Structural component
What is a rafter?
The sloped beams that give a roof its shape and carry everything laid on top of it, sized by tables the code has published for a century.
Updated September 12, 2026 · Every figure links to its source · Sources
DefinitionComponentAlso called: common rafter, roof rafter
Rafter — one of a series of sloped structural members, of sawn lumber or engineered wood, that run from the ridge or hip of a roof down to the wall plate and carry the roof deck and the loads on it; the 2021 IRC, Section R802 sets their sizes, spans and connections, and the NRCA glossary defines the term.
What it is
A "stick-framed" roof is built on site from individual rafters, cut and set one at a time: common rafters run from the ridge board to the top of the wall, hip rafters run diagonally at the outside corners of a hip roof, valley rafters at the inside corners, and shorter jack rafters fill between them. At the wall each rafter is notched with a bird's mouth to sit on the plate, and its tail projects beyond to form the eave. Opposing rafters push outward on the walls, so the code requires them to be tied together by ceiling joists or rafter ties near the plate, and collar ties near the ridge keep the pairs from separating in wind uplift.
The IRC, Section R802 sizes all of this from tables: rafter span by lumber species, grade, size, spacing and the snow and dead loads for the region, with rules for the ridge, the ties and the purlins that shorten a long span. On sheathed roofs the deck panels span across the rafters, which is why rafter spacing — usually 16 or 24 inches on centre — sets the sheathing thickness under Section R803.
Why it matters
Rafters are the difference between a roof and a lid. Their virtue over trusses is the open attic they leave — usable space, room for a later conversion, easy access for wiring and insulation — and their ability to frame any shape a builder can cut. Their cost is labour and lumber: bigger members, more skilled framing and, on a long span, purlins or a structural ridge. Old rafters are often undersized by today's tables and carry decades of added load: a second layer of shingles, a heavier covering, solar panels. A sagging ridge line seen from the street is the sign.
On a re-roof the rafters are out of scope unless the deck is off and a problem shows: a split or rotted rafter at the eave is sistered with a new member alongside it, and a cut rafter — for an old chimney, a skylight or a bathroom fan installed without headers — is the kind of finding that turns a roofing job into a framing job. The Structural Building Components Association explains the trussed alternative used on most new houses.
What it costs and who does it
Rafter repair is carpentry, priced per member or by the hour with the lumber, and done by a framing carpenter or the roofing crew's carpenter while the deck is open; larger corrections — a sagging ridge, spread walls, a structural ridge for a cathedral ceiling — need an engineer's design. Roofing estimates normally state that structural repair is extra, priced when found. The directory's guide to a new roof installation covers what the base price includes, and its guide to roof repair what a repair visit should look at.
Frequently asked questions
Short answers; the sections above carry the detail and the sources.
What is the difference between a rafter and a truss?
How far apart are rafters?
What is a rafter tail?
Next step
Find a roofer who does this
Framing findings are the reason a roofing contract should say what happens when the deck comes off. The directory lists roofing contractors by state and city.
Sources
- 2021 International Residential Code, Chapter 8: Roof-Ceiling Construction — International Code Council (ICC)
- Roofing glossary — National Roofing Contractors Association (NRCA)
- Structural Building Components Association — SBCA