AS2047 Window Ratings: What Do N1–N6 and C1–C4 Mean

A label like “N3,” “N5,” or “C2” on a window quotation can be reassuring, but it only applies to the building and the specific window being supplied. In residential housing, N1–N6 and C1–C4 relate to the selection of building elements on the basis of wind action, and the number refers to the wind classification, not the size of the element.

Separate Wind Classification From Product Evidence

Whether or not a particular size or configuration of a window can satisfy a particular wind action requirement for a site depends on a number of factors, including the dimensions of the window, the glazing, the hardware, and how the window is to be installed.

What the N and C Groups Indicate

N1 to N6 relate to non-cyclonic wind actions, and C1 to C4 relate to cyclonic wind actions. The appropriate class is determined by an assessment of the site and the building to be built and is not a matter for the supplier to determine. Site topography, shielding, and the overall configuration and exposure of a building can have a big impact on assessment for similar houses. AS 2047 sets out performance requirements for windows and external glazed doors and requirements for selection and installation. For houses, the site wind classification is determined in accordance with AS 4055; other building types will require a project engineer to refer to the appropriate wind-action standard.

Why N1 Is Not Simply Lower Than C1

The numbers should not be read as one continuous strength ranking. N and C classifications belong to different wind-region contexts, with different considerations for the building. Comparing N1 directly with C1 just because both end in the same number misses the point of the classification system.

Do Not Convert Labels Into A Generic Pressure Table

Pressure tables found online can help explain the terminology, but they cannot approve a window for a project. Figures may represent different test conditions, sizes or performance limits. The applicable edition of the standard, the project wind assessment and evidence for the actual product need to be read together before anyone relies on a pressure value.

This matters especially when a quotation describes a window as suitable for cyclonic conditions. The supporting evidence should identify the tested or assessed dimensions, sash arrangement, glass, mullions and hardware. Changing those details can take the proposed unit outside the scope of the original evidence.

Connect The Classification To The Actual Opening

Consider a villa with a compact bathroom awning, tall glazing above the staircase and a broad terrace slider. They share one project address, but not one construction type. The classification may be common to the building while the product evidence needed for each opening is different.

Size, Glass, and Hardware Still Matter

The opening schedule should record dimensions, operating type, glass build-up, approximate panel weight and hardware arrangement. Fixings, sill details and the surrounding wall also need attention. Large or unusual openings may call for a separate engineering review; a test on a modest casement cannot simply be applied to an oversized sliding door.

For instance, EDUN’s S110 system window offers a starting point for discussing a particular window system. Before using it on an Australian project, the team would still need supporting evidence for the chosen size, glass, hardware and site requirement.

Installation Completes The Chain

Performance is not settled at the factory gate. How the frame is fixed and packed, how flashing is done, and the quality of seals and drainage all affect the installed performance. The installation team must have the most up-to-date shop drawings and system instructions for the assessed configuration.

Write a Better AS2047 Verification Request

A builder assessing bids for external wall installation would find a compact set of documents linked to each opening most useful. It is relatively easy to identify any differences before approval, and then reference back to these documents should there be any changes to the detail at a later date.

Records to Request

Start with the confirmed site classification or engineer’s wind criteria, then attach the opening schedule and current drawings. Supplier evidence should identify the tested configuration, standard edition, size limits, glazing and hardware. Include installation details and exclusions. If a stated rating applies only within a defined range, write that range down rather than assuming it covers larger units.

An EDUN outward-opening window is one possible category to consider, depending on the design. That product direction alone is not evidence of AS 2047 compliance, nor does it establish a project wind rating.

Avoid Four Costly Shortcuts

Many approval problems arise from an initially sensible assumption not being tested. This can be a rating copied from a previous project or a change to the glass specification agreed at the procurement stage. These can become expensive problems after installation.

Checks Before Order Release

Four checks matter. Establish the classification for this site, not a general map. Verify that evidence covers the proposed size. Keep glazing, frame and hardware within the assessed configuration. Finally, establish responsibility for the fixing, sill drainage and wall interface; those details cannot be left between supplier and installer.

The comprehensive range of window systems from EDUN will help narrow down the various systems for a project-specific proposal. However, the ultimate decision regarding compliance will be based upon the nominated window system and associated evidence for the particular site. In long schedules, unusual openings can easily get overlooked. For example, a bathroom awning, a fixed light to a stairwell, and a wide door to a living room all may appear on the same elevation, but in reality they have different glass areas, different operational parts, and different support conditions. Reference to relevant evidence should be included against each opening mark. A single line on the cover sheet saying “compliance met” cannot be audited once construction starts.

Keep that link between product and evidence once work reaches site. Approved drawings should remain with the opening schedule, and substitutions should be recorded as they occur. A revised glass unit, handle or roller arrangement may need further review even if the installed frame looks almost identical to the original proposal.

Store the applicable standard edition and evidence date with the final schedule. Tender documents are often reused, and an old report may refer to a different opening size or a superseded specification. The project record should make it possible to see which configuration was accepted when production was released.

Project Decision

The sequence is practical: confirm the site wind requirement, specify each opening, then establish which evidence applies to the unit being ordered and installed. The EDUN project inquiry route can start a discussion about suitable options, but approval remains a project-specific decision. For unresolved project openings, discuss the specifications with EDUN.

FAQ

Q1: What do N1 to N6 window ratings mean?

A1: N1–N6 are non-cyclonic wind classifications used in Australian housing design. The appropriate class is established for the building site; individual windows still need evidence covering their size and configuration.

Q2: What do C1 to C4 windows mean?

A2: C1–C4 apply to cyclonic wind regions. They are not directly interchangeable with N classifications, and a suitable window proposal must address the site’s requirements as well as the actual glazing, hardware and installation.

Q3: Does AS2047 certification cover every size of a window series?

A3: No. Tests and other compliance evidence may have defined size and configuration limits. Builders should compare the proposed drawings with that scope, including any exclusions or changes to glass and hardware, before approval.