Rafter Vs Joist Flat Roof

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.

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. 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. Roof joists generally join opposing walls and support the ceiling below and or the floor above. A roofing joist is a horizontal member that runs across an open space.

Rafters are the building components that run diagonally from the wall plate to the apex of a roof structure. They can be concealed or exposed and there will be more joists than beams. 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. Depending on the construction they may lie flat or be pitched.

In traditional timber they are nominally 2 inches thick and typically 8 to 10 inches wide. In many modern construction projects prefabricated roof trusses are used.