Structures constructed on concrete slabs are in direct contact with the ground. Unless they are properly insulated, the slab can become extremely cold and damp. Some form of insulation should be placed between the slab and the ground before the concrete is poured. Insulation can be added to an existing structure by excavating around the edges of the foundation to a level below the frost line and adding 2 in of waterproof insulating material to the sides of the slab.
Insulation rated R-5 is required for all slab-on-grade floors. Two methods for insulating slab-on-grade floors are illustrated in Figure 3-23. Table 3-6 lists the maximum heat losses in terms of watts and Btu/h per linear foot of exposed slab edge, as recommended by the Electric Energy Association. More information can be obtained from the FHA Minimum Property Standards.