Open cell spray foam on roof deck & vapor retarding primer
I’m buying a home in the Boston, MA area. I know I am in climate zone 5. When I decided to purchase the home was already framed and the roof deck/rafter bays were sprayed open cell spray foam. I do not know what was used for the roof underlayment, but I know there are asphalt shingles. The rafter bays are made out of 2x12s and are completely filled with foam. The attic is a walk up and will be finished living space including a bedroom, sitting room, and bathroom. The HVAC equipment and ducts are behind the walls with access doors and hatches for service. I’ve attached a picture. There are supply ducts in the attic, but I don’t know if there are return ducts as the duct work is not totally finished. I need to check with the builder and/or HVAC installer.
I’ve read a lot on this site about needing a vapor retarder in cold climates when using open cell foam on a roof deck. I’m under the impression that it would be needed for my installation. So my plan was to ask the builder to prime the drywall of the ceiling and walls of the attic with a vapor retarding priming sealer. However, I just read Joe Lstiburek’s article ‘Cool Hand Luke Meets Attics’ that seemed to imply I may not need the vapor retarding primer if the attic has supply/return ducts, although since those ducts are in the finished space, I have concerns about the area behind the walls where the HVAC equipment and ducts reside.
So my question is, what do the experts here recommend to make sure I don’t have moisture problems in the attic?
Thanks in advance,
GBA Detail Library
A collection of one thousand construction details organized by climate and house part