A common joist must be cut away to give way for floor openings, such as stairways. The wall-opening ends of cripple joists are framed against HEADERS, as shown in figure 6-17. Specifications usually require that headers be doubledsometimes tripled. Headers are framed between the full-length joists, also called TRIMMERS, on either side of the floor opening. Headers up to 6 ft in length are fastened with nails, whereas those longer than 6 ft are fastened with joist hangers.

Figure 6-17.-Framing around floor openings.

Figure 6-18.-Cross bridging and solid bridging. Bridging

Bridging is the system of bracing the joists to each other to hold them plumb and aligned. It also serves to distribute part of a concentrated load over several joists next to those directly under the load. There are two types of bridging: CROSS BRIDGING (fig. 6-18, view A) and SOLID BRIDGING (fig, 6-18, view B). Cross bridging consists of pairs of STRUTS set diagonally between the joists. The strut stock comes in sizes of 1 by 3, 1 by 4, 2 by 2, and 2 by 4. Solid bridging consists of pieces of joist-size stock set at right angles to the joists. They can be staggered for easier installation. Cross bridging is more rigid than solid bridging and is more frequently used in construction. Bridging should be provided for all spans greater than 6 ft.