Very broadly, foundations can be categorised as shallow foundations or deep foundations. Shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils. Deep foundations are necessary where the bearing capacity of the surface soils is not adequate to support the loads imposed by a structure and so they need to be transferred to deeper layers with higher bearing capacity.
Strip foundations (or strip footings) are a type of shallow foundation that are used to provide a continuous, level (or sometimes stepped) strip of support to a linear structure such as a wall or closely-spaced rows of columns built centrally above them.
Strip foundations can be used for most subsoils, but are most suitable for soil which is of relatively good bearing capacity. They are particularly suited to light structural loadings such as those found in many low-to-medium rise domestic buildings - where mass concrete strip foundations can be used. In other situations, reinforced concrete may be required.
Very broadly, the size and position of strip foundations is typically related to the wall’s overall width. The depth a traditional strip foundation is generally equal to or greater than the overall wall width, and the foundation width is generally three times the width of the supported wall. This results in the load being transmitted at 45º from the wall base to the soil.
Approved document A of Building Regulations defines minimum widths for strip footings based on the type of ground and load-bearing wall, although it is generally advisable to consult a structural engineer when designing foundations.
Where ground conditions are poor, settlement is likely, or where it may be impractical to create individual strip or pad foundations for a large number of individual loads, raft foundations may be used. See Raft foundations for more information.
Where the bearing capacity of the surface soils is not adequate to support the loads imposed by the structure, deep foundations such as pile foundations may be used. See Pile foundations for more information.
Additional guidance is available in BRE's Simple foundations for low-rise housing: 'rule of thumb' design.
 Find out more
 Related articles on Designing Buildings Wiki
- Building foundations
- Raft foundation
- Pad foundation
- Pile foundations
- Trench fill foundation
- Types of excavation
- Bearing capacity
- Brick strip foundation
- Approved Document A
- Stepped foundation
- How deep should foundations be
- Footings in foundations
- Types of pad foundation
- Reinforced concrete
- How to design a pad foundation
- Driven piles
- Building regulations
- Rubble trench foundation
‘Structures and structural failure’ at IHBC’s Nottingham School, with Ed Morton (ex Canterbury, York and Westminster to St Paul’s) and John Ruddy.
Ageing gracefully - restorations which retain historical decay.