Abstract: A building element formed as a sandwich of outer panels (22) made from high strength thin-walled geopolymer concrete (GPC) and a high insulation core material (21) of high-density polystyrene providing thermal efficiency. The outer panels are offset from the core material to provide an edge interconnecting mechanism with adjacent elements and, furthermore, the core material (21) includes surface features/profile (26) that abut/mate with corresponding features in the adjacent core material. A building system utilising the element in block or panel form provides simple and fast construction, without the need of skilled labour. Furthermore, since the insulating core provides a locking and locating interconnection means between the elements this effectively results in a zero-loss system due to bridging. When combined with a compressive vertical tie bar system the outcome is a wall construction of exceptional strength and accuracy.