Roof Joist Vs Rafter

Rafters are the building components that run diagonally from the wall plate to the apex of a roof structure.

Roof joist vs rafter.

In traditional timber they are nominally 2 inches thick and typically 8 to 10 inches wide. Without the tie at the bottom the rafters must be supported at their upper end to prevent the rafter thrust at the lower end. The other common case is the cathedral or vaulted ceiling. An syp rafter can span 11.

If you live in an area that requires a shed roof rafter to support a heavy load then an spf rafter can only span 7. Roof rafter span use this table to determine the maximum lengths of roof rafters based on species and grade of lumber spacing dimensions load and slope. However in canada the most common material used in residential framing is wood so that is the material we will discuss here. Trusses and rafters have many common parts including the sloping rafter boards and a bottom joists that form the ceiling of the space below.

Conventional framing the first thing to understand is how a roof framed with wood i joists differs structurally from a traditional stick framed roof. Rafters form the foundation for attachment of the roof boards onto which the final roof covering is fixed. The main difference between joist and rafter is that the joist is a horizontal structural element transferring load from flooring to beams typically running perpendicular to beams and rafter is a structural members in architecture. Both of these are for light roof loads.

The major functional difference between the two is that trusses are built mostly with 2x4s in place of the wider dimensional boards. The load resisting concepts of the vaulted ceiling are completely different. Visit the roof framing page for more information on cutting roof rafters and visit the roof pitch calculator for determining rafter lengths based on rise and run. In a typical roof framed with dimension lumber the rafters rest on the exterior wall top plate at the lower end and bear against a ridge board at the top.

As mentioned above a 2 4 spf shed roof rafter can span 11. The first case is when the ceiling joists are oriented perpendicular to the rafters. Floor joist span use this table to determine the maximum lengths of floor joists based on species of lumber joist spacing and joist size.