Preferred underlayment under metal on unvented roof?
Need to make a final decision on which underlayment to use under a metal roof on an unvented roof system. The roof is currently built as follows: Beams on 5′ centers; 1 1/2′ T&G decking; 3/8″ plywood diaphragm – seams taped; with TriBuilt granulated self adhering underlayment on top of the plywood.
Next I’ll be screwing down 5 1/2″RayCore SIPS panels over heated space and framing boxes over the eaves covering everything with 5/8″ CDX. Still looking at metal roof products but am zeroing in on a high seam (1 3/4″) snap lock system. Roof pitch is 2/12.
Question: What would be the preferred type of underlayment be for this application? I’d do a high temp ice & water shield in a minute but am concerned about the need for the RayCore panels and perimeter framing to dry to the exterior. I&W under the metal roof would prevent that is my understanding.
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