Wind Site Classification Services

Wind classification defines the design wind loads acting on buildings and structures based on their location, terrain, and exposure.
It ensures that dwellings and structures are designed to withstand local wind speeds and pressures in accordance with Australian Standard AS 4055:2021 – Wind Loads for Housing and AS/NZS 1170.2:2021 – Structural Design Actions (Wind Actions).

Key References

AS 4055:2021 – Wind loads for housing (used for houses ≤10 m high).
AS/NZS 1170.2:2021 – Structural design actions – Wind actions (used for larger or non-standard structures).
National Construction Code (NCC) Volume 2 – requires compliance with the above standards.

Wind Classification Process (AS 4055 Method)

Wind class is determined through a step-by-step assessment using six main parameters:

Region (A, B, C, or D) – based on cyclonic or non-cyclonic zones (refer to AS 4055 wind region map).
- Region A: Non-cyclonic (most of southern Australia).
- Region B/C/D: Increasing cyclone risk (northern and coastal regions).
Terrain Category (TC1 – TC3) – describes surface roughness and obstructions.
- TC1: Open water, flat plains.
- TC2: Few obstructions (open country).
- TC2.5: Suburban areas.
- TC3: Dense urban or wooded areas.
Shielding (Full, Partial, None) – measures how protected the building is by nearby structures or trees.
Topography (Slope/Exposure Factor) – increases wind speed on elevated or steep terrain.
Building Height – houses up to 10 m; taller structures require AS/NZS 1170.2.
Design Site Wind Speed (Vdes) – derived by combining region, terrain, shielding, and topographic multipliers.

Determining the Class – Example Summary

For 80 Cobb St, Penshurst VIC, the site lies in Wind Region A (non-cyclonic), on moderately undulating terrain (TC 2.5) with partial shielding from nearby dwellings and trees, and gentle local topography (<5° slope).
Based on AS 4055:2021, the appropriate wind classification is N2 (design wind speed ≈ 40 m/s). This class governs the structural design of roof framing, tie-downs, and cladding fixings.

Typical Report Deliverables

· Regional wind region map (from AS 4055 Figure 2.1).

· Terrain/Shielding/Topography description table.

· Final statement:
“The site has been classified as Wind Class N2 in accordance with AS 4055:2021. All structural and building elements must comply with the requirements for Class N2 construction as per NCC Volume 2.”

When to Use AS/NZS 1170.2 Instead

· Building height > 10 m.

· Irregular or multi-storey geometry.

· Complex topography (ridge, escarpment, or hill).

· Structures other than housing (sheds, tanks, bridges, etc.).

Determining the Class – Example Summary

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