Rafters, beams, and joists are structural profiles that are used to frame buildings. When selecting products, builders must account for spans - the clear distances between supports. Spans are based on uniform gravity loads and may be evaluated for wind. Typically, the design of continuous spans is based on the longest span so that, for example, the shortest span is not less than 50% of the longest span. Other specifications to consider when selecting rafters, beams and joists are moment, shear and reaction capacity for normal load duration; deflection, both in terms of bending and shear deformation; and live load and dead load. Live load is that amount of weight that a structure is designed to support. Dead load refers to the weight of the structure itself.