Why would a roofer ask about wind?
Because the screws, battens and tie-downs holding a roof on are chosen for the wind the site has to survive. A quote that does not name a wind class has either assumed one or skipped the question.
AS 4055 gives a house site a wind class of N1 to N6, C1 to C4, worked out from the site's region, topography and shielding. Under NCC 2025, cyclonic areas are wind regions B2, C and D; Queensland and NSW keep the NCC 2022 definition, wind regions C and D, until 1 May 2027. Fixing details are written for a class: the QBCC repair guide works to C2 (61 m/s).
What do the N and C classes mean?
N classes cover non-cyclonic areas and C classes cover cyclonic ones. The Housing Industry Association describes the AS 4055:2021 range as N1 to N6, C1 to C4, a set of site wind classes that designers, builders and product manufacturers specify against. Within a series, each step up means the site has to handle more wind.
The two series are not one ladder, so a C class is not simply "stronger" than every N class. The design wind speeds behind each class are set out in the standard, which is where your engineer or certifier will read them.
How does a site get its class?
The HIA lists three inputs, and all three are about your block rather than your suburb.
- Region. Where the site sits on the national wind region map.
- Topography. The lie of the land, so a hilltop and a valley floor differ.
- Shielding. Whether the house is protected, for instance by surrounding houses.
Knocking down the house next door can change the shielding, so a class is not fixed for the life of a house. Ask your builder, certifier or the approved plans for the class that applies to your site instead of reading it off a map.
Which parts of Australia are cyclonic?
The answer changed with the new building code. NCC 2025 treats wind regions B2, C and D as cyclonic areas. The older NCC 2022 lists wind regions C and D. Which edition applies to your job depends on your state and on timing, so ask your certifier which one they are working to.
Show the dates
| Date | What happened | Source |
|---|---|---|
| 1 May 2026 | Published; adopted in VIC, WA, TAS and the ACT | Australian Building Codes Board, NCC 2025 state and territory adoption information |
| 1 May 2027 | Adopted in Queensland and New South Wales | Australian Building Codes Board, NCC 2025 state and territory adoption information |
Official source: Australian Building Codes Board, NCC 2025 state and territory adoption information.
WA and the ACT also allow a 12-month transition. The region that covers a specific address is a question for your certifier or engineer, and it is worth having their answer in writing before a roofer prices the fixings.
Why does the class matter when re-roofing in Queensland?
The QBCC guide to repairing sheet metal roofs in cyclonic areas sets out roof sheeting fixings in line with manufacturer specifications for C2 (61 m/s). It does not stop at the sheets: it covers roof battens, roof framing and trusses, uplift forces on the wall studs, pre-drilling timber, split, decayed or insect-damaged timber, and washer sizes. It also must not be used where the class may exceed C2, such as an elevated or exposed block, so a hilltop house needs an engineer's answer rather than the guide.
What should a roofing quote say about wind?
- The wind class the roof is being fixed for, in writing.
- That fixings follow the manufacturer's specification for that class.
- Who confirmed the class: the certifier, the engineer or the original plans.
- What happens if battens or framing are found to need work once the old roof is off.
Our quote checklist covers the licence, contract and deposit side of the same document.
The wind classes and the factors behind them come from the Housing Industry Association, an industry source. The cyclonic regions, adoption dates and the C2 repair detail come from official pages, linked below.