Roof Joist Vs Rafter

Conventional framing the first thing to understand is how a roof framed with wood i joists differs structurally from a traditional stick framed roof.

Roof joist vs rafter.

Rafters form the foundation for attachment of the roof boards onto which the final roof covering is fixed. The major functional difference between the two is that trusses are built mostly with 2x4s in place of the wider dimensional boards. 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. Rafter span tables use these tables to determine lengths sizes and spacing of rafters based on a variety of factors such as species load grade spacing and pitch.

Rafters are the building components that run diagonally from the wall plate to the apex of a roof structure. 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. A joist is a horizontal structural member used in framing to span an open space often between beams that subsequently transfer loads to vertical members. The other common case is the cathedral or vaulted ceiling.

Without the tie at the bottom the rafters must be supported at their upper end to prevent the rafter thrust at the lower end. As mentioned above a 2 4 spf shed roof rafter can span 11. An syp rafter can span 11. Floor joist span use this table to determine the maximum lengths of floor joists based on species of lumber joist spacing and joist size.

This structural support comes in the form of roofing joists ceiling joists rafters or trusses and can be made from a variety of materials including wood metal reinforced concrete etc. However in canada the most common material used in residential framing is wood so that is the material we will discuss here. The first case is when the ceiling joists are oriented perpendicular to the rafters. Both of these are for light roof loads.

The load resisting concepts of the vaulted ceiling are completely different. In traditional timber they are nominally 2 inches thick and typically 8 to 10 inches wide. 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.