Abstract: A modular building design includes a building frame construction of superior strength and rigidity with roof, floor and wall panels designed for insertion in modular frame openings. The design permits complete fabrication of all shell components in a central manufacturing facility and is such that the various elements may be shipped or stored in an essentially flat package configuration. The only tools required for erection on the building site are conventional wrenches and nut drivers. The need for skilled workmen at the site is virtually eliminated.