Garage conversion – GreenBuildingAdvisor

I have clients who want to convert a 23×23 garage into living space heated and cooled by minisplit.

The current assembly is 2×4 walls with T1-11 on the outside — no housewrap or other sheathing or siding.

There is R-11 fiberglass in the stud cavities and pine paneling on some walls, drywall on another.

Inspector is willing to consider it an alteration to a previously conditioned space since there is an old propane heater installed.

Clients do not particularly want to pay for new sheathing/housewrap/siding as I suggested. Also they may not want to pay for new mineral wool cavity insulation and 2” interior foam/strapping behind the drywall.

If they really push for the cheapest option, do I dare just remove the drywall and wood paneling, install fresh new drywall and call it good? For the slab I am thinking 2” foam and two layers of plywood, and R49 blown in cellulose for the attic. Don’t love the half assed wall assembly though — what do we think?