Insulation ratio Zone 4A
I have a very thick (12”?) foundation wall above grade. I’m going to add rigid foam board insulation on the inside and outside of the wall.
if I recall I need at least 16% on the outside correct? So if I’m doing 2” of polyiso (at R-13.5) on the interior then I need ~R-16 total for at least R-2.5 on the exterior? I was thinking of going for at least R-10 on the exterior with 2” of R-5 board..
Am I following the rules correctly ?
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