Rafter Vs Joist Flat Roof

The major functional difference between the two is that trusses are built mostly with 2x4s in place of the wider dimensional boards.

Rafter vs joist flat roof.

In many modern construction projects prefabricated roof trusses are used. Joist is a term used in construction for load bearing planks that run horizontally or nearly to horizontally to ground. Trusses and rafters have many common parts including the sloping rafter boards and a bottom joists that form the ceiling of the space below. 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. 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. Rafters are the building components that run diagonally from the wall plate to the apex of a roof structure. In traditional timber they are nominally 2 inches thick and typically 8 to 10 inches wide.

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.