AS 4055: wind loads for housing

TL;DR

AS 4055:2021 is the standard every builder and building designer uses to determine the wind class for a standard house. It converts the wind region, terrain category, shielding, and topography at your site into one of ten wind classes: N1 to N6 (non-cyclonic) or C1 to C4 (cyclonic). That wind class then drives every structural and product specification on the job: tie-downs, roof-to-wall connections, bracing, windows, doors, and cladding. Get the wind class wrong at design stage and you face a costly structural redesign at certifier. AS 4055 applies to Class 1 and 10a buildings within its geometric limits; go outside those limits and you move to AS/NZS 1170.2.

In plain English

AS 4055 is the simplified wind standard for housing. It packages the detailed wind calculations from AS/NZS 1170.2 into a practical tool that a building designer can apply to a standard house without running full engineering calculations. The output is a single wind class (N1, N2, N3, N4, N5, N6, C1, C2, C3, or C4) that summarises the wind loads the structure must withstand.

The current edition is AS 4055:2021 Amd 1:2024, which supersedes AS 4055:2012. The 2021 edition brought the standard into closer alignment with AS/NZS 1170.2:2021, updated the wind region boundaries (notably moving Toowoomba from Region A to Region B and refining the B1/B2 split in south-east Queensland), introduced the “averaged ground level” definition, and removed Terrain Category 1.5 (verified 2026-05-08: Standards Australia store, AS 4055:2021 Amd 1:2024).

The standard is referenced in NCC 2022 Volume Two Part H1 Structure and the ABCB Housing Provisions Standard 2022 Part 2.2 as the basis for wind action determination for housing within its geometric limits (verified 2026-05-08: ABCB, NCC 2022 Volume Two Part H1).

What it requires

Geometric limits: when AS 4055 applies

AS 4055 applies to NCC Class 1 and 10a buildings that fall within the following geometric limits (per clause 1.2 of AS 4055, confirmed at NCC H1D8 explanatory information, verified 2026-05-08):

Limit	Maximum
Eaves height above averaged ground level	6.0 m
Roof peak height above averaged ground level	8.5 m
Building width (including verandas)	16.0 m
Building length	5 x building width
Roof pitch	35 degrees

If any of these limits is exceeded, the building falls outside AS 4055 scope. The designer must then use AS/NZS 1170.2:2021 directly, which requires specific engineering wind speed calculations. For most standard single-storey and two-storey residential homes, AS 4055 will apply.

The ten wind classes

AS 4055 sets out 10 wind classes covering the full range of wind conditions across Australia (verified 2026-05-08: STA Consulting, Wind Classification Housing):

Non-cyclonic classes (Regions A and B):

Class	Typical location	Design gust wind speed (ultimate)
N1	Sheltered suburban, significant surrounding shielding	34 m/s
N2	Standard residential suburbs, moderate shielding	40 m/s
N3	Exposed coastal (non-cyclonic), hilly terrain	50 m/s
N4	Highly exposed coastal or elevated sites in Region B	61 m/s
N5	Extreme exposure in Region B	74 m/s
N6	Most severe non-cyclonic, rare in residential	86 m/s

Cyclonic classes (Regions C and D):

Class	Typical location	Design gust wind speed (ultimate)
C1	Entry-level cyclonic zone	50 m/s
C2	Moderately exposed cyclonic area	61 m/s
C3	High-exposure coastal cyclonic zone	74 m/s
C4	Extreme conditions, Pilbara coast and similar	86 m/s

Note: N2 is the most common classification for standard suburban residential construction across southern and eastern Australia. N3 applies to exposed coastal sites outside cyclone zones. C classes apply across northern Queensland, the Northern Territory coast, and northern Western Australia.

How the wind class is determined

Four site factors combine to produce the wind class (verified 2026-05-08: STA Consulting, Wind Classification Housing):

Wind region: Australia is divided into regions A (normal), B1 and B2 (intermediate), C (cyclonic), and D (severe cyclonic). The wind region for a site is read from the AS 4055 wind region map or the AS/NZS 1170.2 map. Region drives whether the class is N or C, and the starting point for the classification table.
Terrain category (TC): describes the surface roughness within approximately 500 m of the site. TC1 = open flat terrain with minimal obstructions (coastal headlands, airfields). TC2 = open areas with scattered low obstructions (rural areas, airports). TC2.5 = moderately scattered obstructions (agricultural land, cane fields). TC3 = typical residential estates with buildings and vegetation. Higher terrain category means more protection from wind.
Wind shielding: measures the degree to which surrounding buildings or structures shield the site from wind. Shielding classes T0 (no shielding) through T3 (full shielding) are applied.
Topography: accounts for sites on or near hills or ridges. A site on an exposed ridge will experience higher wind speeds than a site in a valley at the same regional location. Topographic class T0 to T5 is assessed based on the slope of terrain running through the site.

These four factors are combined using the classification tables in AS 4055 to arrive at the wind class. The building designer determines the wind class; the builder’s job is to confirm it’s documented in the structural details and that all products specified are rated to match.

Wind region geography

Wind region	Where it applies
A (Normal)	Most of southern and eastern Australia, capital cities, Adelaide, Melbourne, Sydney, Canberra, Hobart
B1 (Intermediate)	South-east Queensland, Gold Coast and Brisbane corridor
B2 (Intermediate, higher)	Northern NSW coast above Coffs Harbour, parts of central QLD coast
C (Cyclonic)	Northern QLD coast, Darwin and NT coast, WA north of Carnarvon
D (Severe cyclonic)	Pilbara coast WA

WA state variation: the NCC Housing Provisions include a WA-specific amendment (WA Part 2.3) that reclassifies wind Region B sites in WA as cyclonic (C) rather than non-cyclonic (N), and applies higher design event probabilities for Region D north of the Tropic of Capricorn (verified 2026-05-08: NCC WA Part 2.3).

What it doesn’t cover

Buildings outside the geometric limits: multi-storey residential above 8.5 m, commercial buildings, or unusual geometries require AS/NZS 1170.2 engineering calculations.
Structural member sizing: AS 4055 provides the wind class input; the structural standards (AS 1684 for timber framing, AS 3700 for masonry) use that input to size members and connections.
Full engineering wind reports: a wind classification under AS 4055 is not the same as a site-specific engineering wind report under AS/NZS 1170.2. For complex sites (steep ridges, exposed coastal headlands, unusual topography), a full wind assessment is more accurate and may yield a lower wind class than the conservative AS 4055 lookup table.
Bushfire requirements: BAL ratings and fire-resistant construction requirements are governed by AS 3959 and the NCC BAL provisions, not AS 4055. A high-BAL site also typically sits in an elevated wind region, but the two assessments are independent.
Cyclone-rated product testing: product manufacturers must test and certify products to the required wind class under their own product standards. AS 4055 defines what wind load they must resist; the product standards (e.g. AS/NZS 4505 for garage doors) define how to test it.

Practical implications

Confirm the wind class before you price

Wind class drives cost through the structural specification. N1 and N2 use standard framing fixings and bracing. N3 and above require heavier tie-down hardware, additional roof-to-wall connections, and higher-rated products. C1 and above add cyclone-rated fixings, and C3/C4 sites can require significant structural upgrades throughout the roof and wall framing. Pricing a job in northern QLD, the NT coast, or the Pilbara without confirming the wind class first is a significant cost risk (verified 2026-05-08: STA Consulting, Wind Classifications Update).

The practical rule: get the wind class confirmed alongside the soil report, before you finalise the structural specification.

The 2021 edition changed some classifications

AS 4055:2021 revised wind region boundaries relative to the 2012 edition. Key changes that affect site classifications include: Toowoomba relocated from Region A to Region B (higher classification than under the old edition); the B1/B2 split in south-east Queensland was refined; and the “averaged ground level” definition was introduced, which may push sites with significant earthworks outside the 8.5 m height limit. If you have older engineer’s details based on AS 4055:2012, confirm whether the classification is still correct under the 2021 edition (verified 2026-05-08: STA Consulting, Wind Classifications Update).

NCC DTS limits on wind class

Several NCC 2022 Volume Two DTS provisions are limited to buildings at wind class N3 or lower. These include:

Masonry veneer walls (H1D5)
Cavity masonry walls (H1D5)
Single leaf unreinforced masonry (H1D5)
Structural steel framing (H1D6)
Metal sheet roofing (H1D7)
Roof tiles via Housing Provisions (H1D7)
Windows and glazed doors (H1D8)

For sites at N4 or above, or C-class, these elements require specific engineering design rather than relying on the Housing Provisions DTS span tables and specifications (verified 2026-05-08: NCC 2022 Vol 2 Part H1).

AS 4055 vs AS/NZS 1170.2: which to use

AS 4055 is the simpler tool and is usually the first choice for residential housing within its geometric limits. AS/NZS 1170.2 is more detailed and site-specific but more complex to apply. In practice, a building designer or engineer may use AS/NZS 1170.2 when they believe a site will yield a lower (and thus less expensive) classification than the conservative AS 4055 lookup tables. This is common on exposed coastal sites where a full wind assessment can sometimes demonstrate a lower wind class than AS 4055 would automatically assign (verified 2026-05-08: STA Consulting, 4055 vs 1170.2).

As of AS 4055:2021, equivalent wind ratings from AS/NZS 1170.2 are also allowed for the purpose of specifying building products, which removed a previous friction point between the two approaches.

Source link

AS 4055:2021 Amd 1:2024 (paywalled): https://store.standards.org.au/product/as-4055-2021-amd-1-2024

NCC 2022 Volume Two Part H1 Structure (free, ABCB account required): https://ncc.abcb.gov.au/editions/ncc-2022/adopted/volume-two/h-class-1-and-10-buildings/part-h1-structure

ABCB Housing Provisions Standard 2022 Part 2.2 (free download): https://ncc.abcb.gov.au/editions/ncc-2022/adopted/housing-provisions/2-structure/part-22-structural-provisions

References

Standards Australia, AS 4055:2021 Amd 1:2024 Wind loads for housing. https://store.standards.org.au/product/as-4055-2021-amd-1-2024 (verified 2026-05-08).
Australian Building Codes Board, NCC 2022 Volume Two, Part H1 Structure. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/volume-two/h-class-1-and-10-buildings/part-h1-structure (verified 2026-05-08).
Australian Building Codes Board, ABCB Housing Provisions Standard 2022, Part 2.2 Structural provisions. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/housing-provisions/2-structure/part-22-structural-provisions (verified 2026-05-08).
Standards Australia, AS/NZS 1170.2:2021 Amd 1:2023 Structural design actions, Part 2: Wind actions. https://store.standards.org.au/product/as-nzs-1170-2-2021-amd-1-2023 (verified 2026-05-08).
Australian Building Codes Board, NCC 2022 Housing Provisions, WA Part 2.3: Changes to AS/NZS 1170.2:2021 and AS 4055:2021. https://ncc.abcb.gov.au/editions/ncc-2022/adopted/housing-provisions/2-structure/wa-part-23-changes-asnzs-117022021-and-40552021 (verified 2026-05-08).
STA Consulting Engineers, Wind Classification Housing: 4055 vs 1170.2. https://staconsulting.com.au/wind-classification-housing-4055-vs-1170-2/ (verified 2026-05-08).

AS/NZS 1170 Structural design actions, the parent standard that defines the wind regions AS 4055 maps into wind classes
AS 1684 residential timber-framed construction, the framing standard that uses the AS 4055 wind class to size connections and bracing
NCC 2022 Volume Two overview, the NCC volume that references AS 4055 under Part H1 Structure
NCC structure: BCA, PCA, volumes and building classes, the NCC framework within which AS 4055 sits
NCC bushfire BAL, a parallel site-specific assessment that often coincides with elevated wind regions