Abstract: A volumetric modular building system comprising a reinforced concrete inverted “tee-beam” module. The module has a series of integral cross-walls which are spaced to coincide with the dimensions of the rooms and corridors constituting a section of a building, these rooms being formed by a matched pair of such modules acting in parallel, separated by, and adapted to support between them, a suspended concrete floor, external infill walls, internal partition walls, fixtures and services. The dimensional control of the modules is ensured by means of a removable structural steel framework gauge attached to and forming a part of the casting mold adjacent to the ends of the integral cross-walls. The legs of the gauge serve to locate and secure, during casting, top and bottom steel bearing-plates which are in turn separated, regulated and perforated by vertical steel tube tie-rod sleeves embedded locally near the ends of the concrete cross-walls.