Vented and unvented ceiling, Zip System, metal roofing, underlayment question
I am seeking some advice, and have been researching for quite a long time, but can’t really seem to find the best answer for our situation.
Currently building New Construction in Climate Zone 5. Using ZIP System for the walls and roof.
In the center of the home, we have Unvented Cathedral Ceiling. We decided to use Unvented design, and insulate with Closed Cell Spray Foam.
On the two sides of the home, we have Vented Ceiling, with unconditioned attic space, insulating with fiberglass batts.
We plan on installing a metal roof.
My question is, in trying to avoid moisture issues, is it preferable to use asphalt felt as the underlayment over the entire roof? I am reading it is preferable to use over Unvented Ceiling. Not sure if this is ideal over the entire roof assembly. I initially was looking into Grace I&W, but am now reading that might not be the best idea. Especially if the Unvented Cathedral needs to dry to the exterior, correct?
Any advice would be greatly appreciated.
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