf
Option #2: 1/2 or 3/4 inch Styrofoam, 3/4 OSB – $0.70-$1.00/sf
Option #3: Delta-FL, 1/2 Styrofoam, 3/4 OSB – $1.30-1.60/sf
Thanks a lot.
Kurt – I would go with option #2. However, it’s important that you select a foam with a higher compressive strength. You can actually buy DOW Highload foam that has a compressive strength of 100 psi vs the normal 25 psi if you’re concerned about the pool table weight.
Since reading about your recommendations for Advantech, I’ve done a bunch of research and talked to their technical department. What a product, and what helpful people on the phone! Their normal recommendation is Advantech over a 6 mil+ polyethylene vapor barrier for a concrete floor. That’s it – wow. Of course, they were fine with either Delta-FL or Styrofoam for warmth. They said Advantech (3/4) can handle 500lb point loads. That would mean 2,000lb for a pool table. Since a heavy pool table is 1,000lb, no problem. Thanks for all of your help.
Kurt – AdvanTech is an amazing product. In fact, we won’t build a house today without it! Good luck.
Todd- What can you tell me about using Platon for a dry/insulating layer instead of foam? We didn’t consider foam until reading your article. Also, we want to install the subfloor layers before framing the basement walls. Should we put the foam boards on the cement block walls before installing the flooring layers? It has been recommended to leave a 1/4″ space for the flooring to allow for expansion when installing the subfloor over the Platon; is this necessary for foam as well? And I am not usre what pressure treated sleepers are and am unsure if it is necessary. Thanks!
Maura – It doesn’t “really” matter much which you install first although most would recommend doing the floor first. If you choose foam for the floor then run it up tight to the wall, leave a 1/4″ gap between the sub-floor and concrete/block wall for expansion. The sleepers are sometimes used and sometimes not used. It really comes down to a personal preference and there are many different variations of the same theme.
Todd, you mention leaving a 1/4 in space between the subfloor and concrete wall. Beneath the subfloor, we are putting PT sleepers around the perimeter of the room and then encasing the foamboard between the sleepers, alternating with sleepers in between each foam board sheet. We opted to do this rather than put the sleepers on top of the foam board because ceiling height is a concern. My question: should the sleepers around the perimeter of the floor also be 1/4 in from the concrete wall instead of right up against the wall in order to allow for expansion?
Also, which size Tapcon screws do you recommend for 3/4 in foam board over the vapor sheet covered by 1/2 in plywood? We will ultimately put down laminate flooring.
Thank you. This discussion has been so helpful!
The gap certainly is good protection against expansion. Frankly most plywood is quite stable and unlikely to move much so it’s not a huge concern.
I would use 2-1/2 or 3″ screws.
Thank you!
great article. I plan to follow your recommendations in finishing up my basement.
I have couple of questions that I needed help/clarification
As mentioned in one of your responses that I could go with foam and advantec board on top of it without using sleepers if height is an issue.But if i use less than 1 inch of foam, you recommend using poly first, then half inch foam and then 3/4 advantec.
Can you elaborate on the poly and its installation ? I mean what product do you recommend and how would you install it ? anything to look for ?
also what do you for the mechanical area ? leave the concrete floor exposed ? My furnace and water heater are tucked in corner. Also what do you with the walls around them ? right now i have fiberglass blanket against the concrete walls installed by the builder ? I plan to get the finished part of the basement, spray foamed (closed form) for 2 inches but since there is not much space behind the furnace and the water heater, I am not sure what to do with it. what do you recommend for both the floors and the concrete walls ?
Thanks so much for all the info
Tariq – When you use thinner layer of foam you need to install a vapor barrier. Thin layers of foam just aren’t thick enough to stop water vapor movement. You can simply install a layer of 6 mill poly on the slab and tape all the seams. Then you can install the layer of foam followed by the sub-floor.
As far as your mechanical room it’s really a matter of compromise. Do you want to remove the furnace? Probably not, so it may make sense to leave the existing insulation in place unless you suspect some type of mold problem.
You’re on the right track with the spray foam and floor insulation. You just need to compare pricing and what options are most important to you. Good luck.
Todd I live in Lubbock Texas had a lot of rain basement is leaking had about 36 gallons of water I wet vac.up. Friend of mine said to use swimming pool paint to seal the basement floor and walls. But I was reading some other blog not to use it because pressure would build up and shift the foundation. Any Idea what to use to seal it with?
Mark – You actually need to fix the drainage problem. It’s almost impossible to “seal” out water due to the pressure. I would recommend a sump pump system or exterior drainage improvements.
Todd
Thanks for the great article and advice. Is it recommended to apply a concrete waterproofing paint such as Drylock prior to putting down the 6 mil poly and foam board? Or is it necessary to let the concrete floor breathe I am reading conflict opinions on this topic.
Joe – First off thanks for the compliment. Concrete doesn’t need to breath contrary to popular belief. In fact, concrete needs water in order to continue the chemical reaction that creates strength. So concrete frankly likes water!
I don’t think using a sealer is necessary. I think as long as you put down the foam and seal the seams well there will be no issue.
Todd,
What do you think about sodium silicate penetrating sealers? like Conseal 1000?
Then place Xps 1/2 inch glued or tap conned to concrete…then floating laminate over that.
thanks.
Ed
epellico@hotmail.com
Ed – That approach certainly should cut down on some moisture. Some sealers work better than others but none are 100% effective. I would try sealing a small area, then testing with a piece of plastic taped over it to see if there is any moisture build up.
Todd
I have a few questions. I am going to put 1″ T & G pink board on the basement floor with 3/4″ T & G treated OSB on top of that and then use tapcons to screw it directly into the concrete.
1. Is the pressure treated sleeper level that you recommend truly necessary or is my method going to be equally effective?
2. The house is about 7 years old and there are minor settling cracks from one side of the basement to the other (no evidence of any water problems) Do I need to seal/repair these cracks before I put the pink board down?
3. When I lay out the pink board does it matter if the OSB subfloor is layed in the same direction, or should I avoid having the seams of the pink board be directly under the seams of the OSB (obviously the seams of the pink board will be sealed)
Thanks
Chris
Chris – There are many variations on the floor and yours is another method that many people use. I would definitely seal any cracks before you start, better to be proactive than wish you had later. Be sure to seal the foam seams. I would try your best to avoid overlapping seems but it’s not necessary. Good luck.
….just a thought on this topic:
….would 3′ tar-tape be effective on slabs cracks in this particular situation?
…my water thought theory says yes, but would appreciate constructive criticism..
I’d use cementitious joint filler vs a tar based product.
Hi, great site Todd.
I have a question on building a subfloor.
1.5 inches of foam seems to be the general consensus to make a vapor barrier. So if I use 3/4 or 1 inch foam this is not a proper vapor barrier, correct?
My floor is about 6 ft below grade, which is also below the frostline. I’m guessing that 3/4 XPS, which is R4, should be enough to prevent condensation because the ground temperature should never get lower than 32 degrees. And also be a “good enough” vapor barrier if I seal it correctly and ensure the materials above it (Avantech & Carpet) allow vapor to pass (which should be very minimal to begin with). Is my thinking correct here or am I missing something?
The only reason I am considering 3/4″ is because nobody seems to stock 1″ in T&G anywhere near me and they won’t special order it because they have to buy it in pallets of 48.
Thanks,
Phil
Phil – You’re on the right track. The only other question is whether you have lots of moisture under the slab, do you have under slab drains? any signs of excess moisture? If it is dry historically then I say you’re ok.
Well, there is a lot of moisture in the ground, however I have drain tile on the inside and outside of the foundation and although my sump runs alot, I have never had moisture inside.
But since the ground is so wet I’m concerned about vapor coming up through the concrete. That’s why I’m leaning more towards something that allows a bit through rather than sealing it with a full vapor barrier like I did the walls. (I should have done the floor first, but I changed my mind on a subfloor after seeing how effective the foam on the walls is)
It seems to me that something like Dricore doesn’t offer enough insulation to stop condensation, and a full 1.5 inches of foam for a vapor barrier just gets to be too high. But then again, I really don’t know what I’m doing other than what I’ve read here and elsewhere…
Phil – Concrete doesn’t care if it’s wet, frankly it helps it continue to get stronger over time. On the other hand, carpet, flooring, etc don’t like water at all. What about applying a concrete sealer first, followed by the thinner foam?
I’m not too concerned about the concrete, but I am concerned about odor down the road.
The local building inspector recommends putting down poly first, then the foam and OSB. He thinks without the poly I will have too much dampness between the foam and concrete despite the fact that the foam will breathe some. I have also read about keeping the vapor barrier on the warm side however since vapor comes from the concrete in this case it may be a bit different. If I put a vapor barrier in anywhere then I can’t glue the foam or flooring down and have to tapcon, which of course pokes a bunch of holes in my vapor barrier anyway. And as I understand it, sealants aren’t any more of a vapor barrier than the 3/4″ XPS which has a permeability of about 2.
Maybe I’m just overthinking this, but I really want my basement to not smell like, well, a basement. The more I learn the more confused I get as all the locals seem to have different opinions.
Thanks for your help,
Phil
Phil – I can tell you we’ve done several basements this way and they all have worked very well. For me the key is always sealing the foam properly. I highly recommend Tyvek tape because it seals VERY well to foam board. Then you can seal around the perimeter with spray foam.
Sorry to keep bugging you, but when you say “this way”, do you mean vapor barrier, foam, then subfloor? Or sealer?
I used an off-brand version of housewrap tape on the walls because that’s all my nearest home store had. I think I’m going to re-tape it with Tyvek brand because it doesn’t seem to be sticking very well.
Thanks again,
Phil
Phil – I mean we’ve done several with just foam, seams sealed.
Thanks again for your help Todd.
Unfortunately, a nasty (and timely) thunderstorm caused a couple of leaks. I’ve had small periodic leaks from the windows and the first floor in high winds and every time I get it fixed it seems like another pops up in a year or two. So I gave up on the XPS idea and went with Dricore.
I’ll be putting it 1/4″ away from the wall foam and framing over the top. That way any future leaks will run down the foam and under the floor to dry out without hitting any wood on the way. Not the ideal solution, but probably better than future water getting in between the subfloor and foam.
Hi Todd,
I’m looking to finish my basement (w/ no water issues) using the foam board insulation and framing recommendations you’ve made along with a Dricore subfloor with carpeting. The Dricore website recommends building the frame on top of the Dricore. I had an idea to modify your method and I wanted to run it by you.
I was thinking of covering the walls with the foam insulation and sealing it with Tyvek tape and spray foam like your recommend. Then I would lay down the Dricore and get that set in place with a small gap from the wall to allow it to breathe. Then frame on top of the Dricore as per their recommendations. This should eliminate the need for either the composite decking base or for any pressure treated lumber. What do you think?
Todd – I think it sounds like a good plan. With any of these things each situation is always a bit different. Good luck.
I am designing a house and looking at how to insulate the basement floor in the walkout basement which will be used as living space (including the master bedroom suite). I have the following questions about your described design.
1. You recommend glueing the foam board to the concrete. I was considering putting Delte-FL between the foam board and the concrete
to better handle moisture should that become a problem (I plan on using 2″ XPS). Is this a bad idea (will it make the floor to unstable or is it just a waste because exposing the XPS to moisture is never an issue).
2. You recommend putting in sleepers, which concentrates the floor weight on particular sections of the foam board. Can the sub-floor be placed directly on the foam board and screwed into the concrete?
Please comment on these, both as independent ideas and used together.
arch – There are so many different ways to approach this topic and frankly many of them are good solutions.
1. Moisture isn’t an issue with xps when it’s thick enough so using the Delta-FL frankly is added expense for really no gain and it adds more overall height.
2. You can screw the sub-floor through the foam and into the concrete. However, that will require far more “concrete” anchors. If you install sleepers there are fewer anchors but you need to nail/screw the sub-floor down to the sleepers.
XPS foam can be purchased in at least two compressive strengths. When used in high loading situations you can use the higher PSI version to compensate for the higher loading.
I am not worried about moisture coming up from the concrete through the XPS. I am worried about what happens to water that otherwise makes it past the waterproofing strategy used throughout the basement (or should a toilet overflow, fish tank leak, etc). As stated on another website, the Delta-FL would preserve small drainage channels under the foam board that would provide an air space for drying (and a path to a drain if the problem was severe enough). Height is not a problem as this is new construction that can be sized as needed (and Delta-FL is only 5/16 thick).
Given gravity and water’s clever way of exploiting any imperfection in any seal, if water is introduced into a system where XPS is glued to the concrete, wouldn’t that water get trapped somewhere where there is little mechanism for it to dry or drain out?
Arch – I don’t discount those worries. However, small amounts of water won’t hurt concrete, it actually makes concrete stronger. The real issue with water is will it cause mold and mildew to grow. If water gets under your floor you need to worry about any wood, carpet, etc that has “food” for mold. Without the food, there will be no mold. Again I don’t think it will hurt anything to use it, I just think it’s a bit of belt and suspenders. I’d rather spend that money on a better exterior waterproofing membrane.
Hi, thank you for such an informative website. I am wondering if what I want to do is a good idea or bad idea:
We have a basement in Maine that is unfinished. I am thinking about installing the foam insulation against the walls and installing 2x4s, and some sort of paneling like you did for your storage room. However I am not sure if I want to insulate the concrete floor or install a floor as the basement is a computer lab/storage room/workout room. Also I probably will not install any type of ceiling. Is this insulating the walls and putting up walls a waste of money if that is all I do?
Thanks again,
James – Not a waste at all. Basement walls are typically about 50 to 60 degrees year round. If you think of them as a large radiant heat/cool surface then it’s pretty easy to realize that insulating the walls is a good idea. I would insulate any walls that you can afford to do.
I forgot to add this question as well:
Should I also insulate and frame/wall behind our furnace/oil tank? Our furnace is in the corner of the basement.
Hi,
I have put 1 inch foam and 3/4 inch advantech as my sublfoor in my basement. Most of the basement would be carpet except for the bathroom and bar. Initially I was planning to put tiles in the bar and the bathroom area over 1/2 inch cement board but the carpet installer who came to take measurement was concerned that the tiles would crack because of the foam present under the Advantech ?
Do I need to be concerned about installing tile over this subfloor ? or there any additional steps i need to take to make sure tiles would work ? are there any other products that I can use in a bathroom with shower ? Can I use laminate flooring instead ?
Any help would be greatly appreciated.
Thanks,
Tariq
Tariq – Couple thoughts.
1. There are some pretty decent sheet vinyl products today that would work well.
2. There are groutable vinyl tiles on the market today that look very nice, get the look of tile without the cracking potential.
3. Could install the high density foam in those areas, then be sure to screw the 3/4″ floor down very well, probably 12 to 18 inch centers, in addition I’d probably use an underlayment like Schluter Mat.
Hey Todd,
First of all great site. I have a couple of questions hoping you might be able to help me with.
Remodeling my basement, on top of the concrete floor there is an asphalt tile that is a real pain to get off was wondering if I had to remove that before putting the floor down?
If I used the high density foam would that be enough strength to support a bar?
Also the floor has sunken in floor drains and the floor is not level in those areas(slopes about 3ft around the drains, drains are sunken in about 1″) do you have any recommendations for this.
I planned on putting a layer of poly on top of the tile(have moisture problems on occasion). Then 1/2″ foam on top with 1/2″ subfloor on top of that.(Height issues)
Thanks for your help,
Frank
Frank – Sounds like you’ve got some challenges. First off not sure exactly what an asphalt tile is. I’d be a bit concerned about foam sitting on asphalt as they two typically don’t get along very well (asphalt has a tendency to eat foam). Aside from that if it were me, I’d get up the old tiles, level the floor (either self leveler or wood sleepers), then foam, then sub-floor.
Todd,
I have a basement floor that slopes towards a drain in the middle. It seems the original owner intended on using this room as a garage. It poses a challenge for me to get the floor level before I install a sub floor.
1. Would you suggest using self-leveling compound in a situation like this, or something else?
2. Is it OK to bury the drain in the middle of the room with something like self-leveling compound?
Rich – Self leveler will work fine. I wouldn’t bury the drain, I’d extend it if possible and put in a floor drain plug. Never know when you might need it.
Hey Todd,
Thanks for the help before and now I have another question. Around the perimeter of my basement a french drain was installed. The concrete poured on top doesn’t go against the wall. There is a gap it looks like for the water to go down. Over the gap there is a piece of stripping or something that looks like it is to direct the water into the french drain if it runs down the wall. I was wondering what you think i should do about installing the floor and if I should leave it open. I’m also putting the foam on the wall so if I should leave a gap it really won’t matter.
Also I’m installing a bathroom with a custom built shower and was wondering if I should put foam under the shower or omit it here.
Thanks for your help,
Frank
Frank – Without a photo it’s hard to say exactly what I would do. However, I think it’s wise to leave a space in that area for the floor so water can get to the drain. I think the foam can probably go down to the floor as water behind it should be able to get down.
The shower is an interesting issue. For that situation I would discuss it with some tile guys. It might be possible to install the extra strong foam board, then the membrane, then scratch coat, then tile but I’ve never done it so I hesitate to recommend that approach.
Todd,
Great site! Thanks for all the advice. I’ve learned a lot and plan to follow the floor and wall insulation recommendations for my basement.
I have a couple questions about insulating floors. To avoid the extra height from sleepers I plan to use 1″ XPS with 3/4″ Advantec over the top and tapcon/powdernail into the floor.
1) Regarding XPS thickness, if 1.5″ is the recommended minimum thickness on walls to avoid moisture issues, why is 1″ acceptable on floors? Do they not experience the same potential condensation issues because the ground below slab stays warmer than the air outside a wall? Is the need to foam all edges and create a vapor barrier not as great with the floor?
2) I have a pool table (est 1000 lbs, 26psi load through the legs) that I want on top of the subfloor. Owens makes the 60psi foam in 1″ thickness but Dow does not. With the Advantec distributing some of the load I think it will handle the 3:1 static loading recommendation. However, an alternative design I’m considering is to build solid pressure treated “pads” to match the pool table footprint that would sit directly on the slab. I would install the XPS around it. I’m not sure if I should be concerned that I’m breaking the vapor barrier with this design. What are your thoughts?
3) I plan to tapcon/powder nail through the OSG and XPS into the floor. Is there a rule for how deep into the concrete the screw/nail should go?
Thanks,
Dave
Dave – Thanks for the compliment. You seem to speak my type of language….might you be an engineer? :)
1. There is no “correct” answer to this question. The 1″ thickness is mostly due to what’s considered practical. Adding more than an inch would cause so many issues with height that most people use 1″ as the cut off. You’re also correct in assuming that the moisture problem is a little better on the slab although I think an argument can be made that there’s no difference. As far as foaming the edges I think it depends on how you do this. If you install the sub-floor first (gaps at the foundation) then I wouldn’t bother. If you do the wall first then the sub-floor I think you might consider sealing the gaps to prevent moisture from coming up to the finished floor edges. Again..no “right” answer here.
2. I would go with the higher strength foam even if you just buy enough sheets where the table will sit. I’d skip the blocks. Frankly between the AdvanTech and the foam being fully supported I can’t see an issue at all.
3. I think you’ll need to experiment a bit with this. My gut feeling would be to use 2-1/2″ long fasteners which would provide 1″ of penetration.
Good luck!
Todd – thanks for the feedback. Right on track about the engineering background. I was unable to find high load foam in less than full lift quantities. Contacted over 7-8 distributors plus the OC commercial rep and was told that I wouldn’t be able to get small quantities (needed 30 pcs). So even with the pool table, I will go with a 250 strength (Pactiv) board that was stocked locally. I may use some pads in the floor or small risers to distribute the pool table load.
A follow-up question on GSPro foamboard adhesive: do you have a rule of thumb for how panels you can bond out of a can? I have to mail order the cans and have no feel for how many to order.
Thanks again,
Dave
Dave – The amount of foam varies greatly. We typically don’t use very much, dabs at the corners and mid-points. If I had to guess probably 6 to 8 sheets per can if you go lightly.
Thanks for all the info. I put an addition on Michigan’s Lake Huron. Pun intended. We went 15′ into a hill that has a natural sprng in it. When they dug the basement they created a saucer shape under the slab and back filled with pea stone. Now I continually have spring water 4″ under my slab. In the summer only, with the warm moist air I have a lake on my floor and damp walls about 3 feet up. The room will only be used for storage.
Reading your comments I plan on
1) putting down 1″ t&g Dow foam to the wall
2) tape the seams
3) put 3/4 t&g floor decking down leaving 1/4″ gap from the wall
4) use Great Stuff to fill the gap between the wall and the decking
The area is 15 X 25 and I can go from wall to wall without worry of the floor moving. Do you think I can go without gluing and nailing and let gravidy do the work? Should I use a vapor barrier?
Thanx
Ed
Ed – Wow……First off I’m not sure I’d put a floor down until you fix the water problem. I’m thinking you might want to install a sump pump to lower the water level.
Todd
I think my attempt at humor made it sound worse than it is. I’m not sure I can lower the water level without major digging into the hill outside. I do have a sub pump set up but it runs every 2 to 3 min without any effect on the water level under the floor. Without the pump running the water stays at a constant level under the slab but there is a constant flow of spring water under it keeping it cold in the summer. I only have a problem in the summer when the warn moist air off the lake comes in contact with the cold cement. I was hoping that inslulating the floor and walls would stop the moiture problem. With that said do you think this would help and if so are the steps in my earlier post correct?
1) putting down 1″ t&g Dow foam to the wall
2) tape the seams
3) put 3/4 t&g floor decking down leaving 1/4″ gap from the wall
4) use Great Stuff to fill the gap between the wall and the decking
5) Should I use a vapor barrier?
6) Do you think I can go without gluing and nailing and let gravidy
do the work?
Thanx again,
Ed
Ed – This approach may work. At the very least I would highly recommend using AdvanTech as the sub-floor as it’s manufactured to deal with water and moisture. #5 I would recommend one considering how much water you have. #6 I doubt it….but I suppose you can try.
Todd:
Great site and info. Your knowledge is greatly appreciated.
Currently we have Delta-FL and laminate and it is very cold on the feet. Due to the layout of the stairs we cannot get big items into the basement. Therefore I am essentially limited to subfloor tile products (dricore etc). I am thinking to put in Barricade (2’x2′ subfloor tile backed with XPS) for the insulation value.
The basement is dry with average humidity levels in the summer.
Questions:
Can I put these subfloor tiles on existing laminate?
If not, is there a problem installing these over the existing Delta-FL?
Regards David
David – I wouldn’t put them over the laminate. However, I think putting it over the Delta-FL would be ok. Does the specification for it mention what type of sub-floor restrictions if any it has?
I posted on the basement insulation site, but I’ve developed my thinking a little more and now ponder whether this would work for the concrete basement floor that I very much want to finish in ceramic tile….6″ poly, 1″ XPS foam, 3/4″ AdvanTech, 1/2″ HardiBacker, thinset and 1/4″ tile. Foam held in place with screws that go through AdvanTech to concrete (so 2 1/2 ” long???), the cement board to AdvanTech only. Will this make for a warmer and dry floor, or should I just tile the concrete and then put throw rugs down? Thanks.
Elizabeth – That method sounds fine. I would swap the Hardibacker for Ditra (http://www.homeconstructionimprovement.com/schluter-ditra-tile-underlayment/). It’s easier to work with, warmer, and an all around better tile backer in my opinion.
Good luck.
Okay. My hub’s an architect and saw that in Fine HB so I’ll showcase it for him. What about the screws for holding the AdvanTech to the concrete. Do they have to be 2 1/2 inch long and if so…what kind and how many? Thank you so much for responding so quickly! em
Elizabeth – 2-1/2″ Tapcon screws should do the trick or you could try using powder actuated masonry nails. The number will really only depend on how well the sheathing “sits down” on the floor. You want a solid surface for the tile.
Good luck.
Todd,
Thank you for all the info. I am removing drywall from finished, uninsulated stud walls in my basement and will have closed cell spray foam applied. For my concrete floor I would like to use 1″ xps and probably advantech on top. Question #1 – Would an adhesive be sufficient for holding the concrete, xps and advantech together without fasteners? #2 If so, do you have a recommendation? #3 I believe the treated base plate of the wall was installed directly to the concrete floor, will this present a problem since everywhere else has a vapor barrier? I am hoping to be able to leave the current stud wall in place.
Matt – I think you need at least some fasteners to keep things down tight.
I wouldn’t bother removing the old wall. Just seal what ever you do up to that plate.
Good luck.
Hi Todd,
I posted a basement wall question that you answered – thanks – now I have some questions re the floor (I haven’t done the walls yet).
1. I have read nearly all of the basement floor questions and answers and notice that although you initially recommend sleepers over the XPS and under the AdvanTech, you seem to accept the elimination of sleepers in subsequent posts, so………..what would be the advantage of sleepers, and what would be the drawback without them? I’d rather not have to install them to eliminate the height and effort but would if it was essential.
2. My house has a perimeter wall with beam/post supports sitting on reinforced footings – I recently installed – into my poured concrete basement slab. As the house is very old I needed to replace all of the beams and posts, and I just finished doing this. I am spreading the house load onto the posts and also onto some of the walls that will be “load-bearing”. I have not installed these walls yet (don’t worry I have cripple posts supporting the house) so I am thinking of building these walls first – with pressure-treated bottom plates – and then install the 1″ XPS and 3/4 AdvanTech up to the walls. Do you see anything wrong with this method? If this would compromise the basement moisture-control I would add the foam and floor first but I am worried that the weight would compress the floor over time. What would you suggest, or would both work?
3) Continuing on the above weight concern, regarding the stairs I have yet to build, should I build these to the basement floor (allowing for height of floor on bottom step) or build these onto the sub-floor?
Thanks so much for your expert advice.
Cheers, Dave
David – The reality is there are so many ways to insulate a basement slab. The sleeper version works well when there is a chance of a bit of water. For really dry basements you can put the foam directly down. Honestly there really isn’t much difference. Sometimes sleepers are easier to fasten down then you can get a good solid plywood layer down.
All structure should sit on the foundation, NOT foam. Not really an option and it shouldn’t really cause a moisture problem.
Build the stairs to the slab, account for the flooring height.
Good luck.
Awesome – thanks………..David
When attaching walls directly to the concrete vs the subfloor (as recommended for bearing walls), consider doubling up the PT base plate so you’ll have something to nail to after the subfloor goes in next to it and eats up height.
…LOVE this site, BTW.
Hi Todd,
I thought that I was done with asking for your help, but sorry, here’s another concern/question: I mentioned to a contractor friend about my (your) basement wall and floor sealing plan using the XPS and AvanTech and he said that sounds fine but did I know that ants just love closed-cell products. He has installed and is still installing it but he has also seen many cases of ant infestation with the ants boaring tunnels into the XPS and doing something with the contents – moving it, eating it, who knows. Have you heard of this?
It seems to me that if ants infested the floor they could damage the integrity of the XPS structure and eventually its performance apart from just being “yucky”.
To mitigate this I was thinking of wrapping the exposed ends with the tyvec tape – maybe that will keep them from starting their journey??? What do you think?
Cheers, David
David – I’ve heard from some people that in certain parts of the Country there are some insect issues. I haven’t seen the problem here in New England so I’m not aware of any particular solutions or problems. Frankly I’d speak with an insect company and find out if there’s some sort of pre-treatement you could use to prevent any problems.
Good idea……..I was just wondering if you had come across this ant problem before.
I am in the Northern California Sierra Nevada foothills and its notorious for its ants – they are small and don’t bite but are a pain in the rear when they are looking for moisture/water.
Thanks for the suggestion.
Cheers, David
David – California sure does have insect problems…I wonder if Termites like it as well? If you get an answer be sure to share with everyone here! Thanks!
Hello Todd, I’m so glad I found your website on basements. There is so much misinformation out there concerning basement finishing that I almost gave up my project. I have concrete walls and floor and there are no water issues other than the ocassional dampness during the summer. I painted the walls with dri-lock. I live on Long Island NY and I will install heat in the finished space. I am using 3/4 inch Dri-core panels on the floor because I dont’have any headroom to spare. XPS will raise the floor too much. I know from your website there is no perfect way to finish the basement but please give me your thoughts on the way I intend to finish my basement. Do you see any problems with it?
insulate the rim joists with 2 inch XPS
2″ xps on wall with tyvek tape and foam the edges
2×4 walls on top of Dri-core floor pads. The stud walls will be 1/2 inch away from the XPS
and so will the Dri-core.
insulate the walls with paper faced fiberglass insulation and 1/2 inch sheetrock.
install carpet on the Dri-core.
Thanking you in advance
Demetri
Demetri – Thanks for visiting the site.
Your method sounds good. Good luck!!
Hi Todd, I have read much of your website and I am unsure about 2 things.
1. when placing 2 inch xps board on walls what is the correct finish where it meets the the concrete floor? Do you leave a space? Do you seal it with spray foam?
2. When using Dricore floor panels do you frame the 2×4 walls on top of the panels or on the concrete floor?
Thanks Again
Demetri
Hi Todd,
What are the disadvantages of using DriCore, Delta-FL, or Barricade over the full insulating process with subfloors? Also, I’ve read the latest building Science Consortium recommendation about not using vapor barriers for either walls or for floors to let the walls/floors dry inwards, and yet it seems that using polyethylene vapor barrier on top of the concrete floor is still a standard practice. Do you recommend vapor barriers for the floors? Will DriCore, Delta-Fl or Barricade tiles prevent inwards drying and cause wetness to be trapped underneath?
Thanks,
Victoria
Victoria – Are you referring to the 2002 report by the Building Science Consortium? If so that is old data and I frankly don’t agree with it. Regardless anything you put down on the floor will trap moisture in the slab, poly, carpet, DriCore, it really doesn’t matter. The issue here is keeping that moisture away from materials that might promote mold. I recommend a vapor barrier under any type of wood, carpet or non tile flooring.
Hi Todd,
No, I was referring to this article from 2009:
http://www.buildingscience.com/documents/information-sheets/5-thermal-control/basement-insulation/?searchterm=vapor%20barrier
“The best insulations to use are foam based and should allow the
foundation wall assembly to dry inwards.”
This what they say about the floors:
“Basement floor slabs are best insulated underneath with rigid insulation: both extruded or expanded polystyrene have been widely used with success. Although the energy savings of sub-slab insulation are not as significant as basement wall insulation, such insulations do offer a significant improvement in comfort and moisture damage resistance (including against summertime condensation).
When slab insulation is provided, a sheet polyethylene vapor barrier should be located over the rigid insulation and in direct contact with the concrete slab. As the slab will only be able to dry upward, the slab should be allowed to dry before finishes are applied. Impermeable interior floor finishes such as vinyl floor coverings should also be avoided.”
Obviously, this is not an option for us since we will have to insulate on top of the floor. Would you use poly on top of the concrete or just foam ot DriCore etc. w/o poly?
Also, would you recommend Barricade or DriCore if we do not have have enough headroom to do XPS foam/sleepers/subfloor?
Thanks,
Victoria
Victoria – I highly respect most of their work. What I have a hard time with is this notion of having to let it dry inward. To me, there is no good reason to let it do that. For me, if the moisture is left under the insulation/vapor barrier adjacent to the concrete then so be it. Concrete is always full of water, it will never completely dry out. I did my graduate research on advanced concrete material science and I’m convinced it will never dry out. So…letting it dry inward means letting it expose water vapor to finished flooring materials.
Anyway….Barricade and DriCore are both good products. They will both make the floor feel warmer and they provide a nice airspace under the flooring.
Thank you. So you think it makes sense to put poly under insulation/DriCore/Barricade? What about the walls? Why not install poly between concrete walls and XPS following the same logic?
Thanks,
Victoria
Victoria – Yes poly on the floor is a good idea. If you read one of our wall insulation articles you’ll see that when you use a couple inches of XPS foam it acts as a vapor barrier. There is some literature that suggests that 2 inches of XPS foam may in fact be a semi permeable although I think the amount is negligible.
Todd/Victoria,
I am in same boat, debating between Barricade & Dricore due to height issues. In response to the comment regarding placing a vapor barrier down, then the tiles, i was in contact with a rep for barricade tiles and I asked:
“Should we install a 6 mil vapor barrier first, and then place the tiles on top of that, for better protection vs possible moisture seeping through the tiles up into the finished floor?”
Response from the rep:
“No, do not install vapor barrier. Our tiles are milled to create an air tight, gasket seal vapor barrier. You do not need, and we do not recommend,
anything other than our tile to be laid on the concrete.”
So just an FYI for people that are thinking of doing this. I thought it would be good to place a 6 mil barrier too, but according to them, they say no.
Thanks,
Steve
Steve – Thanks for sharing. I’m a huge believer in following specifications. In this case, I think that’s a marketing thing. They are trying to sell their product with as many benefits as necessary. Saying you can eliminate the vapor barrier is a plus in their book. My experience tells me that the poly won’t hurt their product and it won’t affect how it sits on the floor. But that’s just my 2 cents.
Hi Todd,
I would like to thank you for taking the time to answer my questions. I have found your remarks to very informative in what seems to be a very controversial issue. I like many others would like your advice on finishing my basement in Northern Illinois. After reading all your advice from others I have some questions regarding my project.
I want put 1″ xps on floor than 5/8″ or 3/4″ T&G OSB. Walls will be 2″ XPS all seams taped with tyvek tape including floor/wall and gaps filled with spray foam. 2″x4″ studs framed against XPS and filled with unfaced fiberglass insulation and finished with 1/2″ drywall.
1.Must the OSB be Pressure treated or AdvanTech or can I use regular T&G OSB?
2.Should the floor be installed first than the walls?
3.Does the bottom plate need to be P.T. when installed on XPS?
4.Do I need a thermal/capillary break between the bottom plate and XPS. If so Suggestions.
5.Can I install the wall first on top of a ripped length of XPS say 6″ wide then tape seams when I do the floor?
6. The side wall will need supports about every 3′ from the sill plate to the joist for the top plate. Will those supports need to be pressure treated as they will sit on the foundation wall? gasket needed under plate?
7. After filling the rim joist with 2″ XPS and sealing seams can I fill the rest of the cavity with unfaced insulation?
Thank You again for all of your time and expertise.
Mike
Mike – You’re very welcome and I hope you’ll come back often for other projects!
1. I would use AdvanTech, regular OSB would be a disaster if you ever get water, pressure treated isn’t the best option in a finished space in my opinion, chemicals!
2. Honestly I’m not sure it matters all that much. By doing the floor first you can better insulate the entire slab.
3. I would still use PT in case you get any water that might wick up. Certainly doesn’t hurt.
4. If you build the wall on top this is not necessary.
5. sure.
6. I would install blocking between the rim joist and first joist, up off the concrete, then no need.
7. yes
Good luck!
Thank you Todd,
Also for the floor XPS Do I need H.D. XPS if I will have a pool table? I am having trouble finding 1″H.D. I found 3/4″ and 2″ only. Would the 3/4″ be ok?
Thanks again,
Mike
If you use 3/4″ plywood I think regular XPS will be fine when it’s 1″ thick.
Hi again Todd,
Having trouble finding Advantech locally. Could I use dry-ply SIF 3/4 T&G? Also having second thoughts on the sub-flooring. Thinking about using DRI-core. Have you any thoughts about this product? It seems to be very strong and is only 7/8″ thick. If I use these panels do they need to be secured to the concrete? Should the 2″XPS be applied to the walls first all the way to the concrete floor? Since the walls are built on these panels will I need a P.T. floor plate? What do you feel would be the best approach? Any considerations I should take?
Thanks again for your advice,
Mike
Not familiar with DryPly but it’s probably similar to AdvanTech. DRI-Core is a great product and we’ve used it before. I wouldn’t put it on insulation. However, it will make the floor MUCH warmer. According to their site there should be no attachement:
Installation
* In your selected starting corner, lay the first panel with the groove sides against the temporary 1/4” spacers.
* Press-fit panels together with a tapping block and hammer, making sure seams are tight.
* Stagger panel seams similar to a brick wall pattern. Complete one row at a time across the room allowing for a 1/4” gap around walls and room obstructions.
* Use DRIcore leveling shims for any floor variations less than 1/4”.
No need for a PT plate with this product.
Thanks for your input,
Just to clarify I will not put insulation on floor, but Should I install the 2″ XPS on the wall first? Should the insulation set on top of the DRIcore or extend all the way to the concrete floor? Also would the floor be warmer if I use EXP vs. DRIcore?
Thanks,
Mike
Mike – If you use DRI Core I’d insulate the walls first then install the DRIcore.
XPS foam will definitely be warmer. However, DRIcore will provide a huge benefit over flooring on the concrete. DRIcore is far easier and faster.
Hi Todd,
With the advice and help from your site I have insulated my basement walls and I am preparing for the floors. I am going to use the 1″ foam and then the 3/4 Advantech ply on top. I have a question re the adhesive for the floor. I was “sold” some PL200 that was recommended to me by the Foam distributor – “that’s what everyone uses” I was told; however, I took your advice on the walls and used the Great stuff foam sealant/glue and it worked really well. There is more moisture on the floor than the walls so I want to make sure I use the correct adhesive there. What do you recommend for the floors: caulking adhesive (like PL200) or the spray foam like Great stuff?
Thanks for your help………….David
David – Either one will likely work ok. THe Great Stuff Pro Adhesive works really well but PL200 will do the trick as well.
Thanks Todd…………David
Good day Todd,
Just wanted t say great article. You techniques and building science are definitely sound, and endorsed by other contractors.
I will note that Mike Holmes (of the Canadian HGTV show Holmes on Homes, Holmes in New Orleans & Homes Inspection) did a show on the same technique for finishing a basement, and has stated this method for numerous shows of basement (and upstairs) renovations.
Mike even used a similar technique for walls on a second story addition that went wrong from a previous contractor, where he used rigid foam as exterior sheathing (with the proper bracing of the structure to take into account the lack of plywood sheathing), and spray foam onto that to really bump up the R value.
Now onto my questions:
My basement is currently finished on the outside walls and flooring. I am not happy with the current flooring colour and finish. It is currently carpet (and an out of date carpet at that). There is also no bathroom in the basement, and I will be adding a sewer pump and piping in the floor for that. My questions:
1) Does your finish with the strapping (or without), allow for ceramic or porcelain tiles to be added to the bathroom assuming I use ditra? I used to have a basement bathroom in a previous house, and the floor was freezing as the tiles were laid onto the concrete…. I want to avoid that.
2) I am considering adding the pex tubing for in floor heat throughout the basement. I want to use a hydronic system. Can I add the pex in between the strapping to add the in floor heat? What problems could I anticipate other than the obvious (leaks, etc)?
3) I really want to have a carpet free basement due to our cats. With in floor heat in between the strapping, do laminate/engineered hardwoods work with in floor heat? Can I anticipate any problems such as expansion?
4) I am not planning to remove my interior wall finish in the basement (only baseboard trim). I am planning on just bring the foam & plywood flooring 1/4 to 1/2 inch away from the drywall walls, and spray foaming the gap. Does this technique seem like a sound way of tying into existing insulated walls?
5) Would 5/8 inch plywood or OSB be an acceptable substitute for 3/4 inch plywood for the flooring assuming I placed the strapping 16 inches on centre or less?
Thanks again for all your time with the article, and I really enjoyed the answers to the questions of others you provided to others on this page.
Ryan
Ryan – Thanks for the kind words. I really enjoy sharing my experiences with folks so I’m happy you found the site.
1. If you’re going to do tile I would be sure you use 3/4″ tongue and groove plywood over the sleepers.
2. I think it’s certainly a possible solution. I would suggest going over the details of that with your heating/plumbing contractor. It really wouldn’t be much different than installing the tubes on foam board under a concrete slab.
3. Laminate and engineered floors work great with radiant heat. I have engineered floors in my home and they work great. Again it’s really important to check with your flooring folks to be sure the floor you select is rated for radiant use.
4. Yes – I would be sure to use low expansion foam. Be sure the foam doesn’t come above the sub-floor, you need expansion room for the flooring.
5. Not in my opinion for areas with tile.
You are very welcome. It’s why I write the articles.
If you’d like to help me out you can LIKE us on face book or SIGN UP for our email subscriptions.
Good luck!
Have you used a product called TYROC over the concrete floors? I am currently trying to decide whether to use DRYCORE or TYROC but have not been able to get any reviews concerning this product.
Demetri
I haven’t used it but it sure does look promising.
Hey Todd,
Great info here. This has become my best go to spot for basement info. The thing is. There is so much info and so many variations of how things can be done, I’m have a problem making a decision/understanding.
My questions are about the sub floor;
My basement floor is pretty dry and I really don’t want to do a subfloor. I’d rather do carpet padding and carpet.
Not sure that’s a good idea?
I’ve been reading some of the post about the Advantech and I like the idea mainly because its seems like this method would not cut down on my ceiling height.
Option 1. Looks like you’d use the 6 mil poly directly on the floor and then the advantech on top of that. What doesn’t make sense to me is that I’d have to make holes through the advantech and the POLY to secure it to the floor, thus created gaps in the poly.
Option 2. add foam to the step above; So it would be poly – foam – advantech
Option 3. thicker foam and advantech – no poly
Given that my basement is dry (well, as dry as basements are). How would you approach this if ceiling height and cost was a concern, but you wanted to be sure it was done right?
Let’s start with what are your goals? Do you want to insulate the floor? Do you just want to keep things dry? How much headroom do you have available?’
Depending on how you answer those then you can select a method. There are LOTS of methods including (in addition to plywood and foam).
– Use some of the sub-floor products like: DRIcore, TYROC , these will give you separation from the concrete with no insulation. However, they will make the floor warmer.
If you use poly you are correct, there will be some holes, it’s still better than no poly.
Considering you say ceiling height and cost are your biggest worries I’d use something like DRIcore. It works very well, it will make the floor feel warmer and I’ve had good results with it.
I guess it makes to insulate and keep dry. (: I have one room that has a low point at 7’7″ and everything else is ok.
Lets say that I want dryness first and comfort next
Does 6 mil poly, 3/4 foam, and plywood sound ok?
And if so, I already have my walls up so, would I seal the poly up just as it meets my pressure treated bottom plate? no gaps?
Thanks in advance for your help
Your method will work fine. Frankly it’s not the cheapest but it will give you a nice finished product. If your walls are up already i would just tuck that poly up the walls a few inches and tack it in place.
Still doing research Todd, what about delta fl? How does it match up against the dricore?
I guess I should be more specific. Delta fl with 7/8″ osb plywood.
Delta FL is a good choice also. All of those are proven products with a good history.
Todd, I was just wondering If you had to choose between dri core and barricade which would you go with? Thanks
They are two slightly different products.
1. Barricade will give you some insulation value but the system is tight to the floor.
2. DriCore will give you an air space below but no insulation value other than the air space.
So…the questions is…which is more important to your basement, insulation or an air space? Any past water issues? That really is the issue.
I will be in a new construuction home (starting later this month) so I hope there are no water issues but you never know. It was my understanding that the barricade had channels that helped drain and dry any water that gets under it also so I was leaning that way.
I think it does have some channels. DriCore has a more significant “open” space under it. I think you’ll be good with either one.
With barricade should I do the floors first and then build the walls on top of it or walls first then barricade up to the wall?
Floors first.
I know with the XPS you are supposed to fill the gaps along the perimeter with spray foam, the barricade instructions say to leave a half inch gap against the walls should I spray foam it as well? Also they say its not necessary but would you lay plastic under the barricade? If so would you tape the seams or just overlap it? Thanks
I would leave the gap open, that way if any water does get behind the XPS is will fall into that gap.
I would follow their recommendations pretty closely, if they say no poly then I’d skip it.
Todd,
Wouldn’t the air gap from the flooring then allow moisture into the space between the xps and your insulated stud wall? Would venting the Dricore to a mechanical room be sufficient to allow the condensation to evaporate? I plan to use Dricore on all the floor except the laundry/mechanical and build steel stud walls on top. Do I need some type of ventilation to draw that moisture from under the sub floor?
I think you’re making this a bit more technical than it needs to be. The idea here is to give good separation between concrete and other building materials that might be conducive to mold and mildew. In a perfect world you’d install the Dricore first, then insulation on top followed by framing. But frankly I doubt it makes much difference. I think that having the air space under the panels is sufficient to help with drying. I can’t imagine having to install ventilation under the floor.
Not trying to repeat questions here..(I did read the whole page!)
But… I think the wall should be insulated first in my situation??
I am bringing the 2″ foam down to the floor going over a french drain system along the wall. I’m thinking that doing the floor second will allow any water that may come down the back of the foam to go under the raised floor (Delta/Tyroc etc.) instead of possibly getting to the laminate?
So: insulate walls…bring flooring within a quarter inch of wall….spray foam the 1/4″ gap…stud out on top of subfloor..
Sound OK?
Alot of people are saying that TYROC is the next step in the progression of subfloor panels. If there is a pipe leak ABOVE your subfloor it won’t get ruined unlike the OSB on a Dri-Core panel
I’m leaning towards it.
Thanks again for all your help!!
Roger – Your detail should work fine. I’d bring the flooring up tight to the foam. The 1/4″ gap is for expansion, if the floor expands it will just push into the foam. I wouldn’t bother trying to foam that gap either.
Best of luck!
Todd, One more question!! (yeah right)
Seriously, I am at my wits end dealing with my basement floor.
I need to remove the paint in order to bond the leveler properly.
I have rented a dual disc grinder with the proper tips but this didn’t work too well. The stripper I tried didn’t work either.
I may try a shot blaster too.
I wanted to pass an idea by you…kind of a variation on the sleeper method to save some head room.
What do you think of putting composite decking 5/4 directly on the floor with the Advantech on top? I could use composite shims to level where needed under the 5/4. I would keep the 5/4 12″ on center for added strength.
This would save me the $$ on the shot blaster, leveling and a subfloor product. And would offset the cost of the composite material.
I would then install laminate on top of the Advantech.
Do you see any problems with a vapor barrier/mold? Should I be putting any plastic down? I think my floor would be similar in principle to the square tile subfloor products. Any potential leakage would still get to the drain and there would be an air gap too.
Thank you for taking the time to advise on this. If you agree that I am on the right track you will have succeeded in removing a HUGE road block in my project!!!! THAKNK YOU!!!
I have done numerous how to posts on car related items. I also did a detailed post with pictures when I took out my basement center lally column and installed some big MC-Channels. I like to help out on the things I know, and I REALLY appreciate your time and guidance.
Roger – Your approach should work pretty well. I guess my only question would be whether you plan on putting any substantial loading on that floor like a pool table. In that situation I wouldn’t recommend it as “decking” isn’t really structural.
I would lay a sheet of poly down first, even though you’ll be drilling or shooting fasteners through it into the concrete. Other than that it should work very well.
Good luck.
Glad I could help.
Definitely putting the pool table down there! (It’s in pcs. in a spare bedroom from the last house.)
I thought the Trex would be strong enough? At least as strong as the OSB on the Dri-Core? I don’t know really…….
It may very well be. There are “purist” that would cringe and “wig” out over this issue. Frankly I’d do it in my own home…but not a customers…make sense?
Got it…Thanks!
I’m looking to insulate the entire floor in my basement. This is a new basement with no walls, etc. I plan on using 2″ XPS on the walls and then insulate the floor the way you described. My question is will I be able to build all my walls directly on top of the insulated floor? I’m alittle worried that over time the foam under the stud walls will slowly collapse. Would you recomend using the sleepers or just placing the 3/4″ directly on top of the XPS? Thanks for the help.
Regardless of the approach you choose, XPS has a fairly high compressive strength. So long as you don’t build LOAD BEARING walls on top of it you’ll be fine. Some folks choose the sleepers because they want to ensure that the plywood is attached to something else vs trying to attach it directly to the concrete. Both methods will work fine.
Do you have any articles or videos on building a load bearing wall in the basement? Currently we have load bearing beams ran down the center of the house with temporary jacks supporting it. We plan on building a wall which will have 3 bedroom doors throughout the entire distance. I understand you have to have load bearing headers above the doors but is the rest of the framing normal? Also would you use 2×4’s or 2×6’s for this wall? Thanks again for the help.
Lots of your question is best answered by your local building official. However, in general here are the basics.
Today most people frame load bearing walls with a minimum of 2×6 lumber. Depending on the size doors you can likely get away with dimensional lumber door headers. Having said that, if you go to your local lumber yard (one that has an engineering department or specification group) they can generally design the header and tell you what size options are available. For example, they might tell you for a 30″ wide door opening that a triple 2×10 header will work. If you have a wider door they may specify an engineered lumber header.
The other issue at play is the foundation. Bearing walls work great in a basement, however, they typically need a thickened slab/footer in order to transfer the bigger loads. A traditional slab is typically not strong enough alone to take bearing wall loads.
Thanks for all the great information. In regards to the concrete supporting the load bearing wall how do I determine this? The house is a single level modular home with a walkout basement. It was built in 2001. We purchased this on foreclosure and have no information on the concrete psi strength.
Well you would need to know if there is a “Strip Footing” down the center (assuming this is where your wall is going). Sometimes a contractor will pour a strip footing the entire length of the house instead of trying to form up a footing pad at each column. The strength of the concrete isn’t really the issue, it’s the thickness and depth of footing.
I would recommend going to your local building code office, and seeing if foundation plans were filed when the building permit was issued. Most states, cities and towns do require this information to pull a permit. If you can find those drawings they will shed a ton of light on the situation.
Why are you switching to a load bearing wall? Are you going to remove the beam that is supported by the columns?
If you’re only framing a wall between columns (and the columns are staying) then it’s not really a load bearing wall.
The basement is completely unfinished. All they have supporting the beam is them steel temporary jacks. There are no columns at all. The concrete floor shows no sign of them installing any columns either. The load bearing beam is down the center of the basement. Is it common practice to build that “strip footing” in under the concrete floor?
It’s not that common, sometimes we do it to simplify the foundation. Without the plans there’s no way to tell.
Hi Todd,
First of all, your site is fantastic. I have learned more from here and building science than anywhere else – the comments helps too. Unfortunately I haven’t found an answer to my problem.
I have a 50yr old ranch house 30′(ease&west)x40′(north&south)full cinder block walled basement and the whole slab slopes towards the middle of the north wall where a sump pit used to be and is covered in 12×12 vinyl tile. Variation of 2 3/4″ over ~25ft. I had an interior french drain installed on the south and east walls where water was coming in, on the N&W walls I have a carport and patio and there is no sign of moisture on the blocks after 50 yrs, and the old sump pit filled in. The slab is in great shape, no cracks or major high or low spots. My questions are:
1. Can my floor be insulated using sleepers to level it, or should I use self-leveling compound? If I use the compound, is 2 3/4″ too thick? Does it even need to be leveled?
2. Do I have to rip up the old tile to level or insulate?
3. My ceiling at the highest spot in the floor is only 86 1/4″, not counting a 2-3″ drop ceiling due to existing plumbing. Can I get away with 3/4″ foam and 19/32″ adavntech, or will that not be stiff enough?
4. Would it be easier just to get the slab torn out and a new one installed? Much more costly?
I have pictures if need be…
Thanks again for all your knowledge and assitance!
Mike – It’s my pleasure and I’m sure glad you find the site so useful.
1. The first question is, does it feel as though the floor is unlevel or do you only know it based on measurements? The key here is comfort and how furnishings will sit, dressers sitting so they look level, etc.
If you need to level it there are many options. However, most self-leveling products typically are 1″ or less. There are some commercially available ones that can do thicker but they are usually installed by specialty contractors.
For your situation, if you decide to level it I’d use sleepers. Instead of cutting tapered ones I’d run them perpendicular to the slope and cut each row a different thickness. This poses a problem with the foam however, as each layer would be a different thickness and that might be fairly impractical.
2. For leveling yes, for insulating no. Depending on the age of the tile there is a very good chance it contains asbestos. If you can leave it that would be a good thing!
3. Both would work fine. Obviously the more foam the better R value. If you go with a thin layer I’d probably recommend a vapor barrier first as the foam won’t act as one at that thickness.
4. That will cost you big money!
Thanks again for visiting the site. I’m working very hard to get more exposure for the site. If you found the site useful I’d love to have you help me out by either LIKE’ing our Facebook Page or signing up for our Newsletter. Thanks!!
Todd,
If I had a facebook I’d like it! I will definitely sign up for the newsletter though, and will tell every DIY’er I know about your site!
The floor really doesn’t feel that uneven, you can see it if you really look across the floor, but everyday use doesn’t reveal it. Some furniture noticeably rocks (1/4″ maybe) and has to be shimmed or adjusted, but over all it doesn’t feel uneven. Its only really noticable near the old sump pit where there is a more exaggerated slope. Would it work to lay the foam down and cut some pieces to fill in the dip near the sump pit, or spray foam the dip maybe? Or should I just foam right against the concrete and level that part with sleepers on top?
Knowing that I can at the very least begin insulating my floor is a relief! It’s been 3 months and two floodings without a playroom or an office! The drain I had installed was very similar to the one you linked to in the Homeowner’s Blog and has been really effective through the May storms we had in South Central PA.
Thanks again!
I would just shim the area near the old sump pit. In fact, if that sump pit is not longer used, I’d fill it in first and then level the floor above it as best you can before you install the foam. This way you help prevent water from coming up from below.
Good luck and keep us posted!
Todd,
Awsome site thanks! I have looked and asked and you have given more information on this one page than I have found anywhere.
I am starting the design process and hoping you could help with a few questions. First the basics two year old home, no moisture issues in basement as yet; 9 ft poured concrete walls with fiberglass insulation in rim joists; builder installed fiberglass on walls to below grade; home in southern Ohio.
1. Can I leave fiberglass in rim joists as is, should I add XPS foam over, or should I remove then replace with XPS foam? (I plan to install a drop ceiling if this matters)
2. I have a large area (600 square ft)that I plan to leave unfinished with storage and utilities and do not plan to insulate walls or floor (will leave builder installed insulation in this area on walls). If I insulate floor in proposed finished area how do I handle the floor transition at the door opening? Also, how do you deal with the raise in floor height at bottom step (doesn’t code require the same height rise on all steps?).
3. It seems like installing the XPS on the walls first (and across top of wall taping/foam all seams) then installing XPS on the floor (taping all seams and tape/foam at the wall junction) followed by T&G subfloor (4-6 tapcom per sheet) with 1/4″-1/2″ gap around wall perimeter for expansion would do the best at sealing the entire basement wall and floor (concrete) from the finished interior. Am I wrong in this method? Critcisms…
4. What is the best way to deal with the 9′ walls to minimize wasted material? I planned to lay on side longways like sheetrock then cut sheets to fit at top. Suggestions?
5. The breaker box is mounted on the wall in the proposed finished area, how do I best insulated around/behind without removing the box or creating moisture issues behind? Is this even possible without removing?
6. With the unfinished utility/storage area I planned to simply put up a partition wall with at 36″ door for access. I was going to sheetrock both sides and install kraft faced fiberglass insulation (kraft facing warm side). Is this sufficient?
Thanks in advance for any advice you can give.
Todd – Glad you found the site useful. Below are some comments/responses to your questions.
1. I really don’t like fiberglass in the rim joist area. I’ve seen far too much of it with mold because it’s nearly impossible to install a good vapor barrier. If it were my house I’d remove it and install XPS or Foil Faced PolyIso in the rim joist area.
2. The builder installed fiberglass on the concrete walls really bothers me. Is the fiberglass in direct contact with concrete? If so that’s really bad!
The floor height issue is one that ultimately leaves many people opting out of insulating their basement floor. However, there are some ways you can deal with the issue that are not overly disruptive.
– For the utility space I myself would just leave a small step into the space. The problem however is a code issue. If you go to sell the house that small 2″ step can be considered a code violation by many. Minimum step height is typically around 6″. You could also create a ramped transition if it really bothers you.
– The stairs are a bigger issue. The code requires that stair heights match within a certain tolerance. So around here we try to have stairs be 7″ rise with a maximum deviation of 1/2″ from stair to stair. So basically you’re left with a couple options. You could rebuild the stairs (OUCH!) based on the new finished basement slab elevation. Or you leave an area at the base of the stairs un-insulated, probably tile it, then have a step up into the finished space with the insulated floor. This still leaves you with the issues I mentioned above for the utility space. Again you could try ramping it.
3. That will work fine. Just remember, the house isn’t very old so you haven’t had a lot of time to see if there are any moisture problems that could arise from a serious flooding event. By doing all this work you do run a slight risk of “hiding future water problems”.
4. We’ve found that installing the sheets vertically is MUCH easier than horizontally. We used to do them horizontally but hey have a tendency to ‘fall’ before the adhesive dries. When you do them vertically they stand up better during the drying process. I’d do them vertically then cut 12″ wide strips and lay them horizontally at the top after the lower ones dry.
5. The best approach is to loosen the box and slip foam behind it. If you can’t do that then I’d insulate up to the sides of it.
6. That will work fine.
Good luck!
Thank you for the quick response. If I might follow up:
2. The insulation is in direct contact with the concrete. It appears to be CertainTeed fibergalass with perforated white polypropylene backing. Here is a link to their site:
http://www.certainteed.com/resources/30211339.pdf
Should this be removed?
3. The house hase a black rubberized sealant on the outside of the foundation walls. We have had record rainfall for the last couple of months and overall for the year and not a drop (knock wood) in the basement. Is there a rule of thumb as to how old the house should be to see the reaction to “serious flooding events”?
Will the hidden future water problems be related to both floor and wall insuation or just one?
If I do not insulate the floor I seem to avoid the transition issues. Can I still do the 6 mil poly and Advan Tech (per mfgs. recomendations) or should I go with something like dricore to help create a “warmer” floor (or can I just do poly and a laminate flooring over top per flooring mfg recomendations)?
If I might be so bold, If this were your house, how would you proceed?
Your expertise and advice is truly invaluable and much appreciated. Thank you.
I’m not going to pass judgment on that product from CertainTeed. I can say that many of the ‘blanket’ insulation products have worked ok and some have not. If it were my place I’d at least cut a small hole and inspect it.
No real rule of thumb, I just try to point out to folks that while two, three or even four years might seem like a long time it’s nothing in the life of a home. The lot will tell you more about your likelihood of having water than anything else.
I really like the dricore system for laminate floors.
For my homes….I’ve always gone with tile. Our new home has radiant heat which means we’ll definitely tile it at some point. The reality is tile will be very forgiving if we ever get water. While not warm it’s surely the safest.
Good luck.
Todd,
Lots of good information on your website, finding it very useful. In an effort to save headroom in my basement, I would like to install pt 2×4 (ripped to 1″ height) sleepers directly on the concrete 16″ O.C, put 1″ rigid foam in between the sleepers, and 3/4″ T&G on top.
I plan on installing a mix of carpet and tiles on top of the plywood, so I would like to have the increased strength from the plywood and sleepers being directly attached to the concrete mainly for the tiles, but need to save as much height as possible. Does this seem like a reasonable option?
I am concerned if I just went with 1″ rigid foam across the entire floor, with the 3/4 plywood, and no sleepers that the structure would not be strong enough to put tiles on top. Thoughts?
Thanks
I think your approach is a good solution. I would use something like Ditra for the tile underlayment.
Todd, great info. Lots of jobs being completed correctly because of your help.
First off, I live in Minnesota, where it has been hot and humid recently.
I have a question, and could really use your advice — I insulated my basement with 2″ XPS, sealed the joints with Great Stuff, and sprayed 2lb closed cell foam in the rim joists. As a test, a year after installing, I removed a small sample of XPS. Wet. Condensation. Moisture is on the XPS, not on the concrete block.
I cut out a bunch more samples. There is no moisture down near the floor, gradually more all the way up to the 2lb spray foam, which is right at ground level. No moisture behind the spray foam. South side of the house has the most moisture but there is a small amount on the north side.
I am sure the ground is moist, but I resloped my landscaping before putting up the foam board, and my house is near the top of a hill… I also put two coats of Drylok on the wall. So the problem is not standing water driving in.
Humidifier is set to 45% and has not been running all that heavily. Basement smells and feels dry.
Thoughts? I am tempted to tear everything out and ventilate the wall instead of insulating it… not fun. I am also tempted to believe the wall is sealed up enough to not cause any health problem if mold were to start growing, but that would be me being stubborn-stupid.
Would be happy to send pictures if you are interested.
Thank you very much,
Mark
Mark – The moisture is located between the foam and concrete correct? That’s exactly what I’d expect to find and that’s exactly why I tell people they need 1-1/2″ or more of XPS. The XPS acts as a vapor barrier and keeps that moisture from entering the framing. Am I correct about the location?
Wow, you are quick!
Yes, moisture is between the foam board and cinder block. Just hanging out, having a good time, not going anywhere. You say this is expected, i.e. not a problem?? Due to hot humid outside air and the coolness of the cinder block?
Thanks!
Yes…it’s exactly what I’d expect to happen. The concrete blocks are full of moisture, all the time (inside the micropoors of the concrete), that moisture can condensate and get trapped between the concrete and foam. The good news is it’s not getting past the foam. Foam and concrete are not food sources for mold so mold will not grow back there.
So basically what I’m telling you is there’s not problem. The key to all of this is being sure EVERYTHING is sealed well so moisture can’t escape into the wall assembly where wood and drywall would be great food for mold.
Awesome. I agree there are no problems yet at least, especially since the block is still pearl white.
Do you have any recommendations for air quality monitoring? All I find is bad reviews. Ideally I could give myself some peace of mind by checking the air periodically to confirm it is within safe limits.
Even more ideal would be constantly checking levels like a carbon monoxide detector … need Einstein to climb out of the grave and invent that.
I wouldn’t worry much about it. Without a food source mold will not grow. Focus on controlling humidity and air exchanges. All will be ok.
I am close to starting construction. The walkout basement will use your scheme for insulating the ground floor (2″ XPS) and walls (1″ XPS and 3.5″ fiberglass cavity). But from reading all the stuff on here, I am unclear about expansion/contraction issues.
1. If the XPS is glued to the slab and the sleepers are nailed to it, since this is new construction, they would be attached to a very “young” slab. Could contraction cause a problem with such an arrangement?
2. The floor will be put down first, then the walls. For the non-weight bearing interior walls, they will be built above the insulation. The question is what should they be built on top of: the XPS, the sleepers, or the advantech?
1. I’m not concerned about the shrinkage in the slab (it’s microscopic). I would let that slab cure as long as you can before installing the floor. Just to get as much moisture out before you lock it in.
2. Put the non-load bearing walls on top of the AdvanTech.
My contracter, architect, and structural engineer all recommended against attaching the sleepers to the concrete and to instead glue them to the insulation (and the insulation will be glued to the concrete). My layman’s instinct is there is not much to cause movement anyway, so any attachment scheme will work fine. But if movement is a concern, can any adhesive be trusted long-term? If glueing sleepers is a bad idea, is that just your opinion or is there some documentation I can refer my builder to (because unless he changes his recomendation, I will go with what he recommends).
Don’t you love all the opinions you get? :) I’m a licensed structural engineer as well and I really don’t see an issue with it. The reality is I’m skeptical of most adhesives. If you really want to go that route I’d try to find a really good urethane foam adhesive as urethane adhesives work very well.
Todd,
Thanks for the page – it is a great resource. I am considering using another product due to the low ceiling height: Roberts Harmony 3-in-1
http://www.robertsconsolidated.com/files/support/PDS_70-100-12_12_1.pdf
Have you had any experience with this product or any initial thoughts on it?
Thanks,
Mike
I’ve never used it. From a quick inspection of their posted specifications it probably will work fine as a vapor barrier but it only provides 0.39 R value or essentially no insulation value.
Good luck.
Hi Todd,
I commented a few months back about leveling my basement floor. I’m going to start that project this weekend. I want to insulate and use Advantech, but here are the obstacles and my options as I see it:
1. The main beam running under my floor joists in the center of the basement is low. I would have to use 6mil poly, 3/4″ XPS and 7/16 OSB in order to meet ceiling height code for obstructions, which is 6’4″ (19/32 is 3/16″ too high, not counting a finished floor). Is that an acceptable subfloor? Will it be rigid enough for sheet vinyl?
2. If that won’t work for a subfloor, I could go with DriCore, but how well does that product tolerate height variation? I’m going to be filling in a low spot where an old sump pit was with some quikrete and top it with self leveling underlayment, but the whole slab is sloped from all sides towards the old pit. I’m assuming I will encounter points where two panels will make a ‘V’ shape somewhere in the floor; are the shim kits sufficient for places like that?
I’m attempting to finish 960sqft, so I don’t want to start something only to find out I have to go a different route after having invested $2k in the first.
Thanks!
Mike
In a perfect world I’d jack up both sides of the floor joists and install a new flush beam with joist hangers. That’s obviously a big job (wiring, plumbing, heating, etc could be in the way) but i would clearly eliminate the head room issues.
In your situation you might want to consider not insulating the floor or possibly installing an electric radiant heat system covered with a thin layer of flowable fill.
The 3/4″ foam will provide some comfort (very little vapor barrier) however trying to attach 7/16″ sheathing over it will be hard to do. Finding a fastener that will grab enough to suck it tight yet not pull through the 7/16″ will be hard.
The DriCore probably won’t work that well either unless you can level the roof well.
Sorry I don’t have any better solution to offer.
Thanks for the info. I think I’ll look into the flush beam, i have a 30’x40′ ranch and it seems as though that would be pretty straight forward. Do you know approx what I can expect to pay for something like that? I did a little research, and it doesn’t seem DIY friendly…
If I didn’t insulate, how would I do the floor? I have old vinyl tile all over it now and would prefer to just cover it up… which was my goal with the insulation and OSB. Could I just lay the poly and 23/32 t&g advantech?
Better is a relative term… replacing the beam may in the end be a ‘better’ option.
Thanks again!
You certainly can install a layer of plywood over the old tile. If you do that I’d recommend using an exterior grade plywood or OSB.
Cost for something like that will vary greatly. The first questions is how many electrical, plumbing and heating interferences are there? Those might be very expensive to re-route. If there are none or very few then the carpentry side of things is somewhat straight forward for a good crew.
Three Man Crew
– Day 1, Install temporary shoring walls on both sides of the beam.
– Day 2 cut old joists.
– Day 3 install new header beam and hangers.
– Day 4 clean up, remove shoring
Looking at probably $4K to $6K for that without electrical or plumbing type work.
If there wasn’t the potential for things to go horribly wrong, I’d do it with a couple of friends. My main drain line is running over the beam along with the line from my condenser unit… I can redo the electrical, but it sounds like its going to get expensive.
Even though the ceiling is going to be low, I think I’ll just put plastic and advantech down, it’ll still be within code. I have some low spots I’m going to try and fill in, but since I’m not using 3/4″ xps, should I use a thicker osb? Would 1″ make that much of a difference in sturdiness from 23/32″?
I’d use 5/8″.
Todd,
Your site is just awesome! Thank you so much for sharing all your knowledge and being so generous with your time.
I’m about to redo the lower level of my bi-level (living space is on slab and one wall is earth bound). No interior drain or sump. I intend to follow your recommendations for wall construction but am stuck on choosing the best flooring option.
I have a very low ceiling; 7′-2′ from ceiling to slab (and 6′-7″ where the main HVAC trunk line runs thru). I just tore out carpeting where water seeped in at the base of the foundation wall. Have had occasional mustiness in the past but this is the first time there has ever been water in 12 years. (I live in NJ where hurricanes are rare but after weeks of rain followed by “Irene” dumping 11″ more — we had the highest water table ever recorded. Most of my neighbors also had water for the first time ever.
So, aside from the question of investigating exterior drainage issues, I’m torn between I should allow airflow or, preferably, maximizing insulation. What is your opinion of one of these methods over the other…
1) Dricore, 1/8″ vinyl (1″ overall) VS
2) poly, either 1/2″ or 3/4″ XPS, 5/8″ Advantech, 1/8″ vinyl (1’1/4″ – 1-1/2″ overall)
Also, there is old vinyl flooring which is (mostly) intact. Should I leave it or have tested and try to remove.
I know you can’t predict the weather but this much water does seem to be a decades phenomenon. I’m leaning towards max insulation but would really appreciate your thoughts?
When you say you have such low ceiling heights I’d be tempted to just tile it over something like Schluter Mat http://www.homeconstructionimprovement.com/schluter-ditra-tile-underlayment/
This way you have a flooring that won’t be affected by water and the Schluter will likely insulate it a tad.
Otherwise I’d go with option #1 above.
Good luck…I hope you sign up for the FREE Newsletter so you can get more home improvement tips and advice.
Todd,
Let me start by saying I’m part way through my refinishing project and am very happy with the insulating results so far. I have insulated the floors, walls and rim joists with XPS foam. Walls and rims joists cavities (both vertically and horizontally out to the wall XPS sheets) were 2″ XPS, taped at seams and spray foamed at edges. On the floors, I used 1″ high compression XPS with 3/4″ Dryply over the top, tapcon’ed to the concrete floor. I’m not adding any heat to the basement yet but my family has already noticed the basement is warmer. Thanks for the great advice, it’s working!
My question is a followup one about the subfloor. I didn’t level the concrete before putting down the subfloor. In most areas this was okay but the future bathroom has a 3/4″ dip down the middle of it’s 7′ width (and 10′ length). It is noticable and I’d like to fix it. I’m considering two options to avoid tearing out the entire bath floor and using concrete leveler:
1) Back out the tapcons, pull the 3/4″ plywood only, rip shims at various thicknesses to put between the 1″ XPS and the 3/4 plywood and then re-tapcon into the concrete from the plywood.
pros: flat floor for tiling; possible cons: concentrated pressure on the XPS.
2) Tile the bath room floor as is, building up the level in the center with cementboard in the center and feathering to the sides with mortar before laying Ditra over top for the tiles. Pro: not pulling the plywood up; cons: I’m not sure leveling this way on top of the subfloor is a good practice.
I’d appreciate your thoughts & suggestions.
Dave
Ideally I’d do the following:
1. Pull the plywood and foam in the bathroom.
2. Use flowable fill to level the bathroom floor.
3. Re-install foam and plywood.
Thanks for all the good info.
I have a basement which was finished by previous owners. They did 2×4 directly on the cement. Then did batt insulation and vapor barrier and then drywall. Now about half of the wall has mould growing and the drywall is very soft for about 2 feet from the floor.
We have noticed that the dryway was grading into the house in this section. The dryway was redone and the grading was fixed. I’m going to remove this section and then rebuild with 2inch on the floor and wall but I’m thinking if I get weeping tile issue since its a 60 year old will the 2inch Foam on the floor be a good idea or would something like drycore be a better idea to channel the extra moisture.
I’d go with the Dricore based on the previous history with water. Good luck.
I have a bathroom i am putting in my garage and used 2×12 treated joist. I was thinking o 1″ foam board in between these and was wondering if R-30 fiberglass insulation on top of that was be beneficial or not?
Thanks
I would prefer to see you use 1-1/2″ or 2″ high density foam followed by a 2×10. If you want extra vapor protection you could put down 6 mil polly ahead of the foam. Good luck.
Hi Todd,
First off your site is great and very helpful. I have used information off of it to work on my house. Thank you for your time and effort on it. I am going to be working on the flooring in my basement. I have a few questions. Before that just some quick info on my basement. The floor was at one time covered in tile( probably asbestos as it is an old house)it was removed years ago. They left behind the black adhesive/mastic which may also contain asbestos. That was painted over by previous owner with an epoxy paint. The paint in areas is flaking not doubt to poor bonding with the remaining adhesive. Also my wife wants the walls to stay unfinished. They are cinder block, painted over with waterproofing paint. So my questions are as follows:
1. Do I have to remove epoxy/adhesive or can I go over it with rigid foam?
2. What do I do at edges? Leave a gap? Can I put trim over it to make it look nice?
3. When I use tapcons should I put a dab of adhesive on them before sinking them so seal hole they make in foam? I would not be using sleepers due to height issues.
4. Lastly, my floor slopes to middle of basement where there is a dividing wall. Do I have to level it or can I go with the slope as it is flat without ridges etc?
Thank you so much for this site and your time.
Adam – My pleasure….glad you like the site. I hope you’ve signed up for my FREE Weekly Newsletter that offers lots of great tips for your home.
First a question: What are you going to cover the foam board with?
Covering the old adhesive is fine and far cheaper than getting it removed.
Leave 1/8″ gap at most.
You can if you like, not super critical in my opinion.
Following the slope is also fine so long as you don’t mind the slope.
Good luck!
Hi Todd,
Just wanted to add one more question…we run a dehumidifier year round in the basement and seem to have no resulting moisture issues. Before we started using it the side of the basement with the floor issue would “weep” during certain weather. Does this mean I’d be better off using a Delta FL or Platon plastic sheeting rather than rigid foam?
I think either will work fine. They both have pro’s and con’s. The foam has more insulation value but not as easy to install, the Delta/Platon are easy to install, less insulation value.
Hi Todd, great site.
I plan to Insulate the floor as you suggested although without the sleepers.
In ripping out the current floor I discovered that the previous owners covered up the drain. What it the best way to deal with the drain in order to maintain the vapor block throughout the floor.
Thanks in advance!
If you have no use for the drain (dry basement) then I’d tape over it to seal it. Do NOT try and plug it off as you may need it someday. I’d make a note for yourself with the location in case you need access to it in the future.
Just wondering if it’s recommended to do the floor before the walls in foam board… I’m hoping to do the walls first as our government (canada) provides grants for insulating basement walls and then I was going to do the floor in the futures…
Thanks again.. your information is invaluable.
It really doesn’t matter.
I’m looking to frame walls in my basement but also put down rigid foam. Should I frame first then fill the left over concrete floor with the rigid foam. Also, I’m hoping to use bluwood (http://bluwood.com/) . if I use this material do I need to put anything between the wood and the concrete floor when framing?
Thank you
I’m not familiar with bluwood. However, a quick scan of their site seems as though they don’t warranty for direct contact with earth which is pretty similar to direct contact with concrete in my experience. So I’d probably recommend a vapor barrier to start with.
It doesn’t really matter much which you frame first, if you do the wall first you might need blocking in the wall after the floor goes in to help with base trim.
So if I were to install the frame directly against the concrete I should first put a vapour barrier in between the concrete and the frame?
No….you need to read my articles on insulating walls.
http://www.homeconstructionimprovement.com/how-to-insulate-basement-walls/
Todd-
Fantastic website!
Quick question: I have about 1/2″ to 3/4″ inches max of space to put in a floor due to the ceiling height requirements in my basement. I have a perimeter french drain and two sump pumps so I have no water problems on the floor of any sort. Its dry and currently painted. Would putting a thick carpet pad on the concrete and then covering it with carpet be OK? Will the conditioned air from the basement eventaully cause condensation problems with the cold basement floor (maybe lead to mold on the carpet from below?)
Any ideas on how to solve this? Some options I thought of:
1. layer of mil plastic (sealed and taped), then some 1/2 foam(taped at the seams), a thin carpet pad, and then the carpet? This may put me right at 3/4″ or over.
2. layer of mil plastic (sealed and taped), thick carpet pad, then carpet. This would keep me under 3/4″.
My primary concern is wetness and mold issues on the carpet.
Which approach would you go with?
Thanks!
Nico – Thanks for the compliment. I hope you’ll consider signing up for our FREE Weekly Newsletter.
Frankly I’d just go with carpet/pad that’s made for slab on grade construction. Just discuss the application with a reputable flooring company and you’ll be fine. It’s done all the time.
Hi Todd,
I’ve been looking for Foamular 250 1″ for my subfloor – however, I’ve struck out everywhere – only finding 2″.
I have seen Dow Super Tuff-R 1″ at HD and was wondering your thoughts on using this – as good / any issues or downsides? It has an aluminum foil on one face, not sure if this would cause problem and if OK, would I put the foil side ‘up’ or against the concrete? I’ll be putting 3/4″ Advantech T&G on top.
Thanks for the advice – love the site!
You definitely don’t want the foil against the concrete. It will oxidize and corrode. I guess I’d put down some poly, then the Tuff-R. It should work fine. Regular 1″ blue board or pink would also work fine.
Glad you’ve found the site useful. I hope you’ll consider signing up for our FREE Weekly Newsletter.
Ok, thanks Todd. I’ve found Pactiv 1″ at Lowes in this area – a brand I wasn’t aware of before in my searches. Seems to have 25psi rating – I think I found the way to go unless you’ve seen anything negative on the Pactiv(?)
Happy Holidays!
I’ve never heard of it before, is it a closed cell XPS foam?
Hi Todd,
Seems to be a closed cell XPS – also goes by Green Guard.
http://greenguard.pactiv.com/residential.aspx#xps-insulation-board.xps-insulation-board
w/ Regards,
That will work just fine. Good luck!
Hi Todd,
Quick question – when it is mentioned to ‘seal’ the seams on the xps panels, is this simply the Tyvek tape on the xps seams or do you recommend caulking in between the sheets of foamboard prior to taping?
Thank you for all the great info!
Tony
The tape works fine.
Todd,
Your site is the best. Congratulations to you for making it a fantastic resource and actually caring to answer people’s questions. That’s rare on the web.
I live in Ontario Canada – cold winters and humid summers.
Basement is concrete block walls and poured concrete slab. I have completely gutted it due to a sump pump failure/flood. I’m following your advice for the walls (1.5″ Dow Styrospan SM sealed with Tyvek, bluwood framing and Roxul batt in the framing). Half the basement is a poured concrete crawlspace 4ft high. I will leave the concrete floor untouched there as it is where the sump pump is. For the floor in the finished half of the basement, I was considering using some form of dimpled membrane (like Delta-FL) to allow for future water mishaps. On top I was considering FiberRock (http://www.usg.com/fiberock-aqua-tough-underlayment-panels.html) which is a fiberglass underlayment (I used it in my tub surround in the bathroom). On top of the fiberrock, I would lay cheap laminate that can be replaced if it gets damaged due to water. I am trying to avoid any wood on the floor as I know that water mishaps are inevitable in the basement (hot water tank, washer, sink, watermain) – so i’m not as concerned with the moisture in the concrete. I figure the Delta-FL will allow for small water mishaps to drain underneath towards the sump pump hole, and the fiberrock would survive a major mishap (3-4″ of water). I would only have to dry it and put down new laminate. That way, i can have water mishaps and not have to gut the place and start over like I am doing now. Fiberrock is much more expensive, but I figure, i’ll never have to replace it.
I appreciate your time, thanks.
Norm – Thanks for your kind words. I hope you’ll consider signing up for our FREE Weekly Newsletter, it’s full of tips, advice, product reviews and much more.
Your approach sounds good but I think there is one problem. I haven’t used FIberock but I did check out their specifications and this is considered an underlayment. Underlayments typically imply that there is some sort of sub-floor below them. In fact their spec’s say you need a sub-floor capable of meeting a L/360 Deflection limit. So the questions is, will Delta FL do that? I’m really not sure. Maybe a product like AdvanTech or something like that. It’s not meant to be wet all the time, but it does amazing in short periods like during rain when a house is being built.
Good luck.
Thanks for the suggestion Todd. I looked up AdvanTech and sounds like a very viable solution. Now to see if I can get in Canada. Hopefully Lowes or Home Depot carry it.
Thanks again,
Norm
There is at least one other similar product on that market…think it’s a GP product. Basically you want a sheathing product that is made to get wet during construction. This would be better than having a bunch of pressure treated wood under that floor in my opinion.
Hi Todd, Great site! Thanks for all the info.
I have a question about insulating my basement floor. The only 1 inch XPS insulation that I can find readily available at the big box stores is 15 psi. Is that strong enough or can I get away with 3/4″ XPS that is rated at 25psi?
I guess even if the 15psi is enough I’m still curious if I can get away with 3/4″ XPS to save that ever precious head room.
Thanks,
Troy
Troy – The thickness of foam on the floor isn’t anywhere as critical as walls. I’d recommend a 6 mil poly vapor barrier, then the foam. So sure, 3/4″ will work, less R value but still way better than no insulation. Best of luck. Please consider signing up for our FREE Weekly Newsletter.
Todd,
Great sites, useful information, have used many techniques that I have read on your different sites. Going to be finishing basement and had questions about insulating the concrete floor.
Just so i understand your method for the insulated sub floor, its 1″ Styrofoam, then 3/4″ treated decking sleepers, then 3/4″ advantech (or other sub-floor material), then finished flooring, is that correct?
A few questions i have
1. Can XPS be used in stead of Styrofoam?
2. How far apart should the sleepers be spaced?
3. What is the point of the sleepers, wouldn’t they cause more compression in the Styrofoam, since the load is not distributed over the whole foam panel, its only being distributed by the width of the treated decking sleepers?
4. Due to ceiling heights, can we remove the sleepers, and put advantech directly on the Styrofoam?
5. If we use 1/2″ foam for low ceilings, we place 6 mil vapor barrier first, then foam, then subfloor, do we still need to glue the foam to the vapor barrier, or everything will be held down when we attach the subfloor to the concrete?
6. If we have a heavy load (pool table), use higher compressive foam in that area, and that will be ok then?
Thanks in advance
Steve
Steve – Thanks for stopping by.
1. That intent is actually to use XPS.
2. Typically 12″ or 16″ on center.
3. Sometimes it’s easier to fasten the sleeper, then lay the plywood and fasten to the sleeper. Vs trying to get the plywood to lay flat by Tapcon’ing it.
4. Yes
5. Glue is not necessary.
6. Yes.
Todd,
Thank you so much for your website. I have just finished my 2″ XPS on my walls and sealed the rim joists. I am heading to the lumber yard later today to pick up my wood for framming. I am looking ahead and I’m thinking about putting a laminate hardwood down. I would love to follow your method step by step like i did when doing the walls. However I am worried about ceiling height. Would I be able to put 1″ XPS glued down with the foam adhesive, and then lay my flooring right on top of this. The laminate wood is a snap together type which does not need to be glued or nailed to a floor. Again thank you so much for your great website. Mike S
Mike – You can try but the results can be less than desirable depending on how flat your floor is. The foam is plenty strong, it’s just a matter of how well it “sits” down.
Todd,
I would like to insulate my basement floor, but have some cracks I would like to repair first. Do you have or know of any good articles on how to repair cracks in basement concrete floor slabs? Are there particular products you prefer over another, like epoxy, flex foam urethane, etc.?
Thanks,
Steve
Steve – I like to use products from Sika. I would recommend a urethane crack sealer as it will adhere the best.
Todd,
I found two products, seem like they are the same, but one I can only find on amazon, where the other is found at home depot, so it seems and looks as if they are different products.
Sika Corporation 10 Oz Concrete Crack Repair C4CR520 (amazon)
Sikaflex 10.1 fl. oz. Concrete Fix (model # 187783, HD)
They are both polyurethane based products. Would either of these products do?
Thanks,
Steve
Either will work. I’m more familiar with the Sikaflex, it’s a good product.
Todd
I apologize if these questions have been asked/answered already but the thread is long!!
1) Insulating basement floor – planning 1″ xps with 7/16th OSB. I want to just glue the xps to concrete then OSB to the xps skipping the tapcoms. I will use tapcoms to secure the walls to the floor. Can I skip the tapcoms and just use glue?
2) I want to paint the floor first – any reason NOT to do it? Thinking this will help to keep concrete dust down
3) I can’t bring the xps into the furnace room – how do I seal/finish the floor here? Spray foam? Caulking?
4) xps on floor and walls – what should I do first?
Thanks!
Marc – Below are answers.
1. You can try but it most likely won’t work. It’s nearly impossible to get the foam and plywood to sit plat, especially thin plywood like that.
2. You can…but if you stick with your plan at #1 things will be even worse as the glue won’t hold to the paint.
3. Do you mean how do you transition the floor? I’d use a transition strip.
4. I like to do the walls first but that’s me, no really difference.
thanks for the answers
1. Trying to save myself some work, guess not. Should I put caulking in the pilot holes before putting in the tapcoms?
3. Do you mean how do you transition the floor? I’d use a transition strip.
No I mean how do end the xps in order to seal it? I can’t just leave it “open” correct? I need to close/seal the edge of the xps?
Best advice I can give you….don’t try to save too much time…if you rush…you won’t be happy with the results :)
You can seal the edge with some foam then put a transition strip in to protect the edge.
Hi Todd,
First I am glad I signed up for newsletter its a nice update on tools and such. Thank you again for helping the general public with your insight. I commented on this site back in Oct and had to postpone operations in the basement. By way of refresher I have a cement floor covered in old adhesive from tile that is covered by an epoxy paint. Questions:
1. Can I skip the insulation and put down Advantech over cement and tile over that or use a moisture barrier?
2. Can I just tile over painted floor with tapconing down backerboard after scuffing paint with sandpaper and thinset over it?
3.Or can I get away with 1/2 inch foam with poly under it as height is an issue?
Any suggestions for a way to go would be very helpful. Thank you for your time and site!
Adam
Option #2 is your best bet considering your existing conditions. I would not recommend AdvanTech directly on the concrete. 1/2″ foam isn’t going to do much.
Good luck!
Hi Todd,
I have few questions for you:
My basement floor will be like this:
10mil ploy + 1″ pink foam + 23/32″ AdvanTech subfloor + engineered wood floor.
The basement wall will be 2″ pink foam + 2″x4″ frame with fiberglass + 1/2″ drywall.
questions:
1. should I build 2″x4″ frame on top of the 1″ pink foam or on top of the AdvanTech subfloor?
2. I have interior french drains around the concrete wall. When I put bottom wall frame plates, it will damage the french drain and also it may cannot hold well if I use Tapcon, because many places the concrete may less than 1″. How should I handle this issue? Is there another way to fix the bottom wall frame plates or can I just leave them without any Tapcon?
thanks,
James
1. I’d install it over the AdvanTech…that helps solve problem #2. Let the foam and AdvanTech span over the drain.
2. Use Construction Adhesive and screws into the AdvanTech.
Good luck.
Todd-
Thank you for all this info you give, money is tight for everyone so the one’s that can do it themselves (like me) like to ask questions and do it the right way and the best way.
I like the XPS board and I am going to isulate the walls, rim joist with spray foam with (foam it green)then top off with normal insulation and then do the floors…. My question is should I do the complete floor? what I mean by that is should I lift and adjust the steps and put the XPS and T&G under it? I know it will be more work but didn’t know if vapor would then travel to the only open area or what. Im not afraid of hard work… Also our basement is dry should I use plastic under the XPS on the floor would it cause an issue like you have said for the walls? I dont want to use spray foam on the walls becasue if I have to take it off for any reason … I heard its hard to come off… What’s your option on that too?
Thank you again and your advise is greatly appreaciated.
Mike D. near Toledo, OH
Mike – My pleasure. Honestly, floors are nice to insulate but not necessary. It really depends on your budget, the level of comfort you want, etc. Basements still need fresh air and humidity control in most cases. Good luck.
Todd-
Thank you for the reply. But would it be ok to install the foam board and T&G under that last step of the stairs or would it be a really bad idea?
Mike D.
Do you mean without fixing the stairs? If that’s what your asking I’d caution you as it can be a very bad tripping hazard.
Todd-
My idea was to trim about 1 to 1.5 inches off the bottom of the last step(what is currently sitting on the concrete basement floor). Then lift the whole string of step up a bit more to fit the XPS and the T&G sheet under the last step, then set it back down on top. I know that then the last step will be a little off, but I already have a half inch difference in rise within all the steps.
Thank you again for you input.
Mike D.
I understand what you meant…..you’ll end up with quite a difference…and quite a trip hazard. I would weigh that option very carefully.
Todd,
I am in the process of building a new home. I plan to use high quality exterior waterproofing techniques on the basement, one being Platon membrane under the slab as my vapor barrier (along with icf walls, platon or delta ms wall membrane, form-a-drain, and plenty of gravel). I think this will make for a pretty dry floor without any moisture wicking through. We plan to finish the basement and was curious if you felt that another moisture barrier on top of the slab was necessary? Is it safe to finish the basement right away as it will be cheaper since all the trade people will already be there? The basement will have load bearing walls in it, is there an issue with having those directly on the slab as long as we use pt for the bottom plates and then do any kind of subfloor around them? Is a subfloor and insulation even necessary with a good barrier under the slab? Is there a different subfloor strategy you would recommend knowing we have a good barrier under? Thanks so much.
Aaron – You are certainly investing wisely. Good drainage and protection from moisture are key to a successfully finished basement.
Many of the homes we build today have radiant heat in the slab. This completely removes the “sub-floor” question. In those situations the floor is warm and there’s no issue with a cold floor. Having said that, we’ve built lots of commercial buildings without radiant and without a sub-floor. The floors can be quite comfortable that way as well. So…do you need a barrier on top? No….do you need a sub-floor…No. All of it really depends on budget and personal preference.
Todd….I checked out a product that the orange big-box sold named OVRX Subflooring. It is 1/2″ XPS with 5/8″ OSB attached.
I am thinking about doing something similar using 4×8 sheets of 1/2″XPS and 3/4″ Advantatech. I was going to put down 6-mil poly on the basement floor and then the 1/2″ XPS and then the Advantatech. I was going to attach it all to the concrete as needed to make it lay down flat.
There is a drain in the floor that I wanted to keep functional so I was thinking about leaving a 3/4″ space between the XPS sheets with the spaces pointing towards the drain. I was going to tape the XPS joints to keep the moisture from the concrete from reaching the Advantatech.
Does this sound feasible and do you have any suggestions to make what I propose to work better? (love your site!)
Seems very reasonable. good luck.
Todd,
I live in a 1 year old house that in Colorado that has a floating slab floor. The concrete floor is cracked to an 1/8 inch gap along the expansion joints and is also bulged up along the expansion joints in both directions where joints meet. The surface is smooth and in good condition. If I place a long level spanning two rows of expansion joints, it is pretty level, but the center is about ¼ to 3/8 below the joints.
This situation has been unchanged since I moved in and I don’t see any cracking outside the joints and have not had any moisture issues. I suspect it there was a problem with the pour, but I have never seen this before.
I want to put down XPS sheets, but since XPS foam needs to be in direct contact with the floor, do I need to level out this problem with a floor lever first before applying the foam? Do you have any advice for me?
Thanks
Steve – From the sounds of it the concrete had an issue called “slab curling” when it was poured. Essentially that means the top cured faster than the bottom and the edges of the slab “curled” up. This is fairly common especially if the slab was poured on a hot sunny day.
Depending on what you want to use for flooring it’s likely you’ll need to fill in the low areas. A self leveling floor compound might work really well. Sometimes the high spots are “ground” down….. I think filling is easier.
Good luck.
Todd-
First thank you for your help on other items. The projects have turned out great. I am now back to finishing our basement… insulating the whole thing, floors and walls. I had to get off of it for a time because we had some seepage in a few spots. Got them all taken care of by digging outside and tar and plastic sealing back up. Now about a yr and still no signs of seepage. Now my questions … our basement is poured concrete with pieces of metal in concrete about every 4 feet they kinda look like a divider and are only about eighth inch thick. Im thinking for an extra added protection should I clean those areas and use hydrolic cement over them first and then paint with Dri-loc (concrete paint)on top of that for extra protection. The paint I got basicly free (its a long story) but all I had to do was go pick it up. A friend bought it and was losing his house so he told me just to take it. I have more than enough to do the floor and the walls. I know that this might be just wasting extra time or over kill. But my question… do you think these extra things would help, our would it cause more problems. My plan after I get this done is to use XPS foam board and seal up like you explain on your website. I would love to see what you think.
Thank you.
Mike D.
Mike – Thanks for the kind words. First off sealers like that are ok as an “added” insurance at best. Having said that, if you have it, don’t mind doing the work, then it can’t hurt. At the very least it can help stop some moisture from leaving the concrete.
Good luck.
Hey Todd, I was wondering, if I’m going with the delta fl on the floor, do I drylok for “good measure”? Is using drylok on the floor a bad idea? Will the delta fl do the trick alone?
It certainly won’t hurt….how much good it does is hard to say. Depends on if you want to spend the money and time…can’t say it matters one way or the other.
Ok thanks Todd, I think I’ll keep the money for other parts of the project and skip the drylock.
Todd,
I am planning to convert my garage to heated living space and am trying to avoid having to dig out around the foundation to insulate my garage slab from the exterior. My problem is I know if I submit plans to the permit office they will want some sort of documentation (IE: Manufacturer’s installation instructions) that document that this is an approved method to insulate a concrete slab (from above).
There are a lot websites that recommend this type of installation but they are mostly forums and contractors/DIY websites. None that could be considered “official”.
Do you know of any documentation that could stand up to the scrutinous permitting officials?
Thanks,
Greg
Greg – At least here in this part of the Country most inspectors are used to the detail. For starters you can go to DOW or Owens Corning and download details/specs on how to insulate a slab. I can tell you myself as an engineer these are details that are used very often. Any inspector that questions it, doesn’t really know the subject well enough.
Hi Todd,
I am about to start my basement Reno, after a lot of reading, i am thinking the Delta FL then Barricade 2′ by 2′ on top. this would solve the water and the heat issue, will it? any pros, cons on this one?
thank you ahead.
It’s a great system for any minor moisture issues. It also creates a decent thermal break in essence.
Todd, I need to add a couple of inches of new concrete to my floor to level and remove the existing slope of the subfloor before laying engineered hardwood flooring. I also want to insulate. Can I put a layer of xps foam down first and then pour the new concrete over it and use that as my subfloor?
Only if you can get at least 3-4″ down…..otherwise it will crack
Hi Todd,
For the method you describe at the top of the post, with the sleepers on top of the foam, how far apart would you put the tapcons along the sleepers?
Great info,
Thanks!
It really depends on how well everything “sits” down. No more than 48″….could be as little as 24″. You’ll know if things are holding down well. Good luck.
Todd,
I bought 2″ xps for my basement walls and I bought Dricore 2 x 2 panels for my basement floor, but I have one question. I have height constraints so my only option after insulating the floor is to use pergo and possibly groutable tiles, which is no big deal considering it has always been a cold floor, just painted and partially carpeted. (removed) My question is about the plywood. Can I use OSB or do I need actual plywood over the Dricore to support the pergo floor AND can I use 1/2 inch as opposed to 3/4″?
Also, Thank you so much for giving so many of us great information and a place to read about how to do it ourselves. As a single woman, I feel empowered to do great things to my home on my own. Thanks! Much appreciated!
Judy – Glad you find the site useful.
DRIcore can be used by itself with some finished flooring directly applied. If you can install a layer or 3/8″ or 1/2″ over it the floor will be even better. Best of luck!
Todd, would you secure it to the concrete or leave it floating? would you put polyurethane before a floating floor?
Would Delta Fl then plywood secured to concrete be a better choice or do you prefer the dricore?
I am real close on height constraints. I will have to get creative with the ceiling. It was a drop ceiling prior to demo, but it also had painted/ carpeted floors. I have some ideas though.
Thanks again for your time.
Judy – Dricore does work as a floating floor. We’ve installed it on several basements with success. Delta-FL does show their product being used without plywood in images, but they also mention plywood. The trouble with plywood on top of that product is you’ll have to fasten it down, resulting in holes in the membrane. Whereas the DRIcore doesn’t need to be fastened down.
Thank you, I was worried I might be making the wrong choice. Going with Dricore.
My pleasure. I’d love to hear all about it when you’re finished.
We are putting laminate wood flooring in a basement of a our 1 year old home. We live in the MidWest so the basement gets cool under your feet. Right now we have cement floors. We were planning on putting down .5inch Owens Corning R3 pink foam sheets to try to keep the flooring warmer. Is there anything else we should be doing or should know? The foam dents slightly when we stand on it now, with no laminate floor in it. Will the floor not warp or dent once the laminate is laid down? Do we need to connect the foam to the cement floor? Thanks in advance for your help.
Sarah – 1/2″ foam will help a bit, but it won’t provide a very good insulation value. I’d use more if you can. With flooring over it it will be quite stable. They do make higher density foams as well for floor use that are quite a bit stronger.
Todd,
More as in more thickness? Or is there a higher R value you would suggest?
It really comes down to R value. 1/2″ is more of a “pad” than an insulating layer.
Is there an R value you suggest for cement basement floor in Wisconsin?
Thank you!
Sarah – Really depends on the type of flooring, and how you’ll use the space. In most cases 1″ will make a decent impact on the cold and not create too many issues with regard to floor/ceiling height changes.
Todd,
1″ but R-3 or a higher R value?
Must the insulating foam be connected to the floor? Does there need to be a layer of wood between the insulating foam and the laminate flooring (Mohawk Proclaim collection)?
Thank you.
Sarah – Those details will depend on the flooring manufacturers installation guidelines. I would discuss with your installer.
Todd,
I really like this forum, it is very informative and useful. Somewhere along while reading this forum, I got lost about doing the foundation wall and subflooring.
If doing the subfloor first, do I leave 1/4″ gap from the wall if I’m going to install 2″ XPS on the wall, place composite below pressure treated wood for the framing? Do I still need to place the composite decking below the PT if I’m going to install 1″ XPS foam board or I can just secure the PT thru the XPS board on the floor?
I am really confuse with all these information already. Please excuse my head which is already spinning. Thanks for being patient.
John
John – If you install the foam first there’s no reason for the composite decking. I’d but the foam tight to the wall. Best of luck…you’ve got this!
Todd,
Thanks for the response.
1. I just want to confirm that I don’t need the 1/4″ gap anymore since the wall foam board will go on top of it.
2. The second scenario would be if I go on the wall first, I would use the composite decking under the pressure treated plate, then finish the wall framing. On this route, do I still need the 1/4″ gap between the floor foam board and composite decking? When will I use the spray?
John
1. Correct, no need for a gap.
2. In this scenario, having a small gap and foam sealing it would be best, but not 100% necessary.
Todd,
I really appreciate your advise. I can now discuss this with my friend who is also a builder himself with confident.
BTW, the barricade is no longer available in the U.S. per customer service email:
“The barricade panels have been discontinued in the US. We do however have an insulated panel to offer. Are you familiar with DRIcore subfloor R+? Please find our brochure attached for your reading pleasure. While DRIcore R+ insulated subfloor panels are not stocked in the U.S., there are two options for Purchasing these panels. You can order them online at http://www.homedepot.com. Or you can visit an associate in store at the ProDesk to place a special order.”
Just wanted to share that to everybody here in the forum.
Hi Todd,
I’m doing a full basement reno in my side-split home with a two-level basement. For both levels, I’ll insulate the walls using 2″ XPS foam, glued/sealed with canned spray foam.
However the floor is a bit more difficult. The larger of the two levels (500 sq ft) is relatively levelled so I’ll use a dimpled sub-floor called DMX (similar to Delta-FL), covered by OSB, then my finished floor. DMX has a combination of foam and plastic, and advertises an approx 2.2 r-value.
Problem is on the other basement level (approx 250 sq ft), there is a substantial slope from all sides going to the drain in the middle of the room. The room slopes about 2 inches from all side to the centre. I don’t think I can easily use self-levelling compound because the concrete slab has been painted several times and the paint is not coming off without a fight. So I’ve devised the following plan, let me know what you think:
Install a 6-mil poly vapour barrier directly against the slab, then rip pressure treated lumber (2×4 or 2×6) 16″ OC to level the entire room. These would be installed on the vapour barrier with tapiocas and between the sleepers I’d add foam board and seal with canned spray foam before putting OSB on top.
With this approach I could level and insulate the floor while losing minimal headroom, but I am concerned about moisture in the sleepers if used directly against poly.
Appreciate your input,
Ben
Your situation is not all that uncommon. Pressure treated sleepers are used quite a bit in situations like this and work very well. I think your approach is fine. Good luck.
Thanks Todd. I forgot to mention earlier that your site has been a great resource in my building project.
I have one additional question: I had some wetness a cinder block wall, so I had an internal weeping tile installed with a dimpled membrane that goes up the wall. The top edge of the membrane wasn’t sealed in any way by the contractor. Would you recommend spray-foam sealing the membrane edge before installing the XPS panels or just gluing the panels over and sealing them tight?
Thanks in advance.
I’d just install the foam board and move on. You’d never be able to properly seal that anyway. Good luck.
Very helpful article. 2 questions…
#1 after reading i assume it is best to fasten floor into place as opposed to a floating floor. Is it necessary to accommodate for expansion to prevent bulges in the floor?
#2 does the air space created by the sleepers contribute any insulating effect or add to comfort in some way?
Gary –
#1 – The flooring can float (laminate), but the sub-floor should be fastened. Space should be left at the walls for the finished flooring just as you would do on a normal flooring install. The sub-floor can fit tight to the wall.
#2 – I think it helps, how much is debatable.
Good luck.
Hi Todd,
We purchased a 2-car garage with finished studio apartment above it on the coast of Maine last summer. It use to be the detached garage of another house. The intent is “vacation home” and we are about to renovate the garage into bedrooms. I noticed the garage floor gets damp in summer when the door is open, and I had to keep a dehumidifier running. It’s a concrete slab with 1 row of cinderblock, then studded walls. The exterior is t&g pine with tyvek paper, then fiberglass insulation. The previous owner did a hack job when building the, and I have spent the past few weeks tearing out all the fiberglass insulation because it was full of mice and smelled like mildew. With all the rain we’ve had the floor is dry, and I’ve done the plastic taped to the floor test and no moisture. I’m assuming the damp floor is due to the humidity in summer.
Sorry for the long story, but here are my questions…
I was planning on using a 6mil poly vapor barrier, then OC rigid foam insulation that has the spaces for the furring strips, then 3/4″ Advantech. The foam is 1.5″ thick but has the space for the furring strips built in. I thought this would be great for the Advantech to attach to. The problem is that the stuff is really expensive for a 2’x8′ sheet, and I can’t glue the rigid foam down with the poly below. Do you think I could go with something a little less thick without the poly and put the Advantech directly over it? I also need to frame walls on top.
Thanks, John
John – I’m assuming you’re talking about the floor correct? If so, you’ll find a good advantage even if you use 1″ of closed cell foam board. You’d install the AdvanTech over that, and then use TapCon’s to secure the sandwich. Good luck.
Thanks Todd. Great website – I spent hours on here last night!
6mil poly, 1″ foam and then the Avantech? What length Tapcons do you suggest to secure the sandwich, and how many per 4’x8′ sheet? Can I then just screw framed walls to the Avantech, or should I Tapcon those all the way through also?
What do you suggest for the walls? There is Tyvek wrap under the pine t&g exterior, but I removed all the fiberglass insulation because it was full of mice and smelled like mildew? Should I put new paper-faced fiberglass insulation then drywall? I’m just concerned that the fiberglass will get all moldy again, but hoping that by insulating the floor and taking away the moisture that it will be fine. I was also thinking going with the mold-resistant drywall. Not sure if that’s worth the extra cost or not?
John – The number of tapcons really is only dependent on how flat the sheathing sits. You’ll likely only need 4-8 per sheet. I’d shoot for 1″ penetration in the concrete. From there you can simply screw walls into the sheathing as long as they are non-load bearing walls. As for your walls, in that situation, I’d probably install 2″ blue foam board, seal with GreatStuff, then finish off with fiberglass.
Good luck.
Hi Todd,
I installed the 6mil vapor barrier, foam and Advantech on the floor and it made a huge difference! I now need to insulate the exterior walls and the 2 walls that border the garage area. Should I put a vapor barrier before the sheetrock on the exterior walls, and also on the inside of the walls that border the garage? The garage floor is still bare concrete. The walls are framed with 2×4’s, so if I go with 2″ foam between the studs as you mentioned above, there wont’ be enough room for fiberglass.
John – Glad to hear the floor worked so well. I’m confused, are you insulating all concrete walls? or are some concrete wall (that you’ll frame in front of), and some walk-out (only wood framed) walls? There’s a huge difference for each type of wall. If you’re going to frame in front of concrete then you need to follow my post on insulating a basement wall (2″ foam, continuous, behind the framing), then you can fill the stud bay with fiberglass (skip a vapor barrier, the foam does that). If you’re insulating a basement walk-out wall then follow the article for those.
Todd, I just ran across this web site last night and I’ve been soaking up information ever since! You have a wealth of information and I want to start by saying THANKS for sharing it.
Here is the thing that I don’t see addressed with my design. I just had a new garage built with a workshop attached. Both areas already have 2″ of foam and a plastic barrier under the cement floors. I will (next year after I’m sure the floor is pretty much dried out) be putting a raised floor in the workshop area. Since I already have the barrier under the floor I’m wondering if it’s something I need to do again since the workshop will be heated eventually. (Vapor barrier towards the warm side???) If I do have another vapor barrier would I be trapping many remaining moisture? I’m guessing I could lay down 3/4″ pressure treated sleepers (screwed down) with 3/4″ foam panels in between. I would then top it off with 3/4″ plywood as a finish floor and skip any more vapor barrier since it’s down there (below the cement) anyways. Thoughts? I’d really appreciate your expertise.
Frank – Thanks for the nice compliment.
Floors are a bit different in the fact that having a vapor barrier on both sides won’t hurt anything. In fact, concrete never “dries” out as there is always water trapped in the pore structure at the microscopic level. Having said that, with a vapor barrier uner the concrete you’re in a good situation as the only moisture now that will come up is vapor from the slab (that will never end over the life of the concrete). If you’re doing just a shop that doesn’t have a “finished” floor then I’d proceed as you mentioned without another barrier. I’d use PT sleepers along with AdvanTech floor sheathing and call it good.
Best of luck! Good luck with the shop, I built a great shop a few years ago and love having dedicated shop space.
Todd,
Thanks for the quick response! (I’m amazed at the amount of responses on this thread. I’ve never seen someone so dedicated to answering all questions or comments.)
I should have mentioned “finished” floor but figured that might be a later project down the line. Since it is a possibility (3/4″ T&G flooring), would this change your response as to dropping the 2nd vapor barrier?
Also, quickly scanning all the comments again (there are a ton!), I’m seeing some mention of skipping sleepers all together and the possibility of just 3/4″ foam panels possibly glued down and then just the Advantech glued on top of that. Possible? That would be slick! Thanks again!
Frank – If you’re going to put down flooring it’s worth putting down a poly vapor barrier, unless you do the 3/4″ foam complete over the whole floor (sealed well).
Yes you can skip the sleepers and do foam then plywood. May I ask what type of shop?
Todd,
Since, like I said, probably do a finished floor, I’ll glue down 3/4″ foam board completely with taped seams and then glue the Advantech (3/4″) directly to the foam board.
It’s a small workshop (mostly wood working). Retired and this will be my “man cave!”
THANKS again for be so willing to share your time & talent!
Frank – You’ll likely need to use some Tapcons to secure that plywood….glue won’t do the trick. Good luck.
I won’t disagree – you are the expert …. BUT …. I’ve used adhesive before and it is a nightmare to get stuff off. I would think adhesive would hold the Advantech to the foam board with no problem. Seeing that the foam board is adhered to the cement floor, where would the Advantech go? (I’m also thinking I could go and put the Tapcons in later if any thing started popping up.) Like I say, you know better through hands-on experience – where is my thinking off?
Frank – You certainly can try, and as you said, install the screws after. My experience would suggest things just won’t sit down all that great but it worth a try. The Advantech is the sheathing I’d use for the floor vs regular plywood.
I’m going to give it a shot. I won’t be doing this until next spring but I’ll definitely let you know the results.
THANKS AGAIN for sharing Todd!
New guy here and amazed at the info I found!!! Just read the whole thread and I apologize if this was question was previously addressed. Using the foam board as a water barrier (2″ wall or 1″ floor) I would eventually need to seal off areas that aren’t tight or where obstructions (pipe, drains, outlets, etc.) are and a spray foam would be utilized to fill the gaps. Spray foam in a can is “open cell” (like Great Stuff) and would not work as a water barrier. In fact, I see on at least one web video it actually acts as a sponge and would absorb and hold water. Is there a “closed cell” foam in small cans that you use/recommend?
Paul – I actually disagree on “Great Stuff”. It’s a one component Polyurethane foam, and is a closed cell foam.
“All Dow Spray Foam including Enerfoam, Great Stuff and Froth Pak brands are closed-cell foam.” http://www.theenergyconscious.com/greatstuff-dow.html
I’ve NEVER seen great stuff absorb water and we’ve used lots of it over the years.
I stand corrected! I was reading some thread on another site and caught wind of bad info. Next question would be what is best? I’m guessing that a minimal expanding would be better than the regular stuff? Or, is all pretty much the same?
I believe the regular stuff is better, the “harder” it gets, the less permeable it is (my assumption here based on what I’ve read about foams). Good luck.
Hi Todd.
I’ve read your excellent article, along with every single comment and your responses to them. Nonetheless, I still have a couple of questions for you about the floor. I had intended to follow your general plan, using 2-inch-thick XPS on the concrete basement floor, followed by 1×4 sleepers screwed down through the XPS into the concrete. I plan to secure strips of Advantech on top of and perpendicular to the sleepers and lay PEX in between the strips for radiant heat — hence the 2-ich-thick XPS.
My basement floor is not level. It slopes downward generally from one corner to the diagonal corner. The difference in height from the high point to the low point is about 1-3/4 inches.
I have three concerns: leveling the floor, maintaining an effective vapor barrier between the concrete and the rest of the floor, and maintaining an effective insulation barrier between the PEX layer and the concrete floor.
1. With regard to leveling the floor, I spoke to a construction engineer friend of mine and he said that if I follow your method, the Tapcon screws will pull the sleepers and shims tight to the concrete floor but the portions of the sleepers in between the screwed-down points will be slightly higher, like a pincushion. He said trying to maintain level across the entire 22ft x 16ft. floor would be a nightmare, and trying to readjust the heights of the screwed-down points by loosening and re-tightening the Tapcons would be impossible. So how did you do it?
2. Doesn’t penetrating the XPS with dozens of screws destroy the vapor barrier afforded by the XPS?
3. Won’t the dozens of metal screws penetrating the XPS into the concrete conduct the heat away from the PEX layer and the finished floor above?
I would greatly appreciate any solutions you might have for these concerns.
Don
You’ve discovered the epic battle all of us engineers face. The fine line between a perfect world on a piece of paper and the reality of construction.
Couple thoughts:
– Leveling: One solution would be first leveling the floor with a flowable floor leveling grout. This would help you get the concrete floor closer. Another solution is installing the foam, then using different thickness sleepers to take out the pitch. This would require laying out a grid, shooting grade, and determining the sleeper thickess.
– While I appreciate your friends concern, I’d say that XPS typically doesn’t compress much, so the sleepers likely will not suck down in a very uneven fashion as he might suppose. If it’s really a concern you could use high compression XPS which would compress even less.
– Penetration the vapor barrier: You are correct that this isn’t ideal, however, even with the screws the difference in vapor transmission will be significant. There are LOTS of wood / engineered wood products being installed directly on top of concrete slabs with very thin vapor barriers, even with the small fastener holes I’d argue that the 2″ foam is better.
– Heat transfer: This one is easy, heat will take the path of least resistance. I would have zero concern about the fasteners “taking” heat. You’ll have zero problems heating that floor in this fashion.
Good luck!
Todd,
Re Delta FL, I’m putting it down on a concrete floor for air gap and separation (no insulation). My question is do I install it first then build my interior walls or install it after and have breaks in the barrier. Unlike 6mm Ploy it’s hard to go up the wall with this material. The compressive strength is below but I have no idea if this is suitable for a 8ft wall with shower plumbing in it. FAQ on the Delta site suggest to lay it down first but others I’ve consulted say not to, due to ease of install later (not walking on it for a week) and possible collapse of wall by compressed dimples.
Thoughts?
Compressive strength apprx. 5,200 psf (250 kN/m²)
Ben – You can do it either way…I’d install it after the framing though so I wouldn’t have to worry about smashing it.
todd:
seriously, you are impressive. the number of responses and amount of thought you’ve offered to all of us should win a nobel peace prize!
here’s my odd question:
i live near seattle and our 1979 home doesn’t have quite the seismic restraint i would like to see, especially since we have cripple walls on 3/4 of the basement walls. it’s my understanding cripple walls are more prone to failure in seismic events; therefore, i am planning to do a seismic retrofit of the basement cripple walls.
in doing so, i will be installing plywood on the stud cripple walls on the inside of the wall (basement side). typical details call out drilling 2-3″ diameter holes, about 6 of them, per 4’x8′ sheet, to allow moisture to escape.
my plan is to do the following:
1. install plywood on the walls (i may upgrade the R-11 to R-13 insulation).
2. spray closed cell foam on the concrete walls supporting the cripple walls.
3. place 1″ foam on the floor, all the way to the concrete walls
4. place 3/4″ T&G plywood on top of the foam, stopping such that i have about 1″ between the spray foam and the plywood.
5. build a 2×4 wall from floating subfloor to joists, maintaining the space noted in #4
6. finish walls and install carpet
so, these questions come to mind:
1. how do i terminate the spray foam on the half-wall of concrete where the concrete surface transitions to plywood/stud wall? do i overlap the spray foam directly on the plywood, or will this introduce a path for moisture to try to escape (note: i’m planning on using non-treated plywood since it will not be in contact with concrete)?
2. similarly, where my plywood stops at the floor joists above, how do i transition the insulation here? i plan to spray foam the joist cavities against the rim joist.
3. should i also insulate my wall sitting on the floating subfloor going up to the joists, or is this overkill or would it have issues with condensation or anything like that?
4. do you have any recommendations for an advantec-like product in the pacific northwest?
5. in lieu of using 3/4″ T&G ply, i might use 1/2″ and try to use 1.25″ of foam for the floor. do you know if they make 3/4″ panels, or is it typically 1/2″ or 1″? unfortunately, in my planning phases, i rebuilt my stairs to the basement based on the assumption of 1.75″ of subfloor + insulation and 3/4″ carpet when i calculated my risers.
thanks! you rock!!!
Mike – Glad you find the site so useful. I’ll do my best to brush on these topics…
1. This is a tough question. Certainly no perfect answer. Is the bottom wall plate treated? If so…i’d leave a small gap between plywood and top of wall (plywood needs to be attached to plate for seismic so not a big gap). Then I’d probably use some bitchathane as a flashing…then spray foam. This leaves an air gap between concrete and plywood, instead of locked in with foam.
2. No worries here…just spray foam…the foundation would be my issue below…here there’s not a concern in my mind.
3. I’d likely not do it…unless you really needed the extra r value. Air flow is good!
4. Georgia Pacific has a similar product i believe.
5. I’d stick with 3/4″ on the floor for the T&G….you won’t be happy otherwise.
Good luck.
for question 1:
yes, i do plan to leave a gap between plywood and concrete. the sill plate there is likely treated (though i have yet to open the wall to verify).
i’m not sure i follow you on the flashing. could you elaborate? would the flashing just go on top of the concrete, butted up to the plywood, or would the flashing wrap up along the plywood a few inches presumably to a point that i would spray foam?
i assume you’re implying that i shouldn’t seal the gap between concrete and plywood so that air/moisture can pass through. wouldn’t this then also allow cold air in?
I would use a piece of self adhering waterproofing 4-6″ wide, stick it to the lower couple of inches of plywood, then drape it down over the concrete. Then when you spray foam up the concrete you can go over that and up onto the plywood. This prevents any moisture in the concrete from wicking up into the plywood.
wouldn’t this also effectively trap the moisture from the concrete wall (which is dirt on one side and spray foam on the other side) and force it to go up into the 2×4 exterior cripple wall?
i suppose if i left a gap for that moisture to “escape”, that moisture would just rise up and be trapped in the cavity between my finished basement wall and the subfloor joists of my main living floor (which doesn’t sound great either).
this is very nerve wracking…
Now you can understand why this is all so difficult to navigate. Basements are a balancing act. Ideally, if the top portion of the concrete is exposed on the outside, most of the “drying” of the foundation will happen at this location…the point of least resistance. Obviously the sill plate will be exposed to moisture, and hopefully it’s a treated plate. This detail doesn’t give me all that much heart burn.
thanks again todd. some of the walls of the concrete are exposed, but it’s only maybe 10-20% of the buried surface area.
but, if this detail doesn’t give you heartburn, i will take your advice and march on forward with it. thanks again.
ok, a few more questions if you will (thanks again for all the responses!):
1. underneath my current flooring (engineered hardwood) is a sheet of 6mil poly. should i reuse this and lay down the 1″ XPS over the top of it?
2. for my cripple wall (which has R11 fiberglass in it that i plan to install the plywood over for the seismic retrofit): would spray foaming 2″ of CCF in those cavities, then doing the plywood, then doing 2″ more of CCF on the plywood work? or, waste of money and i should just reuse the existing fiberglass?
same cripple wall: if i did spray foam the cavity where the fiberglass currently resides, and then plywood, would installing 1″ or 2″ XPS on the plywood (with CCF along the edges), be a good approach instead?
3. for my upstairs floor (which the basement is under): would my hardwood floors be warmer if i sprayed 1″ of CCF on the underside of the subfloor?
4. for my 2×4 wall which will be set on the new insulated floor with a gap between it and the CCF’d concrete, can i put a 1/2″ or 1″ XPS board under the drywall? or, waste of money?
thanks again!
Mike –
1. It can’t hurt to leave it in place.
2. If you spray it with 2″ of foam, then I’d likely re-install the fiberglass over that, then install the plywood.
2a. This doesn’t seem like a great idea…it creates a double vapor barrier situation…possibly trapping moisture around the plywood.
3. I’m not sure I’d do that….I’ve never done it…but the foam may cause some issues with that floor….I’d probably stick to fiberglass in that situation.
4. Again…be careful of a double vapor barrier situation.
Good luck.
new home with no water issues. If I just want carpet in the basement can I just do 1/2 XPS glued down, pad and then carpet?
Possible…i’d check with the carpet installers and see if the pad/tack strips will work in that scenario.
Thanks,
Been reading a lot on here but have never noticed dates. When did you write this original article?
Also, have you ever heard of SuperSeal? The sell a dimpled membrane product specifically for carpet installs.
http://www.superseal.ca/
This article is about 5 yrs old. I’m not familiar with that product.
Todd – I really appreciate all of the information on this site. I am in Cincinnati on the top of a hill with a dry unfinished basement I am thinking about finishing mine using 1″ Foamular XPS on the floor with 5/8″ OSB over top. The stairwell comes down in the middle of the basement and has been framed with drywall all the way around the stairwell. Can I just lay down the XPS up to these walls? If there is a gap in the foam board for the area under the stairs, does that defeat the point of carefully sealing all the seams of the foam board? Would I need to tear out the existing walls around the stairs and put down the foam board everywhere? I will also have the area where my furnace, water heater, and floor drain are are that I was not planning to put foam board on the floor. Appreciate your help.
David – In a perfect world (one we do not live in :)) you’d seal up everything as you suggest. But that’s not often easy to accomplish so in most cases the stairs are just sealed up to. Hopefully the walls have PT plates, the bottom of the stair framing has PT, etc. Leaving the furnace room unfinished is very typical. One thing you should be very cautious of is whether your stairs were designed for this “lift” in the sub-floor. Otherwise you’ll have a code violation and trip hazard.
todd,
for the foam on the floor, is it okay to use non-tongue and groove panels? or, will you get cool spots or places where moisture will want to escape?
Mike – I’m not sure there is any significant difference.
I’m finishing my basement this summer and I am so grateful to this site for all the info it contains. It has been a HUGE help so thank you so much! That said, I’ve got a couple questions.
First, you say, “We recommend using 3/4″ thick pressure treated decking.” I’m having trouble finding any decking material that isn’t trex or a trex-like material which just seems like a big unnecessary expense. The big box stores around here, Northern Utah, definitely don’t have anything, and the lumberyards don’t seem to carry anything other than the more exotic, expensive, hardwoods for decking. I am, admittedly, a rank amateur when it comes to basement finishing, and perhaps slightly more than a novice when it comes to building/woodworking so it is very possible I’m simply misunderstanding what it is you are recommending here.
Second, You say, “This method works great if you don’t have many doors and you can deal with the higher sub-floor at the stairs.” Dealing with the higher sub-floor at the stairs is what I’m unsure of. Will modifications need to be made to the stairs or does this just mean it may be an annoyance to have a higher sub-floor?
My third and final question is regarding the current framing in the basement. There is some load bearing framing in the basement. This sub-floor setup will be taller than the base plate of that framing. Are there any issues that can arise from this?
Thank you so much for any answers/advice you can offer. Sorry if these are dumb questions. I just want to be thorough and do things right the first time.
Clint – Thanks for the kind words…..never any “dumb” questions…so hopefully I can help.
1. Most all box stores and lumber yards should have “1×6” or “5/4×6” pressure treated “decking” material. I can’t imagine a lumber supply place not carrying it as it’s used on so many decks every day across the Country. Some places may not call it decking…just ask for 1×6 pressure treated.
2. This is an important issue. Stairs are designed such that each step rises the same amount with only a very small allowance for differences. This prevents tripping. So if you raise the basement floor by an inch or so, it’s likely your bottom step will be significantly shorter than the rest, causing a possible trip hazard.
3. No issue…you may need to add blocking to help with base trim.
Good luck!
hey todd,
thanks again for your diligence in responding to all these questions. one more for you.
i’m the guy that is doing a seismic retrofit that involves putting plywood on the inside face of the exterior pony wall studs. i’m now thinking i will also utilize an interior wall for a shear wall (i.e. it’ll have plywood on it too). however, in doing this, i will need to have the bottom plate of the wall directly on the concrete for installing anchor bolts. otherwise, the rest of the floor i plan to install is 1″ foam and 3/4″ T&G advantech subfloor. then carpet.
will i lose my semi-vapor barrier if the stud is on the concrete? any details you can recommend for this? the finished wall will be sheetrock.
also, do you know a typical basement slab thickness for 1979 construction (seattle area)?
thanks!
I wouldn’t worry about that. If anything, put down poly under the plate. If I was a betting man….that slab is likely 3-4″ in thickness.
Hi Todd,
if I am mainly concerned with limiting the subfloor thickness and maximizing the R-value, what would be the problem with using high-density foam (eg. 100psi compression strength) and then a thin layer of OSB? And is it possible to avoid OSB entirely? I am thinking of installing a vinyl floating floor.
thanks
-Garry
The trouble is getting an even floor when you’re done. A concrete floor isn’t perfectly flat, the foam won’t sit perfect, so the 5/8″ to 3/4″ sheathing helps even it all out, and create a surface that’s stiff enough for the flooring. You can try it, I’m not sure you’ll like the results.
Hi Todd, thanks for your previous response.
Regarding the issue of flatness of the concrete: could self-leveling cement address this? I estimate my existing slab is within a 1/4 inch over 400sqft: would you recommend self-leveling cement?
thanks
-Garry
Garry – That can work, but self leveling mortar can be tricky.
Hello, Am currently insulating the basement of our new home using your system. 2 inch xps adhered to the walls ( we used great stuff as an adhesive and it worked great.) we are now on to the floor and have applied the one inch xps….but now from reading some of the above posts it seems we should have installed 6 mil poly before the foam. Will that be an issue? And also we were planning to use 2 layers of 1/2 inch osb on top of the foam….again…some varying posts above. some yes to osb, some no. Your clarification would be helpful. Great site btw.
Greg in NH
Greg – The poly helps keep down moisture. I’d use 1/2″ of PT plywood, then 1/2″ of AdvanTech. That should give you a floor that will last. Good luck!
Amazing article.. Todd
I have a home that was built in 1920, Chicago, with cinder block foundation. I occasionally get some moisture from the subfloor, probably 1″ concrete in some areas, but nothing that create puddles. I have waterproofed the outside, drain tile with a sump and all gutters discharge along with the sump to the back yard. I think I just have a high water table under the home.
I was thinking of adding Delta- FL rolls underneath the boards for the just in case situation.
What are your thoughts?
Thanks from Chicago!
James – I’d probably put down a vapor barrier first, then the Delta FL. It’s just always a worry that the moisture will be a problem.
What is the advantage of using the insulated Dricore tiles vs. the regular Dricore tiles? Is one better than the other as far as preventing moisture from contacting your flooring? Is one easier to install? Do you still need to put down a poly vapor barrier underneath or can they be applied to concrete?
putting water pressure tank in barn room, should I lay 6ml poly on concrete then foamboard then sleepers or put the foamboard down first then poly then sleepers?
poly, foam, then sleepers.
So much helpful info, thank you! I have a finished basement that was tiled in the 50’s and after tearing up the carpet that was on top of it, it seems like someone tried to scrape up the tile at one point and gave up on the job, leaving me with half exposed thinset, and half cheap, thin tile. Rather than removing the rest of the tile and doing that hellish job, could I put Delta FL or a similar product, then lay vinyl planks on that? Or even put a subfloor on top of the plastic, then tile on top of that? Main question is how to make the floor level enough for tile and create warmth and a vapor barrier. Advice please! Thank you!
Easiest thing to do is use a self leveling compound and shim the floor.
Hi Todd, love the information here. My question is I am going to be building a new house with a walkout finished basement should I put insulation underneath concrete or am I wasting my money? Shouldn’t all be done on top of concrete ? Thanks for your advice
I absolutely recommend it under the slab, at least around the perimeter if cost is an issue.
Hi Todd. Thanks for providing so much valuable insight and advice. I have a question about insulating my basement floor. My plan is to use poly, 1″ of XPS, PT sleepers, and 3/4″ advantech. Do you think this system will be able to withstand high load points such as a pool table? Local building supply companies don’t carry high compressive strength xps.
I think it’s fine, I’d probably more the sleepers to 12″ center to center though.
Thanks for the reply Todd. One follow up question…for the sub floor system I described, which do you feel is more important – keeping the PT sleepers or increasing the foam from 1″ to 1.5″ (assuming i can’t do both and the basement has been dry to-date).
It’s a toss up…really I’d do whatever is easier for you.
Hi Todd,
Thank you for this great set of articles.
Question about the minimum height
My unfinished basement’s slab floor to bottom of floor joists measurement is 7′ 4″
If I finish with an insulated floor (2 1/2″) and ceiling of say 1/2″, that leaves 7′ 1″ height.
I read in the first paragraph that most states have a 7′ 6″ minimum, so even without
doing anything I am already out of code (if it were finished).
In looking through NH codes, I found that NH’s code is 7′ minimum (https://www.concordnh.gov/DocumentCenter/View/9288), so I may be in luck.
What are your thoughts regarding this?
Is 4″ clearance enough space to do a proper to-code as of 2018 floor and living space?
Thanks!!!!
Tony
Tony – looks like you’re ok with the 7′ requirement, and in some places you can drop lower for a beam. What will you do for the ceiling?
Thanks for the response.
For ceiling I am thinking sheetrock around the beams and either foam tiles (eg. drop-ceiling type) or paneling. Main concern is to allow access underside of first floor when the need arises.
Any recommendations? pros & cons?
Thanks
You’ll need several inches to install a drop ceiling is why I was asking, further reducing the available head-room you have.
Hi Todd,
Great article. There are no dates listed here so I’m unsure if you’re still replying to this page, but here goes.
I live in Minnesota, climate zone 6b. My house is a 4 level split. The basement is below grade, but the lower level is a walkout. I do not have a moisture problem as far as I can tell – sump well is dry 100% of the time, not moisture marks on the slab or walls.
I would like to put 3/4 XPS foam on the lower level. It’s partially finished, and the extra 1/4 I save (instead of 1 inch) allows me extra headroom and means I don’t have to trim anything off the existing doors.
Do you think 3/4 XPS is worth it? That’s R4. Should I include 6 mil poly as well? Thanks!
R4 is better than none :) Poly certainly is a good idea.
This is a wonderful site. Thank you for sharing your time and wisdom, and for a great afternoon read!
We’d like to finish the front section of our basement (11′ x 17′ x 80”) in our 1880 fieldstone foundation New England home to use as play space and exercise room. We used to get water in one corner during rainstorms but believe that replacing the driveway has resolved that problem (no water in past 18 months), at least for now.
Our plan is to insulate the walls with blown-in closed cell foam, but not sure what to do for the basement floor. I’ve read over all your comments but still not sure how best to proceed.
Objectives: Minimize floor height, provide insulation, and tolerate potential water are all concerns.
We were thinking of putting down some type of foam board (or something else), and vinyl floating floor, over which we could put area rugs, but from what I’ve read above not sure that’s the best idea.
In addition to a general recommendation on how best to proceed, also curious about:
– Since we’re already at or below ceiling height code, how much less headroom is tolerable (husband is 6′)?
– How much floor insulation do we need in New England to make the floor reasonably comfortable in the winter (average floor temp now is 50)?
– How much will more or less floor insulation impact heating requirement and comfort?
Thanks!
Ann – Glad to hear you’re doing the foam on the walls. That in itself will make most of the difference. In fact, with your limited headroom, I’d likely suggest not insulating the floor. We build many homes here in NH that have no insulation in the finished basement floor. It’s great if you can, but the wall insulation really is the bigger deal.
Thank you Todd for all the great info!
I believe I’ve read everything but maybe missed questions / recommendations prior to tile installation?
House:
Southern Wisconsin, Walk-out basement dug into the hill above the lake. High humidity in the summer-professionally installed HVAC-integrated high efficiency dehumidifier.
Project:
Install tile throughout basement, but ceiling height is a factor.
Plan:
sikaflex for cracks, poly, xps, cement backer board, tile.
Prior to reading this, I was debating thermostat-regulated electrical radiant heat. However I’m not sure I’ll have enough clearance for everything and may have to cut down on the xps thickness as is.
Question:
What are your thoughts on forgoing the radiant heating if I insulate with this method? Is tile still cold to the touch with this method?
.
Hi!
Love your site and knowledge :) a few questions before I kick off my basement reno.
Info: Home we purchased in Montreal (10 year old), is an ICF build so walls already have 2″ foam. Concrete floor is dry, no cracks and no signs of water issues. I dont know if they insulated below slab. Everything looks super level.
1) I was going to go with 1.5 XPS, tuck tape seems, foam around perimeter that meets ICF foam wall.
2) I was going to place OSB directly ontop of XPS (do you have a reco on thickness?
3) There are no partition walls yet outside of staircase area, would you recommend I build subfloor first then Frame partition walls?
4)for the utility room that has furnace and a storage room, would you reco I just stop the sublfoor in those areas at the partition walls, or try and install into those rooms. (cant recall if you mentioned if it makes a difference having some rooms with no subfloor.
5) I think last question, do you need to tapcon the OSB into concrete? can it just be glued down or a I am overthinking all the screws into cement is a worry ? and all the holes are no big deal.
Thanks in advance feel free to add any other recommendations.
Thanks for the nice compliment.
1. 1.5 is great, try to get the high density version if possible.
2. at least 5/8″….3/4″ would be better.
3. Yes I’d do the floor first.
4. I wouldn’t do the utility room floor.
5. It’s likely you’ll need to screw it down, or it won’t stay correctly. If you use 3/4″ OSB it won’t take many fasteners…maybe 6-8 per sheet.
question on avoiding using foamboard on the floor..I want to carpet the concrete slab of my newly built house. (6 years old)..I will only be finishing off roughly 3/4 of the basement..my initial plan for the floor was, poly liner, 3/4” osb then carpet..if I skip the foamboard for a cost savings, will the poly along be ok?
Really need to see what the carpet installer recommends for the carpet on the concrete
why do you need sleepers? cant you just nail plywood panels directly to foam to better distribute the weight instead of all the weight being in area on foam where sleepers are? wouldnt this save money and ceiling height as well?
It’s difficult at best to nail a subfloor through foam into concrete. It just won’t work well, too much bounce.
Thanks for all of the knowledge you share. I am somewhat of a DIYer, lol. I would like to insulate my concrete basement floor, however, the floor is slanted which leads to a drain. We water proofed the basement, but I would still like to keep the drain open. How would I go about insulating and possibly placing vinyl flooring over?
Not sure I have a good solution in that case. Maybe you shim the entire floor up to remove the slope, but leave the drain.
Great article, thank you for sharing. My question is in regards to the 2×4″ PT sleepers and the 1″ foam. With 2×4 (or 2×3) measurements being 1.5″ and the 1″ foam having a .5″ gap, is that ok? In other words will having a .5 in air gap between the sleepers (above the foam) be ok or will I lose insulation R value this way? Should I instead rip 1″ (exactly) PT boards to fit them exactly at the same height as the foam boards?
Thanks in advance!
Hi Todd, Guess what – NO QUESTION! Just wanted to leave a note that I have gone over these questions and responses at least three times over the last few years. I get it because of all the interesting questions and the GREAT responses. I just wanted to say THANK YOU as I have used the techniques described here and have been beyond satisfied with the results. You are to be commended for sharing your knowledge AND consistently answering all these questions (that at times are very repetitive). As my wife would say: “You definitely have a man crush on that guy!” (Yes, that is the ultimate compliment!!!)