As I've covered extensively in my waterproofing section, basements are cool, damp places. You can't just throw any ole insulation up. You need to be aware of your options, and have a game plan going into your finishing project.
Is Rigid Foam Insulation the Right Insulation for your Basement?
Your choice really comes down to blanket insulation (aka fiberglass) or XPS. Most homes use fiberglass, but rigid foam insulation, although more costly offers a few extra features. Let's take a look.
Blanket Insulation: This is very common mainly because it is very cost effective. Usually made of fiberglass and it typically has some type of facing attached: paper, foil, or vinyl. This was the option of choice in Jason's basement and I wouldn't discourage anyone from going this route.
[NOTE from Jason: The builder for my house had pre-installed my fiberglass insulation so the choice was pretty easy for me. Living in the moderately warm climate of Virginia and not having any obvious moisture concerns and a limited budget I opted to just use what was there. Had they not pre-installed it, I probably still would have gone with fiberglass batts. ]
XPS - a.k.a Extruded Polystyrene - a.k.a Rigid Foam Board: This is what I installed, and the topic of this article. Boards come of varying thickness up to 2in. 
You get a thermal capability of R5 per inch of thickness. I recommend going with the 2in thick for an R10 rating.
The board is more expensive than blanket insulation. Average cost for a 4'x8'x2'' sheet was $30/sheet. My typically sized basement took about 35 sheets. That adds up to a cool Gee! Obviously a good chunk of change. By comparison, drywall for that same basement was $400.
Other: There are other forms of insulation like loose-fill which is usually blown in or the sprayed in foam type. The trick there is to make sure you have the proper density to ensure adequate thermal capacity. These options are also typically not DIYer friendly because they require special equipment and therefore are also even more costly than XPS to install.
XPS Benefits:
So if you are going to pay nearly double the cost for XPS, what benefits do you get? I argue peace of mind. I've contended that at some point, every basement is susceptible to water. Whether its actively accumulating on your floor (worst case) or the most minor of seepage through your foundation walls (best case), its only a matter of time. Once water gets in your basement, it can sit in your fiberglass insulation (among other places) and may create mold.
XPS is extremely water resistant and subsequently mold resistant. Unlike the fiberglass insulation, it will not hold the water needed for mold to develop and spread. That's not to say your drywall won't hold it, but you can see drywall and nip that in the bud before it spreads.
Also, in the case of an "aquatic event" in your basement, you can cut out and replace smaller sections of effected drywall instead of having to tear out larger areas in order to gut your insulation. How easily can you see your insulation? Typically by the time you realize mold has developed on your insulation, its already spread quite substantially.
Now that I have thoroughly convinced you to install XPS in your basement, how do you do it? It's quite easy actually...
Installing rigid foam insulation
Allow me to break down the major components.
Prep Work - I've talked about basement waterproofing paint before. I recommend you do this before XPS installation for added peace of mind. I had no problems applying the XPS to my painted walls. Aside from any other wall treatments you want to do (I highly recommend reviewing my interior waterproofing article) the prep work basically involves making sure you have a clean dry surface. Take a shop vac and wet towel to your walls to get rid of all those cob webs!
Tools/Materials Needed:
Box Cutter - Used to score the XPS
Drywall Saw - Not 100% required but I found that with 2'' thick XPS, the box cutter did not sufficiently score the XPS to be able to snap pieces off. It did OK when scoring along the 4' lengths, but not to well along the 8'. If you don't have one, this Stanley is under $10 and gets great reviews. You'll need it when installing or repairing drywall anyway
Caulk Gun - Another frequently used tool on non-basement finishing projects. You'll need this to apply the adhesive
Foam Board Adhesive - You can get this at your local HD, s
helves and shelves of it! I'm sure there are other adhesives that COULD work, but they make one specifically for applying foam board. Make sure you use it! It is specifically designed not to burn the foam. Other more aggressive adhesives may burn your foam board instead of adhering it to the wall. I used about 1 tube per sheet of XPS.
XPS - Duh! I had to make multiple trips to HD to get the 30+ sheets home. Not because of the weight, but the size is awkward to transport. I had to strap them to the roof of our Pilot. Driving with 10 sheets at a time looked silly enough - couldn't imagine doing it with 30. Plus I spread the purchase over 2 credit card billing cycles to help ease the financial burden.
Application Tips -
1. Don't be stingy with the adhesive. Apply liberally - specifically in the corners and along edges of a piece.
2. Use something to hold the boards in place while the adhesive cures. I had all my framing lumber already in the basement so I just used that. You don't need a tremendous amount of pressure - just something to keep the board in place and firmly up against the wall.
3. Like drywall, install full pieces covering windows and later once the adhesive is fully cured, come back and cut out your openings with the drywall saw.
4. Try to keep the seams tight. Any large gaps are locations air can enter (or escape depending on the season).
5. Finish the job with some tyvek tape across the joints. Larger gaps (where unavoidable) can be filled with expandable foam.
Simple right? This job is certainly low on the DIYer difficulty scale. Pretty low on time commitment too. Certainly a bit higher on cost, but if your budget allows it, its provides an excellent insulating option and peace of mind. If you have any questions, please leave them in the comments below!
- Adam
Hi, Jason,
Thank you for sharing your experience and knowledge gained! This is a great site for the inexperienced but eager DIYer like myself.
Do you know how XPS rigid foam boards perform in a crawlspace, where the home is pier and beam? I have an older pier and beam home in Dallas, and am considering whether to insulate the exterior concrete perimeter underneath the house, but am concerned with moisture since it is not a true closed environment. Additionally, one corner under the house is a near "mini basement/workroom" with almost 6 feet of headroom, about 350 sq. ft total area, with a concrete floor and walls. Would love to be able to insulate this area and actually use it in colder winter months.
Thanks for your thoughts.
Hi Wil - Thanks for coming by the website. My XPS knowledge is limited to the closed environment, aka the basement. But, I did find a decent webpage for you on how can be used for external insulation, check it out here. Good luck! - Jason
My basement has some old insulation above the frost line as well as some 2x4s nailed down to the concrete walls. We are going to finish the basement and remove all of the old insulation (we've seen some small skinks/lizards hiding in there as well as on our porch), and we want to use XPS boards along the walls before studding out and drywalling. I'm not sure how to properly remove the 2x4s, though. Should we just cut the nails so that the surface is flat for the XPS, or is there a better recommendation?
Carlos - Wow Lizards - thats a new one to me. We dont get many lizards in Chicago. Maybe a few mice that look like lizards, but I digress. I would remove the 2x4s before installing the XPS. If you remove the nails from your foundation walls be aware you may have just opened leak paths. I would recommend going back and sealing them with some sort of hydraulic cement and toping it off with a fresh coat of waterproof paint. See our article on that! - Adam
Hi Jason, I am a Midwest (MI) resident with both egress windows and daylight windows in my unfinished basement. I like the rigid idea but I'm wondering if R10 will be enough or if I should add fiberglass insulation between studs too? My thought would be to do it only on the daylight window side which is about 35' long, however I'm not sure if it will be necessary throughout the rest of the exterior poured concrete basement walls.
Thank you,
Sherri
Sherri - Perhaps Adam will chime in on this as well as he's out mid-west expert. I think your instincts are correct. You do not need additional insulation on top of the rigid foam board on the non-exposed walls. I suppose adding insulation on the exposed wall can't hurt and won't be very expensive, maybe a hundred dollars or so for the batt insulation. Good luck with your basement renovation - sounds like you have a great plan. - Jason
Thanks you so much for the confirmation, I have found great things on the site already so I know I'll be visiting again!!:o)
Sherri - I agree with Jason's comments. I debated over this very point for my basement as well and since I was finishing my basement in the winter, it was good timing for a test. After I installed the XPS, I felt like it stayed warm enough so I choose not to suplement the XPS with fiberglass batts between my studs. Supplementing with batts on one wall that receives less sun exposure probably wouldn't hurt and certainly would cost less than doing the whole basement. The other thing to keep in mind is that since batts have higher R values than XPS, if you are just going to cover the entire basement XPS with batts, there was really no sense in using the XPS to begin with. Good luck! - Adam
Aside from R Value, there is still some benefit to using batts in the stud wall in addition to XPS on the foundation wall (as opposed to fiberglass batts without using XPS). The benefit is that the fiberglass won't be coming into contact with the concrete and the XPS is acting as a vapor barrier, so you avoid the inevitable mold issue with fiberglass coming into contact with the bare foundation wall.
XPS isn't classified as a vapor barrier, but everything else you said is correct. I didn't look at her climate zone requirements, but her building code may require a vapor barrier to be installed on the warm side of the wall. And personally, if people can afford to pay a little more, I'd highly recommend using Roxul over fiberglass any day.
Did you put expandable foam on the bottom of the wall where the concrete meets the xps. I have read conflicting approaches to this.
Thanks.
Hey there Jason,
So unfortunately my contractor and I have parted ways, and he's got my money. (Hopefully Amex wl step in and I will get some of my money back).
I'm at insulation, drywall stage. Electrical, plumbing and hvac rough have been done and passed code. (Due to me going to county, getting another permit card..the old card mysteriously disappear, per said contractor)
But anyways, I've been reading more and more about rigid foam, which I even ask my contractor if there was anything that could go on wall, before stud that would've help moisture issues. He said "oh no, we will just use fiberglass insulation it should be fine", in fact he said he would only insulate walls facing walkout, And not concrete walls....but the sad thing is I wuda been willing to pay for rigid foam..
So, how can I now add rigid,( by myself and son);), now that the stud walls are up?? Can I cut, try to get it in there, seal with can of close cell(if it even comes in can) and the approved taping and then use fiberglass insulation??
Please help and Thanks
Natasha - Sorry to hear that. From what you described, at this point it doesn't make a whole lot of sense financially or functionally to go with XPS. The downfall of XPS is that you don't get as much R value for the thickness. If you have to cut it up to fit between studs, you are going to have to cut it VERY precisely so as not to loose R value from having gaps between the studs. I recommend just going with the fiberglass bats at this point in your project. Its a shame your contractor didn't really present you with the option. On the plus side, your basement should stay slightly warmer in the winter and cooler in the summer!
Good luck! Adam
Thanks a lot. I'm thinking I can put the 2" bwtn the stud, and seal with the foam board adhesive. It's going to be a lot of work, but I so don't want to use any fiber batts. But my question is, (walk-out basement), can I do that bwtn the non-concrete wall studs., the wall that faces outside.?
Hi Adam - getting ready to apply foam sheets to our basement and not sure how to go about applying drywall over top once the sheets are on. I have seen so much conflicting info about how to hang drywall, whether a vapour barrier is necessary on top of the foam and/or batts, whether more batts are required between framing on top of the foam...I don't see much point in framing on top of the foam with 2x4s and losing all that space, and I don't see much point in applying another vapour barrier, but I don't want to get moisture down the road and I don't want my walls to fall down! A guy at the home store suggesting applying smaller strips to the foam and hanging the drywall from this. Any advice you can offer as to how you did it? Just out of curiosity, which part of the country are you in? We are in Canada, so application may differ depending on how far south you are.
Hi Jen - Yes, one downfall with the XPS is you will loose some space in the room. My basement had rather large room sizes with my layout so I wasn't as concerned. If you use the thickest (2") XPS, you will loose 2" (XPS) + 1.5" (Frame) + 0.5" (Drywall) = about 4" depending on how much you space framing off XPS.
As for vapor barriers - I too researched this quite a bit and found sooooo many conflicting articles. Create one to keep moisture out, don't do one because it will trap moisture between the walls... etc. Quite frustrating. To mitigate this, I used waterproof paint on my walls - if you haven't read my article on that, check it out! Between that and the XPS, I considered myself good and did not use anything additional.
You could use thinner XPS, they come in many sizes, but just remember the thinner you go, the small the R rating. Since I am near Chicago, Illinois the winters can get quite cold so I wanted the thickest I could get - I imagine you would want the same for those Canadian winters? Good luck with your project!
Thanks Adam - so just to clarify - you say you lost 1.5" for framing - can you share a bit about how you framed? Did you do a typical vertical frame job like you'd see with batting insulation (if so, did you use batting on top of the 1.5" gap, or just not worry about it?), or did you do something different? I've seen a few different vids with different techniques. Trying to wrap my head around it all...
Jen - Sorry had a brain fart there - not 1.5'' should be 3.5" Was thinking of the 2X4 in the wrong direction. I framed in the traditional method as if you would install batting insulation. I did not install the batting insulation however. I figured the R10 XPS would do the trick for me.
I know I'm a few years late to this thread but since it still comes up fairly relevant in google I thought I'd chime in here. Adam, you are incorrect here. Before advising people on these issues, you should know what climate zone they are in and what the local min building codes are beforehand. (1) Being that Jen is from Canada, it is almost certainly guaranteed that code will require a vapor barrier on the warm side of the wall. he lower half can be the typical 6 mil poly or anything similar that is code compliant, and the upper half can be more of a smart membrane with greater permeability but it still must adhere to the same code. (2) You've spoken about insulation for heating/cooling purposes, but never touched on the most critical part of the equation, and that's air and vapor movement and thermal barrier and the resultant condensation problems that can occur. This is actually the main cause of mold in basements. The reason why 2" of XPS or an adequate layer of EPS foam is advised, depending on your climate zone, of course, but particularly in colder regions is because the R10 against the concrete provides an adequate thermal barrier and will prevent condensation from forming on the warm side of the wall. All gaps and seams but be properly sealed as well. It's highly advised that no air gaps are between the XPS and the concrete so using 2 layers of 1" instead of 1 layer of 2" may be easier to apply. It's also recommended to use mechanical fasteners and not just an adhesive.
Again, in colder regions, it's most definitely advisable to then put up a 2x4" wood stud wall spaced 24" OC with a pressure treated base plate. If you have the room to accommodate a 2x6" frame then do so. In either case, full the std cavities with mineral wool like Roxul and NOT fiberglass insulation. Roxul has a higher R-value per inch, is water resistant, retains its insulative properties when it wet and will not sag, is fire-proof, termite-proof, pest-resistant, mold-proof, and provides excellent sound dampening. You then must apply the vapor barrier (all sealed with acoustic sealant + tuck tape) followed by a 1/2" layer of drywall.
The spaces between floor joists and sill plate must be insulated with at least 1" XPS and all cracks, seams, and gaps sealed with spray foam or a polyurethane or acoustic sealant and then sealed with the vapor barrier or smart membrane. Rigid foam is combustible so by code must be sealed in by a thermal barrier of either drywall or 5.5" of Roxul, with the latter providing added insulation in a critical heat loss zone + provide sound dampening to the above floor. In the end, you should ideally want a min R20 wall. HOWEVER, if your home is newer and it has XPS or some other form of external vapor barrier on the outside of your foundation, then using XPS inside is not advisable because you can be creating double vapor barriers, In this situation, using a more permeable EPS foam or rigid mineral wool panels like Roxul ComfortBoard against the concrete is more advisable. The rest of the wall will be constructed as described earlier.
Todd, I agree with your theory. I live in Minnesota, and am currently finishing my basement space, a 1951 single story rambler with block wall foundation. Here is what I did:
- First off, I made sure there was no moisture problems to begin with. The first year of owning the home, there was a few spots where rain water came through after a really bad storm. After re-grading and extending downspouts, we have not had any rain issues in basement. Been dry as a bone.
- Next step, installed 1" XPS (pink board) insulation directly over interior of block foundation using Foamboard adhesive (blue in color), taped the seams and caulked the corners.
- Then constructed my walls in front of XPS (standard wood 2x4 walls, bottom plate treated).
- After running my plumbing and electrical, I filled my stud bays with Roxul.
- Then, cover my walls with a vapor RETARDER, not barrier. I chose to use a product called MemBrain by CertainTeed. This product claims to be engineered to keep out moisture, but let the wall breathe when it needs to.
- Finally, cover with drywall.
After a ton of research, I have found so many conflicting theories on the best way to insulate a basement. It's enough to make your head spin! I have spent more time thinking about the best approach to insulating my basement than any other part of the project. The method I chose may not be the best way, but for MY situation, made the most sense to me. Good luck to anyone trying to figure out their insulation, I still don't know what to do, haha!
Thank you Steve! Excellent summary and a very complete approach. Thanks for posting. - Jason
I have a 1950's brick rambler with walk out basement in Northern Virginia. I placed 2" xps board against the cinder block foundation wall all the way around (above grade side and below grade side.). I built a 2x4 stud wall against all of the exterior walls.
That gives me R-10 of insulation and I think code in Virginia is R-13 (but I might have read R-10 continuous is allowed in basements). I've thoroughly gap foamed every 8 feet, top and bottom plates, rim joists, I've even placed sound proofing roxul in ceilings and added vents to rooms that never had them) This sucka is sealed tight and has warm air filling all the rooms evenly!
My question is for my house being in Zone 4, is placing Roxul R-15 in the stud bays of the above grade basement rooms a good idea, or even necessary? Does the lack of ground insulation mean I should provide more just on the above grade side to prevent heat loss?
I would then leave the below grade basement rooms with empty stud bays. Or should everything be roxuled? Or none of it and the xps is enough insulation?
Ditto on the head spinning with conflicting information.
By the way I'm a year into my basement project and this website has been invaluable. Jason I believe you are located in Virginia so I'm hoping your experience can help me out of this conundrum.
There is a This old house video on Youtube that show how to attach 1X3 inch strips to the XPS wall.
it looks like a good way to save space
Why is there a window at knee height on your basement wall?
Cheryl - My geometry teacher always told us, "don't go on looks unless you are getting a date"... The bottom of the picture is not the floor line. The window is at a typical height.
Jason,
Thanks for the great insight!
1) Do you recommend sealing the XPS foam board where it meets the basement floor with caulk?
2) If using XPS foam board (which has a 'vapor barrier'), and I live near Chicago, what do you recommend between studs? Batt insulation? Would you still use a batt insulation with a vapor barrier? If so, would using 2 vapor barriers cause any issues?
Thanks!
You don't want a vapor barrier in a basement. There is quite a bit of info about this on the Building Science Foundation.
The entire idea is to manage the water vapor that originates from concrete. You don't want cold water vapor to meet warm air. That leads to condensation. The XPS is actually very slightly permeable to water. This is a good thing.
Some people erroneously state that XPS is the vapor barrier. That's not technically correct in the traditional sense. It does provide a barrier, but not the impermeable barrier that is usually thought of when using plastic sheets. Again, this is good. You actually want to facilitate the movement of the water vapor and XPS does this ... very slowly.
As the water vapor moves through the XPS, it is slowly equilibrated with the warmer temp of the room. Thus, condensation is prevented. So, you want: concrete, XPS, fiberglass insulation or empty void, dry wall, paint. That's it. Some fill the framing void with fiberglass insulation (no backing!), others don't.
Again, no vapor barrier. This includes the paint on your interior (drywall) walls. You want vapor to move all the way from the concrete into your living area ... and vice versa.
Good luck.
Oh, and yes, you generally use the foam in a can to seal at the bottom and top of the foam boards.
Do you use waterproof paint (dryloc) on the concrete before the XPS?
Again, incorrect advice. According to the Building Science Corp, in colder climate zones you need a vapor barrier on the warm side of the wall and it's required by code. You are correct that there are a lot of issues with vapor barriers and condensation, which I explained in my previous comment above. To help prevent this, enough insulation must be applied to create the required thermal break, and this is typically considered to be ~R10. If insulating on the inside, using rigid foams like high density EPS isn't a bad thing because they are more permeable and some air movement through the concrete isn't such a bad thing. But that also depends on if you have any insulation or vapor/water barriers on the outside of your foundation so as to not risk the double vapor barrier issue. If you use enough XPS or ISO foam (which has foil on both sides and is actually considered a vapor barrier) then you may not require a stud wall or a secondary vapor barrier. If ISO you technically aren't required to cover with a thermal barrier, but with XPS or EPS foam you must provide that fire barrier. If a studded wall is not required, you can install furring sticks on the foam and attach the drywall onto this. This will leave an air gap between the drywall and the foam. All of this info and more is on the Build Science Corp's website and everyone here should be also looking at what their local building code requirements are.
Do you frame your wall up tight against the board?
Yes. Frame it up tight to the XPS.
Hey guys! So, I am just finishing the waterproof paint application on my basement walls and am thinking it is getting close to time for XPS but I want to make sure that I don't have any water issues going forward. (I'm the kind of guy that likes things done right the first time, (If possible.)) I have added a total of 4 cubic yards of dirt to the exterior next to the foundation to improve the grade away from the walls and ensured a 6' gutter run-off all the way around the house. My question is; do I need anything additional to the paint and XPS/spray foam/tape to ensure a good vapor barrier? The last thing I want is to deal with mold/mildew issues. Thanks guys! Love the site! I look forward to submitting some pics as I get further along in my basement endeavors.
Don't you need to add drywall on top?
I have been said that the XPS is flammable.
Yes, all EPS and XPS foam must be covered.
Should I hang XPS horizontally or vertically? Notice you went with horizontal; reason for that?
You can hang it either way. Many come with tongue and groove joints but either way I recommend putting a bead of polyurethane or acoustic sealant or spray foam between each panel and around the wall parameters and sealing all seams with tuck tape. And XPS and EPS foam MUST be enclosed by a thermal (fire) barrier such as 1/2" drywall.
Hello, if you install rigid foam insulation to a concrete basement wall can you leave it unfinished like that or do you
have to install drywall on top of the insulation?
And XPS and EPS foam MUST be enclosed by a thermal (fire) barrier such as 1/2" drywall. PolyISO foam does not have to be covered, but double check with your local building code.
Is the foil faced rigid board the PolyISO that you mention? If so, can I apply paneling to it? I have a 9 x 16 "room" in my basement that I want to "fix up" to look decent, but on a strict budget. Can I apply paneling to the rigid board? If so, how? It's the thick board so I don't want it to take up much more space and also don't want it to be too permanent as I may want to expand the "room" at a later time, so don't really want to drywall at this point.
I'm curious on the best approach for insulating over a membrane in the basement. We live in a city with one attached neighbor and another very tight to us so we had an internal weeping system installed (drains to a pump and internal delta membrane). I was contemplating putting up rigid insulation on the walls in the basement overtop of the membrane then framing to lock it in but was told this could create condensation between the rigid insulation and membrane which may become an issue. Any tips on how to insulate and frame a basement over the membrane?
Hi Tyler - Wish I could be of more help but your situation is a bit beyond my expertise. Sorry, good luck. - Jason
Do you know if the walls have to be perfectly smooth to install XPS properly? We have an old basement and there are ridges where the wood frame was when they poured the concrete. Should we file those down before installation?
Hi Laura - No, they do not have to be perfectly smooth - you should be good to go. - Jason
Jason, my basement's walls are also rough. They are 1890's large stones with 2-4" irregularities in depth along the surface. I plan to glue 1.5" XPS to the walls (I live in NJ), with panels adhering only on the areas of the stone that jut out the most. Should this give it enough tooth to stay put? Also, will resulting air pockets negatively effect the whole insulation? I'll cover it with 1/2" drywall and framing pushed right up against the XPS. Thanks a lot for your insight on this. Jeff
DON'T use XPS foam panels in your situation = epic fail. You need to do research on foundation walls like yours and speak to your local building inspector to find out what code is. But using rigid foam panels here is a big mistake. Read up on it on Build Science Corp's website. I don't know the best answer by maybe having a professional come in and spray foam it is the best option, and I'm guessing you'll need at least R15 or so. And not to keep repeating myself on this forum but there is a lot of misinformation going around... your local code may require a vapor barrier so look into that... but the spray foam classifies as one.
I hate to keep having to say this, but Jason is not correct. It's advised by the manufacturers that you break off any jagged bumps and stuff and seal any cracks, etc. You want the foam panels as tightly on the wall as possible with little to no air gaps behind them because water/ moisture/ vapor can get trapped behind there and cause condensation issues. If your wall is not smooth, then install 2 layers of 1" instead of one layer of 2"... they will bend and conform to the contours of your walls easier. You should also use a combination of appropriate foam adhesive and mechanical fasteners. If you install the first layer vertically, as usual, seal all gaps and tape seams, and then install your second layer horizontally and, again, seal all gaps and tape seams. Building code will require you to cover any EPS or XPS foam with a thermal (fire) barrier like drywall.
Todd, what do you recommend for a basement wall where I have pipes basically right on the wall. Does it make sense to put the rigid board in pieces around the pipes?
Hello, in live in Wisconsin i bought my first and it was built in 1960. I want to finised my basement but my question are 1st one wall is supported with metal support beams, 2nd i want to seal the wall with 1/2 inche thickness 4'x8' pink insulation foam along with the fiber insulation but not sure if the 1/2 is good enough?
1/2" isn't advisable, as it doesn't provide an adequate thermal break, and I highly advise against using pink (fiberglass) insulation in basements, particularly those that are damp. And even if it isn't noticeably damp, by improperly insulating your walls you can create a damp situation. I'd use Roxul over fiberglass any day!
Since I am getting ready to finish my 1600+ sq. ft. basement I have been researching the right way to insulate it for a long time. This is the first step that I will need to do and thought I would just pass on what I have learned and what I am planning on doing. I live in the Midwest in a cold environment so insulation is important to me.
The first thing I learned, and probably one of the things most people overlook in trying to make their basement more comfortable, is that you need to insulate the rim joists. Most homes, mine included, have fiberglass batting shoved into the cavities. There are two problems with this. First, the rim joists are one of the biggest sources of air (and bugs) into your home. The fiberglass insulation isn’t airtight so air will still get past it. Second, there is a lot of air exchange happening in that spot with the cold outside air and the warm inside air. The result of this can be moisture. As stated in other posts, that is a problem for fiberglass insulation as it can promote the growth of mold. I will be removing all the fiberglass insulation in my rim joists and replacing it with a piece of XPS that will be sealed with expanding foam around the edges.
Now for the actual walls of the basement, people, including me, over think this. If you have a newer home, you may actually already have XPS on the outside of your foundation. This is a very common practice and actually the preferred location for the board. If your home doesn’t have it, which mine does not, then it can be a good idea for the interior wall. So the next thing I had to do was to figure out whether or not I should use the XPS and then additional fiberglass insulation between the studs? For me, in the climate I live in, the simple answer was yes. And the reason I say yes is that it all comes down to R-value of the insulation. I live in zone 5 and the recommended R-value of insulation in a wall is R13-R15. If I put a 2” thick board of XPS up on my walls first, that gives me an R-value of 10, this means I need to put in additional insulation of R3 to R5 to achieve the recommended level. If I want to save room and only put up a sheet of 1” thick board then I get an R-value of 5 for the board. Thus, I need to add an additional R8 to R10 of insulation into the wall cavity.
Sorry for the long post. :) Hope this helps some people.
Very insightful, thank you Theodore. - Jason
for rim joists, I recommend PolyISO foam, not XPS foam
PloyISO also has a slightly higher R value
Either way, the gaps have to be sealed and the R-value difference is only about R1.7... but the polyISO doesn't technically require a fire barrier. But it's not pest-proof (no foam is), tho the foil can help. Either way, I'd put in 5.5" of Roxul for the reasons I described above.
If, in the end, you installed 3" of XPS or put 2" XPS and an inch of EPS, this must be covered by a thermal (fire) barrier like drywall. And if your method adheres to your local building code, then you should install furring sticks between the foam and your drywall, so as to leave a small air gap between the two. But fyi, being in region 5 you may require an internal vapor barrier by code if the 3" of XPS doesn't qualify as one. Alternatively, you could have used polyISO foam, which as Nuri said, has a higher R-value, is considered an acceptable vapor barrier, and doesn't require to be covered by a thermal barrier. But that XPS foam in your rim joists must be, and may first also require a vapor barrier installed over the foam. Personally I'd recommend 5.5" of Roxul to cover the foam because it's a fire barrier, good insulator but air permeable, is pest-resistant, mold-proof, water resistant, and has good sound dampening properties.
I went with 2” rigid foam, attached 2x2 furring strips (5” tapcons thru strips and foam to concrete), then filleted R11 batt insulation in half to fit in the 2x2 wall cavities to get R15 total.
We have a room in our finished basement that we want to put rigid insulation onto to keep the cold out. The problem is the room is only 5' wide so we don't have room to build the frame for the wall board installation. We'd like to put the rigid insulation up, but do the framing & wallboard in the warmer weather. Is it ok to do a phased installation like this & will the rigid insulation help keep the cold out without the wallboard installed?
Thanks!
All XPS and EPS foam must by law be covered by a thermal (fire) barrier and if that is all you're putting in there for insulation, then you need furring sticks between the foam and the drywall. And fyi, people seem to be so unaware of this, but depending on your climate zone you may be required by code to also install a vapor barrier on the warm side of the wall, so check with your local code. Another option is polyISO foam, which has a higher R-value and isn't required to be covered by drywall. Lastly, again, based on your climate zone, R10 alone might not be sufficient, so if you are planning to stud the wall then install at least R14 Roxul (and vapor barrier if required). Alternatively, install thicker layers of polyISO because it also classifies as a vapor barrier... seams all sealed and technically doesn't require drywall.
Hi quick question... I currently have the basement preframed from a previous owner. They had a rodent problem so I had to tear all the old insulation out. I'm thinking about the foam board and not sure if its an option for something preframed. Can I install it behind the frames where I can slide it in? It will leave a gap between the board and the studs. Also can I put it in between the studs in other areas? Thanks so much for the help.
No solutions but we areally going through same situation. Dodd you find a solution?
Foams are not rodent proof. Some have started incorporating pesticides in the foam, however. Using rock mineral wool like Roxul should keep pests out (considered pest-resistant and insects like termites hate it, but they will burrow thru foam!) and it has so many better qualities over fiberglass. You might even need any foam anyway... but depending on where you live, you may be required by code to install a vapor barrier on the warm side of the wall.
How far does the adhesive go? How many 4x8 insulating boards will you get with one tube? Do you recommend also using a few tapcon screws with washers per board?
I just put a bunch of 2 inch thick XPS on my foundation walls and I ended up using about a full tube of adhesive per 4x8 board. I believe the author also mentioned that about a tube per board was good.
Another hint - I tried to apply my adhesive so it was vertical to the wall. It seemed to make sense to me in that if I did it horizontally, it could potentially trap any moisture as it would provide a bit of a shelf. Not sure if there is any validity to that, just thought it made sense.
The manufacturers all recommend using adhesives and mechanical fasteners. nd they also advise that the panels must be flat against the wall with no air gaps that can trap moisture between the foam and the concrete. If your wall is uneven or a little bumpy, spray a little spray foam in the areas so the gaps are filled and consider installing 2 layers of 1" instead of one layer of 2" because the 1" pieces bend easier. You still have to seal everything up. And if you did this, run the first layer horizontally and the 2nd layer vertically (or vice versa). XPS foam must also be covered with drywall as per fire code and I wouldn't recommend putting drywall directly on top of the foam.
Why can't the drywall (basement board) be glued directly to the POLYISO board?
Hi Jason,
We are keeping our ceiling open in our basement with our floor joists exposed. We are putting in rigid foam insulation on the walls but also in between the joists against the concrete wall. Any thoughts on how to cover that up when we finish the walls? We plan on framing over top and drywalling the walls so what can we do between the joists?
Thanks!
Chris
Put in 1" of XPS foam between joists and seal joints with spray foam. This foam must be covered by a thermal (fire) barrier and 1/2" drywall counts... but personally I'd put 5.5" of R20 Roxul over the foam... added insulation, is a fire barrier, provides sound dampening, is pest-resistant, etc. If you want to fill all of the space between the floor joists, not for insulation (because that's not advisable) but for sound dampening between the basement and main floor, then install Roxul ComfortSound or whatever it's called... I can't remember. But it's just a sound dampening product and not considered insulation.... I'm going to put in my ceiling and internal walls to keep the house quieter. Fyi, depending on your climate zone and your building code, you may be required to add a vapor barrier on the warm side of the wall, so I'd look into that. And, again, depending on your climate zone you may need additional insulation between the studs. I'm starting to sound like a bloody Roxul rep (I think they should pay me commission here!) but I'd install that (ComfortBatt) instead of fiberglass. It's a little more expensive but I have explained several times throughout this thread it's benefits over fiberglass, so read them above. I'll never use fiberglass batt again! Lastly, your foam wall will need to be sealed in with a thermal (fire) barrier like drywall to meet fire code.
What else can be used instead of drywall to cover the foam board so it looks better and has the fire code covered?
Cam XPS foam board be used to replace sheetrock/drywall in a below
ground basement apartment?
I was going to put in new flooring( as soon as I feel confident what flooring is not
toxic to humans/animals). There was black mold in the bathroom walls.
Now all the sheet-rock/dry wall has to be removed. The basement doesn't have any water leakage. Even below ground, it's seems dry. But moisture is always in cement/cinder block. Which allows mold spores to grow into wall materials.
I'm trying to find any products that can retard mold/mildew from growing in hidden places. Is XPS a "nontoxic" product to use as replacement for sheet-rock/drywall? I'm 60 miles north of San Francisco, CA. It's not that cold, but damp winters when we have rain. Calif has prop 65 compliance and CARB about toxic product/materials being used in building.
Thank you.
You can use bleach to kills the mold and there are procust like Mold Off or something like that. Be sure to clean very well. Question is, was your drywall placed directly onto the concrete?? Were there wood studs and were these placed against the concrete wall?? Was there pink insulation in there, again, touching the wall?? If yes to any of those, then there's your answer... none of those should be touching the wall.
After cleaning all the mold, determine if you have a moisture problem before installing a new wall. Seal any cracks and if you need to consult with a specialist, I would. Btw, you mentioned cinder block... they are different to poured concrete foundation walls so what might be good for concrete walls isn't necessarily good for cinder block walls. The cavities between the blocks could be filled with water, for eg.
Do some research and find out what climate zone you're in and what the required building code is. Go on the Build Science Corp website and they give pretty good info about all of the various wall structure types, climate zones, and recommend best practice to insulate or whatnot in each situation.
Fyi, contrary to popular belief, XPS can actually absorb water; albeit, a small percentage relative to its weight. Point is, don't consider it to be a product to seal a wall. And painting a wall isn't the most effective thing either because wicking moisture will eventually pop it off. Consider a penetrating concrete sealer. But again, I'd do research and consult with local pros.
I've decided to tackle my basement and am ready to begin....thanks in part to the confidence built from this site. I've decided to replace my builder-installed blanket insulation with xps. My question refers to the small nail holes in the cinder block wall where the builder secured the blanket insulation. Do these holes need to be filled before putting xps up, or is that just an unnecessary step. If I fill these, what would I fill these with (i.e. mortar, cement patch, caulk, etc.) Thanks a ton.
Hi Ed - To be honest.. I don't know. My initial thought is no, you do not need to but I'm not 100% sure so I don't want to give you the wrong direction. I would check with your XPS provider/manufacture and see what they say. If you get a definitive answer would you please re-comment back here so we can all know the answer? Thanks! - Jason
here's the answer...yes
here's a great video from This Old House
Thanks David, great video! - Jason
I should add that there is some controversy about the video...specifically about nailing the tie rods further into the wall and potentially out the other side a bit.
With that said, I would still patch those holes.
FYI, I'm in leesburg, and your site has been great as I plan my basement refinishing project.
Is it an issue if I have to build the framed wall out an inch or two away from the rigid foam boards?
Thanks Chris
Hey Chris - No issue, you'll just need to put in some fire blocking. Read here for more info on fire blocking.
Hi Chris, If I add some Fiberglass batts in the stud after I have followed all your introduction,should I need a poly-vapour barrier? Thank you! Please let me know a.s.a.p, because I am d.i.y my basement now and stucked here....
We want to do a mini fix-up of our unfinished basement to create an area for the kids to watch TV with their friends. All we wanted was to make the walls look nice and not be so cold, and throw down a piece of outdoor carpeting. Our idea was to take the 1" XSP boards and attach it to the bare concrete walls, and then paint it. We are not planning on framing, drywalling, etc. Is there anything wrong with doing that? Are we creating any hazards for fire, mold, etc.?
Hi Kathy - Sorry, I can't really advise on that issue specifically. My guess is that there's no issue as paint rarely creates a fire hazard but that's not really my area of expertise. When you decide to buy the XPS I would talk to the sales person there and get an official opinion - or check in with your local building department - they will almost definitely have an opinion. - Jason
I just have a simple basement that I would like to insulate. I don't need it finished as it won't be a true living area, but would appreciate the R-value. Could I just paint the insulation? I just don't want to look at bright pink when I'm doing laundry.:)
Hi. I need some help please. Im about to finish my concrete basement walls. I live in northern Ontario where winters are cold. I plan on attaching 1 inch foam board insulation to the concrete wall and seal all seams with tuck tape. Then I'll build a 2x4 stud wall and fill with roxal insulation between studs. Will this be enough insulation? And I've read that with the foam board on the concrete I should NOT use poly vapour barrier between stud wall and drywall. Is this true?? I don't want problems in the future.
Please help!!
I skimmed this page and didn't see this - so sorry if it's already been mentioned.
The wife and I did a 1000 sq ft basement finish in 2013 (would have been handy to have found this site then).
We did XPS on the block walls, doing the same as you mentioned - glue on the back, then 2x4's to hold them in place. This got old quick. It didn't help that some of the XPS boards were slightly warped (pay attention at the store when you purchase these). We ended up having to cut sheets into smaller sections to get them to cooperate = added install time.
Tube after tube of foam adhesive, this was getting expensive. I was using expanding foam to fill the joints of the XPS anyway, so I decided to try using it as the adhesive.
Spray a thin line of it in an S pattern on the back, press to the wall, place a 2x4 to hold it in place. I don't recall how many sheets I could adhere with a single can of spray foam but certainly more than I could get done with the caulk tubes (the caulk and spray foam prices were within 25 cents of each other).
I've also used this method for doing the sill plate / rim joist. Cut the XPS to fit pretty close, spray foam on back, press in place, spray foam the perimeter of the XPS, move onto the next. It's crazy how much energy is lost for the relatively little area that's there. Those fiberglass batts just don't cut it.
Firstly, the manufacturers all recommend using mechanical fasteners and not just an adhesive. Secondly, a simpler solution would have been to install 2 layers of 1" instead of one layer of 2" because they can bend and conform to uneven walls easier. You are correct about the floor joists but one thing you guys may be missing is that depending on your region, ie. climate zone, you may be required to install a vapor barrier or smart membrane that conforms to code on the warm side of the wall. Lastly, all XS and EPS foam, be it on the walls, on the floor/ slab, and in between the floor joists bust be sealed in with a thermal (fire break) such as 1/2" drywall. In the joists, personally I'd place 5.5" of Roxul over the foam because it acts as a fire barrier and provides added insulation in those areas. Oh, and if your local building code requires you to have a vapor barrier, then that has to also extend up and into the floor joists and sealed over the foam you put in... then cover with Roxul and/or drywall.
I'm just in the planning phase of a future basement remodel. My plan is to finish off about 3/4 of the basement area. The remaining 1/4 is the laundry area, furnace and storage. I only planned on using the XPS in the finished areas. Do you see any drawback to that? Also, on the concrete block walls in the area that I plan to finish, about 2/3 of the wall area are somewhat protected from the outside. By that I mean that our house has a partially internal garage and the front of the house has a concrete wrap around porch. So the basement walls that are under these protected areas have always been very dry. The remaining 1/3 of the basement wall area has the upper two rows of concrete block exposed to the rain and snow. I was thinking about using 2 inches of XPS in that area and then only using one inch of XPS on the basement walls in the areas that are more protected from the exterior by the internal garage and wrap around front porch. Do you see any issues with that? I was planning on also using spray foam or cut pieces of XPS in the rim joist area. The rim joist area seems to be the main area where the coldness comes through. Please let me know your thoughts.
Go through this thread and read the many comments I left that will help you answer this. Moreover, XPS isn't used to seal your basement from water seepage, it's an insulation. You don't see a moisture problem on your existing concrete because it's exposed and water vapor can easily evaporate through. Problems arise when people don't insulate properly and/or use the wrong products for their application/ situation. If you live in a cold climate, then yes, I'd insulate all of the walls. And if your house is a newer construction it probably has exterior foundation insulation and other water barriers, so depending on what those are, using XPS in the interior may not be the best choice. Read up on the Building Science Corp website and find info about homes built like yours and for your climate zone. There are also multiple videos on youtube that cover this topic but take what people say with a grain of salt. Read up on BSC website and find other credible sources like building organizations and government sites, and can't hurt to speak with your local building inspector and get info from them.
After you studded your walls against the foam board, did you add fiberglass insulation? If so, which one? I have been getting mixed results when researching, use paper backed, dont use paper back, use vapor barrier, use vapor retarder, dont use any vapor barrier or retarded with the xps foam boards. I am at a halt before I can start drywalling.
I intend to apply Owens Corning Foamular 2 inch to interior concrete block basement walls. There are existing framing base plates attached to concrete slab floor. The floor and the wall do not meet at square edge-- a bit curved. Thus, there will be about a two-inch gap between foam board and wallside of stud. Framing will be covered with drywall. I live in Northern Virginia. I would appreciate your thoughts.
I am in the pre-planning phase of finishing my basement. I live in a brand new home (under 1 year). We have a Tuff-n-Dri basement waterproofing/insulation system installed on the outside of our home. Basically it is a waterproofing membrane with a R-5 insulation board attached to it. It came with a 30 year warranty.
My questions are; EPS or XPS board for walls in my situation? Do I still need a vapor barrier before drywall? Would painting the block wall in Drylock be advisable in my situation?
Any help or info anyone could generate would be awesome. Thanks!
Everybody, please read this article :
http://www.greenbuildingadvisor.com/blogs/dept/musings/how-insulate-basement-wall
Todd - from the BSC site.... (it says no interior vapor barrier...
In most basement wall situations, the foam plastic insulation material will need to be covered by a fire/ignition barrier. Half-inch gypsum board usually provides sufficient ignition barrier (check your local building code). When this ignition barrier is supported on a stud wall, the cavities of this wall may be filled with supplemental insulation. It is important that the airtight foam insulation assembly be continuous behind the framed wall. No interior vapor barriers should be installed in order to permit inward drying.
Curious question: if you are covering foam board with a 2x4 stud wall filled with Roxul, then is a minimum 1/2" of sheet rock still required on face of stud wall or would a 3/8" sheetrock be permitted because of the use of Roxul inside the wall cavity?
Jason,
I bought your E-book which has been very helpful. I need to insulate my rim joist before I install my sheetrock ceiling. They are cantilever overhangs which I installed blocking between the inside and outside which is most likely overkill, uggg. Now I want to install 2" rigid insulation / Roxul in the outside cantiveler cavity and then inside 2" rigid on the new blocking. What type of rigid inulation do you recommend? Poloyiso or XPS? What is best pratice?
I have a very unfinished basement that is used to store my stuff. My key concern is that the walls are uneven rubble stone that is not only uneven but also not square.. That is the walls push-out and I can't imagine being able to use adhesive to hold the insulation panels in place. TWO concerns on using it. One, how to hold it against the uneven wall and dampness & water being trapped behind the rigid insulation. Any ideas?
Hi Ken - I afraid I can't give you any educated answers for stone walls. I'm only familiar with block installation. My "guess" would be to frame your walls first, then apply your insulation to the framing and leave the stone untouched. - Jason
Jason, I live in Massachusetts. When I moved in to my 60 year old cape 10 years ago, I painted the entire basement-including the floor, with waterproof paint. I intended to finish the basement fairly quickly and had one side framed in , but that's as far as it got. I'd like to finally finish the project but I'm not sure which type of insulation I should use now that the walls have been framed. Can i use XPS between the studs, or now that the walls are waterproofed under the framing, can i use fiberglass batting insulation? Which would you recommend? Thanks
My recommendation would be to use fiberglass batting between the studs. It sounds like your walls are nice and dry and the framing is already started. Good luck! - Jason
Hi there! This site has been very helpful, thank you! I have a cinder block house and the basment is already framed. I had it waterproofed (french drain, dimple matting, and waterproofing paint) but the paint is only halfway up the wall. I'd like to add insulation and figured batt insulation made the most sense since the walls are already framed, but wasn't sure if I need a vapor barrier or something else between the batts and the wall. Any suggestions? I'm in NJ
I have had 3 different bids on doing our basement and 3 different ways they approach insulation and drywall. I'm utterly confused and overwhelmed. #1: 2X4s an inch away from cement walls, no insulation and drywall on top. #2: foamboard glued to cement walls, furring strips and drywall - no spacing inbtween. #3: 2X4s, pink insulation and drywall. I live in Indianapolis. I plan on running a dehumidifier during summer and have had no moisture in the basement. Which is the right way?
Hello, could I use 3/4" rigid foam board on my basement walls then build a stud wall and then put fiberglass insulation between the studs plus another vapor barrier? You
Question:
I just came across your very interesting website. I have the rigid insulation on my basement walls and I am about to put the stud wall up. My question is how much space should I leave between the studs and the insulation? I was told that the studs should not touch the rigid foam insulation
Yes, it should not touch. Good luck! - Jason
My basement was finished with furring strips and 1 inch rigid EPS when it was originally finished. The house was a foreclosure and sat vacant for a few years. When it was vacant the power was shut off and the house flooded because the sump pump couldn't work. When I moved in a gutted the entire basement and now I am finishing it. I would like to use rigid XPS, but the plumbing for the laundry room and old bathroom are right up against the concrete block. Any suggestion on what to do here? I've not been able to find any information on rigid foam around existing pipes. Thanks
My uncle is a contractor. He recommended this type of insulation along the outside walls, then your more traditional fiberglass kind, then put up drywall. What is your opinion?
Hey Rhonda - That's definitely an option. I guess it depends where you live and what kind of R-value you're trying to achieve. -Jason
Can I use styrofoam insulation between the joists in my basement. I have a well in my laundry room. Walls are insulated and dry walled
Hey Richard- Most experts agree that there isn't really a reason to insulate between conditioned spaces unless your doing it for acoustics. I wouldn't use a vapor barrier between floors, but others may disagree. Good luck.
-Jason
Can I glue either side?
Hey Jame - You should be able to glue either side...just make sure your glue doesn't dissolve the foam.
-Jason
Hi, thanks for your informative website! I live in the Northeast. I have an unfinished basement. The ceiling has batt insulation with paper facing up against the 1st floor flooring. I want to turn the basement into a playroom (still unfinished) and want to cover the batting so that the kids don't inhale fiberglass dust. I am a single mom. I do not want to hire out so drop ceiling (cost) or drywall (too heavy for me) is out. Can I put XPS on the joist over existing batt? This is more for esthetics than insulation benefit. Question is, will the XPS trap moisture between it and the batt? Any insight is greatly appreciated!
Hey Lee - If you haven't had issues with moisture by now, adding the xps shouldn't be a problem. You could also put up 1/4 plywood if you're trying to keep the cost and weight down.
- Jason
Hi Jason. I am partially refinishing my basement. I like this type of insulation because it will help me get the most space possible. the basement is small. Do i need to put drywall on top of this insulation or can i just put something decorative? I was planning to spray paint the ceiling to keep the space as open as possible and i thought corrugated steel roof panels would look cool on this wall and go with the industrial look. thank you
Hey Linda - You don't technically have to put drywall over it. I like your industrial chic vibe.
-Jason
Hi, in all the articles on this site, I see nothing that addresses "draft stopping." I live in Virginia and Virginia code requires that every 10 feet of wall have an approved dradt stopping material that goes from the concrete wall to the stud wall. Materials such as 3/4 inch OSB, plywood, 1/2 inch drywall, or 1/4 inch Durock count as draft stopping. The draft stopping has to bridge the space between a stud wall offset from the foundation wall, and has to run parallel to the studs... i.e. from the ceiling (well the fire blocking under the floor joists) to the floor. With that requirement, what's the point of using XPS? Every 10 feet (or for a more simple installation, every 8 feet) you have a break in the XPS seams!
Hey Matt - Not sure I understand your question. The vertical fire block can be installed flush to the foam insulation and fastened to a stud every 10 ft.
-Jason
Ok. This will seem very unusual. We are planning a "themed" basement, that will look like an ancient temple or tomb, ala Indiana Jones. We would like to use XPS behind the framing. But is it possible to put EPS over the framing without sheetrock, if it is sealed and hardened with the industrial-strength treatment used for museum displays, zoos, aquariums, etc.? The EPS will be used and shaped to create the faux stone walls.
Perhaps this question was too esoteric.
My apologies; I just saw your private response. For some reason it went to my junk email.
Hi Jason,
I am hoping you are still actively reviewing this website! It has been a huge help.
I am planning my basement remodel. Background:
- I have poured concrete walls, with most of it below grade.
- I have already installed a backup sump pump with battery backup.
- I have added about 4 cu yards of dirt around the exterior of my house to help the water flow away.
- I live in Wisconsin.
- The house was built in 1995.
I am planning to frame in the basement and am really confused on what I should be using for insulation. Connected to the joist are 2x4's that but up against the concrete (this would be considered the top plate of the framing wall.) I believe these are there to prevent any kind of shift of the house?
Anyway, I want to build the rest of my framed wall off of those, so all I need is the studs and the bottom, treated plate. Problem is, I don't know what insulation to use. If I have to use XPS, I would have a gap due to the 2x4 top plate. I would prefer to faced insulation roles with a vapor retarder, but am not sure if that is sufficient. Any help would be great appreciated!
Hey Beau - I think you're referencing what's called bridging for your top plate. If it were me, I'd move that top plate out and use fiberglass insulation for your application.
- Jason
My daughter and son-in-law are buying a brand new house that we observed as it was being built. I noticed a corner in the basement where there is a door to the outside. Against the wall not containing the door on the floor for 10 ft and against the wall containing the door on the floor heading away from the corner for 5 ft there was styrofoam about 2 inches thick by at least 4 inches above the floor level; I don't know how much below basement floor level. I was told that it is a thermal block. I don't know exactly what that is and I don't know why it isn't further along the walls. Now that I think about it a little bit more, I have a feeling it has to do with the fact that in the vicinity of the door, it may be much colder outside because it is not under ground. So, answerman... am I right? I was able to push the styrofoam toward the wall and there seemed to be slight space in between the floor and the styrofoam. Is that normal should there be a sealant or some sort of there?
TIA
Hey Matthew - I love that you referred to me as, "answerman". I'm having a little trouble following where the styrofoam is located, but sounds like you might just be seeing where the foam was used as a concrete form. If you can peel it away and there's concrete underneath, then I'd say that's the culprit. Feel free to email me a picture.
-Jason
Hi. Great info! What do you recommend using on the floor? I plan to install laminate flooring. I know some people who have laid rigid insulation directly on the concrete floor and the laminate directly on the rigid board. What are your thoughts?
Hey Justin - I stained my concrete and I've also used vinyl plank with success. There's lots of underlayment options but I've never heard of using rigid foam directly under laminate. If you're not concerned about losing too much headroom you could install rigid foam with OSB on top.
Hope that helps,
Jason
I live in PA and when they installed our internal french drain they cut the finished walls about 2 feet up so the studs and wall need to be rebuilt. They used batt insulation behind the drywall. I'm going to rebuild the bottom part of the wall and am not sure what to do for insulation. Should I just use batt because that's what's already in the rest of the wall or should I use XPS with or without batt on top of that behind the new lower part of the wall being built? I know XPS is better but am not sure how much it matters seeing as how the rest of the wall already has batt installed. Thanks.
Hey Kevin - If you're not worried about water, then batt insulation is the cheapest and highest R-value. Given its the lowest 2 feet, you probably don't even need to replace it unless you have a walkout basement. The ground will do the insulating for you.
-Jason
Hi there..... I have been trying to find out the best way to reduce mildew odor coming from a small crawlspace below our entryway. I thought I would be using a combination of DryLok Paint and vapor barrier plastic.... but now Ive been reading that it may be best to go with the rigid foam with NO vapor seal because the idea is to not trap the moisture but to keep the warm humid air from touching the cool concrete wall... So Im going to try this... Here is my question... what do I do about the concrete slab floor in this small crawlspace?.... cover it with the rigid foam? Paint it with DryLok? or cover it with vapor barrier plastic?.... and last question, we are putting a tile floor above the entryway over new plywood subfloor... Im reading that I should NOT use a vapor barrier between the crawlspace and under the subfloor.... should I use regular soft insulation?... again looking to minimize mildew odor traveling up into the our foyer above.... Thanks!!!
Hey Edward - I would just seal the concrete slab, Drylok is a good option. I agree that you don't want to create what they call a "diaper" wall and trap all that moisture. I would use an unfaced batt insulation under the entry way.
Best of luck,
Jason
I know you posted this article a long time ago, but I just came across it. I am planning to use 3 inch XPS, 2 x 8 sheets (the distributor does not have 4 x 8 sheets in stock). For attaching to the walls, I plan to use some adhesive, but also use plastic fasteners, probably two per sheet. So, my sheets will be glued and screwed to the poured concrete foundation wall. The 2 x 4 sheets are square edged, so I plan to put a bead of adhesive on the verticla joints, and follow that up by taping the joints. Do you have any other suggestions?
I am planning on using Dow Super TUFF R glued to my basement walls, with 2 x4 framing up against the TUFF R. I wanted to use THERMAX, but can't find locally. The Tuff R has foil facing on both sides, like Thermax, but one side is blue and I don't think the foil on that side is the same as Thermax. If I put the silver foil side to the cement wall, do you think I can use EnerBond foam adhesive ( which is recommended for Thermax), or do I have to use a foam caulk type adhesive like PL300 from Loctite? I really prefer the Enerbond ( or Great stuff wal and floor foam adheasive), but don't want to use an adhesive that will eat in to my foam board. All advice is welcome. Help !
I removed face brick off basement stair walls. One wall is against a partially finished basement. The other is against the garage wall. Where this wall is below the grade of the garage floor, I THOUGHT OF USING 1/2” pink extruded rigid foam. Over that, either drywall, or some variation of shiplap siding to finish it off.
I’m trying to skinny this because it’s a narrow stairway.
I assume you covered the pink board with drywall?
You said that "If you live in a colder climate (like Michigan, Canada or the North Pole)" you will want to add 2" of rigid foam insulation between the concrete and the studs. What if you live in a warmer area? I live in southern Virginia in the mountains. It gets "cold" but not like Michigan, Maine, or Canada. The coldest sustained temps might be the 20-30s.
Is 2" still recommended? or is 1 1/2" ok? Or is the rigid foam not even necessary? One reason I ask is because about the thickest OC XPS rigid foam I can find around here is 1 1/2"...
Can I install 1 in XPS then FG in the bays against osb? I want to maximize the insulation on the above grade wall. I put 2 in XP’s on concrete walls and finerglass between the bays. Thanks!
I’m working with a local carpenter to finish my basement. He stated that I don’t have to insulate my cement walls since the exterior of my home already has 2” compressed foam insulation. Would this be a correct statement?
Hi - nice thread. Lot's of good info. I have a simple wall prep question: planning on using rigid foam over a poured concrete basement wall. Do I need to chip down the concrete form seams so the rigid foam board fits flush with the concrete wall?? Thanks!
After I waterproof paint and install the foam sheets on my concrete basement wall, can I just attach drywall directly to the foam wall? Can I skip framing on the wall?
Can I put 2 layers 1 1/2 inch XPS to give an R-value of 15 with no fiberglass.
Apply sealant to edges of xps and don't need to tape?
Hi, thanks for all the information this site. I plan on insulating with XPS. My basement wall has a "step in it." That is, the lower half of the wall is built with larger block than the upper half, leaving a ledge (for some reason it's sloped a bit) half way up. Would you recommend following the contour of the wall with xps, and tape all the seams, rather than leaving a gap behind the XPS and the wall on the upper half? Thanks!
Hi Jason, I'm planning on getting started on our basement anytime now but have noticed a lot of places are out of the xps board (due to problems related to the pandemic). However, when available again I'm planning on doing as you did (2" X 4' X 8' sheets). My question is: I see some are "faced" and some "unfaced". I'm assuming they are referring to the thin sheet of plastic found on each side. Wondering which one to use. Which did you use?
Thanks,
Bruce
Hey Bruce - I recommend unfaced
Cheers, Jason
I want to insulate andd finish a room that is ALL concrete, even the ceiling. Will the loctite hold the ceiling insulation to it? I have already applied the waterproof paint.
I live in Chicago and I am building a 'room within a room' to decouple my home theater. My exterior basement wall, which is 80% below grade, will be getting 2" thick XPS. I then plan on building a 2x4 wall about 8" in front of it, which will get 2 layers of 5/8th" drywall. My question is, do I need to put up a wall right next to the XPS and fill it with batting? Or can I just leave that gap open between the XPS and the wall I'm building 8" away from it.
Can I paint the boards go’s a decorative look?
Estimated savings in heat bills?