Rafter Vs Joist Flat Roof

In many modern construction projects prefabricated roof trusses are used.

Rafter vs joist flat roof. Rafters form the foundation for attachment of the roof boards onto which the final roof covering is fixed. Depending on the construction they may lie flat or be pitched. A roofing joist is a horizontal member that runs across an open space. 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.

Joist is a term used in construction for load bearing planks that run horizontally or nearly to horizontally to ground. Rafters are the building components that run diagonally from the wall plate to the apex of a roof structure. 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.

Roof joists generally join opposing walls and support the ceiling below and or the floor above. In traditional timber they are nominally 2 inches thick and typically 8 to 10 inches wide.