A common rafter is a standard, straightforward rafter running from the wall top plate to the ridge at a consistent angle, representing the most basic and frequently used rafter type in traditional roof framing, distinguished from specialized rafters like hip or valley rafters that address more complex roof geometry.
These rafters form the bulk of a traditional gable roof’s structure, repeated at regular spacing across the roof’s length, each cut identically since they all span the same distance at the same angle.
Because common rafters follow a consistent, repeatable pattern, they’re relatively straightforward to calculate and cut compared to the more complex geometry hip and valley rafters require.
What Does a Common Rafter Involve?
- Consistent length and angle throughout a simple gable roof
- A birdsmouth cut at the wall plate connection
- Connection to the ridge board or beam at the peak
- Regular spacing matching the roof’s overall framing plan
Why Are Common Rafters Important?
As the primary structural members in a traditional gable roof, common rafters carry the bulk of the roof’s load and covering, making their consistent, accurate cutting essential to a roof surface that’s flat, properly aligned, and ready to receive sheathing and roofing materials. Because these rafters are cut identically, an error in the initial calculation gets repeated across every rafter in the roof, making accuracy at the outset particularly important.
On more complex roof shapes involving hips or valleys, common rafters still form the main body of each roof section, working alongside the specialized hip, valley, and jack rafters that handle the more geometrically complex transition areas.
Common Rafter vs. Hip Rafter
A common rafter runs at a consistent angle across a simple roof section. A hip rafter runs diagonally at the corner where two roof planes meet in a hip roof design, requiring more complex geometric calculation than the straightforward common rafter.