Roof underlayment between sheathing and rigid foam: Does perm matter?

I’m plodding along with my shed/workshop, and still using it as a test case for materials/techniques/education for the future shop/garage and for future house improvements.  I’m now in a orthopedic… I’m plodding along with my shed/workshop, and still using it as a test case for materials/techniques/education for the future shop/garage and for future house improvements.  I’m now in a orthopedic…Read MoreGreenBuildingAdvisor