The invention concerns a method and a product in the erection of a building. In the method, the frame of the building is mainly constructed from beam pairs (1) consisting of floor beams (2) and external wall beams (4) hinged on each other by a hinge (6). On the building site, the wall elements (20) are assembled and, if desirable, given a surface treatment in a horizontal plane from standard building materials on the external wall beams (4). The wall elements (20) assembled in a horizontal plane, supported by the hinges (6), are lifted to an upright position, locked by means of locking screws (10) and joined to other wall elements (20) to form a continuous wall. The roof structure of the building is assembled and given a surface treatment on the wall elements (20) from the ground, lifted aside by means of a crane to allow the wall elements (20) to be lifted up, and finally lifted up onto the upright wall elements (20) to form the roof of the building.