To open cell foam attic or not?
We live in NC (climate zone 3A) in a 10 yr old 2 story home, with walk up stairway to attic (2nd floor is insulated, so attic floor is T&G, 3/4” plywood, that runs all the way behind the knee walls to the soffit area, and is glued and screwed down. Attic venting is ridge and soffit vents. Attic ceiling is 10’ with 600+ sq ft of storage space, which could easily be retrofitted for another bedroom. Heat pump mechanicals are located in attic knee wall space, as well as insulated flexible reflective duct work going from mechanicals to ceiling vents of 2nd floor bedrooms, for heating /cooling.
Like most attics, the temperature in the attic varies from the 20’s in winter to 110+ F in the summer. So I was thinking of having the attic open cell foamed to keep the temperature more consistent. In that way the mechanicals wouldn’t have to work so hard, to include temperature variations in the air in the insulated flexible duct work. So I had an estimate from a local, reputable, professional icynene installer. The company advised they would totally foam seal the attic, ceiling joists, ridge and soffit vents etc., and thus the attic temperature would not have the extreme temperature variations. I asked the contractor about moisture, mold, leaks and “overcooking” the asphalt shingles, and got a reasonable explanation re all four, which I won’t discuss here. However, in speaking to some friends who are engineers and/or contractors, they expressed concern the asphalt shingles would wear out a year or two earlier than they would, and how the attic would “breathe” and / or acclimate to humidity changes.
So my question is two fold. Would Green Build advisor members recommend I proceed with open cell foam, and if not, what other options do I have to achieve my goal of minimizing temperature variations? I’m not really finding other options.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part