Ceiling Joist Roof Rafter

Roof rafters don t need to be parallel to ceiling joists when rafter ties are used.

Ceiling joist roof rafter.

Ceiling joists can serve as rafter ties to resist outward thrust on the walls from the rafter loads if they are installed parallel to the rafters and in accordance with code. If your project had a rafter length of 8 or less a safe and strong method is to use 2x8 framed 16 on center. This board forms the bottom member of each rafter and of course the ceiling of the space below. The joists might then be covered with osb or plywood to form an attic floor for storage.

The are similar to trusses in this regard. As a general rule roofs that have a high human occupancy rate should be framed with rafters every 16 structures such as sheds or barns can be frames with rafters every 24 again make sure to consult local codes. They are nominally 2 inches thick actual width usually 1 1 2 inches and come in a variety of widths from 8 to 12 inches. Pictured at left is a 2x6 rafter spliced together using 3 4 plywood.

If you are framing a cathedral ceiling there are a couple ways to deal with the need for rafter ties. Joists are the parallel horizontal beams that run across an open space joining opposite walls in a building to support both the ceiling below and the floor above. You can possibly remove them altogether of you include posts in the gable walls to support a structural ridge. Rafter ties help tie the roof rafters together structurally eliminating the need for ceiling joists.

Backing for the ceiling finish is obtained by nailing 2x blocking flatwise to the plates between the rafters behind the frieze blocking to provide a nailing surface for the ceiling drywall. In unfinished space an attic insulation is typically laid between the joists. The rafter tie is attached to the top of the rafters such as the topmost point in a cable or hipped roof. There are times however when the first joist may have to be held away from the plate as much as 32 in depending on the pitch of the roof and the size.

A structural ridge is the standard alternative to ceiling joists. In this design the tops of the rafters attach to a load bearing ridge beam that runs along the length of the roof. Joists are traditionally made from timber.