Abstract: A building construction includes load-supporting walls made up of precast modular members, each member being an elongated member having a web and channel-shaped ends such that when they are laid in vertical rows with adjacent rows abutting end to end, the channel members form closed vertical pillar chambers adapted to receive concrete poured in situ and cured to form pillars. Cladding is attached directly to the so-formed walls and floor members including elongated reinforced precast channels are laid side to side with concrete poured in situ about the channels and over them to form an integral floor.