Ridge beam
A ridge beam carries half the roof load down to posts at each end. Structural. Distinct from a non-structural ridge board. Used in cathedral ceilings.
Ask Chalkline about this →A ridge beam is a structural member at the apex of a pitched roof that carries approximately half the roof load down to posts (or load-bearing walls) at each end. The rafters or trusses attach to the ridge beam from each side, transferring their load through the beam to the supporting structure below.
Key distinction from a ridge board:
| Property | Ridge beam | Ridge board |
|---|---|---|
| Structural function | Carries half the roof load | None (just a nailing surface) |
| Sizing source | AS 1684 (or engineer) span tables | AS 1684 |
| Section size | Typically 240×45 mm to 450×63 mm LVL or Glulam; larger if engineered | 75×35 or 90×35 mm |
| End support | Posts or load-bearing walls | Not load-bearing; supported by rafter framing |
| Where used | Cathedral ceiling, skillion-end gable, post-and-beam | Conventional pitched roof with collar ties or ceiling joist tie-down |
A common defect on small renovation jobs is using a ridge board where a ridge beam is required. The roof “looks fine” but slowly sags as rafter tension overcomes the inadequate ridge support.
When a ridge beam is required:
- Cathedral ceilings (where ceiling joists do not run wall-to-wall at the ceiling line). Without ceiling joists, the rafters can’t transfer thrust laterally; the ridge takes it as a beam.
- Open-plan rooms where a tie-beam at ceiling height is not architecturally acceptable.
- Skillion-end gable conversions where part of the roof is converted from conventional pitched to a vaulted form.
- Post-and-beam construction.
Sizing. AS 1684 publishes span tables for ridge beams in MGP and F-grade pine; for longer spans or where the architect wants a slimmer section, LVL or Glulam beams are common. The engineer or designer specifies the beam to span and load conditions.
Typical sizes for residential:
- Up to 3.5 m span, light load: 240×63 mm MGP12 or 240×45 mm F17 LVL.
- 3.5 to 5.0 m span, normal load: 300×63 mm F17 LVL or Glulam GL13.
- 5.0+ m span: engineered solution required; sizes vary widely.
End-support detailing.
- Post under each end of the ridge beam: a load-path-clear post running down to a footing or load-bearing wall. The post bears full ridge load.
- Engineer-detailed bracing: a ridge beam at an angle to the building’s main framing requires bracing to prevent rotation.
- Connection at ridge to rafter or truss: typically via top-flange hangers (e.g. Pryda, Mitek) sized for the rafter dimensions and load.
Common defects:
- Beam under-sized: visible sag in the roof line within years.
- No post under the end: the ridge beam load is being carried into framing that wasn’t designed for it. Wall studs deflect.
- Wrong connection: rafters skew-nailed instead of hung. Ridge separates from rafter at load.
- Substituting ridge board for ridge beam: very common on small DIY-style renovations. Discovered at inspection or after the first heavy snow / strong wind.
For builders.
- Confirm the design specifies a ridge beam or ridge board before quoting. Adding a structural ridge beam mid-build is expensive.
- Engineer’s certification for any non-standard ridge beam (anything outside AS 1684 span tables).
- Confirm the load path to the foundation: posts under ridge ends sit on slab edge beams or footings, not floor joists.
Also known as: structural ridge, ridge member.
Category: Materials / structural timber / framing.
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Last updated: 2026-05-14. Verified: 2026-05-14.