Spray foam retrofit question
I’m in the middle of a big remodel where we gutted almost the entire house down to studs, and are building it back up. We left one full bathroom intact, and one wall of he bathroom is exterior. Today we removed the exterior sheeting and can see that the current wall system from inside out is 1/2″ drywall –> 1/2″ pressure treated plywood –> 2×4 studs with fiberglass batt insulation–> 1/2″ sheathing –> (used to be cedar shingles).
We are redoing the rest of the house to have the following wall system: 1/2″ drywall –> 2×4 studs with blown-in insulation (cellulose or fiberglass, unsure yet [or mineral wool if we can find it]) –> 1/2″ sheathing –> peel and sick WRB/ARB (vapor permeable) –> 1.5″ Rockwool Comfortboard 80 –> 1×4 furring strips –> exterior cladding.
For the bathroom, I don’t plan on opening it up from the inside, so I won’t insulate it at the same time as the rest of the house wall cavities. After some minor framing repairs, I want to insulate from the outside before we put the sheathing back on.
Total area of the wall is about 100 sq ft, minus a 6 sq ft window. My first thought was to find an open-cell spray foam kit and do it ourselves now. But the pressure-treated plywood is giving me pause. Does that plywood act as a vapor barrier? Does it matter?
I know I could put batts back in, but the framing is pretty cobbled, so it would be lots of patchwork. In general my approach was to use a blown-in/on product to fill all the voids.
Any recommendations on what to do here would be great.
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