The roof system shown in Figure 24.1a is a complex roof composed of planar latticed trusses. Each truss resists the load acting on it independently and transfers the load to the columns on each end. To ensure the integrity of the roof system, usually purlins and bracings are used between trusses. In Figure 24.1b latticed trusses are laid orthogonally to form a system of space latticed grids that will resist the roof load through its integrated action as a whole and transfer the loads to the columns along the perimeters. Since the loads can be taken by the members in three dimensions, the corresponding forces in space latticed grids are usually less than that in planar trusses and hence the depth can be decreased in a space frame.