Are you considering building a structure? or just trying to increase your construction knowledge? Either way, continue reading to learn more about the different types of foundation and when to use them. For an overview of all things foundation repair please click here.
The 5+ Different Types of Foundation
While there are many different types of foundation, each falls into one of two categories: shallow foundations or deep foundations.
Shallow foundations are primarily used for structures with less weight over its total footprint such as sheds, shipping containers, parking garages, and more. These can be installed in depths as little as 3 feet.
Deep foundations, however, are commonly used for heavier structures where the soil is active. These structures include houses, stores, offices, skyscrapers, and towers. To install a deep foundation it is not uncommon to reach depths of 20-200 feet depending on the size of the structure.
Shallow foundations are also called spread footings or open footings. They are created by excavating and grading the site of your structure to the depth of your footings. The footing is then poured, visible to the world during the early stages of construction.
There are many kinds of shallow foundations: individual footing (isolated footing), strip footings, and raft footings (mat footings).
Each foundation must be carefully chosen and customized to your location’s climate, soil, and weather conditions.
Individual Footing aka Isolated Footing
Isolated Footings are one of the most common and the most simple footings around. They are typically used when it is absolutely certain that the soil underneath will not be shifting under the entirety of the building.
An isolated footing carries the structure by dividing its weight between columns. These columns are typically connected by a plinth beam.
These columns rest on top of concrete pads directly on top of the soil.
In order to determine the size of the pads necessary, you must know the soil’s SBC (safe bearing capacity) and the total load on the column. The total load on the column is divided by the SBC of the soil.
If a column has a vertical load of 15T, and the SBC of the soil is 15T/m2, then the area of the footing will be 1m2. Again, this is a rough estimate, and a designer or engineer will make adjustments based on climate and many other factors. Unlock the Foundation Repair Ultimate Guide – your comprehensive resource for understanding and addressing foundation issues. Gain valuable insights and expert advice today!
Strip Footings aka Wall Footing
Strip footings are continuous strip of concrete that is used to spread the weight of a load-bearing wall across an area of soil.
The underside of strip footings should be designed as not to allow frost or water to penetrate. As this could cause soil erosion and shifting.
Where the soil has a low SBC a wide strip footing will be constructed in order to spread the load over a greater area.
If it is found that soil with a higher SBC is located slightly deeper, a deep strip footing will be used.
Raft Foundations aka Mat Foundations
As the name suggests, a raft foundation allows the structure to “float” directly on top of the soil.
These foundations are most commonly found in structures with basements. The bottom slab of the basement acts as the foundation for the entire structure. By using a raft foundation, the structure will settle uniformly.
One might use a raft foundation, where the soil is too weak to receive the full load of a structure in a small area.
There are many different types of deep foundations, however not nearly as many as shallow. Because deep foundations can be more expensive for smaller projects, they are used only when the surface soil is incapable of supporting the load, soil movement is common, or weather conditions are unfavorable. Deep foundations allow for a structure to be built just about anywhere, bypassing the surface soil and building your structure directly on bedrock.
All deep foundations follow the same model. Each, presses or installs supporting cylinders (concrete, steel, or other) deep into the earth. The structure is then built on these cylinders.
Pile foundation is a type of deep foundation, in which the loads are taken to a low level by means of vertical timber, concrete or steel. There are many moving parts and things can get complicated, for more details click here.
The pile foundations transfer the load through friction (in case of friction piles) or through both friction and bearing ( in case of combined end bearing and friction piles).
These are used when:
- no load-bearing strata can be found at any reasonable depth below the structure
- A load-bearing stratum exists, however, it is at a depth that makes the strip or spread footing uneconomical.
There are 8 different types of piles
- End bearing piles
- Friction piles
- Combined end bearing and friction piles
- Compaction piles
- Dolphin and Fender piles
- Anchor piles
- Tension or Uplift piles
- Sheet and Batter Piles
Caissons are watertight structures made up of wood, steel or reinforced concrete built above the ground level and then sunken into the ground. Caissons typically do not have a footing. For an in-depth look at this foundation click here.
Finally, we have pier foundations, these are common in houses and other smaller structures. To find out more about pier and beam foundations please click here.
There are so many different types of foundation it is easy to get confused. We are creating another guide for an in-depth look describing their differences. That way you never get confused again.