Strutting beam

A strutting beam is a designed beam that picks up roof strut loads, from the underpurlins supporting the rafters, where there is no load-bearing wall conveniently below to carry them down. It is sized to AS 1684 or by an engineer.

In a conventional roof, the underpurlins that prop the rafters pass their load to struts, and the struts need to land on something solid that carries the load down to the footings. The first choice is a load-bearing internal wall. But open-plan layouts often have no wall where a strut wants to land, so a strutting beam spans between two supports (walls or other beams) and gives the strut a designed landing point. The strut sits on the strutting beam, and the beam carries the concentrated load back to its end supports.

The detail that matters is that a strutting beam is engineered: its size, span, and end-support fixings come from AS 1684’s span tables (or an engineer for anything outside them), and it must bear on supports that themselves carry the load to the ground. It is not a hanging beam or a lintel doing a different job, and you cannot substitute a smaller member because it “looks big enough.”

For a builder the practical points are to use a strutting beam (not a guess) wherever a roof strut has no load-bearing wall under it, to size it from AS 1684 or the engineer for the actual strut load and span, and to make sure both ends land on real support down to the footings. Landing a strut on anything but a wall or a strutting beam, a ceiling joist, a non-loadbearing partition, drops the roof line and is a common cause of sagging ridges in renovations.

Also known as: Strut beam, counter beam (in some usage).

Category: Roof framing / Conventional.

Related

• Roof strut
• Conventional roof framing

See also

• Underpurlin
• Load-bearing wall

References

• AS 1684 Residential timber-framed construction, Standards Australia (verified 2026-06-02)

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Last updated: 2026-06-02. Verified: 2026-06-02. Quarterly review for currency.