Gable Roof Components

Rafters

• The rafters are the two sets of diagonal framing members that run from the peak, down to overlap the tops of the walls on both sides. Rafter angle is determined by roof pitch. Roof pitch is calculated by the number of vertical inches of rise, to a horizontal foot of roof. The angle cut for the top of the rafter is typically the same for the bottom, providing a vertical face for the roof's edge trim, known as fascia, on the rafter tail ends. The rafters are attached to the ridge at the top, and the wall cap at the lower end. Rafters are typically spaced every 24 inches.

Ridge Beam

• The ridge beam is supported by the rafters at each gable end of the roof. Then rafters between the gables are attached to it, providing additional support. Think of the ridge beam as the roof's spine. As long as this spine is level and well supported, it will hold the weight of the roof, even with a rafter (rib) or two sagging slightly. The ridge is typically centered on the house structure, between the two side walls.

Joists

• The walls are tied together by joists. A joist is a lumber framing member, that is nailed to the top caps of both walls. Like rafters, they are spaced every 24 inches. The joist supports the attic floor and the ceiling of the floor just below the attic. In addition, they hold the walls in position and help bear the force of roof, which presses down and out, through the rafters. In modern construction, joists are attached through light metal brackets, known as hurricane ties, or joist hangers.

Trusses

• A truss is a triangular prefabricated frame that takes the place of the rafters and joists and does away with the need for a ridge beam. The truss is comprised of two diagonal rafter-like top braces, known as upper cords, and one horizontal joist-like member known as the lower cord. The center of the truss is supported by a vertical brace, called the king post, and diagonal braces known as webs. Trusses are set every 24 inches, attaching to the wall top plate, much like joists. They are connected on top by the roof decking without a central spine.