How to insulate a partially open unvented ceiling/roof?
We’ve had a leak and ceiling damage in a 50 yr old house with a flat roof in zone 4A. Part of the ceiling is gone, damaged, part still intact with its fiberglass.So there are cavities with part fiberglass. There is no ventilation in the cavities. This part of the roof was re-roofed a few years ago and some sort of foam board was added on the exterior (presumably between the old rubber and new TPO) at that time. The is no condensation currently with the cavities open.
My question is how to insulate the open parts now without rotting the roof. We had thought to cut and cobble foam board (exactly what sort is also a question ) But we are unsure of how to keep moisture from going around the side of the vapor barrier of the fiberglass, presuming the part of the cavity next to it is not filled completely. (We could do that I guess??) The second issue is of possible moisture getting between the foam and the roof deck. What sort of foam would you recommend? Poliso (with its highter R value)is not available locally. Or is there something better we should use or do??
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