Rafter

A rafter is one board in a roof frame, cut to the plan's pitch and set in place by a carpenter. It runs from the ridge down to the exterior wall's top plate, and the roof sheathing, underlayment, and tile sit on top of it. Framing a roof this way is stick framing, or conventional framing.

Opposing rafters want to spread. Gravity pulls the peak down and the feet kick outward, so something must tie the two sides together. IRC Section R802.5.2 uses the ceiling joists, provided they run parallel to the rafters and sit in the bottom third of the rafter height. Where the joists run the wrong way, add 2x4 rafter ties at most 24 inches on center. Collar ties are separate: 1x4s in the upper third of the attic, up to 4 feet apart. Leave the ties out and the ridge board becomes a designed ridge beam on walls or columns.

The payoff is the space underneath. Rafters leave the volume between them open, so a great room can vault to the ridge and an attic can hold rooms. The Building America Solution Center puts it bluntly: a roof carried by truss framing cannot be used for living space. Rafters can. That volume also suits a conditioned attic, with insulation at the roofline and ducts inside the cooled envelope rather than superheated attic air.

For example, a Rio Verde custom home with a vaulted great room is stick framed over that room while trusses cover the rest. The cost runs the other way: trusses arrive engineered and crane on in a day, while a rafter roof is cut and squared over days by skilled carpenters, every span taken from Section R802.4.1 tables or an engineer.

A truss is a finished assembly; a rafter is one member that works only once tied. Rafter notches and holes follow Section R802.7. Cutting a truss member takes a design professional's approval under Section R802.10.4.