Types of footings are selected based on soil condition, building load, available space, slope, groundwater level, and structural design. A footing is the base part of a foundation that spreads building loads safely into the soil and helps prevent uneven settlement. Common types include wall footing, spread footing, isolated footing, stepped footing, combined footing, sloped footing, raft foundation, strap footing, pile foundation, and floating footing. This guide explains each footing type, its uses, benefits, limitations, selection factors, and site checks for safe construction. Brick & Bolt describes footings as rigid structures that transfer loads to soil or underlying strata.
Quick Summary
The main types of footings are wall or strip footing, spread footing, isolated footing, stepped footing, combined footing, sloped footing, mat or raft foundation, strap footing, pile foundation, and floating footing. Each footing type is chosen based on soil bearing capacity, structural load, slope, space restrictions, groundwater level, and settlement risk.
What is Footing?
Footing is a rigid structure that transfers the load to the soil or underlying strata. These rigid structures are constructed beneath the building pillars or at the construction site.
Types of Footing
- Footings can be classified into different types based on their applications. Each foundation footing serves a specific purpose, such as addressing geological, structural, and spatial challenges to ensure resilience and stability in construction projects. Some of the major types are as follows:Wall Footing/Strip Footing
- Spread Footings
- Isolated Footings
- Stepped Footings
- Combined Footings
- Sloped Footings
- Mat or Raft Footings
- Strapped Footings
- Pile Footings
- Floating Footings
Different types of footings have their advantages and disadvantages. It is important to select the right type of footing based on its application and project requirements.
Wall Footing/Strip Footing
The capacity to distribute the entire weight of the load-bearing structure across the ground area makes strip footing suitable for shallow foundations. This is also known as wall footing. The continuous masonry strip distributes the pressure of a load-bearing wall over the ground. The soil’s carrying capacity is considered to determine the strip footing’s base width, as these two are inversely correlated.
Uses of Wall Footing
This is mainly used to support a long foundational wall, such as the sides of a house. Load-bearing walls that run parallel also use strip footing.
Spread Footings
This type is preferred in structures where the load of the entire structure needs to be distributed over a broad area of soil. Spread footing ensures that the distributed load does not exceed the safe bearing capacity. Their capacity to offer a reliable foundation for columns or posts makes them the most preferable choice for various construction projects.
Uses of Spread Footing
This type of footing is used in agricultural structures, institutional construction, and bridge construction.
Isolated Footings
The primary purpose of isolated footings is for individual columns or posts. The isolated footing’s capacity to support and distribute the load of each column to the ground makes it suitable for columns spaced apart. This type of footing could be used in conjunction with wall footings to provide additional support. The isolated footing can be a square, circular, or rectangular slab of uniform thickness.
Uses of Isolated Footings
Isolated footings are used for small structures such as sheds or porches. If the soil is soft and the water table is high, they can also be used for the four walls of a building.
Stepped Footings
Stepped footing is preferred to keep the metal columns away from direct contact with soil. This distance prevents corrosive effects. They carry the load of metal columns and transmit this to the ground below. In recent times, stepped footings have become less common. Footings are layered on top of each other by stacking concrete segments between each layer. This type of footing is also known as a step foundation.
Uses of Stepped Footings
This type is used in retaining walls, basement walls, and other structures built on sloped sites. It is highly preferred in areas with significant elevation changes.
Combined Footings
The name itself suggests that this type of footing supports two or more columns/pillars. This type of footing can be in square or trapezoidal and Rectangular. Generally, combined footings are preferred when the individual footings overlap and lie close to each other. This type is also preferred in soil that has a low load-bearing capacity. Because it distributes the load between columns to prevent settling. Space constraints in the construction site make it unavoidable.
Uses of Combined Footing
When two or more foundation walls are close together, this foundation can be used. It can even be used when there is a difference in the height of the foundation walls.
Sloped Footings
Because of the sloping top or side face of this type of footing, it is identified as sloped footing. Formwork construction often prefers this type of footing over others. It aligns well with or counters the natural slope of the terrain. A sloped foundation enhances stability by adjusting the footing’s angle.
Uses of Sloped Footing
Sloped footings are used in hillside or sloped terrain, retaining walls, bridges, architectural designs, piers and columns, and for seismic considerations.
Mat or Raft Foundation
This foundation covers the area, including the beam, slab and whole area with an RCC slab. This foundation is called the mat foundation. These footings save the heavy structures constructed on marshy sites and soft soil. The intrinsic stiffness in the raft foundation reduces dislocation motion.
Uses of Mat Foundation
This foundation is used for large buildings, bridges, and structures with high loads and challenging soil conditions.
Strapped Footings
The Strapped footing uses a strap beam to connect the inner and outer columns. This footing does not transfer any load to the ground. Instead, the total pressure will be distributed below the footing. Columns are arranged in such a way that the centre of gravity (C.G.) of combined loads of the two columns passes through the centre of gravity (C.G.) of the two footing areas. In general, it acts as a bridge that stabilises and supports structural elements in construction footings.
Uses of Strap Footing
Strip footing is used in load-bearing walls, residential buildings, basements, commercial buildings, retaining walls, sloping sites, and high-rise buildings.
Pile Foundation
The piles are long, vertical load-bearing structures inserted into the ground to provide foundations. The piles are made of concrete, steel, or wood. This footing is mainly preferred in the area of soft soil strata. This footing offers better stability if the soil’s carrying capacity is deficient and the groundwater level is high. It helps the structures to prevent them from sinking into the ground.
Uses of Pile Foundation
This can be used for the construction of a building that has very heavy, concentrated loads. This includes high-rise structures, bridges or water tanks.
Floating Footings
This type of footing is used in buildings to counteract potential damage from frost heave. This can either extend below the frost line or insulate the structure to prevent any damage from freezing ground temperatures.
Uses of Floating Footing
This type of foundation is used in soft, compressible soil, areas with high water tables, seismic zones, marine environments, landfills, and reclaimed land.
Conclusion
Types of footings should be chosen based on soil condition, structural load, slope, space, groundwater, and settlement risk. Wall, spread, isolated, stepped, combined, sloped, raft, strap, pile, and floating footings each solve different foundation needs. For ordinary buildings on good soil, shallow footings may be enough. For soft soil, heavy loads, high groundwater, or special site conditions, deeper or wider foundation systems may be required. Safe footing design should always be supported by soil testing, structural drawings, proper execution, and site supervision.
FAQs
- What are the main types of footings?
The main types of footings are wall or strip footing, spread footing, isolated footing, stepped footing, combined footing, sloped footing, mat or raft foundation, strap footing, pile foundation, and floating footing. Each type is selected based on load, soil condition, slope, space, and settlement risk. - What is the purpose of footing in construction?
The purpose of footing is to transfer building loads safely to the soil and spread pressure over a larger area. It helps prevent uneven settlement, shifting, cracking, and structural instability. A footing also provides a stable base for walls, columns, and foundations. - Which footing is best for a house?
The best footing for a house depends on soil bearing capacity, number of floors, wall or column layout, groundwater level, and slope. Isolated footings are common for RCC frame houses, while strip footings are used for load-bearing walls. Soil testing and structural design should decide the final type. - What is isolated footing used for?
Isolated footing is used to support a single column or post. It spreads the load from that column into the soil. It is common in residential and small commercial RCC frame buildings where columns are spaced apart and soil has adequate bearing capacity. - What is the difference between combined footing and strap footing?
Combined footing supports two or more columns on one common base, while strap footing connects two isolated footings with a strap beam. Combined footing is used when individual footings overlap, while strap footing is useful near property boundaries where eccentric loading must be balanced. - When is raft foundation used?
Raft foundation is used when soil bearing capacity is low, loads are heavy, or individual footings would cover a large part of the building area. It spreads loads through one large RCC slab and is common for basements, large buildings, and soft soil sites. - When is pile foundation required?
Pile foundation is required when upper soil layers are weak, groundwater is high, or structural loads are heavy. Piles transfer loads to deeper stronger soil or rock layers. They are commonly used for high-rise buildings, bridges, water tanks, marine structures, and soft soil sites. - How do engineers choose types of footings?
Engineers choose types of footings by studying soil bearing capacity, building loads, column spacing, site slope, groundwater level, settlement risk, space limits, and local rules. The selected footing must safely distribute loads without exceeding soil capacity or causing harmful settlement.
Sowjanya Siddanoor