Detached Garage Insulation & Conditioning

Hi all, I’m looking for advice on insulating and conditioning a 16.5' x 22.5' (372 sqft) detached garage in northern Michigan. It's slab-on-grade with 7' walls, a gable roof peaking at 11', and exterior 1x10 tongue and groove pine siding. We use it as a bar/entertaining space and want to keep it comfortable year-round—thinking of installing an 18,000 BTU mini-split. The interior walls and gable ends will be finished with more tongue and groove pine. There’s currently no ceiling; the rafters and ties are exposed, and I’d like to keep that look. The roof is uninsulated, but I may insulate the roof deck when it’s eventually replaced (the current one is in good shape). Since I don’t want to cover the exterior siding, exterior house wrap isn’t an option. Based on my research, I’m planning to insulate the stud bays with R15 Thermafiber mineral wool, use CertainTeed’s MemBrain as a smart vapor retarder, seal the sill plate, and then install interior tongue and groove over that—same for the gable ends. Does this sound like a solid plan? Any suggestions for improving it? Also, since there are no gable vents, would adding passive or humidity-sensing mechanical vents (with existing soffit vents) be recommended? Thanks in advance! submitted by /u/BF_Injection [link] [comments]

Apr 24, 2025 - 16:18

Hi all, I’m looking for advice on insulating and conditioning a 16.5' x 22.5' (372 sqft) detached garage in northern Michigan. It's slab-on-grade with 7' walls, a gable roof peaking at 11', and exterior 1x10 tongue and groove pine siding. We use it as a bar/entertaining space and want to keep it comfortable year-round—thinking of installing an 18,000 BTU mini-split.

The interior walls and gable ends will be finished with more tongue and groove pine. There’s currently no ceiling; the rafters and ties are exposed, and I’d like to keep that look. The roof is uninsulated, but I may insulate the roof deck when it’s eventually replaced (the current one is in good shape).

Since I don’t want to cover the exterior siding, exterior house wrap isn’t an option. Based on my research, I’m planning to insulate the stud bays with R15 Thermafiber mineral wool, use CertainTeed’s MemBrain as a smart vapor retarder, seal the sill plate, and then install interior tongue and groove over that—same for the gable ends.

Does this sound like a solid plan? Any suggestions for improving it? Also, since there are no gable vents, would adding passive or humidity-sensing mechanical vents (with existing soffit vents) be recommended?

Thanks in advance!

submitted by /u/BF_Injection
[link] [comments]