Roof strut
A roof strut is a compression member transferring load from an underpurlin to a load-bearing wall or strutting beam in conventional roof framing, sized off AS 1684.
Ask Chalkline about this →A roof strut is a compression member that transfers load from an underpurlin (which supports the rafters) down to a load-bearing wall or a strutting beam in conventional (stick-built) roof framing. It is sized off AS 1684.
In a conventional roof, the rafters are propped at mid-span by underpurlins so they do not have to span the whole way unsupported. Those underpurlins then have to get their load to something solid, and the strut is what does it: a timber member in compression running from the underpurlin down to a loadbearing internal wall (or to a strutting beam where there is no wall conveniently below). The strut angle, size, and what it lands on are all part of the AS 1684 design.
The thing that goes wrong is the bottom of the strut. A strut only works if it lands on something that can carry the load down to the footings: a loadbearing wall with structure under it, or a designed strutting beam. Land a strut on a non-loadbearing partition, on ceiling joists, or on a wall with nothing under it, and the load has nowhere to go, the ceiling sags, the wall deflects, or the roof line drops.
For a builder the practical points are to set struts to the AS 1684 size and angle, to make sure each strut lands on a genuine loadbearing wall or a designed strutting beam (not a stud wall that just happens to be there), and to check the load path continues to the footings. On a renovation, removing or relocating a wall that a roof strut bears on is a structural change, not a cosmetic one, and needs the load picked up elsewhere first.
Also known as: Strut, roof strutting member.
Category: Roof framing / Conventional.
Related
See also
References
- AS 1684 Residential timber-framed construction, Standards Australia (verified 2026-06-01)
Last updated: 2026-06-01. Verified: 2026-06-01. Quarterly review for currency.