2 also can be attached to each other by rivets the wall sheets 20 constituting the wall surfaces have such a width that their edges extend in between the leg members of each of the opposed support sections 1 comprised in two uprights 1 34 positioned to the side of each other the sheets 20 are mounted in the wall system by simply being moved down from above between the uprights and the support section leg members thereof before support sections 1 generally indicated by the horizontal girders 1 39 34 of the same type as the sills and uprights are mounted the sheets 20 are locked in a suitable manner to the sections and the space between the sheets is filled with some type of insulation not shown a horizontal girder 1 39 34 or a horizontally attached window part 1 iv are mounted as follows the horizontal girder 1 39 34 or the horizontal window part 1 iv consist as mentioned before of the parallel extending support sections 1 which are coupled together by means of specific lengths of the connecting section 2 having a length of substantially 50 mm the girder or part is cut to a length corresponding to the distance between adjacently positioned upright support sections 1 34 at the ends of the support sections forming.