Underlayment in Roof Assembly with Zip Sheathing
I have roof condition that’s it appreciate any wisdom on.
From the inside out: cathedral ceiling with R30 Rockwool batts, zip sheathing, 2in of XPS, and horizontal 1×4 battens, waiting on exposed fastener metal roof. In climate zone 4, GA.
In short, I am rethinking my choice on zip only for the weather barrier, and wondering if I put a synthetic underlayment over the battens, would that mess with the air gap/ ventilation under the shingles, but above the deck?
I have had a couple drops inside from screw holes where the rafter was missed in securing the batten. I would imagine once the roof is on it should be a non-issue, but thinking if a simple synthetic underlayment would be cheap insurance, if it didn’t cause any other issues.
Appreciate any thoughts, or something I may be missing.
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