“Water and ice” type membrane on roof?
I will be putting a metal roof on OSB, unvented (spray foam and fluffy, unless I change my mind) in zone 6. I’m unsure what is needed below the metal, if anything. I’ve read on GBA that an impermeable membrane (ie water and ice) is meaningless on an already impermeable arrangement. Is the membrane needed for other reasons? And since this is such expensive stuff (water and ice, anyway) is there an alternative?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part