You may not see your home's foundation, but it plays a major role in your home's structural system, and a stem wall is an integral component of many house foundations. Typically, it's a short masonry wall that stands between the concrete footing at the base of the foundation and supports the house floor system and walls above. Construction stem walls can be found on homes in many different parts of the country.
A stem wall sits between a buried concrete footing and the house's first floor, tying these two elements together. Made from steel-reinforced concrete or masonry block, it is anchored to the concrete footer and has bolts along its top edge that secure the sill plates, or mud sills, which in turn are secured to a wood floor system or a wall frame. For houses with concrete slab floors, the slabs may overlap onto the stem walls or stop just inside the interior faces of the walls.
To help understand how a stem wall works, it is helpful to look at the different types of home foundation systems. Slab-on-grade foundations typically consist of a concrete slab poured inside the area defined by stem walls. Monolithic, or "thickened edge," slab-on-grade systems feature a slab with a thick perimeter so that the slab and footing are combined into a single element; these systems do not include stem walls. With conventional wood-frame floors, the ground inside the stem walls is excavated to create a crawl space or basement area, and the floor frame spans across the tops of the stem walls. In some cases, the interior area may be backfilled with dirt so that the stem wall is supported by compacted earth on both sides.
Stem walls serve as an effective way of tying the footers and floor together in areas with poor soil quality, where footers may have to be buried quite deeply to safely support the structure. This type of foundation also makes it easier to support a home on a sloped or uneven lot, as the stem walls can be built to different heights based on the contours of the land. Finally, stem wall foundations serve as the strongest and most effective ways to anchor a home to the ground in areas subject to hurricanes or heavy winds, according to BobVila.com.
Stem walls take longer to construct than some slab-on-grade foundations due to the need for greater excavation. This system also costs more on average than a monolithic foundation, according to Cogdill Builders, Inc.