Joists

Figure 1-60.—Ceiling frame tying exterior walls together. JOISTS Joists are the most important framing members of the ceiling. Their size, spacing, and direction of travel are given on the floor plan. As mentioned earlier, the spacing between ceiling joists is usually 16 inches OC, although 24-inch spacing is also used. The size of a ceiling joist is determined by the weight it carries and the span it covers from wall to wall. Refer to the blueprints and specifications for size and OC spacing. Although it is more convenient to have all the joists running in the same direction, plans sometimes call for different sets of joists running at right angles to each other. Interior Support One end of a ceiling joist rests on an outside wall. The other end often overlaps an interior bearing partition or girder. The overlap should be at least 4 inches. Ceiling joists are sometimes butted over the partition or girder. In this case, the joists must be cleated with a 3/4-inch-thick plywood board, 24 inches long, or an 18-gauge metal strap, 18 inches long. Ceiling joists may also butt against the girder, supported by joist hangers in the same manner as floor joists. Roof Rafters Whenever possible, the ceiling joists should run in the same direction as the roof rafters. Nailing the outside end of each ceiling joist to the heel of the rafter as well as to the wall plates (fig. 1-61) strengthens the tie between the outside walls of the building. A building maybe designed so that the ceiling joists do not run parallel to the roof rafters. The rafters are therefore pushing out on walls not tied together by ceiling joists. In this case, 2 by 4 pieces are added to run Figure 1-61.—Nailing of ceiling joists. 1-35