This paper describes aspects of the behaviour of large span flat multi layered spaceframe roof structures. Initial discussion is based on some standard double layered frames. For larger spans, the most effective mechanism is to increase the overall depth. One option is to use a triple layered topology. Adding an extra layer to a standard two way square on offset square converts a torsionally inadequate frame into a rigid system. Unfortunately the density or member count per unit area is large with the vast majority of members having very low forces and yet add to the cost. A further step is based on the use of multiple layers of stable tetrahedron arranged in a diamond lattice. This geometric arrangement leads to a larger structural depth than conventional double or triple layered spaceframes. In effect the geometry has four layers of members, but many members are absent which leads a reduced density of members and permits shorter members to achieve larger spanning capabilities. Being composed of stable units, the torsional stiffness of the frame is utilized. The open nature of the structure also allows for additional members to be added in critical areas. It is shown that clear spans of 100 metres are feasible with members that can be man- handled. The geometry is within a class known as infinite polyhedra.

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