Walk-Out Basement Wall Insulation

By Todd Fratzel on Insulation

Insulating Wood Framed Walk-Out Basement Walls

Walk-Out foundations create an interesting dilemma in when considering wall insulating details. I’ve written extensively on the subject of how to properly insulate basement walls which deals with concrete (and block) walls but I’ve never addressed the occasional wood framed walk-out walls that exist in some many homes today. In this article I want to discuss the options most suitable for insulating these wood framed exterior walls that exist in homes with walk-out basements.

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Typical Wood Framed Walk-Out Basement Walls

Typically we see most wood framed walk-out basement exterior walls insulated with fiberglass insulation and some type of vapor barrier. This detail is used in millions of homes in the exterior walls above grade with some success (the industry is slowly moving away from this detail, but it’s still the most widely used today). So if this detail works ok above grade, why might it not be the most suitable solution in a basement? The answer really revolves around the high humidity levels that typically exist in a basement regardless if there’s a walk-out wall or some other means of egress like a bulkhead.

Many times when we remove fiberglass insulation from a wood framed basement wall we find signs of mold and moisture. In most situations we find frost (during the winter) building up behind the fiberglass, on the surface of the exterior sheathing, around nails (from siding and framing). Moisture from the basement penetrates the wall system, hits the back side of the sheathing and exposed fasteners and condenses and forms frost on cold days. This cycle goes back and forth through the seasons and helps promote mold and mildew growth.

Improved Wood Framed Walk-Out Basement Wall Insulation Details

If you’re going to take the time and money to properly insulate the rest of the conventional foundation walls it’s definitely worth spending a bit more money and time on the framed walk-out walls as well. There are several options to consider including:

  • Spray Foam – One of the best options is to have the framed walk-out walls spray foamed with closed cell foam. The spray foam will not only provide the highest R value but it will also create the tightest wall system preventing air infiltration and moisture movement. This option is the most expensive and also requires a professional installation in most cases.
  • Flash & Batt (Spray Foam & Fiberglass Combination) – A process that’s getting lots of attention and I’m seeing more on job sites is called “Flash & Batt”. In this detail the stud bays are “flashed” with spray foam, typically about 2″ of closed cell foam which creates both a good starting layer of insulation value (higher R value per inch than fiberglass) and it seals the wall against air infiltration which drastically improves the efficiency of fiberglass insulation (fiberglass significantly loses R value when air infiltrates the wall section). This option is more cost effective than the one above but typically involves a spray foam contractor plus yourself or additional labor for the fiberglass.
  • Foam Board & Fiberglass – Another option is to use a combination of closed cell foam board (XPS Foam Board or Polyiso Foam Board) and fiberglass insulation. This detail is a great option for DIY’ers and general contractors that don’t want to involve a specialized contractor like spray foam applicators. In this approach a layer of XPS or Polyiso foam board are cut to fit in the stud cavity tight against the exterior sheathing. Then the foam is sealed to the framing using canned spray foam. This effectively seals the stud bay from air infiltration and vapor transmission. In order for this to work effectively the foam board should be a minimum of 1-1/2″ thick (2″ preferably). Finally the stud bay can be filled with unfaced fiberglass insulation. It’s VERY important not to install a vapor barrier over the fiberglass as this would create a double barrier trapping any moisture between the insulation and vapor barrier.

Walk-out Basement Wall Insulated with DOW Foam Board

Example Basement Walk-Out Framed Wall Insulated with Foam Board and Fiberglass Insulation

In the picture above you can see a fairly typical walk-out basement wall. The wall has two features that are fairly common, on the left side of the photo is a portion of the concrete foundation wall that sits about 4′ above the slab due to the changing grade along the side of the house. On top of the wall is a wood framed wall which transitions to a full height completely wood framed wall at the rear of the house. For this walk-out wall there are several details to consider:

  • The exposed concrete foundation wall (above left, and lower) is covered in closed cell foam insulation board. The next step will be to frame a short wall in front of it (it will have a decorative cap on it after, instead of framing the new wall all the way to the ceiling). In this case the lower portion of the wall is insulated exactly as I’ve discussed in my Basement Insulation Article.
  • Each stud bay was insulated first with 2″ of DOW XPS foam board. The pieces were cut so they fit easily into the bay. Then a can of spray foam was used to seal the foam board to the framing. It’s best to do the spray foam last after all the foam is fit so you can use an entire can before it clogs up.

DOW Foam Board Sealed in Stud Bay Cavity with Spray Foam

  • Lastly, the remaining stud bay is filled with unfaced fiberglass insulation. It’s extremely important that a vapor barrier is NOT installed over the fiberglass with this detail. It will trap moisture in the stud bay leading to serious problems.

Basement Walk-Out Framed Wall Insulated with DOW Foam Board and Fiberglass Insulation

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 author of Tool Box Buzz and Today's Green Construction. 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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50 Comments

  1. Andrew says:

    Great Article!

    Good work!

  2. Scott S. says:

    Thank you Todd for all the great articles on insulating cement basements!

    Scenario:
    I am working towards finishing my basement. I have a standard split-level mid-western home (cold winters, hot summers). 4 ft cement walls in the basement and another 4 ft of wood wall above that. I would like to frame up 2×4 walls on the inside of the cement and have the “shelf” look around/above the cement rather than framing 8ft studs all the way to the ceiling. I plan on applying 2″ rigid foam insulation to the cement, framing a 4ft wall, run wiring, inserting bat insulation between studs, and finally sheet rocking the entire wall. I plan on attaching the 2×4 wall to the cement floor using Tapcon screws (treated sole plates).

    The basement windows are roughed in with only 1.5 inches between the top of the cement and the bottom of the rough sill. It would be nice to have a continuous flat shelf the entire length of the wall rather than cutout around windows.

    My question is: How do I attach the top plate of the new 4ft wall to the existing wood wall above the cement with the limited space between the top of the cement and bottom of the window sill?

    Possible Solution:
    Lay treated 2×4 “studs” (about 4″ long) flat on the top of the cement wall, and attach them to the top plate of the new 4ft wall and the base of the existing wood wall on top of the cement? That would fill the 1.5″ space between the top of the cement and the bottom of the rough sill. Then insert 1.5″ rigid foam insulation between these “studs”, apply expanding foams between “studs” and rigid foam. Then cap the shelf with a 1×8 board. That would leave me flush with the rough sill, add stability to the top of the new 4ft wall, and allow me to attach sheet rock to the shelf.

    Do you see any problem with this solution? Do you have better suggestions?

    Thanks in advance!

    • Todd Fratzel says:

      Scott – Great question and one that is relevant to lots of homes. First I’d would establish the finished elevation you’re looking for. In many of these details the shelf becomes integral/flush with the finished sill trim on the window. That should give you a bit more space. From that you should leave yourself 1/4″ of space to shim the trim piece. Ideally you get a piece of foam on top of the concrete knee wall to stop cold from penetrating up through the trim cap. Sometimes when I’ve done this detail, I’ll install some blocking over the foam, into the concrete wall with Tapcons, near the top of the short framed wall, then you can tie the wall into the block. This holds the wall tight to the concrete/foam. Then the cap on top is just covering up the foam and nailed down through the front of the framed wall. Make sense?

      • Scott S. says:

        Is there any potential issue with puncturing the rigid foam with tapcon screws as you suggested? Any concern with moisture creeping in to the bat insulation through those holes?

        In regards to finishing the window trim, I was planning on adding nice 1×8 board painted white on top of the rough sill. That should leave me flush with the finished shelf if I use 1/2″ sheet rock on top of the cap. That was my plan anyway.

        • Todd Fratzel says:

          Scott – The potential is small, but if you’re concerned you can spray foam the block, and the tapcon to seal it. Good luck!

  3. Ken W. says:

    Todd,

    Another good article on a relevant issue. My questions relate to existing and future mold adhering to the wood framing, especially the stud section of the framing either touching the damp cement foundation wall or very close to it – say ¼ inch away. How do you prevent existing mold and moisture from reforming on the sections of 2×4 touching or close to the foundation wall?

    1. Where a small air space is present between the stud and the wall – say ¼ inch away from the wall – do you recommend spray foam in this space?

    2. What about using the new anti-mold paint primer from Rustoleum/Zinsser?

    Per their website:

    Zinsser Mold Killing Primer is a water-based fungicidal protective coating that can be used to paint over and kill all existing mold, mildew, moss, fungi, odor causing bacteria and any other fungal organisms. The Mold Killing Primer contains an EPA registered antimicrobial to prevent the growth of mold, mildew and other fungal organisms on the paint film.

    Do you or any of your readers have any experience with this product?

    Ken W.

  4. Kevin Dickerson says:

    Todd, it appears that you a top-notch contractor who believes in “doing it right the first time”. I have learned a great deal from you by reading your posts. Thanks for taking the time to write these tips for us people who DIY. Kevin

  5. Tony Principato says:

    Todd, I’ve read your articles on basement insulation which were very helpful. I live in the northeast and my basement has a framed walk-out foundation on approx. 40% of the walls, the balance being poured concrete. The basement is dry most of the time, perhaps because of the walk-out, and I don’t want to create a dampness problem.

    Your opening comments say, “If you’re going to take the time and money to properly insulate the rest of the conventional foundation walls it’s definitely worth spending a bit more money and time on the framed walk-out walls as well”. This sort of implies to me that the big benefit is in the concrete walls. So, I’d appreciate your thoughts on just insulating the framed walk-out portion of the foundation. Is this worthwhile or would it just be like insulating half a wall?

    Also, I’m wondering about R-values. Adding 2″ insulation may produce an R-value of 9-10. What R-value should I be working toward in Zone 6?

    • Todd Fratzel says:

      Tony – Not sure I understand your question. In the article I discuss the options I’d recommend for the walkout framed walls. In my opinion, it’s best to include some sort of foam in addition to just standard fiberglass. Every State has requirements on minimum insulation values typically listed in the States adopted Energy Code. In many places the R value depends on the entire system of insulation in the home, so it’s not specific to the foundation walls. R10 is a good start, but certainly not as high as would typically be required. In most situations you’re looking at a requirement of at least R19 or greater. Good luck.

      • Tony Principato says:

        Todd, thanks for the prompt reply. I’ll look into the R-value aspect as you suggest. The first part of my questions is very basic. My basement is 60% concrete, 40% framed walk-out; all without insulation. I don’t intend to insulate the concrete portion for several reasons. My question, though, is whether it makes sense to insulate the framed walk-out or is that a waste of time and money without insulating the concrete. For example, I wouldn’t insulate a wall without closing the windows.

        • Todd Fratzel says:

          Tony – Absolutely worth insulated the walkout walls. The difference in the basement temperatures from just doing that will be significant.

  6. Brian says:

    Hi Todd,
    What about the concrete frostwall below the slab? It needs to be insulated with rigid insulation but everyone seems to disagree on which side of the wall? Also, we want to tie the floor slabs (interior & exterior) into the top of the frostwall by with rebar but how do we deal with thermal bridging?

    • Todd Fratzel says:

      Brian – Yes, lots of opinions out there and there are several ways to skin the cat so to speak. If you’re starting from mew construction I’d do the following:

      – Insulate the interior of the frost wall below the slab with 2″ foam board insulation.
      – Insulate below the slab with 2″ of foam board insulation.
      – The wall insulation should come up flush to the top of the slab (thermal break). This means there is 2″ of foam exposed at the slab surface around the perimeter, not a big deal. This also means that we never tie the interior slab to the frost wall, with a good sub-base it doesn’t matter. This also means exterior slabs can be tied into the wall as the insulation is on the inside.
      – Finally insulate any above slab concrete walls with foam on the inside as well.

      Good luck.

  7. Brian says:

    Thanks Todd.

  8. Constantin says:

    Hi Todd,

    Thank you for great article! I have a related question.

    You mention that “Lastly, the remaining stud bay is filled with unfaced fiberglass insulation. It’s extremely important that a vapor barrier is NOT installed over the fiberglass with this detail. It will trap moisture in the stud bay leading to serious problems.”

    However in another article
    http://www.homeconstructionimprovement.com/basement-wall-insulation-detail/

    You say somthing different as a last step: “Install a vapor barrier. Either use faced insulation in the wall cavity or install a vapor barrier (if you use Spray-In-Place Cellulose Insulation you may omit the vapor barrier).”

    Can you help to understand the right way?

    Thank you!

    • Todd Fratzel says:

      Constantin – I can understand your confusion. These two situations are nearly identical with one major exception. In the case of the foam board against the concrete, that layer is continuous. In the walk-out basement example, the studs interrupts the foam insulation. The discontinuous foam can allow moisture from the outside to get into the stud bay, and that’s why I wouldn’t use a vapor barrier in that case. The other situation is sealed very well from the outside. Honestly, I prefer to use the paper faced in the other example vs plastic which I never use in a basement.

      Good luck.

  9. John says:

    Hi Todd,

    I have a summer house on the ocean in Maine that’s built on a concrete slab. The bottom floor is all garage, framed with wood, with living quarters above. We are converting 3/4 of the bottom floor to bedrooms, while leaving 1 garage door in place and keeping that area for a workshop. In all areas except the workshop I recently took your advice and put down a 6mil vapor barrier, foam insulation and Advantech sheets screwed down with Tapcons. I am totally amazed at how well this came out!

    I also removed all the old moldy insulation from the exterior walls and ceiling, and I now need to re-insulate the exterior walls and the walls that border the new workshop area. The exterior walls are framed with 2×4’s, so I’m just wondering what the best approach would be to insulate. The exterior is pine boards with Tyvek paper under it on the studs, which I see from the inside. Since the Tyvek paper is already a vapor barrier, should I be using an unfaced fiberglass before installing the sheetrock?

    The other concern are the walls that border the workshop space. The garage door is old and the floor is still bare concrete, so that area I expect to still get some moisture. What do you suggest for those walls and between the ceiling joists?

    Thanks, John

    • Todd Fratzel says:

      I didn’t see this post when I responded above.

      So you’re insulated all wood framed walls, not against concrete. Ideally you’d insulate the full 3-1/2″ cavity with foam (2″ and 1-1/2″ thick?). TYVEK is NOT a vapor barrier. It’s an air infiltration barrier. I would install a 6 mill poly over the foam board before drywall. I would use the same detail on the wall adjacent the garage (vapor barrier on finished side). Good luck!

      • John says:

        Thanks Todd – No concrete walls, just the floor and 1 row on cinder block on top of the slab. I did insulate the row of block with foam and will block it in with studs. The rest is built with 2×4’s on top of the cinder block. I did find out that Tyvek is not a vapor barrier after I posted the questions above, but just so I am clear – by putting the poly under the drywall, the wall can still breather through the other side through the pine exterior? Can I use fiberglass insulation instead of the foam?

        • Todd Fratzel says:

          Yes, most homes are built with Tyvek (or similar), wall sheathing, studs bays filled with fiberglass or cellulose, then a vapor barrier followed by drywall.

  10. Steve S says:

    Hey Todd,
    I have a full basement with the backside being a full 8′ walk out block wall with a 4′ frost footing under that. this wall is very large (about 38-40′) and I loose a lot of heat through that wall every winter. Id like to insulate that wall but I want to make sure it is done right. there is also a curtain drain around the outside of the basement floor that moisture can drain into. (typical) I was wondering, do I seal the wall? do I stud right against it? if I use hard foam insulation do I attach that to the wall, the back of the studs or stud against the foam board? leave an air gap between the block wall and foam board? hang any plastic on the block wall?

    • Todd Fratzel says:

      Steve – I’d install 2″ of XPS foam board in front of that wall, and seal all the seams well. Then I’d frame a wall in front of it (the framing can be tight to the foam, which helps hold the foam up). Insulate the stud wall (Roxul is a great product in the basement), do not use a vapor barrier.

      Good luck.

      • Steve S says:

        Hey Todd, thanks for the advice. Would you recommended doing this to all the walls? Or just the walkout wall? Figuring the wall opposite is completely under grade and the two side walls are 3/4 under grade? Or would it be ok to just foam board and insulate the box?

        • Todd Fratzel says:

          I recommend insulating every wall in the basement. The foundation walls need to be done with the foam board detail, the question then is for the framed walls. For those I again like using foam. No vapor barrier for either application.

      • Steve S. says:

        Hey Todd,
        One last question, you said no vapor barrier, did you mean on the block or insulation? Should the batts be unfaced?
        Thanks again
        Steve

  11. Ron Marr says:

    In the process of insulating a typical Midwest walk out basement. My project is much like Andrew’s in the first comment on this article.
    One of the basement poured concrete 8″ thick walls is approximately 38 feet long. The first 9 feet of the wall is the full 9 (yes 9) feet high; then the next 14 feet has a 6 foot high concrete knee wall followed by a 4 foot high concrete knee wall for the remainder of the wall. On top of all the concrete knee walls a typical 2 x 6 stud wall has been framed in filled with unfaced fiberglass and of course covered with poly.
    I’d like to remove the fiberglass in the stud cavities since there appears to be significant air infiltration and replace it with foamed in foam board and fiberglass and cover with drywall.
    On the poured cement, I would like to use Dow’s 1 1/2
    ” slotted edge XPS which is attached using a 1 x 3 furring strip covered by drywall creating about a 3 1/2 inch “ledge” – about 2″ of which would be un-insulated concrete – between the knee wall and the sole plate of the stud wall. Because of plumbing it is nearly impossible to put another framed wall in place where the concrete knee run.
    Any suggestions on how to handle the “ledges” being created?
    Thanks

    • Todd Fratzel says:

      Can you put insulation on top of the ledge? The rest of the plan sounds good.

      • Ron says:

        Should be able to glue 1 1/2 inch XPS to the cement part of the ledge and then out to the foam attached to the cement knee wall without problem.
        Where I get stumped is how to attach the drywall to cover the foam on the ledge. Is gluing the drywall to the foam enough and then how would you attach the metal edge for the drywall?

  12. Cliff Steenberg says:

    I used your method of insulation, 2″ Dow blue foam insulation board installed directly against the outer sheathing in the stud cavity and sealed on the edges with Great Stuff spray foam, with fiberglass batt insulation installed against the foam board, in the framed wall that sits on top of a 4′ poured foundation wall.
    My intention is to do this to the rest of my framed walk out walls as well. I did this back in August of 2015.
    I put up a stud wall against the blue foam insulation on the foundation walls that I also installed per your instructions.
    It wasn’t until after New Years that I finally got around to doing the electrical so that I was ready for the building inspector to look at my work before putting up drywall.
    When he came, one of the first things he did was to lift the fiberglass insulation to look at the blue foam board installation. Frost had formed on the inside of the foam board, causing the fiberglass to stick to it. I live in Wisconsin.
    You explained in your article that by not installing a vapor barrier over the fiberglass insulation, moisture wouldn’t form in the wall cavity. But it did anyway.
    I also installed 2″ blue foam board in the full height wall portion of this room I’m working on, without any fiberglass insulation in it. It remained dry.
    The inspector said he would go with either: 1)the foam board with fiberglass batts and a vapor retarder installed over that, or, 2)I could add another 2″ layer of blue foam board over what was already installed, with no fiberglass and vapor retarder. I chose #2.
    As I said before, I followed your installation instructions as you describe them in your article. Could the moisture build-up be due to not installing the drywall right away after the fiberglass insulation? Cliff S.

    • Todd Fratzel says:

      Cliff – This happened because the drywall and paint were not installed. If you search for the vapor transmission values for latex paint you’ll see that it’s considered a vapor retarder, just like the first option your inspector suggested. The reason we don’t put a full vapor barrier over the fiberglass is to prevent a double barrier that can trap moisture. This doesn’t surprise me at all, it’s a timing thing. Sounds like you waited quite some time before electrical and drywall correct?

      • Cliff Steenberg says:

        It was just over 5 months that the walls were insulated before the inspector found the frost. In order to get him to pass the installation, I went ahead and installed the extra layer of 2″ blue foam board insulation.
        Everything you describe in your article and in your reply make total sense, but after finding the frost under the insulation , I’m a bit skeptical about doing the rest of my walls that way. The doubled-up 2″ blue board is more expensive, but it does give me an R-20 value in the walk out walls.
        I am going to send a copy of your reply to the building inspector to see what he thinks about the drywall and latex paint as a vapor retarder. At this point, I am stuck with doing whatever he says needs to be done to pass his inspection. Thanks, Cliff S.

        • Todd Fratzel says:

          good luck…I certainly understand your hesitance. I’ve seen this happen before, and I’ve also taken apart walls that were properly done, drywalled, and painted, and no frost issues. This is complex stuff….never a perfect solution that’s for sure.

  13. Greg L says:

    I have a 2 year old home with a walkout basement. The above grade portions (not covered by block) are framed and insulated with rock wool batts and have a vapor barrier (this was done before moving in). The rest is just exposed basement wall and floor. The exterior foundation had foam insulation installed around it. Do I still add foam insulation to the block walls or will that trap moisture? And if I don’t add insulation, do I really just build framed wall right up against the block without insulating it? I see many ways of doing things but often it says not to insulate the inside block walls if they were insulated outside. This seems like I’m losing too much heat if I don’t insulate them but don’t want to cause a moisture issue.

    • Todd Fratzel says:

      Greg – It’s absolutely ok to insulate both sides. Concrete block and concrete in general are always full of water at the microscopic level. In fact, concrete materials that are completely submerged in water will be stronger over the life compared to concrete that is not. Fear not …. interior foam insulation will not cause a problem. Good luck.

  14. Steve says:

    Hi Todd,

    Does the 2nd option, Flash & Batt, require a vapor barrier (sealed plastic over the fiberglass)? I had a professional give me a quote and he told me they would spray 2″ of closed cell foam, then install fiberglass batts, followed by sealed plastic.
    Why is this option OK for a vapor barrier but option 3, Foam board & Fiberglass, states do not install a vapor barrier.

    Thanks Steve

    • Todd Fratzel says:

      Steve – Good question….was it truly a vapor barrier or a some type of semi-permeable barrier? I would NOT install plastic as this basically locks the cavity and won’t allow any drying.

  15. Enigma says:

    Todd,

    Thank you for this very informative article. I am hoping you can help with some guidance in my situation. I am a hesitant do-it-yourselfer who often has bad luck, so I want to ensure I am doing the right thing here.

    I recently moved into a 10 year old house in MA and found small spots of mold building up on the fiberglass of the framed walls of our walk-out basement.

    The basement is unfinished, and the 1/2 and 3/4 walls that are sitting on the foundation just have unfaced fiberglass and a plastic barrier stapled over it. I am not looking to do the whole basement right now, but I want to fix the fiberglass/mold situation until we eventually finish the entire basement.

    If I were to just install the 2″ XPS and fiberglass, can I leave the foundation below the walls uninsulated or is the insulation of the foundation an integral part of this?

    Also, is it okay to just leave the internal fiberglass insulation exposed to the rest of the basement, or is installation of some kind of barrier necessary? I am hoping to essentially leave the basement in the same condition as you have in the last picture of your article, but I am concerned that other comments have noted frost issues in cases where drywall/paint was not applied over the insulation (or maybe even basic codes I am not aware of that may say not to leave exposed fiberglass).

    Any help you can provide is GREATLY appreciated and thank you again for this information!

    • Todd Fratzel says:

      You are asking some great questions. In your situation you can definitely leave the concrete alone until such a time that you want to finish the basement. That won’t affect the framed walls at all. It’s likely you’re finding issues because the plastic vapor barrier was not properly sealed, allowing moister to get between the plastic and sheathing. Be very sure all the plastic is sealed well when you’re done.

      The code question is tough. Typically it’s not acceptable to leave plastic vapor barrier or exposed fiberglass in a living area because it’s a fire hazard (flame spread issue). I’ve seen LOTS of times where it’s been allowed in “unoccupied” basements. It really is a question for the local code enforcement official.

      Good luck.

      • Enigma says:

        Thank you for taking the time to respond, I really appreciate it!

        I am, however, a little confused by your comment to make sure all the plastic is sealed well when done.

        Our current insulation from what I can see inside is:
        Plywood => Unfaced Pink Insulation (with mold) => Plastic

        I assumed that the vapor was likely coming through the exterior wall and condensing on the cold plastic (and soaking the pink insulation). Based on what I understood from your article, I was planning to get rid of the plastic altogether and go with a new setup of:

        Plywood => XPS => Unfaced Pink Insluation => Drywall
        (With the drywall being a maybe depending on code)

        Is this not correct and should I be applying a layer of plastic somewhere?

        Again, I really appreciate the help! I don’t want to screw this up :)

        • Todd Fratzel says:

          Travis – Not exactly how it works.

          – It’s likely that if the plastic was not sealed, that moisture from the interior side (basements are very damp) got into the wall cavity and condensed on the back of the cold plywood. We see this a lot!

          – New system: your plan works fine, if…big if…you install the drywall, tape it, and paint it (the latex paint is a semi-permeable vapor barrier). However, that isn’t necessary if you’ve got enough foam insulation that’s sealed to the framing. If you install a minimum of 1-1/2″ of foam, seal that to the framing, then you’d be ok without the drywall as far as moisture goes.

  16. Nathan says:

    Todd –

    Thanks for the great info. We have a half wall foundation that sticks out 3″ and have decided we DO NOT want to build shelf, and instead build one continuous wall.

    The issue is we will have approx 8.5″ (3″ foundation + 2″ rigid foam + 3.5″ 2×4 frame) of open space from where the original 2×6 end that are sitting on the frame to where the drywall will eventually go up. (Right now the 2×6 are filled with batt insulation with vapor barrier by builder).

    Is that space a problem? How would you suggest handling that? Thank you!

    • Todd Fratzel says:

      Nathan – I’d remove the batt insulation, insulate the stud bays with foam board and tie that foam into the foam on the foundation. Then just frame straight up.
      Good luck.

  17. Gary Sullivan says:

    Todd, I like all your articles. Thanks. Can XP be fitted like this in currently unfinished my basement between the upper floor joists to keep warm air from my upstairs living quarters from being pulled down to my unheated walk out basement? What about using Polyiso for those joists? Humidity is a problem here in Georgia thus the reason I may do my basement wall cavities as you show above. Thanks!!!

  18. Scott T. says:

    Hi Todd,

    You mentioned I’m the article about nails entering the stud cavity from the outside siding, etc. How do you apply 2″ foam board with existing nail protrusions?

    Thanks. Scott

    • Todd Fratzel says:

      Some of them we bend over, but most we try to get the foam to encapsulate them. Use a block of wood to tap the foam onto them. Ideally there are not too many, as the siding hopefully was nailed into the studs.

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