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AS 1684.3: timber framing in cyclonic areas

AS 1684.3 is the timber-framing standard for cyclonic areas (wind classes C1 to C3). It ramps up fixing density and tie-down hardware over the non-cyclonic AS 1684.2.

By Chalkline. Last updated 25 May 2026. Verified 25 May 2026.

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AS 1684.3 is Part 3 of the residential timber-framing standard, covering cyclonic areas. It is the deemed-to-satisfy framing path for the cyclone-prone north of Australia, and it is the cyclonic counterpart to the non-cyclonic AS 1684.2. Same family of rules, much higher loads: the difference is how hard the wind pulls, and therefore how much the frame has to be fixed down (verified 2026-05-25, AS 1684 series).

Where it applies

AS 1684.3 covers wind classes C1, C2, and C3, the cyclonic classifications, which occur in the cyclone wind regions of Far North Queensland, the Northern Territory Top End, and north-west Western Australia (verified 2026-05-25). The wind classification is established under AS 4055.

The scope has a ceiling: C4 is outside AS 1684.3 and needs engineer design, just as N5 and N6 are outside the non-cyclonic part. If the site classifies above C3, the frame is not a span-table job.

What changes versus non-cyclonic

The structural logic is the same as AS 1684.2, but the cyclonic loads drive two big differences:

  • More fixing, denser. Member sizes and especially the connections step up. The tie-down and bracing demands are far higher than a non-cyclonic frame of the same geometry.
  • Specific fixings are mandatory. In cyclonic areas, the nominal fixings (standard skew-nailing) that AS 1684.2 allows at many low-wind joints are not acceptable. Every connection in the load path needs a calculated specific fixing, the cyclone straps, hold-downs, rods, and bolted connections of the tie-down system, sized to the cyclonic uplift.

In short, a cyclonic frame is the same shape as a southern frame but tied down far harder, with proprietary connectors and rod systems where a southern build would use a triple grip or nominal nailing.

How it fits the NCC

Following AS 1684.3 is a deemed-to-satisfy path for the NCC structural performance requirement (NCC 2022 Volume Two H1D6(4)) on Class 1 and Class 10 timber-framed buildings in cyclonic areas (verified 2026-05-25, ABCB NCC 2022). The span tables are published as separate supplements for the cyclonic wind classes, timber species, and stress grades, the same supplement system as the non-cyclonic part.

For a builder in the north

  • Confirm the wind class first. C1, C2, or C3 sets the whole frame. Building a cyclonic frame to the wrong class, or to a non-cyclonic spec, is a catastrophic failure mode in a cyclone.
  • No nominal fixings. Do not carry southern habits north; every connection is a specific, calculated fixing. A skew-nailed joint that passes in Sydney fails the standard in Cairns.
  • Get the cyclone hardware right. The tie-down chain runs on rated straps, hold-downs, and rods; install to the schedule and fill every fixing.
  • C4 means an engineer. Above C3 the span-table path stops; the frame is engineer-designed.
  • For the general AS 1684 framing system and the span-table method, see the AS 1684 overview and how to read the span tables.

Also known as: AS 1684.3, cyclonic timber framing standard.

See also

Last updated: 2026-05-25. Verified: 2026-05-25. Quarterly review for currency.

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