I'll appreciate any advice, and have a few specific questions: 1) How concerned should I be about making any changes since my joists are in the cement? Some builders do, however. However, I don't see any signs of a water problem such as mold or discoloration. My wife and I had been planning to simply put up drywall, but reading your posts has lead me to believe that this would be a very bad idea. What I am trying to understand is how best to insulate the exposed concrete foundation wall to avoid moisture/condensation issues. Ok, thank you very much. (They also tend to have roofing polyisocyanurate, which is higher R/inch, but not suitable for use under a slab due to it's moisture wicking characteristics.) To which I ask a followup question: if we use PI at the interior concrete boundary, then won't any interior vapor barrier at the drywall/finished surface create a diaper wall? Install dimple membrane on entire wall surface, then 2" Foamboard over membrane, then and regular batt insulation between stud wall A. Walls that are 50% or more above grade, must be added in with above grade walls in your calculations, and insu-lated to the same R-value. For more information on the problem, see this article: "Combining Exterior Rigid Foam With Fluffy Insulation.". I think this solution would cause a problem at the stairs. I plan on putting XPS against the interior side of the block and on the top part of the block that juts out, butting the XPS up to the wooden sill. Some need to be poured into the slab, and I think they probably work best, and there are some that basically act as a faux baseboard that you seal so the water stays 'behind' the moisture resistant baseboard. Response to Charles Chen Thank you again for your help and time! Laura, gap and in this gap there is condensation forming. You can take this approach if you want. Your experience is a good confirmation of the reasoning that has led me, for years, to advise builders to avoid the use of fiberglass batts and polyethylene on below-grade walls. I will move Q. Other options: Should I cut off the 2x4 wall just above concrete height and isolate the concrete part from the wood framing above it, and then use only foam on the concrete part, leave the 2x4 wall uninsulated, and use whatever I want on the above-grade wood-framed wall? ...". My problem is the one wall (about 7 feet wide) is right next to the stairs coming down to the basement. Would flashing tape between the floor and rolled up the dimple mat work for this? Are there any negative of doing this, such as allowing moisture to build between layers of XPS? ", Q. 3" reclaimed fiber Polyiso faced in a Zone 5, confusion reigns View our Privacy Policy here. ", Q. Everything on here contradicts what we do. The concrete wall is cold. It's better if the plywood & floor EPS extend all the way to the wall EPS, which puts a thermal and capillary break between the slab and all of the wood (including the bottom plate) and exposes more bottom plate for attaching the drywall & kick board trim. I am in the process of finishing my basement. I excavated the perimeter, pressure washed the foundation, removed and reinstalled the footing drain, (filled with sediment from 1970), damproofed the wall, installed 2" closed cell foam board, covered the foam with painted galvanized metal roofing screwed with tapcons to the concrete (use impact driver, not hammer drill!) The walls are out of plumb and I will have to construct a 2x4 wall and will fill it with bat insulation … 2.5" of polyiso also get you there, and you can also often find recycled polyiso. Briefly, it's important to insulate your foundation and rim joist area; and this work will make the concrete colder, increasing the risk that your joist ends will rot. A few comments for Janet Ingles (I'm Martin. A watertight seal on the interior would mean the water is trapped inside the foundation, and prevailing knowledge seems to indicate that would accelerate and expand the breakdown. I have edited the article to reflect your useful additions. Would the basement foundation be poured, then insulated on exterior, then garage slab poured? The main problems are that bugs like to burrow in and under the foam, and the portion of the foam above grade … From the reading I have done, the heat loss in a basement wall is predominantly near the top, and it tapers off greatly as the wall descends into the ground. So what is the recommendation to help with this problem. So I proceeded. 3) Finally, my stair stringer is about 1/2" from the wall. 2. Second response to Jay Lista Because I am limited with what I can do with the walls and electric already in place, about the most I can do outside of spray foam would be to use fiberglass insulation with kraft or foil backing or slide in 1/2" sheets of XPS behind the wall. I have been doing a lot of research, and the recommendations about how to properly maintain this type of foundation seem to be diametrically opposed to the recommendations on how to insulate a basement. Q. This is great information but Would I benefit by layering XPS board? It isn't doing any good, but it isn't doing any harm. However, a more thoughtful response would explain that fiberglass batts and Roxul batts contain air. Other elements of the assembly -- including resilient channel or multiple layers of drywall -- can also be helpful in noise reduction, so you have to consider the assembly as a whole before deciding on the details. 1) I cannot slide xps behind the pipe because there's not enough space, however, I thought of putting xps just above and below the pipe (on the wall) and then foam the gap between the pipe and the xps, and then foam between the XPS and wood framing (which sits on the cement wall) but that would require quite a bit of foam. We see very large heat savings with reduced air leakage in addition to the insulation when this is done right. The interior side sheathing also be tight to the rock wool, with no intermediate air gaps/channels. Thanks for your suggestion. A. "If so, are fiberglass batts ok in this above grade cavity?". How to insulate a daylight basement wall When a basement wall is covered with rigid foam or closed-cell spray foam, the interior air is no longer contacting the basement wall. The rest of basement walls are half cinder block. A. Chuck, Martin, Your article basically reads like this: "R-20 is most cost effective... foam is best... so, use R-20 foam". It is actually recommended for the application you are describing on the following website. The exterior of my basement is sealed with rubber membrane so water wont be an issue but the vapor internally on the cold concrete in winter is my concern. A. I'm assuming using a thicker 2x would accomplish this. My concern is that this advice seems to run contrary to the advice masons give for maintaining this type of foundation. Insulation can be applied full height to the outside, as it will … Response to Don Mikulec Can I adhere the foam to the concrete with Great Stuff or foam adhesive if I don't want to hammer drill it? Q. Thank you Martin. ), Q. ", "Combining Exterior Rigid Foam With Fluffy Insulation. Sharon- what climate zone ? thanks....I won't be doing it myself...insulation contractor will be...I'll discuss and see if they can do...if not, we'll play around with rigid insulation before they install the beam. I would prefer to insulate the exterior of my new home's basement wall. I would like to insulate my new construction house including the basement with 4" of XPS rigid foam on the exterior side. Charlie, The air between the fibers of the fiberglass or Roxul insulation is not divorced from the basement air. The result will be condensation that runs down the concrete wall and pools near the bottom plate of your wall. Q. I have also read that EPS is the go-to rigid foam in Europe, because it is "greener". It would be best to fill this void with something -- either a continuous layer of 1-inch EPS, or compressed fiberglass (perhaps a half thickness of R-13 batt, compressed). If done, I plan on doing the digging and placement of the board myself (fairly easy access to foundation with no impediments for the accessible walls). Don, Add 1.5" of XPS for a total of 2" of XPS. An energy audit identified foundation insulation as my most important step. Roxul sound insulation "Also, I would still like to use Roxul inside the wall cavities that will make up the home theater area. I agree that 3" of XPS or the equivalent negates the need for studs and batts, but that is the very design my clients reject due to cost. If in zone 5 or 7 bump it to 1.5" (R10-ish) for zone 6, or 2" (R13.5+) for zone 7. I wanted to know the building science behind the R Value myths, dew points and thermal bridging to help me educate potential clients. Also, I do notice near the walkout section of the basement, there is frost on the concrete in the winter. I'm wondering while I have these trenches dug, is it still valuable to also wrap the exterior of the foundation in foam board too? Sharon, with a continuous strip of 3/4 inch OSB that bridges the gap between the top plate of the wall and the mudsill -- or pack the gap tightly with mineral wool or unfaced fiberglass. Thanks Martin, I'm working with foam that is sealed and pretty tight so I'm not worried about interior air reaching the concrete. I'm open to that idea of doing EPS floor to ceiling as you suggest and then the 2x4 walls inset. However when at HD, I saw a product called DuroSpan, also goes under the label DuroFoam in Canada, that is 2" EPS with foil like film on both sides which cost almost $10 less than XPS. It would be applied so that order of materials would be: earth, stone wall, aluminized side of bubble sheet, bubble interior of sheet, white polyethylene side of sheet, basement air or foam and then basement air, depending on how close to sill. I've been told that they acidic coal ash is incompatible with the basic lime/cement binder and that the two essentially corrode each other over time and in the presence of moisture. Is this acceptable or should I use Rigid Foam board just left as is in the unfinished sections? Response to Adam Brindowski But HD sells 3/4 inch of owens corning rigidfoam sheathing. There are many pitfalls -- for example, the synthetic stone has to extend below grade to look right, and that sets certain limits on permissible details. It's hard or impossible to waterproof a below-grade concrete wall -- and in most cases any attempt to do that happens on the exterior, not the interior. 4. I am using 1.5"x3.5" SPF wood studs, fastened with tapcom concrete "Should we consider increasing the interior XPS?". Is it the same as nonconcrete walls. I'm guessing no poly, just foam on the concrete then the roxul, then the mold resistant drywall ontop of wood 2x4's. 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