Abstract: A pre-cast building system includes a plurality of modular, pre-cast components. There is an elongate footing component having an upwardly facing longitudinal channel and a longitudinal first keyway section formed therein. One end of the footing component carries a pocket and the opposite end carries an insertion member for interengaging the pocket of an adjacent, aligned footing component. An elongate foundation component is received in the channel. A lower edge of the foundation component includes a second, complementary keyway section that faces the first keyway section to form an elongate keyway that receives a bonding adhesive. An exterior wall component is interengaged with the opposite upper edge of the foundation wall component. A pair of opposing receptacles are formed respectively in the upper edge of the foundation component and the lower edge of the exterior wall component.