Firestone polyiso insulation
I think I would like to use 3 1/4″ Polyisocyanurate in the 2×4 exterior wall stud cavities in a bathroom. As far as I know Firestone is the only company currently producing such a thick piece. This product is intended for roofing applications. This would provide a LTTR of 20.1. Much better than I could get with Roxul or fiberglass. I’m not sure what problems might arise from using this product. I think the main worry would be a moisture issue of one type or another. As a second choice several layers of the DOW Tuff R could perform the same function. I have called DOW and asked if this installation would cause moisture problems and they feel it would be OK. This house has shingles. I would probably use redgard as a waterproofing. Can someone with experience in the matter please chime in to provide some guidance?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part