Slab-on-grade
A slab-on-grade foundation is often the least expensive foundation choice. A conventional slab foundation in Minnesota requires a foundation wall and footing extending below frost depth. Rigid insulation is placed vertically inside or outside the stem wall and/or horizontally beneath the slab edge. An alternative that saves material and cost is a shallow frost-protected foundation with rigid insulation extending horizontally out from the slab edge. The main drawback of a slab-on-grade foundation is that many people perceive this option as a lower quality foundation type. In Minnesota, a concrete slab is often thought of as a basement or garage floor that is harder and colder than a wood floor. A slab is typically built less than a foot above the surrounding grade, which can reduce the street presence of the house as compared to surrounding houses with basements. A wood floor raised above grade may be more appropriate in an inner city neighborhood to respond to the scale and street elevation of neighboring houses. Other issues with slab-on-grade foundations include the need to place all utility and storage functions above grade, and the inaccessibility of ducts, pipes and wires below the slab.