Abstract: A foundation for pre-engineered buildings in accordance with a preferred embodiment of the invention disclosed herein includes concrete footings provided at spaced-apart locations along the perimeter of the building to be erected. Light weight precast reinforced concrete grade beams are set in place with the end of each beam bearing on adjacent footings. Adjacent ends of grade beams extending in a straight line relative to each other are formed with channel configurations forming a keyway and adjacent ends of grade beams extending at a right angle to each other are formed with an interlocking configuration. One of these latter grade beams is formed with a keyway adjacent its interlocking configuration and its associated footing. A light weight disposable form is secured to the top of each footing and is generally U-shaped in plan view including a pair of parallel side walls and a connecting wall.