Cathedral Ceiling in Cold Climate
I’m building an accessory building in my yard in Montreal, Quebec. 15’x10′. 20degree sloped roof 2×6 16″OC. It’s framed and boarded now w/OSB. I want it to be well insulated but not too crazy. I’m really getting confused over which way to proceed with my insulation for the roof specifically. It will be unvented – cathedral. I want to do a corrugated metal roof but all the underlays for metal roofs here seem to be vapour impermeable, so I can’t do CC spray foam in the cavity right? Can’t dry to either side. My other idea is just doing rigid foam boards on top of the OSB roof sheathing and isulating less inside. Maybe half R value outside and half inside and keep everything air tight with drywall and sealant. Does this assembly work? Would the metal roof just cook the rigid foam boards in the summer? So much to consider.
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