Rafter Vs Joist Flat Roof

In many modern construction projects prefabricated roof trusses are used.

Rafter vs joist flat roof.

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

Joist is a term used in construction for load bearing planks that run horizontally or nearly to horizontally to ground. 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. Trusses and rafters have many common parts including the sloping rafter boards and a bottom joists that form the ceiling of the space below.

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. They can be concealed or exposed and there will be more joists than beams.