2 A ceiling frame ties together the exterior walls and resists the outward pressure of roof rafters. One of the main structural functions of a ceiling frame is to tie together the exterior walls of a building. When located under a pitched roof, the ceiling frame also resists the outward pressure exerted on the walls by the roof rafters. See Figure 44‑1. The tops of interior partitions are fastened to the ceiling frame. In addition to supporting the attic area beneath the roof, the ceiling frame supports the weight of the finish ceiling materials, such as gypsum board.
3 Ceiling joist size is based on the amount of weight the joist must carry and the joist span. For example, No. 1 2 × 6 Douglas fir joists spaced 24″ OC can span up to 14′-5″.Joists are the most important framing members of a ceiling. Joist size, spacing, and direction of travel are shown on a floor plan. The spacing between ceiling joists is usually 16″ or 24″ OC, although 12″ and 19.2″ OC spacing may be used. Ceiling joist size is determined by the amount of weight the joist must carry and the span the joist covers from one wall to the other. The table in Figure 44‑2 gives allowable ceiling joist spans.
4 When ceiling joists butt over a partition, an 18 ga ´ 18² long metal strap can be used to tie the joists together.One end of a ceiling joist rests on an outside wall and the other end often overlaps an interior bearing partition or beam. Ceiling joists should overlap the partition or beam at least 4″. Ceiling joists may be butted over a partition or beam. In this case, the joists must be cleated with a 3/4″ × 24″ piece of plywood or an 18 ga × 18″ long metal strap. See Figure Ceiling joists may also butt against a beam and be supported by a ledger strip or joist hangers in a manner similar to floor joists.
5 Whenever possible, ceiling joists should be nailed to rafters. Whenever possible, ceiling joists should run in the same direction as roof rafters. Nailing the outside end of each ceiling joist to the heel of a rafter as well as to the top plate strengthens the tie between the exterior walls of a building. See Figure 44‑4.
6 When ceiling joists do not run parallel to the roof rafters, 2 × 4s can be used as a tie between exterior walls.A building may be designed so ceiling joists do not run parallel to the roof rafters. To prevent rafters from pushing out the walls, ties (2 × 4s or 2 × 6s) are installed running in the same direction as the rafters. The ties are then fastened to the top edge of each ceiling joist with two 16d nails. See Figure 44‑5. The ties should be spaced no more than 4′ apart. The tie ends should be secured to the rafter heels by nailing through the rafters into the edge of the tie.
7 Stub joists may be required where rafters do not run parallel to ceiling joists. When ceiling joists run in the same direction as roof rafters, the outside ends must be cut to the slope of the roof. Ceiling frames may be constructed with stub joists. See Figure 44‑6. Stub joists are necessary when, in certain sections of the roof, rafters and ceiling joists do not run in the same direction. For example, a low‑pitched hip roof requires stub joists in the hip section of the roof.
8 A 1 × 4 ribband nailed at the center of the joist spans prevents twisting and bowing of the joists. Without additional header joists, however, ceiling joists may twist or bow at the centers of their span. To prevent twisting or bowing, a ribband is nailed at the center of the spans. See Figure 44‑7. The ribband is laid flat and fastened to the top of each joist with two 8d nails. The end of each ribband is secured to the exterior walls of the building.
9 A strongback provides central support for the joist span. A more effective method of preventing twisting, bowing, or sagging of ceiling joists is to use a strongback. A strongback is built with 2 × 6s or 2 × 8s nailed to the side of a 2 × 4. The 2 × 4 is fastened with two 16d nails to the top of each ceiling joist as shown in Figure 44‑8. Strongbacks are blocked up and supported over the exterior walls and interior partitions. Strongbacks hold the ceiling joists in alignment and also help support joists at the centers of their spans.
10 When studs and ceiling joists are spaced 16² OC, the joists rest directly over the studs. When studs are spaced 16² OC and ceiling joists are spaced 24² OC, every other joist will align with the studs below.If joists are placed directly above the studs, the joists will follow the same layout as the studs below. See Figure 44‑9. If joist spacing is different from that of the studs below (for example, if joists are spaced 24″ OC over 16″ OC studs), lay out the first joist at 23 1/4″ and then at every 24″ OC.
11 A ceiling frame is constructed over walls that have been straightened and properly braced. In this example, joists lap over an interior bearing partition.Joists for a ceiling frame should be cut to length before they are placed on top of the walls. On houses with pitched roofs, the outside ends of the joists should also be cut at an angle on the crown edge of the joist to accommodate the roof slope. The prepared joists can then be handed up to the carpenters working on top of the walls. The joists are laid flat along the walls, close to where they will be nailed. Figure 44‑10 shows a procedure for constructing the ceiling frame. In this example, the joists will lap over an interior bearing partition.
12 A ledger board is nailed against the wall to provide a nailing surface for lower ceiling joists. Ceilings may be furred down for insulation or sound‑ deadening purposes. Figure 44‑11 shows an example where a ledger board the same width as the joist material is nailed against the wall studs. The ends of the joists are then toenailed or fastened with metal joist hangers to the ledger board.
13 Backing is nailed to the top plates to provide a nailing surface for the edges of the finish ceiling material. Backing may be 2 × 6s or 2 × 8s.Figure 44‑12 shows backing placed on top of walls. The 2 × 6 backing nailed to the exterior wall projects to the inside of the building. The interior wall requires a 2 × 6 or 2 × 8 centered on the double top plate and projecting on both sides of the wall. Backing is fastened to the top plates with 16d nails spaced 16″ OC.
14 Backing is sometimes nailed on top of bearing partitions. Backing may also be used where ceiling joists run at a right angle to an interior bearing partition. See Figure 44‑13. The backing is cut to fit between the lapped ceiling joists and nailed to the double top plate.
15 Blocks and backing are installed between joists to secure tops of walls running parallel to ceiling joists.The tops of partitions running in the same direction as the ceiling joists must be securely fastened to the ceiling frame. See Figure 44‑14. Blocks, 2 × 4s spaced 32″ OC, are placed flat over the backing, which is fastened to the top of the partition. The ends of each block are fastened to the joists with two 16d nails. Two 16d nails are also driven through each block into the backing and top of the partition.
16 For flat roofs, rafters serve as a base for the roof and as ceiling joists. Since joists for a flat roof must support the combined load of the ceiling and roof materials, 2 × 10s or larger framing members are used.Figure shows a section of the framework for a flat roof. Since the joists also serve as a base for the roof, the joists are typically referred to as rafters. The rafters are tied together with a header where they extend past the exterior walls of a building. Shorter, cantilevered joists are called lookout rafters. One end of each lookout rafter is fastened to a regular roof rafter using a metal framing anchor. The roof rafter will be doubled after the lookouts have been installed.
17 A flat roof must have a small amount of pitch for proper water drainage. Figure shows a flat roof overhang. The ceiling material is gypsum board and the roof is panel sheathing over insulation board.
18 Parapets can be framed over top plates. Flat roofs may also be constructed with parapets (short walls) above the roof deck. See Figures and
19 Parapets can be framed into exterior walls. Flat roofs may also be constructed with parapets (short walls) above the roof deck. See Figures and
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