Raftfundering

Raftfundering is a type of shallow foundation used in construction. It is essentially a large, thick concrete slab that covers the entire footprint of a building or a significant portion of it. This slab distributes the building's load over a wide area, reducing the pressure exerted on the underlying soil. Raft foundations are particularly useful when the soil bearing capacity is low or when the building loads are substantial and concentrated.

The primary purpose of a raft foundation is to prevent excessive settlement. In areas with weak or compressible soils, individual footings or strip foundations might sink unevenly, leading to structural damage. The raft foundation acts as a rigid mat, spreading the load and minimizing differential settlement. It is also often employed when basements are part of the design, as it can form the basement floor.

Construction of a raft foundation involves excavating the site to the required depth, placing a layer of lean concrete or hardcore, followed by reinforcing steel, and then pouring the concrete. The thickness of the slab and the amount of reinforcement depend on the anticipated loads and the soil conditions. While it can be more expensive than other shallow foundation types, its ability to manage challenging soil conditions and heavy loads makes it a cost-effective solution in many situations.