Insulate the perimeter of all concrete slabs
Before pouring a concrete slab, install rigid foam insulation along its perimeter.
If the slab isn't isolated by foam, there will be a thermal bridge to the foundation or soil. This makes the edge of the slab cold, compromising energy efficiency and possibly raising the temperature of the slab perimeter above the due point. This could cause condensation and mold growth. The insulation should separate the slab perimeter from all exterior foundation walls, footings, or soil.
Exterior insulation requires protection from the elements. Choose materials that are both nontoxic and durable. Some building codes ban slab-perimeter insulation for fear of termites entering the building through exterior insulation. Other building codes allow polystyrene foam with use of a termite barrier and an integral insecticide.
Learn more in the Green Building Encyclopedia:
Building Science Corp.
Slab edge insulation