The Three Basic Types of Home Foundations

There are three basic types of foundations in use today in the construction of a home.

Slab Foundations

Home Underpinning

A slab foundation is a foundation built directly on the soil with no basement or crawl space. Slab foundations are base in areas where soil conditions are not convenient for a basement, and are the most base foundation found in warmer areas such as Florida, Arizona, California and Texas, or in any place where the depth in the middle of the soil and garage underlying rock is very shallow. Slabs are the quickest and cheapest foundation because they wish less labor, skill and materials cost. They consist of a concrete slab that is typically 6 to 8 inches thick. Embedded within the slab is a grid of supporting ribbed metal rods known as "rebar." Even in locations where basements are prevalent, slab foundations are typically laid to serve as the base for structures like garages, pole barns, and sheds. Slabs are the least costly of the three main foundation types but supply no storage or utility space, as the home actually sits directly on a large platform of solid concrete. Slabs have the disadvantage of being difficult and costly to mend when they rule and crack, and plumbing lines that protrude from the soil upward straight through the concrete can also be costly to repair. In areas where the underlying soil is thick or prone to excessive expansion and contraction, cables are embedded which can be tightened to supply good horizontal retain and minimize the width of cracks.

Crawl Space (Pier and Beam) Foundations

A pier and beam foundation consists of whether vertical wood or concrete columns (piers) that retain beams or floor joists above the ground. The areas in the middle of the soil and the bottom of the house floor is known as the crawl space. These foundations are built whether at ground level or over a shallow excavation that varies in depth, but is ordinarily about 36 to 40 inches deep. The best crawl space foundations have a load-bearing concrete perimeter wall and concrete or steel piers, both having footings below the freeze line of the soil, along with a good wall over the soil to keep moisture under control. Less costly versions have no load-bearing perimeter walls, piers with shallow footings, and no moisture wall at all over the soil. Crawl spaces that enclosed by a wall or by skirting must have vents on every side to allow air to circulate and help keep the soil dry under the home. These vents must be configured to prevent the entry of rodents and snakes. Crawl space foundations are most often used in areas where there is heavy clay content in the soil that can severely damage (crack) slab foundations, or in waterfront or flood prone construction sites where the requisite floor height to prevent water penetration of the living space must be higher than a slab can ordinarily provide. The customary advantages of crawl space foundations are that plumbing lines are facilely accessible for repairs, and foundation village problems are easier and less costly to exact than with slab foundations. A customary disadvantage occurs when these foundations are not properly maintained or are constructed without sufficient ventilation, allowing water or pests to cause damage. Crawl space foundations without sufficient insulation applied to the bottom of the house floor can be very energy inefficient in a cold climate.

Basement Foundations

A basement is a type of foundation which includes an accessible space in the middle of the soil and the bottom of the first floor of a home. This foundation provides living space below the home, below the ground elevation. It is basically a slab foundation with walls and a floor. Basements are most often built in cold weather climates such as the Northeast, Midwest and Rocky Mountains, and in places where the cost of excavation is not prohibitive. Basements start with a hole roughly 8 feet deep, however, some homeowners will opt for a 9 or 10 foot deep basement wall to increase height and volume of useable space. The floor and walls are built, then the house itself is built over that. Basement foundations have the benefit of providing useful space for utilities, mechanicals systems, and storage not ready in the previous two types of foundations. The customary disadvantage of basements is that because they are mostly below ground level, they are vulnerable to leakage, mold formation, and flooding. Basements in wet climates must always have a working drain and pump in the floor to combat flooding.

The Three Basic Types of Home Foundations