DIY Foam Insulation

By Todd Fratzel on Insulation

DIY Foam Insulation for Basements

DIY Basement Foam InsulationBasement Insulation is one of the toughest things to accomplish correctly for a reasonable price. The best approach for insulating basements is having a professional install spray foam. However, it can be quite expensive and it’s a project best left to professionals which flies in the face of many of us DIY folks. So you may want to consider DIY foam insulation as a cost effective basement insulation solution.

Foam Board Insulation is DIY Friendly

Foam board insulation is a DIY friendly product that any home owner can easily work with with limited tools and experience. Best of all the product is relatively safe to work with and won’t cause side effects like fiberglass insulation or spray foam. XPS foam insulation can be cut with a utility knife, handsaw or table saw easily to fit any configuration.

The key to a successful installation is sealing all the joints and gaps. Typically we like to seal the joints with Tyvek tape. The larger gaps are typically sealed using spray foam from a can like Great Stuff. Sealing the joints helps stop air infiltration and provides for the most effective vapor barrier possible.

Benefits of Foam Insulation

Foam insulation is perfect for basements because it won’t promote mold growth, won’t decay, won’t absorb water (closed cell) and it has great insulation R values. Foam board insulation can also provide a very good vapor barrier to prevent the movement of moisture from damp basement walls.

DIY Means Saving Money

The biggest reason we like foam board insulation is the cost savings. DIY foam insulation can save significant money compared to professionally installed spray foam while maintaining some of the great benefits that foam offers. Installing the product yourself can save as much as 60% or more compared to spray installed.

Final Thoughts

DIY projects can be fun and cost effective. Working with foam board insulation is really easy and it’s a project that inexperience DIY’ers can tackle. Be sure to check with your local code officials on energy code requirements to be sure you’re installing a sufficient amount of insulation. Have fun and enjoy your warmer basement!

About the author

Todd Fratzel

I'm full time builder for a large construction company in New Hampshire. I run their design-build division that specializes in custom homes, commercial design-build projects and sub-divisions. I'm also a licensed civil and structural engineer with extensive experience in civil and structural design and home construction. My hope is that I can share my experience in the home construction, home improvement and home renovation profession with other builders and home owners. I'm also the Editor-in-Chief and Founder of Tool Box Buzz. Please feel free to contact me if you have any questions, suggestions or you'd like to inquire about advertising on this site.

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  1. Steve says:

    While I agree that foam board can be done by a DIYer, the insulation value would be considerably less than a spray foam application because of the many joins. Sealing them with tuck tape just isn’t the same.

    But then again, what else could a homeowner do? The do-it-yourself spray foam kits are expensive and create considerable waste.


    • Todd says:

      @ Steve – I actually don’t really agree with you. When you use T&G foam board and seal the joints it works very well. I’ve even seen thermal imaging of it and it does perform.

  2. Dan - Free Insulation Rebate says:

    Great post!

    I have XPS foam insulation in my home and I have no complaints. My energy bills have dropped and the house feels warmer.


  3. Joe says:


    Can I double up on Polyiso rigid foam board? I have a walk-out basement with a 2 x 6 load bearing back wall and am considering using two layers of 2.75 inch Polyiso to get the most of the space.

  4. Joe says:

    Excellent!! Thank you for your help. I was more worried about any condensation having an adverse effect on the wood framing. I do plan on spray foaming the rigid foam in place. You have been very helpful.

  5. Randall Wall says:

    I have cathedral ceilings (2X12 rafters) and am trying to get as close to R-50 as possible and that seems to mean “foam”.

    While there seems to be a plethora of DIY foam kits out there they appear to be more expensive than just hiring a contractor to come out and spray it.

    Are there any less expensive options I have overlooked?



    • Todd says:

      Randall – DIY kits are becoming hard to find and expensive as the Government cracks down on the practice due to health concerns. You can probably get an R50 in other ways. Recently we had a customer who chose to install proper vents for the entire length of roof followed by 12 inches of fiberglass in the joist bays. Next we installed 2 inches of foil faced polyiso. Then the ceiling was strapped and finished. That’s one approach you could take.

  6. FredW says:

    I looked but could not find anything on your site that would show the pros and cons of doing spray foam as a DIY project. I have a 24″ cantilever floor overhanging my walkout basement. Last winter that whole side of the house at the floor level was right out COLD. Not cool, but COLD. My kitchen sink’s plumbing runs up through that space and I can only consider myself lucky that the pipes did not freeze. I have been looking at those DIY foam tanks. It seems I can get one set to do the that whole side of my house.

    Why would I not do it?

    Because the ground slopes down to the walk out, it would be difficult, at best, to get under the cantilever section the whole length of the house to take off the underboard and use foam board and tuck tape.

    I think it would be much easier and faster to spray it from inside.

    Can you give me some dos and don’t or pros and cons?


    • Todd says:

      Fred – Most DIY kits are now banned from sale to private homeowners. Having said that, if you can find one this is the size of job that works best for most DIY applications.

  7. jeff says:

    i am insulating my concrete basement walls and put up 1 1/4th inch underlayment board – fanfold directly on the concrete walls and then atached the furrign strips. shoudl i now put the 3/4th inch foam board between the furring strips. The 1/4th inch is only rated R-1 so although i am in the south i need more insulation.

    • Todd says:

      Jeff – I would put up 1-1/2″ foam directly on the firing strips so there are no gaps, tape the seams well. Then you can attach wall covering directly over the foam with longer nails/screws into the firing. Good luck.

  8. John says:

    I am repairing a cracked, leaking, and crumbling foundation. I am getting ready to start backfilling very soon. I have a fibrous asphault sealer applied to the oustide walls. I was wondering if applying styrofoam insulation sheets that I have pruchased directly to the sealer would cause a problem, like if the asphalt (petroleum baed product) will eat away at the the styrofoam. I am doing this on the outside of the house and will be putting vapor barrier over the outside of everything but thinking about applying it between the sealer and styrofoam as well. Thanks, John

    • Todd says:

      John – I wouldn’t recommend it. I would recommend installing something more like the WARM-N-DRI® Foundation Board that TUFF-N-DRI system uses. I think the foam will break down.

  9. Bill says:

    Hi, Todd,

    Where can I get foam insulation that is cut to 14.5″, to fit into stud bays? I want to insulate a small shed, and don’t want to use fiberglass or other batting type stuff. The studs are 2X4.


    • Todd says:

      Bill – You’ll have to buy 24″ or 48″ wide sheets and rip them down on a table saw or some other saw.

      • Bill says:

        Even if I had a table saw (nope), there would be a lot of waste; 9.5″ of waste from each 24″ width, and 4.5″ from each 48″ piece. I would think that only a table saw would produce a decent and uniform cut. I envision making a tight fit into the bays, so as to get the best insulating value. Also, would like to get a tight fit so to help hold the panels between the ceiling joists. Thanks for the reply.

  10. Philip says:

    This info is really helpful, thanks. My question is about adhering the XPS to a foundation wall that has bumpy seams and even 1″ bumps from the form ties. Should I take the time (and mess) to clean all this stuff off, or will the foam dent enough so it is not held away from the cement? Or, is spray foam really the most practical option?

    Finally, will just 2 inches (R10) of foam be adequate, without the layer of fiberglass? I live in Vermont…what R should I be shooting for? Thanks!

    • Todd says:

      Philip – Thanks for the compliment.

      Typically we knock off really high stuff, the rest doesn’t matter. You can push the foam onto the lower stuff. Great Stuff Pro works VERY well for adhering it.

      The R value question depends on numerous things including energy codes, cost and overall comfort. 2 inches does pretty good in most basements.

      Good luck.

  11. Tom says:


    Is it a good idea to install foam board insulation between the joists in the basement ceiling?
    I would be doing it more for soundproofing than anything, but want to know if it is even worth it. The basement room will be a office/den and with hardwood floors above, it can be a bit noisy down there – trying to do anything I can to cushion the sound.
    Was thinking of doing 1″ foam board glued to the subfloor above between the joists and using Great Stuff around the edges to seal it.

    I am also planning on putting in recessed lights — if putting in the foam insulation will help with sound, is it a bad idea to have the recessed lights in close with the foam, for fire hazard reasons?

    What do you think? Any advice would be helpful.


  12. Richard says:

    Can you please tell me if Polyisocyanurate Can be used inside a building or is it an outside applicatio only product and also in which direction, silver in or out, is it installed.

    • Todd says:

      Richard – Polyisocyanurate is used on some interior applications. You really need to check the manufacturers recommendations. Some of the foil faced products should not be placed directly against concrete as the concrete and foil can sometimes have a reaction that will corrode the foil. Typically the foil side will face towards the more extreme heat or cold as it’s a good radiant barrier. Good luck.

  13. Jared says:

    Hello I am going to insulate my basement using 2′ foam board, however I have 2 or 3 cracks in my poured concrete basement wall the cracks run nearly vertical and are about 1/16th to an 1/8″ thick. I have never had any water from these cracks. Should I seal or repair these and what should I use?


  14. Jared says:

    What do you do with the horizontal joint between the foam board and the concrete slab floor? I will tape the vertical joints between foam boards as you suggest. I will be framing a wall in front of the foam board.

  15. Joe A says:

    Great site. I have used 2″ foam board on most of my basement walls. In the utility area I will not have the framed wall in front of the foam boards. The foam boards need a fire barrier – the only one I know of is drywall.
    Can I place the drwall directly against the foam board instead of framing a wall in front? I do not have a lot of space for a full framed wall.

    • Todd says:

      Joe – Thanks for the compliment. Yes you can place the drywall in front of the foam. However, it will be a challenge trying to get all the foam and drywall tight against the wall so the wall looks good. You could install strapping at the joints after the drywall (and one layer of fire tape) goes up. Then you could use Tapcons or Shoot Nails through the strapping into the concrete.

      Good luck.

  16. Braden says:

    I am re-siding my attached heated garage with wood clad siding to match the house. The current siding, T1-11 (plywood siding), will not be removed as I need to side over the top of the T1-11. Because the windows and doors are reset to a plane that matches the house, I need to use two-inch thick strapping over the T1-11. Instead, I am considering adding 1 inch of XPS over the T1-11 and using one-inch strapping. Since the current insulation is 3 1/2 inch fiberglass with one inch of XPS as sheathing under the T1-11, I am concerned if adding another layer of XPS over the top of the T1-11 will cause a moisture problem. Our climate is cold (zone 6) in Wisconsin. Please reply with your thoughts. Thank you.

    • Todd says:

      Braden, You certainly have a bit of an unusual situation. However, I think the approach is sound with one modification. I would install a house wrap (Typar or Tyvek) prior to the foam board. Good luck.

      • Braden says:

        Thank you for your reply! Your comment adds confidence to my thinking as I am quite an amateur at this. Adding tyvek to the layer is what I planned on doing but neglected to say. Is it better to put the tyvek between the T1-11 and added foamboard or can it go on top of the foamboard (with tape rather than staples)? I’m thinking if it is on the outside of the foam rather than under it, the tyvek can protect the foam a little bit. I look forward to your reply. Thanks again.

        • Todd says:

          Braden, The Tyvek really should go on the T-111. It will allow moisture to escape from the wood, but not come back from outside into the wood. If you put it on the outside, moisture could escape from the wood adn get trapped on the surface of the foam and cause the wood to possibly rot.

  17. Larry says:

    I have a old flat roof house approx 21×45. The roof joists are 2×6 supported on a center beam on 16″ centers. The rubber roof will be replaced and the contractor can put 1.5″ of rigid foam over the existing plywood before the rubber roofing goes on. The roofing contractor can remove the plywood and old 4″ fiberglass batts and an insulation contractor can fill in the joists with closed cell spray foam to the top at $6500.00, which seems kind of high for 472 cubic feet of spray. Would I save a lot by laying in multiple layers of 14.5″ rigid foam up to the top of the joists?

    • Todd Fratzel says:

      Larry – For a flat roof, the best insulation detail is installing foam board on top of the plywood before the roof membrane. Typically the insulation is polyiso with a paper facing specifically used on roofs. Multiple layers are often used to increase the insulation value. This is far more efficient because the layer of insulation is continuous over the framing. For a flat roof, this is the only way I’d go. Good luck.

  18. Emily Wentworth says:

    1.) When you set the vertical panels of 2″ foam board against the concrete basement walls down to the cement floor, so you scoot some Greta Stuff along the front bottom edge of the foam boards where it hits the floor to seal? Won’t this bulge foam out and make it hard to butt the composite deck board to be put on the floor & up against the foam board? (that comps. deck board that will be under the pt framing board)
    2.) With T1-11 as my exterior house wall (and no tyvek wrap or siding), I think it would help to fill the stud cavities (2×6) that are inside the T1-11 with carefully ripped lengths of foam board, then finish filling with foam spray insulation before drywall goes up. The aim is to insulate from T1-11 inwards as much as possible (in Maine!). Someday, would have to tyvek wrap exterior of house over T1-11, then foam board, then vinyl siding, but then there is the problem of the plane of the existing windows that are deeper in relation to the new outer layer. Thoughts?

    • Todd Fratzel says:


      1. Typically we will foam the bottom after. However, the reality is the foam is never perfectly flat to the wall, most concrete walls have a fairly uneven surface. The wall is set up as tight as possible, but it’s not “perfect”.

      2. If it were my place, I’d skip the foam board and just spray foam it. The cost may even be a wash, once the spray foam truck is set up, adding extra depth isn’t likely to cost much more than the foam board. Lots of homes have new siding/insulation placed on after, typically extension jambs are installed to deal with the differing depths of siding.

  19. Martin says:

    Hi there,

    I live up in Ontario, Canada and the insulation code for walls is now R23. I have a breezeway that was an addition built 20 years after the original home. It has 3 exposed to the element walls and gets very cold. It has 2X4 studs with that batt/paper insulation. Probably have R8 in the walls. I want to rip out the plaster and old batt insulation. Then I want to put in new batt (at R 14) and then seal on top of that seal it with rigid foam boards. I have two options……XPS (R 5 inch stuff) or the polyurethane with foil stuff. I want to put 1.5 inches of some form of rigid foam on. What type of rigid board would you use?



    • Todd Fratzel says:

      Martin – Are you suggesting installing the foam on the inside of walls after fiberglass? if so I wouldn’t recommend that, either install it on the exterior, or install just foam in the stud bays.

  20. Keith says:

    Hi, just to clarify…with respect to bumpy uneven poured concrete basement walls…you are saying that it’s ok if the foamboard does not make full contact with the concrete walls and that some air gaps are normal and non-detrimental?

    Also should I insulate the basement floor first and then the basement walls?

    Finally what should I do about the basement floor area which grades toward a drain?

    • Todd Fratzel says:

      Yes, the uneven surface is fine. It doesn’t matter which you insulate first. The slope at the drain is an interesting issue, usually we try to leave it if possible.

  21. Fred Pisaneschi says:

    I read all your articles on basement insulating. My questions are:

    1. Should I seal the foam board ( I went with 2” as you suggested) at the concrete floor with spray foam or some type of sealant to prevent and moisture from leaking through and attacking the steel studs?

    2. When using steel studs, do I need to put plastic or foam underneath the lower track before screwing it down?

    3. What type of tape should be used to seal the foamboard. I read where you did not recommend tyvak tape

    This room is a basement bathroom with a shower.
    I will be sealing the rim joists and sill plate with 2” foil faced polyiso per your article.

    • Todd Fratzel says:

      Fred – Glad you found this information useful.

      1. It’s best to seal it if you can.
      2. In commercial construction we never do that. In a basement….if it’s a very dry basement I wouldn’t bother. If it has any chance of some moisture I’d put down some composite decking first.
      3. DOW makes a tape specifically for this, and I’m assuming OC probably does as well. Most lumber yards carry what you need.

      Good luck.

  22. Fred says:


    I installed 1-1/2″ Owens Corning XPS sheeting on my basement wall which will then get covered with drywall.

    I then decided to go to 2.0″ thickness, so I purchased 4 sheets of 1/2″ which I will glue to the 1-1/2 already up.

    My question is; I noticed the 1/2″ sheeting has a vapor film on both sides. Should I remove this film on the inside , outside, or on both sides or leave it on before I glue it to the 1-1/2″


  23. chad says:

    Great site!

    I was trying to research insulating my rim joist and want to use Thermasheath-3. I have air sealed the rim joist with silicone and was going to cut the foam about 1/2 short all the way around and then seal with great stuff (fire sealant).

    1) Do I need a fire barrier over this product? and if so does it need to be secured directly to the thermasheath as I don’t want to penetrate the foil that is on both sides of the insulation.

    2) does it matter which side faces out as both sides are covered with reinforced aluminum foil facers?

    • Todd Fratzel says:

      Chad – The question on fire barrier really depends on the local jurisdictions interpretation of your local building code. In some places I wouldn’t be surprised if it must be covered, in other places I wouldn’t be surprised if you can leave it exposed. I’d recommend checking with your local building code official. Unless the product says otherwise, I don’t believe it matters which side faces out. Good luck.

  24. Robert says:

    Great site and very informative articles. How high should you install the foamboard to the basement? Should it be high up to concrete wall only or as high as touching the floor joist/or the sub floor? If it is up to concrete and to floor joist only, then there a small gap between the subfloor and foamboard. Will moisture be trapped in there? How do you seal that gap? I will seal the rim joist by way.

    • Todd Fratzel says:

      All of the concrete should be covered with foam board. The gaps should be sealed with spray foam. You should also seal your rim joist with foam board. Good luck.

  25. Helen says:

    Hi..i live in Greensboro N.C. i am insulating an attic converted to living space that was done in 1962. I am NOT taking out existing sheetrock. The sloped part of the ceiling above the knee walls is proving the biggest challenge. The house was built in 1939…So the rafter depth is 5 1/4″ . Can I use the foil foam board in this sloped area, faced toward the roof decking with a 1″ gap above (so it is reflective rather than conductive) and under it use several layers of blue board that rest on top of the sheetrock? This would achieve around an R-16. (Not great but better than the zero I have currently) Would the blue board act as a vapor barrier? this area is a BEAR to insulate because the drywall is already up..but i can access most bays from attic side of knee walls. I have already installed Perforated radiant foil barrier to the bottom of the roof rafters In the Attic area behind the knee wall. ( It is temporarily Stapled So we can have access To this sloped area for sliding in the foam board)

    • Todd Fratzel says:

      Helen – This is an option, how well it will perform I can’t say. I think it will be a struggle to get the foam slid up between rafters while maintaining a fairly tight fit. You’ll know how well it might work once you try the first bay. Good luck.

      • Helen says:

        Hi Todd, Thank you so much for responding to my challenge. Getting the foam board into the bays would just be a friction fit. There is no way I can go back and Spray Foam to seal it. What I have done in about nine of the rafter bays already is this: I slid R-13 fiberglass cut from a roll into the bays topped with a piece of the radiant foil barrier. This leaves about a 1 3/4″ gap for air flow from (Soon to be installed)soffit and ridge vents…and so the radiant barrier can do its’ thing. This probably gives me a tighter fit Than the foam board would…but it requires a lot of time and patience. Again, only r-13…but better than -0-. This is my weakest point in the entire insulation project upstairs. I can get Minimum and above on R values, seal air leaks, etc. but not on the sloped ceiling area. Grrrr! I’ve pretty much resigned myself To accepting this is as good as i can get it. The house will never be airtight anyway. The downstairs has No insulation in the walls…but..The former owner Invested in double pane windows. The walls have Double plasterboard (The precursor to sheetrock)…the stud cavity air space, then diagonal Boards, Then clap board siding, Finished off with aluminum siding added in 1962! Needless to say…I will not be Adding insulation to those walls..because it would be impossible to get a vapor barrier installed. Currently the house has no moisture issues…and amazingly the downstairs is Comfortable without huge gas and electric bills. If I can get the upstairs comfortable… I’ll be content. Thanks again for your input. Helen.
        (PS…The radiant foil barrier really does have a huge impact on reducing heat gain. The best $110 I’ve ever spent.)

  26. mike helminger says:


    where the concrete foundation transitions to a pony wall (say 4ft of concrete, 4ft of stud wall): if the inside faces of these walls are offset by an inch or two, what do you typically do with the foam? leave it as a single piece and have a gap between the stud wall and the foam, or cut the foam into two pieces and glue each one tight?

    • Todd Fratzel says:

      Mike – We typically put foam on the face of the concrete, and a small piece on top. Then you can either frame a knee wall over that concrete, or frame another wall from the slab up. Both work fine.

      • mike helminger says:

        got it. thanks.

        would you do this even if the lip is 1-2″?

        • Todd Fratzel says:

          Yes sir….otherwise you’ve got a spot that will allow moisture out.

          • mike helminger says:

            sorry. i should’ve been more clear. would it be okay to just use spray foam for the lip (which would double as a glue at that part where the foam hits the concrete) and then have a gap between the foam and the studs until it reaches the ceiling?

            if i did this, i struggle to see how to close off the rigid foam at the ceiling/rim joist.

          • Todd Fratzel says:

            I wouldn’t run the foam all the way up like that. I would stop it at the top of the knee wall. Then you can run it in the stud bays if you want (that’s what I do). The key is sealing each joint well.

  27. Felix Perez says:

    Hi Todd. Excellent discussion hopefully my problem is easier than some of what I’ve read here. Essentially, I have a almost cathedral roof with no attic. From the inside its Just the 4×6 beams then the ceiling which are wooden tongue and groove boards and the roof. How do I best improve insulation which in my case would have to be done from Inside the house?

    Thanking you in advance

  28. Felix Perez says:

    Sorry on the typos.. To clarify ; I have a cathedral roof over the living room area with no attic. From the inside, its Just the 4×6 beams, the ceiling which are wooden tongue and groove boards, and the roof. How do I best improve insulation which in my case would have to be done from Inside the house?

    • Todd Fratzel says:

      Really depends on where you live and what the recommended level of insulation is. One approach is filling the spaces between beams with foam, then installing some sort of ceiling over the beams. This would hide the beams so that might not be great. Depending on the strength of the framing, maybe you’d create new “beams” below the new ceiling.

  29. Mike Shelley says:

    I have an existing 2×4 basement framed wall that is 1″ away from the block wall due to a floating basement floor that has a 1″ gap running around the exterior of the basement. I’m looking for the best possible way to insulate these walls before sheetrocking. The house sits high up and has had no water issues. The walls had cheap paneling installed on the basement walls with faced batt insulation installed between the studs and a plastic vapor barrier over the faced side of the fiberglass batts. I have removed all of the insulation and have found no signs of moisture or mold but know the double barrier isn’t correct. I was thinking of trying 3/4″ foam board slid in behind the studs followed with batt insulation in the framed bays. My concern with spray on insulation is that I would not get the desired insulation value behind the studs where I only have 1″ of space. I live in the northeast where we see temperatures of 0 degrees.

    • Todd Fratzel says:

      Spray foam would be a LOT better than the loose 3/4″ foam, it’s not the best situation, but it’s better.

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