Polyiso for fiberglass insulation retrofit
I’m new to this community, but have really appreciated the depth of information available as I’ve been reading though old posts the last couple of weeks.
My wife and I recently moved into a 1974 home in central Virginia (climate zone 4) which has a wall structure of: tongue and groove boards, 2×4 framing with foil faced fiberglass batts in the stud bays, OSB sheathing, felt paper and cedar shake siding.
We do not want to remove the cedar shake siding from the outside of the home right now, so are considering the best way to retrofit insulation in these walls. I have a reasonable amount of recycled 3.25″ fiber-faced polyiso insulation that we were thinking of cutting and spray-foaming (“cut and cobble”) in the stud bays from the inside. We have some places where we are removing internal tongue and groove as part of another project and this approach seems like a good first step based on what I’ve read here and elsewhere. My thinking is that it would provide immediate R-value and air-sealing improvement over the fiberglass, hopefully without creating any new moisture-related problems. I’m curious if others agree or if there would be any drawbacks to the approach. Any thoughts are appreciated! Thank you
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