One way to increase the path-length of insulating soil, between freezing outside air and the ground surface that the found sits on, so the latter never freezes, is to inset the found line back inboard of the building's perimeter.
The slab or subfloor beams then cantilever outboard to support the walls - or else there are columns also inboard, with all floors and roof cantilevering out to suspended walls.
Such inset found line can be as shallow as you like, without need for special FPSP insulation. This design allows completely seamless, bridge-free insulation continuity between wall and floor insulation.
