A building element (10) comprises a substantially metallic, substantially planar core member (20) and a thermally insulating and water resistant sheathing member (30) either side of the core member. The core member is continuous along a substantial length of the building element and a void (40) is created between the core member and at least one of the sheathing members. At least one bridging member (50) is provided in the void and couples the core member and at least one of the sheathing members. A building system and method of construction are also disclosed.