How it works
This is a roof built on site from rafters; for the factory-built kind see the parts of a roof truss. Tap any piece to see its name, or press Quiz me.
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The frame from above
Common rafters run from the top plate of the wall up to the ridge board. At a hipped end, a hip rafter runs from each outside corner to the ridge, and the rafters that stop against it are jack rafters. Where a cross gable meets the main roof, a valley rafter runs up each inside angle. At a gable end, lookouts carry the overhang.
A cut through the roof
Each rafter is notched with a bird's mouth to sit on the top plate, and its tail runs on past the wall as the overhang, ending at the fascia. A ceiling joist ties the feet of a rafter pair together, a collar tie joins them higher up, and a purlin supports rafters partway along.
- The quiz accepts ridge for ridge board, rafter tail for overhang and collar beam for collar tie.
Questions and answers
What are the parts of a roof frame?
A ridge board, common rafters, hip, valley and jack rafters where the roof has hips or valleys, ceiling joists, collar ties, the top plates the rafters sit on, and the fascia across the rafter ends.
What is the difference between a hip rafter and a valley rafter?
A hip rafter runs up from an outside corner of the walls, where two slopes meet in a ridge-like edge. A valley rafter runs up from an inside corner, where two slopes meet in a trough.
What is a jack rafter?
A rafter shorter than a common rafter. A hip jack runs from the plate up to a hip rafter, a valley jack from the ridge down to a valley rafter, and a cripple jack between a hip and a valley.
What is the difference between a collar tie and a ceiling joist?
Both are level pieces joining a pair of rafters. A ceiling joist joins their feet at the top of the walls and carries the ceiling. A collar tie joins them higher up, between the plate and the ridge.