Insulating the underside of precast concrete slab garage
I am designing a garage using precast concrete slabs to allow for the space underneath to be used as conditioned living space.
The garage floor will consist of a waterproof urethane top layer, 2″ concrete topping for the drainage slope, and 8″ hollow core precast concrete slabs. 6″ metal studs will be secured to the underside of the precast concrete slabs.
The question is what insulation to use. I do not want to introduce closed cell foam as this is a renovation and we are trying to avoid closed cell foam’s outgassing issues in homes that are inhabited during renovation work. 5/8″ gypsum board would be used to seal the insulated cavity.
I am concerned that cooler conditioned air would get up to the underside of the precast planks with open cell foam. We are tight on the way the stairs work, so I am not inclined to make this system thicker.
Any informed thoughts on this would be appreciated.
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