Hi folks,
I’m building a 20’x40′ workshop that will have a simple 2″ pitch shed roof. The rafters will be 14″ wood i-joists with ply sheathing covered by metal roof panels. Since this is Vermont I plan to use that 14″ to insulate well. Is it necessary (or desireable) to provide ventilation in the roof structure between the insluation and the exterior sheathing? I will poly sheet the inside as a vapor barrier. I’m also considering using a foam insulation (icynene maybe) rather that fiberglass.
I always get great advice here – thanks in advance.
Terry
Replies
If you use a 20 lb. felt paper over the sheathing board, you don't need to worry about venting the roof. Metal roofs are pretty much self venting with the rib or v-grooves. I also make the assumption that the bottom of the I- joist is going to be your ceiling? If that is the case, insulate with foam and seal everything up as tightly as possible.
A good site to research that type of roof system is BuildingScience.com
Dave