Rafter Vs Joist Flat Roof

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.

Rafter vs joist flat roof.

Trusses and rafters have many common parts including the sloping rafter boards and a bottom joists that form the ceiling of the space below. In many modern construction projects prefabricated roof trusses are used. 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.

A roofing joist is a horizontal member that runs across an open space. They can be concealed or exposed and there will be more joists than beams. Depending on the construction they may lie flat or be pitched. 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.

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.