i’m putting a roof on a heated outbuilding at high elevation in dry zone 5b. just wanna make sure i’m doing it right. it’s 2:12, unvented with (from bottom up), structural deck, 4″ xps, osb cover deck, and fully adhered 60mil epdm. underneath will be batts or fill and drywall with no penetrations (hanging lights).

questions:

1. is ice and water shield really required on top of the roof deck.

2. is a vapor barrier required beneath the roof framing?

3. is it acceptable to screw the cover boards into the structural deck, or do screws need to hit rafters?

cheers.