Typar Roof Underlayment for Unvented Conditioned Attic
A contractor recommended Typar roof underlayment for the roof of my planned Nonvented conditioned attic in CZ3 (fiberglass shingles, oc spray foam underside of OSB).
Vapor perm is very low at 0.41 perms. Typar rep said, “Surround VR roofing Underlayment can be used under non ventilated roof as the perm rating of the OSB or Plywood used is less than one. In many cases a ventilation system is recommended for the best results.”
I’m familiar with the history of this topic. I just wanted to know if anything changed since Martin’s 2015 response to a similar question, “… Most manufacturers of synthetic roofing underlayment do not allow their products to be installed on unvented roof assemblies… I suggest that you install good old-fashioned asphalt felt.”
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