252 Section 2 Foundations and Framing After the headers are installed, the tail joists are attached. One of the tail joists can be tempo- rarily nailed to the trimmer on each side of the opening to accurately locate the header and hold it while it is being nailed. Figure 10-32 illustrates the procedure for fas- tening tail joists, headers, and trimmers. After the first header and tail joists are in position between the first trimmers, nail the second or double header in place. Be sure to nail through the first trimmer into the second header. Use three 16d nails at each end. Finally, nail the second trimmer to the first trimmer. A good nailing pattern for the entire assembly is shown in Figure 10-33. To allow more room for nailing, do not install joists adjacent to trimmers until the trimmers are doubled and nailed. This nailing pattern will support a concentrated load of 300 lb. at any point on the floor. It will also hold a uniformly distributed load of 50 lb. per sq. ft. with any spacing and span of tail joists ordinar- ily used in residential construction. This is true only if the long dimension of the floor opening is parallel to the joist. If the long way of the open- ing is at a right angle to the joists, excessive load- ing may be carried to the junction of headers with trimmers. Anticipated loads should be checked and more nails or additional supports should be provided at these junctions when needed. Metal joist hangers are often used to assemble headers, trimmers, and tail joists, Figure 10-34. They are manufactured from 18 gage, zinc- coated sheet steel. The National Forest Products Association recommends the use of joist hangers or ledger strips to support tail joists that are over 12′ long. 10.4.7 Bridging Studies have shown that bridging may be eliminated if joists are properly secured at the ends and subflooring is adequate and carefully nailed. However, many local building codes include bridging requirements, and general standards suggest that bridging be installed at intervals of no more than 8′. Regular bridging, sometimes called herring- bone bridging or cross bridging, is composed of pieces of 1 × 3 or 2 × 2 lumber diagonally set between the joists to form an X. Its purpose is to keep the joists in a vertical position and to transfer the load from one joist to the next. Partition support Partition support Band joist Stairwell Tail joist Girder Band joist Header Goodheart-Willcox Publisher Figure 10-31. This is a partial plan view of a floor framed for a stair opening and partition supports. Copyright Goodheart-Willcox Co., Inc.