The box-shaped foundations have vertical through passages or form such passages through their connections. They are laid with their open-side upwards and in the openings (30') additional bodies (60) with plate-shaped heads are introduced. The heads are so dimensioned that they are arranged in rows without seams or at a slight distance from each other. The foundation (10) has at least one water outflow aperture (54). The additional body has an insert part matched to the opening. The insert part is so dimensioned that it is accommodated in a press seat in the opening. The foundation has the shape of a double cross with a longitudinal beam and two cross beams (11,13). The width and the length of the two kinds of beams are such that square holes are produced.
