Effective: 17 July 2026
To determine the wind classification for your building site you must consider four factors: the Wind Region, the Terrain Category, a Shielding Factor, and the Topographic Effect. This guide is an approximate reference for residential structures only, based on Australian Standard AS 4055 (Wind Loads for Housing) — for a detailed analysis refer to AS/NZS 1170.2. This approach is suitable for houses up to two storeys, no wider than 16 m, and no higher than 8.5 m.
Australia uses two classification systems: N1–N6 for non-cyclonic regions and C1–C4 for cyclonic regions. Your wind classification must be specified on the AMIA Custom Products order form. If your engineer or certifier has already provided a classification (e.g. N3 or C2), you can use it directly and skip the four steps below.
Step 1 — Wind Region (A, B, C or D, based on location)
Choose your wind region based on the location of your building:
- Region A: Most of southern Australia — low to moderate wind
- Region B: Northern coastal areas — moderate, partially cyclonic
- Region C: Cyclonic coastal strip — north Queensland, WA, NT coasts
- Region D: Severe cyclonic — north-western WA coast
Your council or local certifier can confirm your wind region. It is also identified in the BOM climate maps and AS 4055.
Step 2 — Terrain Category (surface roughness within 500m)
The terrain category describes the surface roughness of the surrounding area within 500 m of the housing site — from TC1 (very exposed, open water or treeless plains) through to TC4 (dense urban). See the full Terrain Category guide for definitions and examples of each category.
Step 3 — Shielding Class (FS full / PS partial / NS none)
The shielding class measures the effect of surrounding buildings, or similar obstructions, on the wind speed at the site.
Full Shielding (FS)
Applies where there are no open areas within 100 m of the site, and at least two rows of houses or similarly sized permanent obstructions surround the house. In Regions A and B1, permanent closely spaced trees taller than the proposed house and extending the equivalent of three rows of houses may provide full shielding. Road reserves or open areas less than 20 m wide adjacent to the site may be ignored.
Partial Shielding (PS)
Applies in intermediate situations with at least 2.5 houses or sheds per hectare, such as acreage-type suburban development. Applies only within Topographic Classes T0–T3. The second row of houses abutting open parkland, open water or airfields may be classified as partially shielded. In Regions A and B1, closely spaced trees taller than the house extending the equivalent of two rows provide partial shielding.
No Shielding (NS)
Applies where there are no permanent obstructions, or fewer than 2.5 obstructions per hectare — for example the first row of houses abutting open parklands, open water or airfields.
Step 4 — Topographic Effect (T0 flat through T5 cliff top)
The topographic class measures the effect of wind on a house on rising ground:
- T0: Very flat terrain, or slope less than 1 in 20 — minimal effect
- T1–T4: Increasing slope gradient — progressively higher wind pressures at the crest
- T5: Cliff face — slope greater than 1 in 3 — maximum topographic effect at the top
The maximum slope is measured at the steepest part of the hill regardless of where the dwelling is positioned. Wind pressures drop as you move over the crest of the hill.
If you are unsure of your wind classification, your builder, structural engineer, or local council can provide it as part of the building approval process. AMIA’s technical team can also assist — contact us at sales@amia.com.au or call 02 6652 5255.
