Foundation Walls
Foundation walls are walls that extend below grade and rest on a footing.  The foundation wall must be able to transfer the weight (load) of the exterior walls and first floor to the footing and withstand the lateral forces applied by the exterior soil.  With modern construction, foundation walls are usually 8 to 10-inch-thick, poured reinforced concrete or 8 to 12-inch-wide concrete masonry units (CMUs or concrete blocks). The thickness of the wall is determined by the weight (vertical load), depth below grade (lateral load) and the material used.  Other materials that are used include brick, stone, cinder block, clay tiles and wood.  Each has its own advantages and disadvantages.

Also see footings.