Fabrication

three equal parts. Each short web meets the top chord at a point that is one-fourth the horizontal distance of the bottom chord. FABRICATION The construction features of a typical W-truss are shown in figure 2-64. Also shown are gusset cutout sizes and nailing patterns for nail-gluing. The span of this truss is 26 feet and roof cut is 4/12. When spaced 24 inches apart and made of good- quality 2- by 4-inch members, the trusses should be able to support a total roof load of 40 pounds per square foot. Gussets for light wood trusses are cut from 3/8- or 1/2-inch standard plywood with an exterior glue line, or from sheathing-grade exterior plywood. Glue is spread on the clean surfaces of the gussets and truss members. Staples are used to supply pressure until the glue is set. Under normal conditions and where the relative humidity of air in attic spaces tends to be high, a resorcinol glue is applied. In areas of low humidity, a casein or similar glue is used. Two rows of 4d nails are used for either the 3/8- or 1/2-inch-thick gusset. The nails are spaced so that they are 3 inches apart and 3/4 inches from the edges of the truss members. Gussets are nail-glued to both sides of the truss. Plywood-gusset, king-post trusses are limited to spans of 26 feet or less if spaced 24 inches apart and fabricated with 2- by 4-inch members and a 4/12 roof cut. The spans are somewhat less than those allowed for W-trusses having the same-sized members. The shorter span for the king-post truss is due, in part, to the unsupported upper chord. On the other hand, because it distances between connections are shorter, the W-truss can span up to 32 feet without intermediate support, and its members can be made of lower grade lumber. INSTALLATION Trusses are usually spaced 24 inches OC. They must be lifted into place, fastened to the walls, and braced. Small trusses can be placed by hand, using the procedure shown in figure 2-69. Builders are required on the two opposite walls to fasten the ends of the trusses. One or two workers on the floor below can push the truss to an upright position. If appropriate equipment is available, use it to lift trusses into place. In handling and storing completed trusses, avoid placing unusual stresses on them. They were designed to carry roof loads in a vertical position; thus it is important that they be lifted and stored upright. If they must be handled in a flat position, enough support should be used along their length to minimize bending deflections. Never support the trusses only at the center or only at each end when they are in a flat position. Bracing After the truss bundles have been set on the walls, they are moved individually into position, nailed down, and temporarily braced. Without temporary bracing, a truss may topple over, cause damage to the truss, and possibly injure workers. A recommended procedure for bracing trusses as they are being set in place is shown in figure 2-70. Refer to the figure as you study the has more members than the king-post truss and following steps: Figure 2-70.—Installing roof trusses and temporary bracing. 2-43