There are three basic types of foundations in use today in the construction of a house.
slab foundation
A slab foundation is a foundation built directly on the ground with no basement or crawl space. Slab foundations are common in areas where ground conditions are not suitable for a basement, and are the most common foundation found in warmer areas such as Florida, Arizona, California, and Texas, or anywhere the depth between the stable underlying soil and rock is very shallow. Slabs are the fastest and most economical foundations because they require less labor, skill, and material cost. They consist of a concrete slab that is usually between 6 and 8 inches thick. Embedded within the slab is a grid of support ribbed metal rods known as “rebar”. Even in places where basements are prevalent, slab foundations are usually laid to serve as a foundation for structures such as garages, barns, and sheds. Slabs are the least expensive of the three main foundation types, but they don’t provide storage or utility space, since the house actually sits directly on a large solid concrete pad. Slabs have the disadvantage of being difficult and expensive to repair when they settle and crack, and pipes that protrude up through the concrete from the ground can also be expensive to repair. In areas where the underlying soil is thick or prone to excessive expansion and contraction, tensionable cables are embedded to provide better horizontal support and minimize crack widths.
Crawl Space (dock and beam) Foundations
A post-and-beam foundation consists of vertical wood or concrete columns (piers) that support beams or floor joists above the ground. The areas between the ground and the bottom of the house floor are known as the crawl space. These foundations are built at ground level or over a shallow excavation that varies in depth, but is commonly 36 to 40 inches deep. The best foundations for crawl spaces have a load-bearing concrete perimeter wall and concrete or steel piers, both with foundations below the ground frost line, along with a good barrier above ground to keep moisture in check. Less expensive versions have no load-bearing perimeter walls, piers with shallow foundations, and no moisture barrier throughout the floor. Crawl spaces that are enclosed by a wall or baseboard should have vents on all sides to allow air to circulate and help keep the soil under the house dry. These vents should be set up to prevent the entry of rodents and snakes. Crawl space foundations are most often used in areas where there is a high clay content in the soil which can severely damage (crack) slab foundations, or on waterfront or flood-prone construction sites where the height The floor height required to prevent water penetration into the living space should be higher than a slab can normally provide. The main advantages of crawl space foundations are that plumbing lines are easily accessible for repairs, and foundation settlement problems are easier and less expensive to correct than with slab foundations. A major disadvantage occurs when these foundations are not properly maintained or are built without proper ventilation, allowing water or pests to cause damage. Crawl space foundations without proper insulation applied to the bottom of the house floor can be very energy inefficient in a cold climate.
basement foundation
A basement is a type of foundation that includes an accessible space between the ground and the bottom of the first floor of a home. This foundation provides living space below the house, below the ground elevation. It is basically a slab foundation with walls and a floor. Basements are most often built in cold climates, such as the Northeast, Midwest, and Rocky Mountains, and in places where the cost of digging is not prohibitive. Basements start with a hole approximately 8 feet deep, however some homeowners will opt for a 9 or 10 foot deep basement wall to increase the height and volume of usable space. You build the floor and the walls, then you build the house on top of that. Basement foundations have the advantage of providing usable space for utilities, mechanical systems, and storage that is not available in the previous two types of foundations. The main disadvantage of basements is that because they are mostly below ground level, they are vulnerable to leaks, mold growth, and flooding. Basements in humid climates should always have a working drain and pump in the floor to combat flooding.