Unit 44 Ceiling Framing Ceiling Joists • Laying Out Ceiling Frames • Constructing Ceiling Frames • Attic Scuttles • Constructing Flat Roof Ceilings
A ceiling frame ties together the exterior walls and resists the outward pressure of roof rafters.
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″.
When ceiling joists butt over a partition, an 18 ga ´ 18² long metal strap can be used to tie the joists together.
Whenever possible, ceiling joists should be nailed to rafters.
When ceiling joists do not run parallel to the roof rafters, 2 × 4s can be used as a tie between exterior walls.
Stub joists may be required where rafters do not run parallel to ceiling joists.
A 1 × 4 ribband nailed at the center of the joist spans prevents twisting and bowing of the joists.
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.
A ceiling frame is constructed over walls that have been straightened and properly braced. In this example, joists lap over an interior bearing partition.
A ledger board is nailed against the wall to provide a nailing surface for lower ceiling joists.
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.
Blocks and backing are installed between joists to secure tops of walls running parallel to ceiling joists.
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.
A flat roof must have a small amount of pitch for proper water drainage.