Insulation and soundproofing
Insulating below slab-on-grade floors
...basements and stay 4 to 5 feet below grade is to avoid frost heave, using dirt to insulate. With a slab-on-grade, the difference is you use 'insulation' to insulate, rather than dirt. This effectively moves the frost line from 4 feet down to just 6 inches, problem solved.
Building above grade on a slab can be a much ...