Unlike the externally visible parts of residential, institutional, and commercial buildings, the foundation is not as easy to admire from the outside, but the foundation has a critical purpose. A building’s foundation distributes the load of the structure to the ground and ensures structural stability. Foundations must have the capacity to withstand both dynamic loads and seismic loads as well as the weight of the building itself.
Factors that determine the type of foundation needed include the type of soil and the availability and cost of land as well as location factors such as the height of the water table, flood zone classification, frost lines, and susceptibility to weather related issues such as storm surges. It is usually best to choose the type of foundation that is used in other local buildings.
Some types of foundations:
- Slab-on-Grade Foundation: Concrete is poured on top of a layer of gravel. A mesh may be spread prior to pouring the concrete to minimize cracking. The edges of the slab are poured thicker to create the footing. This type of foundation is between 4 to 8 inches thick and has reinforcement bars.
- Frost-Protected Foundation: Similar to slab-on-grade except the slab is insulted between two layers of polystyrene sheets, trapping heat from the ground and absorb the heat from the building. This type of foundation is recommended in rural or suburban areas where the ground might freeze.
- T-shaped Foundation: T-shape foundations are often the best choice. The name refers to the construction of the foundation and footing in a certain way. The footing is constructed below the frost line, walls are built and the concrete slab is poured.
- Crawlspace Foundation: This is a raised foundation with concrete columns and a wall that support floor joists. A crawl space with a clearance of 3 feet or more creates a space for wiring, plumbing, and air ducts for easier and less costly maintenance of a home.
- Basement Foundation: A footing is constructed below the frost line, with 8 foot concrete walls and a concrete slab as the basement floor. This type of foundation requires excavation, but it is the preferred design if the type of soil and water table level allow. The basement is often built out and finished to create living space.