Buildings, including residences, are built on different types of foundations. As the name implies, it is the lowest part of your house structure that transfers its load to the soil uniformly.
The types of house foundations vary depending on the design of your house, geographical location, structural load, climatic conditions, soil conditions, and budget.
Knowing the types of house foundations helps homeowners and contractors decide on the exact type of foundation they require. Read on to learn more about the kinds of foundations in use today, and determine what will best suit your home.
We can broadly classify building foundations into two types:
- Shallow foundations: In these foundations, the depth is less than or equal to the width. It is used for soil with a depth of up to 1.5m to support the structural load.
- Deep foundations: Here, the depth of the foundation is more than the width. It typically extends to depths of 3m.
Types of Shallow Foundations
These foundations are considered more economical. Let’s understand the types of shallow foundations and their benefits.
- Spread Footings: Here, the bases are wider than the usual load-bearing wall foundations. The broader base spreads the structure’s weight over a greater area, which provides better stability.Spread footings are suitable for carrying lighter loads when the bearing soil layer is within 3m from the surface. Using this footing is economical when the bearing soil is dense sand or gravel.Stone, brick, Plain Cement Concrete (PCC), or Reinforced Cement Concrete (RCC) are used to construct spread footings.
- Individual or Pad Footing: This is the most commonly used shallow foundation, constructed usually for load-bearing, single columns. The footing takes the shape of a rectangle or a square. Its size depends on the load on the column and the safe bearing capacity of the soil. It generally uses PCC or RCC.Pad footing is preferred for carrying concentrated loads from structures like columns. It is an economical option for relatively lesser structural weight and spaced-out columns.In contrast, the spread footing is used to sustain a line of loads, like that of a load-bearing wall.
- Combined Footing: This is used when columns carry the load from the structure. Architects use this footing when two or more columns are close together with overlapping footings. The shape of this footing is rectangular.
- Strip Footing: Here, a continuous concrete strip is provided below the load-bearing wall. The strip footing helps to spread the weight of the load-bearing wall uniformly across the entire area of the soil. This footing may use either PCC or RCC as well.Architects prefer this footing for supporting load-bearing walls when the underlying soil has good bearing capacity.
- Raft or Mat Foundation: Such foundations are spread across the entire area of the structure to support heavy loads from columns and walls. They are used to prevent differential settling of individual footings. They are designed as a single combined footing for all the load-bearing elements of the structure. These footings are an appropriate choice for expansive soil conditions with low bearing capacity.
- Cantilever Footing: In situations where a foundation at the extremity of the property line cannot extend outside the line, it is joined together with an internal foundation with a strap beam. Hence, it is also called strap footing.
Shallow foundations require less excavation. Thus, they are more economical in terms of labor costs, time, and ecological consequences and may abide by most local building codes. However, if your house is near a river or a sea, the active currents may cause scouring holes and erode your foundation. This is where you require deep building foundations.
Types of Deep Foundations
Let’s look into the different types of deep building foundations in use.
- Pile Foundation: These are used for transferring heavy structural loads, using columns, to hard rock strata deep below the ground level. The rock strata could be located at depths varying from 5m to 50m.This foundation prevents the uprooting of the structure due to lateral loads like earthquakes and wind forces. Pile foundations also prevent differential settling of foundations. They transfer the vertical compressive load partly using the resistance offered by the firm soil surface at the end of the pile and partly through the mechanism of friction developed between the shaft of the pile and the soil.
- Pier Foundation: This consists of cylindrical columns of various diameters. They transfer large loads to the firm strata below, using bearings. Pier foundations are used when the surface comprises decomposed rock laid on firm rock strata.They are essentially constructed as cylindrical column(s) to transfer the large structural load to the firm load-bearing strata.In comparison, the pile foundation is driven through the soil into the load-bearing strata situated at a depth. Usually, pile foundations are used to bear greater loads (e.g., bridges, flyovers).
- Drilled Shaft or Caisson Foundation: These are high-capacity foundations. Drilled shafts can transfer larger column loads than pile foundations. It is used where the hard strata are situated at a depth of 10m to 100m below the surface level.However, drilled shafts cannot be used if soft clay, loose or water-bearing granular soil or soil made up of boulders or artesian aquifers are present at greater depths.
Building Foundations and Basements
Foundations are also classified based on the type of basement the house requires.
- Full Basement Foundation: A full basement foundation matches the floor space of the level above it. It usually has a height of 7 feet. Tall basements are provided for converting into usable space for living or storage.There are two variants of this foundation. The first type is a daylight basement (also called a partial basement). Daylight basements rest against a slope and have one or more sides wholly embedded in the ground. This arrangement provides more light and air.The other type is the crawl space basement. These foundations are built using short walls (typically 4 feet) supported on footings, creating a crawl space. This space could be utilized for storage, installing a furnace, or other equipment. This is less expensive to build than the full basement foundation since this requires lesser excavation, wall material, and labor.
- Concrete Slab-on-Grade Foundation: A slab-on-grade foundation consists of a concrete slab that rests on the ground (the term ‘grade’ basically means ground level). These foundations are used where there is no ground freezing and thawing. This is a crucial condition, as such temperature variations cause cracks and shift the foundation.However, there is a significant downside to this foundation. Since the water supply/drainage pipes and electric conduits are encased in the concrete, the concrete needs to be cut to access the pipes or conduits during maintenance.
How can Design Everest help?
The selection of the foundation is one of the most important and primary decisions that you will have to make when building your house. Experienced agencies, such as Design Everest, have a sustained reputation for helping customers with every construction-related need and query. We can help you arrive at the most optimal decision that best matches your needs. Contact us today for a free quote and consultation.
The choice of foundation affects the longevity of your home. Weigh the options carefully, think deeply, consult experts, and then choose wisely.