A molded plastic truss work includes an upper grid and a lower grid, with a plurality of interconnecting members interconnecting the grids. The upper grid includes longitudinal members and transverse members that extend between and interconnect the longitudinal members. The lower grid includes longitudinal members and transverse members extending between and interconnecting the longitudinal members. The longitudinal members in the lower grid are positioned such that each of the longitudinal members in the lower grid is not directly below any of the longitudinal members in the upper grid. The transverse members in the lower grid are positioned such that each of the transverse members in the lower grid is not directly below any of the transverse members in the upper grid. The plurality of interconnecting members extend between the upper and lower grids, and include a plurality of vertical members.