Foundation

A foundation assembly 1 for a building has a precast concrete frame and a floor 9 surrounded by insulation 14. The assembly is formed from a rectangular frame (fig. 1, 2) having a precast reinforced concrete foundation beam 3 at each side of the frame. An upwardly extending peripheral retaining wall 6 projects upwardly from a top of each foundation beam to form an endless retaining wall. A plurality of juxtaposed reinforced concrete floor panels 8 are mounted on the frame to form a floor. The sizing of the floor panels and associated foundation beams is such that when the floor panels rest on the foundation beams, they form an endless channel 12 extending around a periphery of the floor. A layer of thermal insulation material is mounted within said endless channel to surround the side edges of the floor with Insulation material.