Rafter Vs Joist Flat Roof

Joist is a term used in construction for load bearing planks that run horizontally or nearly to horizontally to ground.

Rafter vs joist flat roof.

In many modern construction projects prefabricated roof trusses are used. Rafters are the building components that run diagonally from the wall plate to the apex of a roof structure. If you have a low sloped roof or flat roof of less than 2 in 12 these evenly spaced planks will be called roofing joists. They can be concealed or exposed and there will be more joists than beams.

In traditional timber they are nominally 2 inches thick and typically 8 to 10 inches wide. The major functional difference between the two is that trusses are built mostly with 2x4s in place of the wider dimensional boards. Roof joists generally join opposing walls and support the ceiling below and or the floor above. These triangulated structures with a high degree of strength and stability due to the geometry used form both the joist and rafter components of a building.

Rafters form the foundation for attachment of the roof boards onto which the final roof covering is fixed. A roofing joist is a horizontal member that runs across an open space.