Foundations

foundation system has two functions. First, it supports the building structurally by keeping it level, minimizing settling, preventing uplift from the forces of frost or expansive soils and resisting horizontal forces such as winds and earthquakes. Second, a foundation system keeps the wooden parts of the building above the ground and away from the organisms and moisture in the soil that both eat wood and cause it to decay.

The foundation is the part of a building that is most likely to determine its longevity. If the foundation does not support the building adequately, cracks and openings will occur over time, even in the most finely crafted structure. No amount of repair on the structure above the foundation will compensate for an inadequate foundation; once a foundation starts to move significantly, it will continue to move. We now have developed the knowledge to design and construct durable foundations, so there is no reason to invest in a modern building that is not fully supported on a foun­dation that will endure for the life of the structure.

In the United States, there are three common foun­dation types. Each performs in different ways, but all rely on a perimeter foundation, i. e., a continuous support around the outside edge of the building.

slab-on-grade foundations

Slab-on-grade systems are used mostly in warm climates, where living is close to the ground and the frost line is close to the surface. The footing is usually shallow, and the ground floor is a concrete slab. Many slab-on-grade systems allow the concrete footing, foundation, and subfloor to be poured at the same time.

crawl spaces

Crawl spaces are found in all climates but predominate in temperate regions. In this system, the insulated wooden ground floor is supported above grade on a foundation wall made of concrete or concrete block. The resulting crawl space introduces an accessible zone for ductwork, plumbing, and other utilities, and allows for simple remodeling.

basements

Basements are the dominant foundation system in the coldest parts of the country, where frost lines mandate deep footings in any case. Like crawl spaces, basements are accessible, and in addition they provide a large hab­itable space. Basement foundation systems are usually constructed of concrete or concrete-block foundation walls. Drainage and waterproofing are particularly crit­ical with basement systems.

FOUNDATIONS