After a 2-year construction project elsewhere on the property, I’m excited to get my garage (which had become a staging area for tools/materials) organized and usable again. But before I start hanging shelves/organization on the drywall, I started to wonder if I should insulate the 3 exterior walls first, to try to make the space more comfortable in the summer and winter (central NC).

The house is ~20 years old, wood studs with fiberglass insulation, and fiber cement siding. The attached garage has 1 insulated wall and an insulated ceiling (bonus room above), but the other 3 walls don’t happen to have any insulation. The garage is a 23′ square with 10′ tall walls (8″ tall cinder block + 9’4″ of studs/drywall). 

The current plan I’m pricing out is to demo the existing cabinets (which I don’t love) + drywall on the 3 walls, add faced R15 batts (to match the rest of the house) + some more outlets while it’s convenient, then replace the drywall. I have a couple ballpark quotes with varying amounts of labor from my side. For context, I’m mostly just trying to insulate the walls before continuing my organization project… however, eventually I’d insulate/replace the garage door and perhaps add a mini split as well.

Keeping in mind that the goal is “better”, not perfection:
1. Cinder blocks: At ground level, will 1 row of these (from the inside) be a huge thermal loss? Would covering them in 2″ of interior foam be a good mitigation? Exterior is possible, but may be unsightly/awkward given the varying topography around the outside.
2. Avoid wasting drywall: Given zone 4a with humid summers, is there any cost-effective way to retrofit insulation without demolishing all the drywall? I’ve heard about dense packed cellulose and foam (both of which would just require holes, not total replacement of drywall) but I’m not sure if either provides an ideal vapor barrier. Thoughts? Objections? Other ideas?

Thanks in advance for helping me think through this!