Foundations are determined by ground conditions.

Raft foundation is required on soils of low-bearing capacity or when heavy column loads cause overlapping of the pads. Raft foundation is useful in reducing differential settlement, especially when the soil nature varies over the area where the building is constructed.

Under raft foundations a reinforced concrete raft is designed by an engineer to “float’ over bad or differentially settling ground. Deep strip type foundation has a minimum 225mm of concrete, sometimes with reinforcement, at the bottom of the trench if the engineer considers it to be necessary.