The foundation is the first piece of a home to be constructed and creates a base for the rest of a home’s components. There are three types of foundations that are commonly used in the U.S.: slab, crawlspace, and basement.
Slab is a type of foundation consisting of a structural concrete slab poured directly on the grade. No accessible space exists in slab construction. Slab foundations are popular in areas (i.e. the Southern United States) where there is a relatively high water table. (Water table refers to the depth in the soil at which you find water).
A crawlspace is an accessible space with limited headroom, typically between the soil and the bottom of the first floor of a home. Crawlspace construction is predominant in areas where there is heavy clay content in the soil.
A basement is an accessible space between the soil and the bottom of the first floor of a home. It usually has more headroom than a crawlspace. Basement foundation construction is predominant in cold climates where the foundation needs to be situated below the frost level.
All three foundation types are usually constructed out of concrete, but can also use concrete masonry units or insulated concrete forms.
Concrete Masonry Units (CMUs) are hollow, concrete blocks. To create the foundation wall, mortar is used between blocks to hold them together, forming the wall.
Insulated Concrete Forms (ICFs) are made of rigid foam insulation forms (a system of support assemblies, including mold, hardware, and necessary bracing to hold concrete) into which concrete is poured. Once the concrete has gained its full strength, the outside forms, the inside forms, or both are left in place to insulate the wall. ICFs are common in regions in which the local building code requires the foundation to be insulated. Another benefit is that the homeowner or builder is able to finish basement immediately, without adding studs.