Ceiling Joist Roof Rafter

A structural ridge is the standard alternative to ceiling joists.

Ceiling joist roof rafter.

In this case the rafter as a whole is actually stronger than it would have been because the splice is more than adequate and the plywood adds to the strength. Rafter ties or ceiling joists acting as rafter ties are required by code unless the house is designed so that the walls or a structural ridge beam carries the full load of the roof. 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. The joists might then be covered with osb or plywood to form an attic floor for storage.

Pictured at left is a 2x6 rafter spliced together using 3 4 plywood. If your project had a rafter length of 8 or less a safe and strong method is to use 2x8 framed 16 on center. In this design the tops of the rafters attach to a load bearing ridge beam that runs along the length of the roof. This board forms the bottom member of each rafter and of course the ceiling of the space below.

The rafter tie is attached to the top of the rafters such as the topmost point in a cable or hipped roof. 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. Rafter ties help tie the roof rafters together structurally eliminating the need for ceiling joists. 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.

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. In unfinished space an attic insulation is typically laid between the joists. If you are framing a cathedral ceiling there are a couple ways to deal with the need for rafter ties. 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.

In this case the framer just needed a longer rafter. Roof rafters don t need to be parallel to ceiling joists when rafter ties are used. You can possibly remove them altogether of you include posts in the gable walls to support a structural ridge.