The space frame can be formed on either a flat or a curved surface. The earliest form of space frame structure is single-layer grid. By adding intermediate grids and including rigid connection to the joist and girder framing system, the single-layer grid is formed. The major characteristic of grid construction is the omnidirectional spread of the load as opposed to the linear transfer of the load in an ordinary framing system. Since such load transfer is mainly by bending, for larger spans the bending stiffness is increased most efficiently by changing to a double-layer system. The load transfer mechanism of a curved surface space frame is essentially different from the grid system that is primarily membrane-like action. The concept of space frame can be best explained by the following example. It is necessary to design a roof structure for a square building. Figure 24.1a and b shows two different ways of roof framing.