Wind rating and corrosion zone lookup

How wind regions work

Australia is divided into wind regions A, B1, B2, C and D. Regions A and B1 cover most of the country and are non-cyclonic. B2 is a transitional band, and C and D are the cyclonic coastal strips of the north, where tropical cyclones bring the strongest design winds. Because cyclones weaken quickly once they cross the coast, the regions are defined as bands measured inland from a smoothed coastline — roughly 50, 100, 150 and 200 km — which is why distance to the coast matters as much as latitude. This tool takes the region from Geoscience Australia's mapped interpretation and shows its basis under the map.

How the site wind class is worked out

AS 4055 combines four inputs: the wind region; the terrain category, which describes how rough the ground is within about 500 m; shielding from neighbouring buildings and trees; and topography, which captures how much a hill, ridge or escarpment speeds the wind up. A suburban house on flat ground surrounded by other houses sits at the low end of its region; an exposed house on a hilltop facing open ground can be several classes higher.

What the W numbers mean

Why corrosivity matters for anything bolted to a roof

Salt carried inland from breaking surf settles on brackets, masts and screws and eats through galvanising. Close to the surf, ordinary galvanised hardware can fail within a few years, so stainless or duplex-coated fittings are specified; further inland, standard hot-dip galvanised brackets with Class 3 fasteners last for decades. Where a bracket or screw touches metal roofing, the roofing manufacturer's dissimilar-metal rules also apply. The corrosion category shown here is an approximate estimate from distance and shoreline type.

Frequently asked questions