The Types of Foundations in Construction

The Types of Foundations in Construction

Whatever the size of the structure, every building has a foundation to help distribute its weight, prevent uneven settling and insulate it against ground moisture. However, engineers take different approaches to achieve these goals. Understanding the differences between these approaches is how to tell what type of foundation a house has.

There are two basic types of foundations — deep and shallow — and different variations within these two styles.

Deep Foundations

Deep foundations can use either pile or caisson methods.

Pile Foundations

Pile foundations are more common among the two deep types and include end-bearing and friction styles. Both rely on sturdy concrete, wood or steel columns deep in the ground. Pillars can be pre-made or cast on the spot.

Piles bore deep enough to reach solid bedrock strata in the end-bearing approach. Reaching that layer ensures more robust support than the surrounding soil can provide. The rock also helps prevent the structure from lifting under lateral loads like heavy winds.

Friction styles use their entire surface area to exchange forces between the softer soil and themselves to ensure structural integrity. These columns can support weights in proportion to their length, so placement has to be consistent to get an even distribution.

Pile foundations are primarily used for heavier structure loads and in areas with high groundwater tables.

Caisson Foundations

Some professionals also call caisson designs drilled-shaft foundations. The approach is similar to a pile foundation but with higher load capacities, typically with on-site casting. 

With this method, an auger bores into the ground to create the shaft or caisson, then a hollow column and rebar reinforce the hole before casting. Once the concrete has cured, workers can remove the casing. Load distribution occurs through toe or shaft resistance or a combination of both.

Due to their high-capacity design, engineers often choose caisson foundations for structures like overpasses, piers, bridges and homes on hillsides or over water. Shaft customization allows for water resistance, underground work, pumping and more.

Shallow Foundations

Shallow foundations come in several styles, including mat, individual footing, combined footing and stem wall.

Mat Foundations

This foundation type is also known as a raft foundation. You can identify this design when the basement foundation "submerges" into the soil, much like the bottom of a raft in the water. It considers the entire structural footprint and uses the basement surface area for more load-bearing support.

Engineers typically opt for mat foundations in high-load situations, meaning the weight from the structure distributed to foundation walls and columns is heavier. Raft foundations help prevent uneven settling that individual footings can experience. As a result, they're more similar to combined footings and take an overall perspective considering each load-bearing component.

This foundation design best suits structures where basements are possible and soil is loose.

Individual Footing Foundations

Individual footing foundations are the most common shallow-foundation approaches and are generally square or rectangular. Under this configuration, a single column shares the load with the surrounding soil and the weight it carries determines its width. Engineers may also refer to this approach as a pad foundation.

Since individual footing foundations are common, you'll readily see them in many structures. You can quickly identify this approach if a building has a single foundation column for support.

Combined Footing Foundations

A combined footing foundation has similar characteristics to an individual footing one, yet it will have two or more pillars sharing the load on a single base rather than one. Engineers employ this design when they want to distribute the building's weight across more than one column. Generally, the pillars stand close enough together that there's some overlap in their load-bearing footprints.

You can identify a combined footing foundation when you observe multiple columns and an individual base surface.

Stem Wall Foundations

The stem wall foundation goes by many names, including spread, strip footings or continuous footings. Engineers use this design when load-bearing walls carry the structure's weight rather than pillars, columns and beams. 

Identify this approach when you observe walls where the bottom portions are made of concrete and about two to three times the wall's width. Spreading out the weight over a bigger area helps ensure integrity and stability.

Typical applications for stem wall foundations include buildings on compacted sand or gravel and those featuring masonry walls.

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