Should I cut the foam board and glue it to the brick in between the existing stud framing and seal up the edges and seams with "great stuff" spray foam or caulk ? This insulation was installed by the contractor shooting the nails into the concrete to affix the insulation to the concrete. How much xps foam is enough? I read the link you posted about combining rigid and fluffy insulation and am confused. Response to David Martin I was pretty pleased with the results except realized a thermo break on the floor would have been a benefit and i did not air seal above the walls, just used fiberglass insulaton. 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. Currently our winter temperatures have been in the twentys for about 3 weeks now. Isn't the interior of a basement considered "below grade"? If you're like me, and don't like risk -- and you don't want to tear out your basement walls in 6 years to fix them -- I suggest that you use rigid foam or spray foam to insulate the interior side of your basement walls. Martin, I think I've found a flaw with your mention of the Canadian study that found R-20 to be most cost-effective. 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? (Click here to see a climate zone map. "Old DIY articles suggested a poly sheet on the concrete followed by 2x4 sleepers with the voids filled with foam and the whole thing covered with 3/4" plywood. Q. Suffice it to say we and the previous owners have invested tens of thousands of dollars into stabilizing and getting this basement dry - I believe we have achieved that goal so now it's all systems go. "I want to put carpet on part of the floor of the playroom area. It is a thin strip of metal conduit which works by collecting water and pumping it out. I have an issue that I would greatly appreciate some input on. Moisture evaporates from the vapor-permeable lime mortar stucco, providing a path for moisture to leave the wall. All locations in NS have fewer than 5000 (base 19C) annual heating degree days (Halifax runs about 4200 HDD/year) so as long as the foam-R/cavity-R ratio is more than 0.2, the code enforcers should be happy with the vapor barrier on the concrete. Interior finish would be 5/8" drywall and sheathes 5/8" plywood whether or not 16" or 24"...roof deck would probably go from 5/8" to 3/4", Hugh, You might want to check out this study in Minneapolis which was sponsored by ORNL and found average savings of 92 therms of gas for interior insulation which would be just $66/year using the same energy prices that were used in the source you cite. I placed the walls directly in front of the foam insulation and then insulated the wall cavities with fiberglass insulation. I would strive to prevent any contact between the foundation concrete and the ground; and also between the foundation concrete and the interior air. If you have rotten sheathing, a rotten rim joist, or missing flashing, you may have to do extensive repair work. Kevin, "My basement has a walkout sliding door. 5. Be sure that you meet your local code requirements for covering the foam with an ignition barrier or thermal barrier. Any feedback is greatly appreciated. I will include a couple pictures to show and tell. Is the application of a dimpled membrane the answer? The advice given for stone-and-mortar walls does not apply to terra-cotta walls. A. Note: Half of my basement is above grade, the condensation is only on the above grade areas. But you are wrong. So you believe that 1/2 ", Q. Would it work to run a bead of Great Stuff along the top of the pink foam?". Nice compilation ... thank you! on both sides or foil on one side and the black material on the other. That is is basement air, and it's moist. However, for average construction where cost restraint is king, the basement is often left as being merely adequate space for utilities, storage, workshops, etc. I think this issue, along with potential for complex moisture management oversights and those attendant problems, when combined with a relatively small documented monetary return by energy saving force me to remind you that basements are not living spaces. It's already studded. Q. Your article basically reads like this: "R-20 is most cost effective... foam is best... so, use R-20 foam". I've designed and built homes with and without basement insulation in my builder days, and there are no comparisons on the comfort side, even though the ROI may not be there. Would it be better to hold rigid foam panels off the floor with a gap large enough that I could fill this entire lower cavity with expanding foam once the bottom wall plate is fastened? Then build my 2x4 stud wall in front of the 2" foam. Far fewer readers are likely to notice Comment #161 on a 4-year-old article. ", A. I'm struggling with a bit of cognitive dissonance regarding the use of vapor barriers in basement and condensation at the interior boundary of the concrete foundation. Im looking on this site and i see R-5, which is 1 inch foam. Don, This is great information but For example, if I used multiple layers of XPS board against the block to achieve a 4 + inch layer of XPS, would I achieve a higher R value? However, all that work is daunting (and potentially wasteful). It seems like where the stemwall is only a foot or two high, we might be able to get away with blowing in something since there are 6-7 feet of wood-framed wall above that will breathe. My ceiling already had fiberglass insulation. Q. Marine Zone 4 and Climate Zones 5, 6, 7, and 8: R-15. Q. Walkout basement interior insulation Again, fiberglass batts are OK. I can easily touch and chip away excess mortar. Basements, however, have specific features that must be kept in mind when it comes to insulating the foundation from the inside—starting with the fact that a variable portion of the walls … I drylocked 2 coats an entire cellar including the floors and it made a huge difference. Thanks for your response. "I have seen a few videos on YouTube of basement CMU walls being mushy and crumbling by being tapped with a hammer. Lastly, interior moisture can condense on the portion near or above grade. With the 2" of foam on the exterior you could put the vapor barrier between the studwall and concrete (rather than on the interior side) and still meet the requirements of the NBC. Frame the basement 6+ inches off the exterior walls and use regular batt insulation In zones 4 or lower an inch of closed cell between the posts and R13 fiberglass everywhere else (including fiber insulation on the posts themselves) would meet or beat code minimum on a U-factor basis, despite the thin spots in the fiber at the posts. Hooray. I understand. They go their own way, away from the home. Q. Response to Don Mikulec (Perhaps you want to see the concrete on the exterior of your house rather than on the interior of the house?). "I was planning to insulate the interior 2x4 walls I want to frame. I've spent the entire day in rabbit holes - my day job can wait, right? I imagine that this dialog will continue, however, even if I can participate. That is why the National Building Code requires a minimum level of insulation in a basement that reaches from the floor boards above your head, down the wall to about two feet below the outside grade level. ;) No, I cannot afford spray foam. Thank you Martin. The dimple mat should extend down to the crushed stone layer under the rat slab so that any water that trickles down the wall will have free access to the crushed stone layer. Although many interior insulation installations are easy to carry out, in some cases it advantageous to call a professional. ", A. Don, The studs are generally greater then 1 - 1 1/2" away from the walls already. A. It's fine to use Type-II (1.5lbs per cubic foot nominal density) or some somewhat less expensive 1.25lb density Type-VIII EPS under a residential slab, but not under the footings. The glib way to answer your question about using a polyethylene vapor barrier to keep concrete walls dry would be, "The reason we know that it doesn't work is because thousands of builders have tried it, and thousands of remodelers and home performance contractors have had to clean up the moldy mess caused by these failures. The home is 20 years old and doesn't have any obvious foundation cracks or seepage issues. For more information on retrofitting rigid foam above an existing slab, see these links: Fine Homebuilding: The Stay-Dry, No-Mold Finished Basement, Fine Homebuilding Q&A: Finishing a basement floor, GBA Q&A: Basement floor insulation retrofit. It's up to you to choose on option. of unfaced expanded polystyrene [R-15]) that allows the foundation to dry inward, and condition the space with air from inside the house. It seems like I could just repoint the walls and seal them up with XPS again, or I could instead do something that allows the walls to "breathe" more. Joe and Dustin, My questions are these: ", A. -- there really is very little vapor that makes it through the foam; that's physics. However, according to a reply above, you mentioned that putting mineral wool in front of the XPS could cause condensation since the XPS would be cold on the interior side, rather than being warm. If more living space is needed, it often makes more sense to acquire it by expanding the aboveground space. How wet is too wet? I'm confident in guessing that it will be much easier to install than dimple mat. These cannot be affixed directly on the wall. I don’t think that fiberglass batts belong in a basement. Climate Zone 4 (except Marine Zone 4): R-10. Even 1/4" fan-fold XPS sold as siding underlayment is better than sealing a non-pressure treated stringer to a damp wall. Spray 2 inch coat of closed cell spray foam at top of EPS board to cover exposed top portion of concrete foundation wall. Many experts would recommend the installation of a plastic dimple-mat product on your wall, followed by spray foam. Yes, you can install two or more layers of XPS. Fred, In looking at the wall detail image, I have a few questions. "I assume the answer is ‘yes,’ so do I insulate the small parts of the tops of the concrete foundation walls that are not covered by the sill plates (8 inch thick concrete with pt 2x6 in top of it)?". Any water collecting on either side of the bubble sheet should drop by gravity into the perimeter drain system, right? This may or may not be a problem, depending on the extent and whether this membrane was enclosed in a finished wall structure with limited air circulation. 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. Any of the following insulation materials are acceptable for this purpose: closed-cell spray polyurethane foam, XPS, EPS, or polyisocyanurate. 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