Insulating and air sealing in an attic with a strapped floor
As part of an insulation upgrade job for my attic, I want to air seal the attic floor and build-up rigid foam at the eaves to try to get more total insulation value in that area (I unfortunately have low heeled trusses).
The problem I’m wrestling with is how to properly detail the floor, particularly at the eaves. The current stack-up from inside to attic is 1) drywall, 2) poly vapor barrier, 3) 1 x 4 strapping attached perpendicular to the bottom of the trusses. Should I detail the poly as the air barrier?
I’ve also attached a diagram of what I was thinking of doing at the eaves – basically stacking up foam until I get 18″ of height. The problem again is how to detail the first layer of foam. The foam itself will basically be a vapor barrier (likely foil faced graphite eps or maybe polyiso) so should I remove the vapor barrier at the eaves to prevent trapping the strapping between two vapor barriers? I could then detail the foam as the air barrier in that section. For air sealing, I was planning on using a combination of acoustical sealant, canned spray foam and Siga Wigluv.
Any advice would be greatly appreciated.
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