Avoiding thermal bridge under doors at slab on grade?
Due to extensive shallow ledge, I’m designing a slab on grade foundation for a seaside home in Massachusetts (Zone 5A). Because of gently sloping topography, neither a thickened slab edge nor a frost-protected shallow foundation seems possible, so I intend to use a frost wall with a slab separated thermally by rigid insulation.
Also, since the outside face of the 12″ dense-packed, double-stud walls above will be flush with the outside face of frost wall, then the siding, rainscreen and sheathing are all that need to be proud of foundation, and I don’t want (or need) exterior insulation on the face of foundation.
If I simply polish the slab for my finish floor (as opposed to sleepers and a wood floor), it seems difficult to thermally break the frost wall from the door threshold. Any thoughts?