Floor heat loss generally comprises about 10 percent of the total heat loss of a house.2 This may sound minimal, but from a comfort standpoint, cold floors are usually not very desirable. Slab-on – grade foundations, or foundations for homes that have no basements, may require the insulation to be placed vertically on the exterior or the interior of the foundation wall or horizontally above or below the floor slab. Continuous vertical exterior insulation placed outside the foundation wall reduces heat loss from both the foundation and the slab. To reduce heat flow from the slab floor to the ground outside, extend the insulation below grade to the footing. Insulate any exposed slab edge above grade.
A homebuilder also can install insulation vertically on the interior side of the foundation before pouring the slab. R-10 perimeter insulation around the edge of a slab is probably the most common type. If the highest known water table of a site is 2′ or more below outside grade, perimeter insulation may be placed in a vertical or horizontal position. If the highest known water table is less than 2′ below the outside grade, perimeter insulation may be placed in a horizontal or L-shaped position.2 Special consideration always must be given to the potential for insect or vermin infestation when using exterior or interior foundation insulation products.