To Vent a Spray Foamed Roof Deck, or Not?
We have a cape with a 10/12 roof in a Northern New England climate (snow!). Originally, the roof was galvanized metal panels, vented at the ridge, gable ends, and ridge cap, and fiberglass batts R-19 were installed, with pink air insulation rafter baffles to provide continuous airflow from soffit vent to ridge cap. Wood strapping of various thicknesses gave the trusses structural support.
The galvanized roof was rusty and we wanted to condition this space. In January 2021, we fully replaced this old roof system with 5/8″ Zip Roof Sheathing and Zip Tape at all seams. We finished the roof in 26 ga. black standing seam metal roofing. We also received a generous grant from the State of New Hampshire to have the roof deck spray foamed. The installer appears to have more than 2 decades experience, and their recommendations are based on an in-person visit and blower door test. We think they know what they are talking about, but we aren’t building engineers.
The installer proposes that we keep the ridge and soffit vents at the eves to provide venting from soffit vent to ridge cap, like before. We already deleted the gable vents. Then, they would spray 6″ of closed-cell spray foam insulation in each rafter bay. The profile would therefore be:
1. atmosphere / outside
2. 26ga black standing seam roof
3. 5/8″ Zip Roof Sheathing
4. Accuvent PVC Soffit Vent
5. 6″ closed-cell spray foam insulation
6. lightweight drywall + semi-permeable paint
7. conditioned attic space with ERV
The internet would have you believe that vented/unvented conditioned attics is controversial.
I would like to know what the code says that the installer can and cannot do. I would also like to know why we should or should not accept the installer’s proposal to keep the vents.
P.S. I read these two articles already, and we tried very hard to live up to Martin’s roof design recommendations (the skylights are a compromise with my co-designer, and are flashed with Architectural Metal Supply EZ-Curbs). I have not found specific advice on a vented/unvented spray foam roof decks when Zip roof sheathing and metal roofing is installed. Most refers to normal OSB and shingles.
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