A-frame roof insulation
We recently purchased a small a-frame in zone 4a as a vacation home.
The construction of the cabin is fairly rudamentary. The roof is composed of asphalt shingle on top of plywood sheathing, which is supported by sistered 2x8s rafters, with a four foot span between rafters. There is currently no insulation or ceiling. Several of the rafter bays are interrupted by skylights.
From reading the articles and comments on this site, I understand the best practice would have been to insulate using rigid foam on top of the roof sheathing. The roof has been recently replaced, so that is not an option at this time.
I understand the next best option would be to do an unvented roof assembly with closed cell spray foam. We are concerned about potential health effects and enviromental impact, and have largely (and reluctantly) ruled out that option.
That would seem to leave us with only vented options. My contractor has proposed either: (1) adding new rafters between the existing rafters to support r-19 batt fiberglass insulation, with baffles to vent; or (2) cut and cobble with rigid foam, with vented airspace behind the foam. I’m not sure at this time how we will vent around the skylights.
Neither these options would get us to code, so we may add rigid foam on top of the rafters to add r value and prevent thermal bridging from the rafters. Our preference would be to use EPS foam.
Having taken the best options off the table, are there any other options we are failing to consider?
Thanks for any help you all can provide!
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