Will I get condensation if my roof insulation isn’t thick enough?
Climate Zone 5B, Eastern Sierras.
I’m converting a detached studio/shed building, (200 sq.ft.) to be an office space, material storage, and do the occasional glue-ups (woodworking glue-ups) when my shop is too full.
That being said, the space will be “somewhat conditioned”, i.e. a little space heater in winter, a window A/C unit in summer, only when need be. I am working on air sealing and insulating.
It’s a monoslope 3:12 roof with 2×6 rafters, and a vaulted interior ceiling. I have planned a 3.5″ air gap/vent channel under the roof sheathing that is connected to continuous soffit and ridge vents. Since my rafters aren’t very deep, and I don’t want to get too carried away with this project because it’s just a “shed/office”, I was thinking of using 2″ polyiso (R-13) in the remaining 2″ space in my rafters. I can attach them to cleats inside the rafter bays, and they will be flush with the bottom edges of my rafters, making one single plane. I will air seal any gaps.
-My question is, can I just put my finished ceiling material (1/2″drywall, or 1/2″ ply) over this, assuming I do airtight drywall or airtight ply? Is this an issue because my thermal insulation layer isn’t thick enough and will result in condensation between the polyiso and the drywall/ply ceiling?
I understand that I can fur out my rafters to get thicker insulation to meet code req., and perhaps do a layer over the rafters, then install strapping, but again, I’m trying to keep this simple. Any advice/insight would be greatly appreciated!
Thanks to everyone!
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