Every new house in Australia is designed for a wind classification, such as N2 or C2. It decides how the roof is fixed down, how the frame is braced and tied, and what wind rating your windows and doors need. Get it wrong on the low side and the house is under-built. Get it wrong on the high side and you pay for strength you don't need.
For most houses, the classification is worked out using Australian Standard AS 4055, Wind loads for housing. It's based on four factors: wind region, terrain category, topography and shielding. Your engineer or building designer assesses it from maps, plans and the site's surroundings. Nobody stands on your block with a wind meter.
C7 - Frame Stage Inspection Checklist
$119.00 AUD
Last updated 12 Oct 2026 · Revision 2 · Free updates for life
Checklist Type: Major (Frame Stage)
Form Factor: Fillable, print-ready PDF (A4, 20 pages)
When to use: Frame stage: after the frame and trusses are up, before linings go in
A 136-point frame stage checklist. Check walls, trusses, bracing, tie-downs and plan features against your drawings before the linings go in, while changes are still simple.
The classes
AS 4055 gives each site a class:
- N1 to N6 in non-cyclonic regions. N1 is the most sheltered, N6 the most exposed.
- C1 to C4 in cyclonic regions.
Typical suburban homes in South East Queensland usually land around N2 or N3, but plenty of sites end up higher.
AS 4055 covers houses within certain size limits, such as height and roof pitch. Larger or unusual homes are designed by an engineer under the more detailed wind loading standard, AS/NZS 1170.2.
1. Wind region
Australia is mapped into wind regions based on the strongest winds expected:
- Region A: most of inland Australia, including inland Queensland.
- Region B: a coastal band including much of South East Queensland.
- Region C: the cyclonic coast, in Queensland roughly from around Bundaberg north.
- Region D: the most severe cyclonic area, on the north-west coast of Western Australia.
Cyclonic classes (C1 to C4) only apply in Regions C and D. A hilltop in Brisbane can get a high N class, but it won't be classed as cyclonic just because it's on a hill.
Distance from the coast mainly matters because it sets where these region boundaries fall. Coastal sites also face salt corrosion, which is assessed separately under AS 4312. That affects what fixings, roof sheeting and steel you can use, but it's not part of the wind classification.
2. Terrain category
Terrain category describes how rough the ground is around your site, out to a few hundred metres. Rough ground with lots of buildings slows the wind down.
- TC1: very exposed, open terrain with almost no obstructions, such as open water or flat treeless plains.
- TC2: open terrain with a few scattered obstructions, such as farmland or grassland.
- TC2.5: a few trees or isolated houses, such as acreage blocks or developing outer suburbs with fewer than 10 house-sized obstructions per hectare.
- TC3: numerous closely spaced obstructions, generally 3 to 10 metres high, at least 10 house-sized obstructions per hectare. Typical suburban housing.
Note that a new estate where most blocks are still empty may be assessed differently from the established suburb it will become. Also, sites next to wide rivers, lakes or open water can see higher wind speeds coming across the water.
3. Topography
Wind speeds up as it flows over hills, ridges and escarpments. AS 4055 assigns topographic classes from T0 (flat ground or valleys) up to T5 (the most exposed hilltops and ridges). The class depends on the slope of the hill and where your site sits on it.
A house near the crest of a steep hill or ridge can jump one or two wind classes compared with the same house at the bottom. In South East Queensland, hilltop sites can rise to N3 or N4.
Turning the house around doesn't change the classification. Orientation doesn't feature in AS 4055.
4. Shielding
Other houses and permanent obstructions around your site block some of the wind. AS 4055 recognises three levels:
- Full shielding: at least two rows of houses, or similar permanent obstructions, all around your site. In Regions A and B, heavily wooded areas within 100 metres can also count.
- Partial shielding: at least 2.5 houses or sheds per hectare, such as acreage development or wooded parkland.
- No shielding: fewer obstructions than that, or open areas such as parks, water or wide roads beside the site.
Be careful relying on shielding you don't control. Trees get cleared and paddocks get developed (or not). A good designer will be conservative where the surroundings could change.
How the four factors combine
The designer takes your wind region, terrain category, topographic class and shielding class and reads the result off tables in AS 4055. For example, a flat suburban block in South East Queensland, fully shielded by houses, will often come out at N2. The same house on an exposed ridge with open land around it could be N3 or N4.
What to check on your plans
- Find the wind classification on your engineering drawings or specification, for example "N3".
- Ask how it was assessed and by whom: the four factors and the values used.
- Check that the same classification is used for your windows and doors (their wind rating), roof sheeting or tiles and their fixings, trusses and tie-downs, bracing, and any garage doors.
- If you think the site is more exposed than assumed, such as a hilltop, waterfront or the edge of an estate, ask the engineer to review it before you sign.
My C7 Frame checklist includes checks on bracing and tie-downs, so you can confirm the frame has been built to match. You'll find it at constructor.net.au/checklists.
Further reading
A Detailed Guide to Understanding Window PerformanceDo you fully understand the performance aspect of windows in your property? Understanding the efficiency & protection provided by your windows is important to ensure optimum living conditions. In this post we discuss everything from thermal performance to solar protection, ventilation & sound.
Double Glazed Windows: Benefits for Your New HomeDiscover the benefits of double glazed windows for your new home. Learn about energy efficiency, sound insulation, security, and more.
Ventilation and Airtightness: Improve Comfort and EfficiencyAchieving a comfortable, healthy home requires balancing ventilation and air tightness. In this article we explore practical methods to improve both. Learn how to prevent air leaks, reduce condensation, and improve your home’s efficiency.
