I'm gutting the interior and redoing the siding of my old house. Unfortunately the exterior walls are only 2×4 which makes it challenging to reach R20 code let alone go above it to make a greener more energy efficient home.
So if you fill the 2×4 cavity with rock wool, then mount 4 inches of rigid foam to the sheathing, would that surpass R20? What would others do in my shoes? Double studding and losing square footage could be a possibility but would seem a lot more expensive.
Also where does the house wrap and vapor barrier go?
Climate Zone 5 (cold winters/hot summers)
Best Answer
Given that typical foams are R5 per inch, 4 inches of foam alone will exceed R-19. Rockwool in the stud spaces will help somewhat on top of that (with a thermal break at each stud, but an additional R11 or so between studs.)