Australian Wind Ratings: What You Need to Know
Wind ratings help determine the structural requirements a building needs to withstand the wind conditions at its location.
In Australia, wind design considers factors including the wind region, terrain, topography, shielding and the type and importance of the structure. These factors can influence structural design, engineering requirements and ultimately project cost.
Two key Australian Standards used in assessing wind actions are AS 4055:2021, Wind loads for housing, and AS/NZS 1170.2:2021, Structural design actions – Wind actions. The standard and assessment method that applies will depend on the building and project requirements.
For larger structural steel buildings, wind requirements need to be considered as part of the engineering process for the individual site rather than relying on a general wind rating alone.
What standards apply to your project?
The two key standards used for wind assessment are:
- AS 4055:2021, Wind loads for housing applies to housing within the geometric limitations defined by the standard.
- AS/NZS 1170.2:2021, Structural design actions – Wind actions provides procedures for determining wind speeds and wind actions for structural design and is particularly relevant to buildings and structures outside the scope of AS 4055.
AS/NZS 1170.2:2021 is referenced by the National Construction Code and incorporates updated knowledge about Australian and New Zealand wind conditions.
For TechSpan projects, wind requirements are assessed as part of the engineering process based on the individual building, location and site conditions.
Factors that can influence wind assessment include:
- Wind region: Different parts of Australia are exposed to different regional wind conditions.
- Terrain: The surrounding landscape, vegetation and built environment can influence wind exposure.
- Topography: Hills, slopes and other landforms can affect the wind conditions experienced at a site.
- Shielding: For assessments where shielding is applicable, surrounding buildings and other obstructions may influence wind exposure.
- Building characteristics: Building height, dimensions, geometry, openings and intended use can all influence structural wind design.
This is why two buildings of a similar size can have different structural requirements depending on where and how they are built.
What Do N1, N2, N3, N4, N5 and N6 Wind Ratings Mean?
N1 to N6 are non-cyclonic wind classifications used under AS 4055 for housing within the scope of that standard.
Generally, the classification increases as the wind conditions become more demanding, with N1 representing lower design wind conditions and N6 representing higher non-cyclonic conditions.
You may also see cyclonic classifications C1 to C4 used for housing in cyclonic regions.
These classifications are useful when specifying housing and relevant building products, but they should not be treated as a universal wind rating system for every type of building.
For larger agricultural, industrial, aviation and community buildings, structural engineers may instead determine the wind actions applicable to the individual structure using AS/NZS 1170.2:2021.
What Changed in the 2021 Wind Standards?
The 2021 editions introduced a number of changes to reflect updated research and understanding of wind events.
For AS/NZS 1170.2:2021, changes included revisions to Australian wind-region boundaries and wind-direction multipliers, along with the introduction of a climate change multiplier that allows future adjustments to wind speeds, particularly in regions affected by tropical cyclones.
The updated standard also incorporates newer wind data and considers emerging types of wind-sensitive structures.
AS 4055:2021 was also updated, helping maintain alignment between residential wind classification requirements and the broader structural wind-action framework.
For anyone planning a new building, the important point is that wind requirements should be assessed using the standards and requirements applicable to the project today, rather than relying on a classification or assessment from an older project.
How Do Wind Requirements Affect Structural Design?
Wind can place significant pressure and suction forces on a building, affecting the roof, walls, connections, structural frame and foundations.
As wind design requirements increase, structural requirements may also change. Depending on the project, this can influence:
- Structural member sizes and configuration
- Bracing requirements
- Connections and fixings
- Cladding and roofing requirements
- Door and opening design
- Footings and foundations
- Overall structural configuration
For larger structural steel buildings, this is one reason wind assessment should be considered early rather than after the building has already been configured.
Can Wind Requirements Affect Project Cost?
Yes. Wind requirements can influence the amount of structural steel, connection design, bracing, cladding, foundations and other elements required for a building.
However, a higher wind classification does not automatically translate into a particular percentage increase in project cost.
The impact depends on the building itself, its location, site conditions, structural configuration and applicable engineering requirements.
Understanding these requirements early provides a clearer basis for structural design and can help reduce the risk of unexpected design changes later in the project.
Why Does the Building Location Matter?
Wind conditions can vary significantly between locations, which is why the project site is considered early in the TechSpan design process.
Factors such as the applicable wind region, surrounding terrain, topography and building characteristics can all affect the wind actions that need to be considered.
Local planning and building requirements may also need to be considered depending on the project and location.
A building therefore needs to be assessed for its specific site and intended use, rather than assuming the requirements from another building or nearby project will automatically apply.
How TechSpan Approaches Wind Design
At TechSpan, site and structural requirements are considered from the early stages of your project.
Through our Concept. Configure. Construct. approach, we work through the requirements that can influence your building before progressing through engineering and manufacture.
Wind design forms part of this process. Our team considers the project location, building configuration, intended use and relevant engineering requirements to develop a structural solution suited to the individual project.
This helps provide greater clarity around structural requirements earlier and ensures the building progresses through design and engineering with the relevant site conditions considered.
Planning a structural steel building? Talk with our team about your site, operational requirements and project.
Frequently Asked Questions About Australian Wind Ratings
What is an N2 wind rating?
N2 is one of the non-cyclonic wind classifications used by AS 4055 for housing within the scope of the standard. The appropriate classification depends on factors including the site’s wind region, terrain, topography and shielding.
What is an N3 wind rating?
N3 represents a higher non-cyclonic wind classification than N2 under AS 4055. It can result in different requirements for building components and structural design.
What is an N4 wind rating?
N4 is another non-cyclonic classification under AS 4055 and represents more demanding wind conditions than N3. The classification should be determined through the appropriate assessment rather than assumed based on location alone.
What is the difference between AS 4055 and AS/NZS 1170.2?
AS 4055:2021 relates specifically to wind loads for housing within its defined scope. AS/NZS 1170.2:2021 provides procedures for determining wind speeds and wind actions for structural design more broadly.
Does every building have an N rating?
No. N classifications are associated with non-cyclonic housing assessed under AS 4055. Larger or more complex buildings may have their wind actions determined under AS/NZS 1170.2 rather than being described simply by an N rating.
Can two buildings in the same town have different wind requirements?
Yes. Site exposure, terrain, topography, shielding, building geometry and other factors can affect wind assessment. Buildings in the same general location should not automatically be assumed to have identical structural wind requirements.