Rafters are the frame boards that supports a roof in a similar way that joists support a floor.   Rafters are not the same as roof trusses, but serve a similar function.  A rafter is a sloped structural member that forms the framework of a pitched roof. Rafters are inclined beams that run from the ridge (the highest point at the apex of the roof) down to the eaves or the edge of the roof, providing support and forming the skeleton of the roof structure.

These members are typically made of wood but can also be constructed using engineered wood, steel, or other materials, depending on the design and construction requirements. Rafters work together to support the roof covering materials (such as shingles, tiles, or metal sheets) and transfer the roof load to the building's walls or the supporting structure.

Rafters are installed at regular intervals, and the spacing between them is determined by factors such as the design of the roof, local building codes, and the materials being used. They play a crucial role in distributing the weight of the roof evenly and providing structural integrity to the overall roofing system.

NOTE: Always use engineering specifications that satisfy local building codes.