Concrete, Block, and Slab Foundations

When building a house, two main types of foundations are used: slab-on-grade or below-grade foundations with a basement slab. Climate,  including high water tables, frost lines, harsh winters, and vulnerability to storm surge and high winds, will determine whether a slab or below-grade foundation is chosen.

Poured Footings

Poured and block foundations both sit on concrete footings, or poured pads that serve as a base for the walls. Footings are constructed in trenches dug beneath the level of the basement floor. These trenches are wider and longer than the walls they support and function like feet to distribute the weight of the wall and the structure above it. Footings provide a firm surface to resist sinking or shifting into the ground or substrate. A footing trench ranges from six inches to three feet deep, depending on the building size and soil characteristics.

Poured Concrete Walls

Poured concrete is more popular for basement construction than block because it is seamless and resists water intrusion. When pouring an integral foundation, aluminum or insulated wall forms are placed on the footings, clamped together, and supported to maintain their shape while the concrete is poured.

Once the forms are set, rebar is placed vertically inside the wall channel to support and add additional strength to the concrete wall once the molds are removed. Concrete is then poured into the mold to form the walls.

Concrete walls should be created as a continuous pour to ensure good bonding and avoid seam cracking where a first concrete layer has already set.

Cement can be poured in place with a cement-pumper truck, or offloaded down the chute of a ready-mix truck if it can get close enough to the foundation. Set-up time depends on the slurry used, the time of year, heat, and humidity. Temporary forms are usually taken down after one week, at which time the concrete is cured enough to support itself. The concrete will continue to cure and emit moisture for much longer. When using insulated concrete forms, they remain in place and insulate the home.