I'm renovating a back room in my 1920's semi in the Northeast. The walls were in horrible shape, so I tore them down. Plus I wanted to insulate and rewire, and it was just going to be easier. The original walls and ceiling were wood lathe, plaster, drywall, dryall (yes, two drywall). The ceiling had blown in insulation (not sure what kind). No vapour barrier anywhere.
The roof is where I'm confused. It is a flat roof, with true 2x10's on 16" centers. On the roof side, it looks like a mix of 8", 10", and 12" wide boards with a 0.5" gap between each running perpendicular to the joists. I've read so much about insulating, but not much pertains to a flat roof. There are no soffits or anything on the side of the house, just fascia and eavestrough.
So, the dilemma is this: How should I insulate the roof, and where do I (if any) put the vapour barrier?
Is a 2x10 cavity too much for spray foam? Should I just double a 6" and a 4" batt insulation? Blown in? Vapour barrier before the drywall (I know I don't need one for spray foam, what about batts?) So many options.