When building a house or any other structure, it must sit on a sound foundation. The foundation provides the support necessary for exterior and load-bearing walls. Contractors use different foundations or foundation combinations based upon the architectural design of the house, the structural components of the land on which the house sits and whether the site is flat or on the side of a hill.
Footings composed of concrete or masonry below the surface of the site support the exterior foundation walls on a closed foundation. The foundation wall surrounds the building's perimeter and extends to the first floor, completely closing the foundation in. In raised foundations, vents periodically positioned around the foundation allow the area to breathe. In slab foundations, the house sits directly on the slab itself or sometimes upon a stem wall, which is a small wall built up from the concrete slab.
Basement walls extend below the grade of the land and serve as the foundation walls upon which the house sits. Also considered a closed foundation, because the walls extend completely around the perimeter of the house and enclose the foundation. Sometimes access to the basement is available from exterior stairs that lead to a below-grade basement door. Part of the basement might be above grade a few feet, depending upon the architectural design of the house.
Stem Wall Foundation
Another form of a closed foundation uses a stem wall foundation on the building's perimeter but includes post or pier support underneath the house at key mathematically calculated places. Engineers complete the calculations for determining where the pier or post supports must occur. Piers or post supports are made from wood or masonry. In these cases, the stem wall may be a few inches or few feet in height. Vents are strategically placed to allow ventilation beneath the house.
Walking along the coast, you might have an opportunity to see an open foundation. An open foundation allows a complete view underneath the house, unless closed in by lattice or walls. The first floor of the house or structure sits above grade supported on piles or piers placed at engineered and mathematically calculated positions for proper load bearing. A house built on piers or piles might also appear on the side of a hill where grading is not advised. Piers and piles are made from steel, timber or masonry.