ADU Garage Slab Insulation
I am in process of designing a garage to be converted into an ADU “Granny Flat” and I am considering insulating the existing slab foundation from above. My thoughts are to roll-on 2 coats of waterproofing (Redgaurd), add 6” sleeper floor joists, and install unfaced fiberglass batts between the joists before installing the subfloor.
I am in the marine climate of Southern California (3C), 12” of rainwater a year and not in a flood zone.
By code, insulation is not necessary on or below a slab foundation here, just a moisture barrier.
Alternatively, I can level the slab with new concrete instead of wood sleepers, but that simply continues the heat sink.
I am trying to not use foam due to costs.
R-15 insulation is required in the walls and R-30 in the attic. All windows and doors will be new, stucco exterior, mini-split AC, tankless gas water heater.
I will check how tight the building is once we’re done with construction.
Is there reason unfaced fiberglass insulation would not work in this building assembly?
Harding Design & Construction
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