Insulating between the rafters in my attic truss of my non attached garage located in NE Oregon zone 5. Garage has a 10/12 roof so the attic truss is a nice storage area, has a finished floor in the attic and asphalt shingles on roof. Garage is wrapped with tyvek on the outside sheeting, sided with hardie board. Primary purpose of the insulation is to keep the attic area cooler during summer. I will be heating the garage in winter also but not that often.
So I'm insulating from the inside. Rafter cavities are vented from eave to peak and I built vent chutes with osb running the length of the rafter cavities with a 1.5" space to maintain air-flow (caulked and foamed for tight seal). Plan is to install batts between rafters against the osb vent chute and sheet over the rafters with osb for the finished ceiling.
The only insulation I can get locally is unfaced batts. With all the truss connections to the rafters running poly to face the insulation will be a pain. Is it necessary to have this vapor barrier with this type of insulation design. I guess same question for the walls downstairs and upstairs?