Abstract: A procedure for manufacturing a building element, such as a door, wherein the surface sheets of the element are affixed to a frame and between the sheets is placed an insulation. The insulation consists of polyurethane, which is injected into the interspace of the surface sheets so that it becomes glued fast to the sheets and to the frame. By the aid of the invention a rigid, tightly sealed and light weight building element is obtained. In another embodiment, at least one surface sheet is provided with apertures which are each covered with a sheet part formed in a plane separated from the surface sheet. A supporting frame is installed between the surface sheet and the edges of the sheet part, and the component parts are all bonded fast together by the polyurethane insulation.