In flat roof framing, what are the main supporting members called?

In flat roof framing, the main supporting members are referred to as roof joists. Roof joists are horizontal framing members that span the distance between supporting walls or beams and provide the pivotal support structure for the roofing material itself. They are designed to carry the load of the roof and any additional loads such as snow, water, or equipment that may be placed on the roof surface.

Rafters are primarily used in sloped roofs and would not be suitable for flat roof systems. Beams serve as primary structural supports that can carry loads and transfer them to vertical elements, but in flat roof constructions, it is the roof joists that perform the primary function of supporting the roof deck. Purlins are secondary members typically used to support the roof covering or other components but are not the primary supports of the flat roof itself.

Thus, roof joists are integral to the flat roof structure, ensuring its integrity and strength under various loads.