What is raft foundation in building construction?

What is meant by raft foundation?

Raft foundations are a type of foundation with high integrity in which four foundation piers are connected together using a large foundation slab to form a massive structure and the foundation piers are connected through beams.

When would a raft foundation be used?

They spread the load imposed by a number of columns or walls over the area of foundation, and can be considered to ‘float’ on the ground as a raft floats on water. They are suitable where: Floor areas are small and structural loadings are low, such as in one or two-storey domestic construction. A basement is required.

What are the three types of raft foundation?

There are five main types of raft foundation:

  • Solid slab rafts,
  • Slab beam rafts,
  • Cellular rafts,
  • Piled raft foundations; and,
  • Balancing (or floating) rafts.

What is the minimum depth of raft foundation?

The minimum thickness of raft foundation is 300mm.

Where is raft foundation applicable?

Raft foundation is generally used to support structures like residential or commercial buildings where soil condition is poor, storage tanks, silos, foundations for heavy industrial equipment etc.

How deep are slab foundations?

The foundation that your house is built on can have a major impact on the structural integrity of your home. A slab foundation is made of concrete that is typically 4″–6″ thick in the center. The concrete slab is often placed on a layer of sand for drainage or to act as a cushion.

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What is raft foundation advantages and disadvantages?

Advantages of Raft Foundation

Mat foundation can be provided where the shallow foundation is necessary but soil condition is poor. It resists differential settlement. Mat foundation requires less earth excavation. Mat foundation itself can be considered as a floor slab.

Is a raft foundation expensive?

Raft foundations are relatively inexpensive and fast to put down, when compared with other types of foundation. Ground excavations are less onerous than for trench excavations, for example, and the foundation and floor slab can often be combined, giving significant savings on materials and time.

Why do you need a raft foundation?

A raft foundation is a reinforced concrete slab under the whole of a building or extension, ‘floating’ on the ground as a raft floats on water. This type of foundation spreads the load of the building over a larger area than other foundations, lowering the pressure on the ground.