Attached Unheated Garage Slab On Grade Frost Heave

[Said the Sky]

Hello - I have a attached garage that is unheated (or is it considered heated to a certain extent as we are attached to the main home?) and we are in frost susceptible soils (silty clays) with frost depth in the area to be around 4' dp. My question would be: do we require the floating slab on grade to have horizontal insulation underneath it? can we rely on perimeter footing drainage to drain the water? (and therefore no frost heave?), can we rely on the home to partially heat the garage? (I assume yes for closer areas, and no for the furthest areas)

the building is sitting on a frost wall at the perimeter and 4" slab on grade interior. Arch shows sonotubes but I am not sure what they are doing...(i've never seen sonotubes used for garage pads before, I think they don't do much but restrain the slab and potentially cause more cracking). Small project no geotech.

tia

 

[le99]

I assume your frost walls are extended to the frost line below. If this is the case, you can install the insulation material at the inner wall faces, and underside of the slab, to cut off the path for cold air to migrate. The slab may only need partial insulation around perimeters, you can find the information on the website of some suppliers.