Metal Roofing Over Purlins
What is the proper roof assembly for a metal roof (such as Fabral Grandrib 3, http://www.fabral.com/residential.php#standingseam) which is screwed to 2×4 purlins 2′ O.C., and covers a vented house attic in a cold climate? In particular I’m wondering if any sort of secondary moisture barrier, like felt paper, is needed between the metal and the purlins? I understand felt paper is recommended when metal roofing is applied over plywood or OSB.
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