Rack Supported Mezzanine. In this example, standard pallet rack is used as the substructure. This can be very cost effective to gain floor space. The carrying capacity of the floor is determined by the capacity of the uprights and beams. The span in the direction of the beams can be 12'. The frame work under is all ready to accept extra levels of storage. In addition, the upright frames can extend thru the floor and again are ready to accept more levels of storage. Stairways and pallet drops can be added as necessary.