I have an old 1000 sq ft house in the Midwest. I have a combination of insulation materials up there- fg batts, blown fg, blown cellulose. I need to increase my attic insulation to at least r 49. Now it's about 30. I am considering doing this myself. My concern is what TYPE of spray foam is right for the attic floor? Closed cell is a vapor retarder that allows some permeability. Will that trap moisture underneath rotting the wood joists? Would an open cell foam be better for allowing drying? I try to reduce indoor humidity as much as reasonably possible. I just have this one concern re: foam. From a performance standpoint, I think it's going to be way superior to fg or cellulose.