Insulated garage: Insulate below slab?
Colder end of Zone 6A, Ottawa Ontario.
Attached garage/workshop, fully insulated/sealed.
I would like to heat the garage to keep it a few degrees above freezing, and temporarily heat the smaller workshop area to a comfortable temperature only when needed. The workshop area will only account for about 30% of the total garage space and will be separated by an insulated wall.
Since this is a new construction I am considering a hydronic heated slab, but I realize this would require insulating below the slab so the cost would not be insignificant.
Since the goal is to keep the garage at a low temperature, would a better approach be to NOT insulate below the slab and depend on ground heat for some of the heating? I believe annual ground temperatures are generally in the 40’s here, so with good perimeter insulation the slab could potentially stay above freezing on it’s own.
I’ve searched around a bit and opinions seem varied, with nothing really “concrete” (pardon the pun) and no real-world data to look at.
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