Abstract: A prefabricated modular building is constructed of a plurality of panels which are readily assembled and locked together without the need for tools (other than material handling and earth moving equipment) at the assembly site. The building is constructed of sets of panels, most of the panels in each set being identical.All of the vertical panels are interlocked by sliding a built in flange on each panel into a built in channel member on an adjacent panel. The vertical structural beams of each panel projects above and below the panels and these projecting ends are received by corresponding spaced receptacles in the horizontal ceiling and floor panels. In addition, an earth barricade on the roof of the building plus wall extensions provide for the covering of the roof and sides of the building with earth.