Exterior rigid foam and interior mineral wool for hip roof
I am planning some envelope and HVAC upgrades on a 1958 brick-veneer home in climate zone 5a (Southeast Michigan). Would the GBA community be willing to check/advise my insulation/roof plans?
Right now I’m looking at the 2nd floor which has three bedrooms, a hall, and a bathroom; I have a manual J calculation complete.
My plan is to bring the attic into the conditioned space and insulate to R49. The attic will not be living space or even used for storage. It’s currently unconditioned and contains ducts for air conditioning (heat un the house is via hot water baseboard).
Proposed roof stackup, from the exterior: asphalt shingles, synthetic underlayment, ice and water shield at valleys and eaves, new OSB, 2x4s on the flat to provide vent space, 2 layers of 2″ polyiso with staggered seams, existing plywood roof deck with taped seams, 7.25″ Roxul batts between the 2×6 rafters. OK? Any concerns?
Is it important to fir out the interior side of the rafters to match the Roxul? I assume it could friction fit just fine in the 5.5″ cavities.
BTW, the reason I am not looking at adding ducts within the existing conditioned space is that there just is little space available; ceilings are at 7″6″. I considered ductless heads in each bedroom but they would be oversized (cooling loads calculated at 2,915 BTUh, 1,926, and 1,642 for the three bedrooms).