Insulating basement walls with closed cell spray foam
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Any thoughts/experience insulating basement walls with 2x4s with a 1 inch gap off the wall and then 2 inches of closed cell spray foam? I was interested in the Insofast system, but I’m worried about the walls coming out uneven if the wall concrete isn’t totally flat.
The home is newly built with tremco watchdog waterproofing on the exterior of the poured concrete foundation.
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The wall is going to "come out uneven" if you use spray foam regardless of if the wall is perfectly flat or not. It is absolutely impossible to get a perfectly flat and even layer of spray foam no matter how competant the installed -- there will *always* be some noticeable amount of pattern/waviness to the finished spray foam layer. Also, you would need a surface to spray against, you can't leave a gap off the wall with spray foam. You would have to put some type of rigid barrier for the spray foam to be applied against.
My recommendation here would be to use rigid foam panels instead of spray foam. If this is new construction, I'm going to guess that you have a poured foundation, so you can apply the rigid foam directly to that. If you're going to finish the interior basement wall anyway, then that will give you your flat finished surface.
Bill
Thanks Bill. The plan was to first frame a wall with 2x4s with a one inch gap between it and the concrete foundation. Then spray 2 inches of closed cell spray foam into the cavities. This way there would be a flat surface to apply the drywall too.
Ahh, that would work, the spray foam would expand into the gap. I still think you'd be better off just putting thicker rigid foam directly against the foundation wall though, getting all your R value that way, and then frame out a wall if needed to house mechanicals. You don't need to frame a regular load bearing wall in a situation like this, so you can do "interesting" things like using 2x3s on the flat, things like that, to make a sort of minimum-depth wall to fit electricals in if you want.
Spray foam is likely more expensive than rigid foam here, and doesn't really buy you anything in terms of advantages. My own preference here would be to use reclaimed polyiso tight to the wall, then framing if required for mechanicals (which includes electric boxes) if needed, and if you use 1.5" deep 4" square boxes and mud rings, you only need a 1.5" deep cavity in the wall to house the electrical boxes and wiring.
Bill