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Old 01-31-2017, 09:38 AM   #1
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Basement Insulation after underpinning

In Toronto. We had the basement underpinned and lowered 2 feet.
Also, interior weeping tile was installed with sump pit, with the black dimpled plastic installed on the interior of the wall, running from just above grade, down the wall and under the new concrete floor.
The underpinning created a "curb" around the entire perimeter. the curd is 2 feet high and protrudes into the basement by about 6 inches.
I framed the basement with 2x4s on 16 centres going straight up from the new floor. Because of the curb, there is a 6" gap behind the 2x4 studs above the curb all the way to the ceiling.
Now I'm trying to decide how to insulate. New code requires R20 in basements in Ontario.
I'm leaning away from spray foam for 2 reasons. First is cost, but more importantly, I'm not convinced that it will adhere (and stay adhered) to the black dimpled plastic. I've used a few cans of foam around the windows and some of the foam has ended up on the dimpled plastic but it can be picked off very easily. The dimpled plastic is secured to the concrete wall with tapcons only at the top, so it is not solid, especially where it bends out and around the curb.

I'm considering using Roxul R22 for 2x6 Steel studs. (it is 16.25" inches wide) I would notch one edge each batt so that it fits in the space between the studes and behind each 2x4 and then butts directly against the the next batt. Does this sound like a good idea? I think it would actually be superior (from an R value pov) that using wood 2x6 as having 2 inches of Roxul behind each 2x4 would stop the usual thermal bridging of the stud.
I would of course apply VB after the roxul.

Any thoughts?
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Old 01-31-2017, 03:29 PM   #2
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Re: Basement Insulation after underpinning

Roxul is certainly the less moisture sensitive of the batt insulations in this case.

Give the framing, I am guessing rigid foam is out of the question now?

The foam should stick quite well to the dimpling. You can't really compared rig applied SPF to the 1 part stuff at the store.
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