WERS Window Ratings Explained: What Uw and SHGCw Mean for NatHERS and NCC Energy Compliance

WERS is the Window Energy Rating Scheme, managed by the Australian Glass and Window Association, and it reports window performance as whole-of-window numbers. Uw is the whole-window U-value, defined by the scheme as accounting for the performance of the frame, edge-of-glass and centre-of-glass components; SHGCw is the whole-window solar heat gain coefficient, accounting for frame and glass together. The NatHERS pathway and the deemed-to-satisfy glazing clauses of the National Construction Code are both written in whole-of-window terms, so a centre-of-glass U-value on a factory datasheet is not a number an assessor or certifier can use.

This page is for developers, general contractors, builders, commercial project owners, interior design and construction companies and FF&E solution providers running Australian projects with a China-supplied window and door package. It sets out what the two ratings mean, where each is used in an approval, and what a factory must produce as evidence.

What Do Uw and SHGCw Actually Measure?

The scheme describes its purpose plainly: it rates whole of window product energy efficiency performance, and enables windows to be rated and labelled for their annual energy impact on a whole house, in any climate of Australia. The numbers that travel into compliance work are defined in its own key to its rating tables:

• Uw — the whole-window U-value that accounts for the performance of the frame, edge-of-glass and centre-of-glass components, calculated for standard sizes set by the scheme rather than for every size on a schedule.
• SHGCw — the whole-window solar heat gain coefficient that accounts for the performance of the frame and glass components. With SHGC there is no distinction between centre-of-glass and edge-of-glass, and it too uses the scheme’s standard sizes.
• Tvis — whole-window visible transmittance, the product of glazing Tvis and the glazing to frame area ratio. Air infiltration is reported separately, at a positive inward pressure difference of 75 Pa.

The scheme also publishes heating and cooling star ratings on a ten-star scale, ranked against seventeen generic window types with a base case of Generic Window 1, described as 3 mm clear glass in a standard aluminium frame. It notes that only the star ratings are building-specific, while the rest of its data sits at the level of the manufactured product. Uw and SHGCw are therefore properties a design team can carry into a calculation; a star count is not a compliance input.

How Is a WERS Rating Produced, and Who Signs Off on It?

To participate, window makers must obtain energy ratings for their products from a rating organisation accredited by the Australian Fenestration Rating Council. The Council describes its role as providing independent verification of product performance, and it was formed with the support of the Australian Building Codes Board and the Department of Climate Change and Energy Efficiency and the cooperation of the National Fenestration Rating Council in the United States.

Most windows can be rated entirely by a two-stage process of computer simulation, which the scheme calls the preferred and most economical option; the modelling software is the same as that used by the National Fenestration Rating Council, and the scheme names WINDOW 7, Optics 6 and THERM 7. Unusual or complex products may need physical testing to establish their basic thermal behaviour, after which a second simulation stage generates the final rating. The inputs come from the manufacturer: drawings, CAD files and material specifications.

Two consequences follow. A rating is tied to one system — frame profile, thermal break, glass make-up, spacer and seals — so changing the glass or the spacer means it no longer describes the product being shipped. And a manufacturer able to build a window cannot automatically produce a rating for it; that is a separate exercise with a separate accredited body behind it. Ask which systems are rated, and in which of the scheme’s categories.

How Does NatHERS Use the Window Numbers?

NatHERS is the Australian home energy rating scheme, and its Technical Note for new homes sets out what an assessor may do with window data; the current version is dated 23 October 2024, for software running the Chenath engine version 3.22 and 3.23. Clause 8.3 states that when modelling windows or glazed doors, assessors must use either the Australian Fenestration Rating Council custom window codes corresponding to the windows on the design documentation, found in the NatHERS and WERSlink custom window libraries, or the WERSlink default library where available, or the NatHERS default library.

The substitution rules are where a China-supplied package is most often caught out. Where the software uses the NatHERS custom window library and the specified window is not in it, clause 8.5 allows an assessor to choose a default window, or a custom window meeting three conditions: identical opening type, for example fixed, awning, casement or sliding; a total window system U-value equal to or greater than the window specified, the example given being that a specified Uw of 1.5 could be modelled as 2.0; and a total window system solar heat gain coefficient within plus or minus 5 per cent of the window specified. Substitutions must be itemised in the assessment notes.

Then comes the sentence that decides a great deal of procurement: substituted values must be based on the Australian Fenestration Rating Council protocol rather than, for instance, the European ratings. A factory quoting a European centre-of-glass U-value, or a whole-window figure from a different protocol, has not supplied a number the assessment can carry. The same Technical Note treats fully or partially glazed hinged and sliding doors as windows, with only the glazed portion modelled as such, and allows a door with less than 25 per cent glazing to be modelled as solid.

The outcome of an unrated product is not rejection but substitution downward: the assessor falls back to a default or weaker window, the modelled Uw moves in the conservative direction, and the shortfall must be bought back elsewhere in the fabric. Which build-up actually moves a whole-window number is covered in our comparison of double glazing, low-E and triple glazing for commercial windows.

Where Do Uw and SHGCw Sit Inside the NCC?

The code does not use the labels Uw and SHGCw; it uses close cousins. The NCC 2025 glossary defines Total System U-Value as the thermal transmittance of the composite element allowing for the effect of any airspaces, thermal bridging and associated surface resistances, expressed in W per square metre per kelvin. It defines Total System Solar Heat Gain Coefficient, for Volume One, as the fraction of incident irradiance on a wall-glazing construction or a roof light that adds heat to a building’s space, and for Volume Two as the fraction of incident irradiance on glazing or a roof light that adds heat to a building’s space.

On the commercial side, NCC 2025 Volume One clause J4D6 governs walls and glazing. Clause J4D6(2) states that the Total System U-Value of glazing, including display glazing, must not be greater than U5.8. Clause J4D6(1) caps the Total System U-Value of wall-glazing construction at values in Table J4D6a, which vary by climate zone and building class: for a Class 5, 6, 7, 8 or 9b building, that table runs from 1.6 in climate zone 1 to 2.0 in climate zone 8, with a separate and generally tighter column for Class 3 or 9c buildings and Class 9a ward areas. Solar performance is controlled through solar admittance under J4D6(5) using Tables J4D6c and J4D6d. Both are calculated under NCC Specification 37, which directs the opaque wall component’s R-Value to AS/NZS 4859.2. For roof lights, J4D5 caps the Total System U-Value at U3.9 and limits total area to 5 per cent of the floor area served.

On the housing side, NCC 2025 Volume Two clause H6D2 offers two deemed-to-satisfy routes. One is Specification 42 using house energy rating software, where clause S42C2 requires 7 stars or more, reduced to 6.5 or 6 stars in climate zones 1 and 2 where a qualifying covered outdoor living area, and in the 6-star case a permanently installed ceiling fan, is provided. The other is the elemental route in Parts 13.2 to 13.5 of the ABCB Housing Provisions, and Part 13.3 is where the window numbers live: clause 13.3.2 governs winter performance through a formula in which U is the Total System U-Value of each glazing element and SHGC is the Total System SHGC for each element, not exceeding 0.7, with allowances from Table 13.3.2a; clause 13.3.3 governs summer performance against a constant from Table 13.3.3a, set by climate zone, floor type and ventilation opening area.

This is the point that cannot be shortcut: there is no single national Uw or SHGCw threshold to quote to a factory. The required values come from the climate zone tables in the current NCC volume or Housing Provisions, adjusted by orientation, projection to height ratio, room type and building class, so they must come from the project’s own assessment or certifier. One NCC 2025 note is easy to miss on apartment work: Part J1 states that for Class 2 buildings, Section J is replaced with Section J of NCC 2022 Amendment 2, with a separate Tasmanian note.

Editions also differ by jurisdiction. The Australian Building Codes Board records NCC 2025 as published on 1 May 2026 and adopted that day by the Australian Capital Territory, Victoria and Western Australia, with New South Wales, Queensland and Tasmania on 1 May 2027 and the Northern Territory not having adopted it. Our page on NCC 2025 adoption dates by state for commercial glazing and waterproofing holds the full table, and the wider view of assembling material evidence sits in our overview of NCC and BCA compliance for building materials from China.

What Does AS 2047 Cover, and What Does It Not Cover?

AS 2047 is the standard most often raised on a China-supplied window package, and it is frequently misread as an energy standard. Standards Australia lists AS 2047-2014, Windows and external glazed doors in buildings, published on 23 September 2014, with the status Pending Revision as at 20 September 2026. Its catalogue scope is requirements for materials, construction, installation and glazing for external windows, sliding and swinging glazed doors including French and bi-fold doors, adjustable louvres, shopfronts and window walls with one-piece framing elements.

Where the code calls it up is the clearer test. In NCC 2025 Volume Two, clause H1D8 satisfies the structural Performance Requirement H1P1 for glazing and windows designed, constructed and installed in accordance with AS 2047 for glazed assemblies in an external wall, within stated wind class limits, with AS 1288 covering glazed assemblies outside that list. Clause H2D7 satisfies the weatherproofing Performance Requirement H2P2 for glazing by reference back to H1D8(1), and Verification Method H2V1 requires that a verified external wall include only windows complying with AS 2047. The energy provisions, Part H6 and Housing Provisions Part 13.3, do not route through AS 2047 at all.

So a factory holding an AS 2047 test report or certificate has evidence about structural adequacy, water penetration resistance and the related construction requirements, not evidence of an energy rating. Those are two trails, produced by different bodies, and a package needs both. Wind classification is a third; our note on cyclone-rated windows and Region C wind classes in northern Australia covers that boundary.

What Belongs on the Window Schedule Before It Goes to a Factory?

A schedule a Chinese window plant can price against Australian energy requirements needs more than sizes and colours:

• The required Uw and SHGCw for each window type, with the source stated: the project’s energy assessment or the applicable code table.
• The opening type for each item, because substitution rules turn on it and it changes the frame to glass ratio that drives a whole-window number.
• The glass make-up in full: pane thicknesses, cavity width, gas fill, coating type and surface position, spacer type.
• Frame material and whether a thermal break is required, since a whole-window value cannot be met by glass alone.
• Wind classification or design pressures and water penetration resistance, recorded separately from the energy values.
• Evidence to request: the rating certificate and rating code for each system, the accredited laboratory or conformity assessment body behind any test report, the scope of that accreditation, and the validity date of each document.

FBM Sourcing works on the procurement side of that list as the client’s sourcing partner in China. We take the Uw and SHGCw targets, the wind and water requirements and the schedule from the project team, turn them into a specification a factory can quote against, and ask for the rating evidence and test reports matching the systems actually offered rather than a neighbouring one. Once bulk production is finished, our own team inspects at the factory before shipment and checks the labels and document pack against what was specified, with photo and video records. We do not issue ratings, certify products or install.

Sometimes, on a large project, the windows and doors alone fill full containers; sometimes the windows and doors share containers with the other product categories of the same project; and sometimes, in one batch, we combine a dozen or more product categories from several projects of the same client into a few containers — always full containers, and for us this is routine, well-practised work.

Frequently Asked Questions

Is a centre-of-glass U-value from a factory datasheet enough for an Australian project?

No. The scheme defines Uw as accounting for frame, edge-of-glass and centre-of-glass performance together, and the NCC works in Total System U-Value, which allows for airspaces, thermal bridging and surface resistances; a centre-of-glass figure describes only the glass.

Can a European window rating be used in a NatHERS assessment?

The NatHERS Technical Note dated 23 October 2024 states that substituted values must be based on the Australian Fenestration Rating Council protocol rather than, for instance, the European ratings, so a European figure cannot be entered in place of an AFRC-based one.

Does an AS 2047 certificate prove energy performance?

No. In NCC 2025 Volume Two, AS 2047 is called up by clause H1D8 for structure and through H2D7 and H2V1 for weatherproofing, while the energy provisions in Part H6 and Housing Provisions Part 13.3 work through Total System U-Value and Total System SHGC.

What Uw and SHGCw values should be specified for a given project?

They are not fixed nationally: for Class 3 to 9 work the caps come from NCC 2025 Volume One clause J4D6 and Table J4D6a by climate zone and building class, with glazing capped at U5.8, and for houses from the climate zone tables in Part 13.3 of the ABCB Housing Provisions or the rating produced under Specification 42.

What should be requested from a factory that says its windows are energy rated?

Ask which systems are rated and in which category, for the rating certificate and rating code tied to that system, for confirmation that the glass make-up, spacer and thermal break in the offer match the rated configuration, and for the accreditation scope of any supporting laboratory.

About FBM Sourcing

FBM Sourcing manages the entire China procurement package for overseas construction projects. Since 2014 we have worked with developers, general contractors, builders, commercial project owners, interior design and construction companies and FF&E solution providers across more than 20 countries and over 1,000 containers, as their sourcing partner in China — from the schedule or BOQ through factory selection, sampling, inspection by our own team before shipment, consolidation and shipping. All quotations, invoices and shipping documents are issued by FBM Sourcing, and sea freight is quoted to you before shipment. If you have a windows and glazing package to price, start at China building materials and FF&E procurement.