Attic insulation details
I am in the planning stages of bringing my attic attic into the conditioned space. The attic was built intended to be finished, including active HVAC returns and supplies. We have a good roof, so exterior foam is a not an option. Walls and roof are being done, just focusing on the roof here.
Here is the plan:
1) Move all the ducts out of the rafters and into the floor or kneewall. This will be done based on an updated manual J and D. The furnace/AC is going to be oversized, plan is to live with it for a year or two, that will be a whole other question to ask.
2) Pull all strapping currently on rafters.
3) Insulate 2×10 rafters 16″ OC:
a. 3″ R20 ccSPF against the roof deck, urethane caulk to airseal double joists, plates etc.
b. 1″ polyiso foam strips, ripped 1.5″ attached to rafters to provide enough space for fluffy insulation
c. 7.25″ R30 Rockwool in the bays
d. Strapping put up again
e. Drywall kneewalls, up rafters, and across the flat ceiling.
What is the best way to close up the rafter bay leading to the soffits? The common approach from contractors seems to be a section of batt that gets shoved in there flash sprayed. Our building inspector mentioned 2x fire blocking, but I had never heard of that being required. I have perforated vinyl soffit covers, should these be replaced or modified (building wrap on interior?).
The roof areas in the knee wall and above the ceiling will have exposed batts. I believe these should get an air barrier. Can I use something like tyvek house wrap or something else flexible and quick to install?
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