Abstract: A method of erecting a foundation structure for a building substructure, in which joists including a horizontal web interconnecting upright side flanges on either side, are positioned butt end against butt end and are fixed in position at a distance of a few centimeters above a substratum. Gravel, macadam or other back fill material is then positioned against the external face of each side flange, whereupon concrete is poured into the joists and is allowed to partly flow downwards, through apertures formed in the joist webs, and onto the substratum.