A wall assembly for forming an external wall on a building structure is disclosed. The wall assembly comprises a cladding (12) and a plurality of vertical formwork members (14, 16) spaced from each other along the wall assembly, and a horizontal formwork member (50) extending along the top of the wall assembly. The formwork members (14, 16, 50) are elongate profiles having a substantially constant cross sectional shape and they are arranged so that the formwork member/s and the cladding form an interconnected formwork defining a formwork space. The cementitious material that is cast within the formwork space is interconnected and forms a single underlying structural frame within the constructed wall assembly. The assembly includes a plurality of connectors (20, 56) extending between each vertical and horizontal formwork member (14, 16), and (50) and the cladding on which it is mounted. Each connector (20, 56) extends from the cladding (12) through the formwork space to the formwork member (14, 16, 50) so that
