Strip foundation is a type of foundation which involves the formation of a continuous concrete strip under load bearing walls. The strip serves as a level base on which the wall is built and spreads the load from the wall to an area of subsoil capable of supporting the wall without excessive compaction.
This can be achieved by using either plain concrete or reinforced concrete and is a popular choice for most projects. It can be constructed quickly and cheaply, especially on sites that have poor soil conditions.
It is also more economical to use a strip foundation rather than pad footings when there are several columns in a building which carry high localised loads. In addition, the formation of a strip footing prevents differential settlement, which is not possible with pad foundations.
The thickness and width of the strip foundation depends on the ground conditions, but it should be at least 450 mm below finished ground level to avoid damage from frost action. This depth is dependent on the soil type and should be inspected by a structural engineer to ensure it complies with the relevant regulations.
In some cases a wide strip may be required to spread the load across a larger area, or it might be necessary to use deep strip foundations where the soil has a low bearing capacity. This can be achieved by using reinforcement to increase the strength of the strip foundation.
Another option is to use a piled foundation. Piles are typically cast in long lengths and can be used to support the walls of buildings.
They are a common choice for foundations in low rise to medium rise residential buildings because they provide better stability and are less expensive than other types of foundation. The construction of a piled foundation is typically much faster than the construction of a strip foundation.
It is important to check that the foundations are well bonded and that the concrete has been properly compacted. It is also important to ensure that the soil has been properly levelled and that any debris, stones and plant material have been removed.
The construction of strip foundations is very straightforward and can be carried out by anyone who has the relevant qualifications. It can also be done quickly and easily with a small mechanical excavator, although it is best to contact an expert contractor for this job.
In most cases a strip foundation is suitable for the majority of subsoils as long as they have a sufficient bearing capacity and can withstand the load being transmitted through the footing. However, it is essential to consult an engineer before constructing any type of foundation, especially if the soil is poor and requires extra reinforcement or where the foundation needs to be able to cope with a heavy load.
The main disadvantage of strip foundations is that they are not suitable for unstable or water-saturated soils and should not be used where the ground freezes to a large depth. They are also not recommended for peatlands or loess soils. They should also not be used in very soft soils with a high heaving resistance.
