Basement Wall – Insulation with Interior Drain Tile & Steel Bracing
Background: I am in the early stages for a basement finish and want it to be as comfortable as possible – plans are drawn but I want to get out in front of the builder on some of the things I know they’ll take shortcuts on if I don’t do it myself, like sticking batt insulation in the wall cavities. Our house is a 1956 ranch in NE Kansas (zone 4) where our soil is more akin to clay and is very expansive. To add insult to injury, the houses in this area were built very low to the ground with terrible grading and minimal opportunity to create positive slope. 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. Worth noting is there are no efficiency standards adopted by Kansas, so insulating the walls is not code, but as I mentioned I want to make it as comfortable as possible and follow best practice in the meantime.
I plan to use EPS (sadly 1.5″ seems to be all I can find nearby) on the walls and in the rim joists and seal off properly with expanding foam, caulk, and tape.
1. We have an interior drain tile system that leads to two sumps – would it be best to put a dimple mat on the wall to be sure if any water does penetrate, it finds its way to the sump wells? If I do this is there a way to seal off the bottom of it, to make sure the water drains into the crack between the wall and the floor? Would flashing tape between the floor and rolled up the dimple mat work for this?
2. We have perimeter bracing that consists of w-steel columns (4″ flanges) poured into the concrete floor and stabilized using the overhead (main floor) system around the entire basement spaced mainly at 4′ intervals. This presents multiple issues to finishing the space, not the least of which is having to pull framing out from the perimeter walls between 4″ (best case) and 7.5″ (worst case) depending on how it lays out. I would like to get the backside of the finished space sheetrock as close as possible to the face of these columns – but I don’t want them to be contacting it directly – so what if I wrapped them in 1/2″ or even 1/4″ rigid foam? Would that be enough of a thermal break?
3. Based on #2, it isn’t hard to imagine some of our walls have bulged and are nowhere close to being on a flat plane and plumb, making it hard to affix a rigid foam panel without having various gaps behind it – is this a significant issue? (FWIW we’ve had a structural engineer inspect the foundation, so overall integrity is not at issue)
4. 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?
5. If we finish the ceilings and walls with sheetrock, does that eliminate the need to cover any spray or rigid foam applied in the rim joist bays with a thermal break?
6. I could easily use 4″ rigid foam insulation if I wanted to based on the wall bracing, but cost and availability seems to be an issue at that width. I’d like to use at least 2″ minimum (2.5″ preferably) if I can find it. Big box stores only seem to carry up to 1.5″ EPS but can find 2″ XPS more or less anywhere. I’ve looked online briefly but haven’t been able to locate any reclaimed stuff nearby. Is there a reliable website that lists where this might be found?
Thank you for these articles and all the expertise – very helpful to the weekend warriors out there like myself. I skipped doing any actual work today to chase rabbit holes here all day instead…
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