We’re planning a first floor bathroom renovation in a 1920’s bungalow located in 4A. To get to at least a r30 ceiling insulation will have to go right up to the roof deck. Metal roof with ice and water shield that sits on plywood, which sits on skip boards. I’ve read up on the articles here leading too…

My plan.

* Spray foam bottom of roof deck all the way up till i meet knee wall of the second floor, thus bringing knee into the conditioned space of the home (the exterior walls of the knee wall is already sealed). Fill the remaining ceiling space with rockwool insulation. Drywall & Paint.

* Alternatively, fill the space with rockwool, 1″ polyiso, drywall & paint.

* Spray foam the soffits and band joists etc, complete with additional fill insulation.

* Over sizing the CFM of the bathroom fan which would be soffit vented. The soffits are currently unvented; the actual attic is gable vented.

So my fears are that the roof deck will be at risk being sandwiched between the effectively two vapor barriers. Or that i figured this wrong all together especially since this is a warm and moist room underneath…