How to address gap between stud wall and concrete foundation wall
I’m wondering how to (or if I need to) address a variable depth gap between a stud wall and a concrete retaining wall below grade. I’ve glued up 1.5″ of foil faced EPS over the concrete, but still, due basically to contractor incompetence, I am left with anywhere between 1″ and 5″ of space between the EPS and back of the 2×6 stud framing (stud bays to be filled w/ Rockwool batts).
I understand in general the concept of filling any gaps to avoid convection loops, but am wondering if that is really a concern in my case, given a.) the use of EPS, b.) the radiative properties of the foil facing, which as i understand, requires some amount of gap to function anyway, c.) the wall is no taller than ~3ft from bottom plate to joists, meaning max ~2-2.5ft below grade, and d.) I am in climate zone 4C. I will also be installing fireblocking at the top plate and horizontally every 10ft or less, which should further limit loops or air movement to some degree.
If it is still critical to close these gaps, my best option AFAICT would be to build up the batts (i.e. R30 @ 7.25″ + R15 @ 3.5″ in the worst case), but this would be extreme overkill for our climate from a total R-value standpoint, not to mention costly.
Would love to hear thoughts on necessity of closing up the gap, as well as alternative solutions. Thanks!
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