Heat loss through the uninsulated basement of an otherwise well-insulated house can account for up to 40% of the total house heat load. That fact should justify spending a reasonable amount of money on basement insulation. But computer simulations, controlled experiments, and field studies consistently suggest otherwise. Since most basements are not fully heated, the below-grade heat loss is so small that, based on energy savings alone, full wall insulation is rarely cost effective and sub-slab floor insulation is never cost effective. Figure 1 shows the calculated annual heat loss from a basement located in a cold climate (Madison, Wis.). Notice the huge difference between the fully heated (68°F) basement and unheated (50°F) basement cases. This is what makes basement insulation different from upstairs wall and ceiling
