US Patent 7703248 Hollow interconnecting panels as lost formwork

An elongated building element (14) to form a series of walls (10) to (13). The elements (14) each have longitudinally extending flanges (21) that snap engage with longitudinally extending grooves (19) in the next adjacent element (14). Accordingly the wall (10) is constructed by joining the elements (14) in a direction transverse their general direction of extension. If so required the elements (14) may be filled with concrete.