I bought a house built on a concrete slab on grade. It's an older house, so no part of the slab was insulated. At some point in the past, previous owners decided to pour concrete around the entire perimeter of the house, effectively increasing the size of the foundation slab so that it protrudes two or three feet out beyond the walls (this appears to have been done at least partially for termite control).
My problem concerns how to insulate the exterior of the slab. Obviously I would have to dig to expose the slab edge that I could insulate, but would this even be possible given that the slab has effectively been extended outwards? Even if I insulated the perimeter of the extended slab with foam boards or a 12" perlite-filled trench or something, the top of it (that you can walk around the house on) will still be exposed to the exterior temperature.
Should I just cover the exposed slab surface on the floor with polyiso (R-7) foam insulation boards instead? The final floor coverings will be mostly wood, with some tile and carpet.
The walls are already insulated to about R-10 or so.