Flat roof insulation
I am about to tear off an old tar & gravel roof as well as the existing sheathing. I know that some of the old fiberglass insulation was water damaged and expect that to be true of more rather than less. The plan is to add a modest 1/4″ per foot slope (that’s all the room we have). I will insulate between the 2×8 16″ on center rafters, deck with 3/4″ ply, add polyiso rigid, another layer of 1/2″ ply, and finally we will lay down a mod bit roof. Over the top will be a modest roof deck. All of this is in a zone 4 region.
Here are my questions:
Shall I lay faced fiberglass insulation into the rafter bays, or unfaced? And should I dense pack it with a 9″ thick R30 product or go with R19 which is made for 2×8 framing?
Shall I add 3″ of polyiso above the 1st layer of decking, or 4″?
And finally I understand that I should install a vapor retarding layer directly above the 3/4″ decking but it’s not clear to me what product would be suitable here. A suggestion or two would be much appreciated.
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