Cellular foil (3) is unfolded between the surface of earth base course (1) and the first floor layer (5) during building the subsoil, which cellular foil (3) is poured over with fill (4) from loose material at least up to filling the compartments. A bedding (2) from loose material, optimally from sand, is created under the cellular foil (3). Geotextile (6) may be incorporated to the area under the cellular foil (3). Bedding (2) of lower grain size than that of the fill (4) is preferably used, wherein the fill (4) has optimal grain size of 8 to 63 mm. Compaction is done by at least eight travels of roller of 10 to 11 tons weight, also including vibrations when the height of fills is exceeding 25 cm above the cellular foil (3).