Window Wind Ratings Explained — N1 to N6 for Melbourne Homes

What does an N rating actually mean?

An N rating is the wind classification for your site. It runs N1 to N6, and it tells us how much wind pressure your windows need to withstand — N1 being a sheltered suburban site and N6 a severely exposed one.

Each class sets two pressures your windows must meet. Serviceability is the everyday strong-wind pressure the window has to handle without damage or excessive deflection. Ultimate is the peak design gust it has to survive structurally. As an example, N3 calls for 600 Pa serviceability and 1400 Pa ultimate in a general position, while N4 calls for 800 Pa and 2000 Pa. The rating comes from your site's wind assessment, and we then select systems tested to meet or exceed it.

What N rating do I need for my Melbourne house?

We can't tell you — and you should be wary of any window company that will. The wind classification is specific to your site: it depends on terrain, shielding from surrounding buildings, topography and the height of the window. Under AS 4055 it must be assessed and supplied by the project's site engineer, architect, designer or builder, not by the window manufacturer.

Assigning an N class to a suburb or a house style would be guesswork, and unsafe guesswork at that. Send us the wind classification from your plans or your engineer and we'll match tested systems to it.

Do I need a C rating in Melbourne?

No. C ratings are cyclonic classifications and they apply only in the cyclonic regions of northern Australia. Victoria is non-cyclonic, so housing here uses the N classifications — N1 through N6. If you've been handed a specification quoting a C rating for a Melbourne project, it's worth querying, because it suggests the classification was done against the wrong region.

Why do corner windows need a higher wind rating?

Because wind doesn't press evenly on a building. As air flows around a corner it accelerates and separates, which creates much higher local suction at the edges and corners of a wall than across the middle of it. The standards account for this by setting higher pressures for corner windows at every classification. At N4, for example, a general window is tested to 800 Pa serviceability and 2000 Pa ultimate, while a corner window at the same classification needs 1200 Pa and 3000 Pa.

This is why we always ask which items on a schedule sit in corner zones. A window that's perfectly compliant in the middle of a wall may not be in a corner, and the compliance certificate requires those items to be listed by number.

What does "exposed" versus "non-exposed" mean for a window?

It describes how sheltered the window is from driving rain and wind — whether there's an eave, a verandah, a recess or an adjoining structure protecting it, or whether it's out in the open.

It matters mainly for water resistance. At the same wind classification, an exposed window is required to resist a higher water penetration pressure than a sheltered one — at N4, 300 Pa exposed against 200 Pa non-exposed, and at N5, 450 Pa against 300 Pa. Test reports also record the wind rating separately for exposed and non-exposed positions, and a system can achieve a lower class exposed than it does sheltered. It's one of the first things we check when a window is going into an unprotected wall.

What is water penetration resistance and what figure do I need?

It's the pressure at which wind-driven rain is forced through a window in testing — a higher figure means the window keeps water out under harder driving rain. It's quoted in Pascals alongside the wind rating.

For housing, the required figure is set by your wind classification and whether the window is exposed or sheltered: N3 calls for 150 Pa non-exposed and 200 Pa exposed, N4 for 200 and 300 Pa, N5 for 300 and 450 Pa. Several of our systems sit well above the minimum — our Apollo and Titan awnings both tested at 1000 Pa. For exposed Melbourne elevations with no eave, we treat this figure as at least as important as the wind class.

Does double glazing change the wind rating?

Not in the way most people expect — the wind rating comes from the frame, the sash and the hardware rather than the glass thickness, and each configuration is tested as a whole assembly in its own right.

Our Comet sliding window is a good illustration: single glazed it tested to N3, and double glazed it also tested to N3 in the non-exposed position. The double-glazed version, though, recorded no rating in the exposed position, where the single-glazed test reported a straightforward N3. So changing the glazing does mean a different test result, and we always check the rating for the exact configuration being supplied rather than assuming it carries across.

How do I know the windows you supply actually meet my wind rating?

Every system we supply is tested to AS 2047, which covers structural deflection, operating force, air infiltration, water penetration resistance and ultimate strength. The test gives the system a wind classification with its serviceability, ultimate and water pressures recorded separately for general and corner positions.

We match those tested figures against the classification on your plans, and the windows must meet or exceed the deemed pressures for your rating. That gets documented on an AGWA window compliance certificate, which lists your wind rating, identifies any corner windows by item number, and carries two signatures — ours as manufacturer and your builder's as installer. We'd rather show you the tested numbers than make a general claim.