The principle aim of a raft foundation is to spread the load of the building across the entire available surface area under the building. This reduces the stress on the ground below, providing a solid foundation that can accommodate ground movement while still maintaining structural integrity. The flat block helps spread the weight over a big area so it doesn’t sink into the ground. Raft foundations are normally used in areas where the ground is inherently volatile and prone to ground movement such as soft clay , sand or dolomite areas.

A raft foundation is a reinforced slab in the correct position on the ground which allows the foundation to move (or ‘float’ – hence the alternate name ‘floating foundation’) along with subtle ground movement avoiding damage (e.g. cracks in walls).

Raft foundations are often being used as a replacement for deep strip foundations as they often prove more cost effective with more advantages.