Guide · Energy compliance
BASIX and 7-star NatHERS: what builders need from windows
Since 1 October 2023, most new NSW homes need BASIX thermal performance equivalent to 7 NatHERS stars. Windows are often where a design passes or fails. This guide covers how window data goes into the assessment, how to choose glass per orientation from our WERS ratings, and what to send us so the certificate and the order match.
How BASIX treats windows
BASIX is the NSW Government's sustainability scheme for homes. It applies to new dwellings, and to alterations and additions valued at $50,000 or more or with a pool or spa over 40,000 litres (NSW Planning Portal). The certificate covers three things: water, energy and thermal performance. Windows sit mostly in thermal performance.
There is no BASIX approval for a window. The assessment models the dwelling, and each window goes in as a size, an orientation, a shading condition, a whole-window U-value (Uw) and a solar heat gain coefficient (SHGC). The BASIX commitments then become conditions of the development consent, and the certifier checks that what's installed matches.
Two ways to assess thermal performance
- DIY method. Built into the BASIX tool for simpler houses: the NSW Planning Portal limits it to a conditioned floor area of 300 m² or less and total glazing of 10–40% of that area. Windows are checked against an acceptable range of U-value and SHGC, using a library of 88 default window selections.
- Simulation method. An accredited assessor models the home in NatHERS software. The heating and cooling loads must come in under the BASIX caps for the climate zone. Homes outside the DIY limits have to use it.
In the simulation method, each window type is entered either as a default window (a generic product with statistically derived values) or as a custom window, which is a real, WERS-rated product. Custom windows are where our rating IDs come in.
| Houses: thermal performance | 7 NatHERS starsUp from an average of 5.5–6 stars. NSW Department of Planning |
|---|---|
| Apartments: thermal performance | Average 7 stars across the building, no unit under 6NSW Planning Portal, BASIX standards |
| Energy standard | Emissions cut a further 7–11%Depends on location and development type |
| Not increased | Homes in climate zones 9, 10 and 11; apartment buildings up to 5 storeys |
| New requirement | Materials index for embodied emissions |
| Relation to the NCC | BASIX applies in NSW instead of the NCC 2022 whole-of-home ratingNSW says BASIX is aligned with and complements NCC 2022; NSW Part H6 sits alongside BASIX |
Outside NSW, NCC 2022 requires 7 stars plus a whole-of-home score of 60 out of 100 for new houses (ABCB). The same WERS window data serves both.
The two numbers
Uw and SHGC, and why both matter at 7 stars
Uw: heat through the window
The whole-window U-value in W/(m²K): frame, glass and edge together. Lower is better in every orientation, and it matters most where there's little sun, such as south-facing glass and cold-climate jobs. Don't give the assessor a centre-of-glass Ug or a frame Uf instead; NatHERS needs Uw.
SHGC: sun through the window
The share of solar heat that gets through, from 0 to 1. A low SHGC cuts summer heat on exposed east and west glass. A higher SHGC lets winter sun warm living areas behind north glass that's shaded in summer. One SHGC for the whole house is rarely the best answer.
Air infiltration
WERS also lists air infiltration in L/s·m². Our CT 70 tilt and turn and fixed windows rate 0.03, hinged doors 0.04, casement and awning 0.22, and SoftSlide sliders 0.64. Where airtightness is a priority, put hinged units where you can.
Using our WERS data
Choosing glass per orientation
Our 340 WERS ratings use Australian Glass Group (AGG) units. The table holds the frame and the glass make-up (6/16/6, double glazed) constant and changes only the coating, so you can see what each step does. The figures are straight from WERS.
| AGG glass | CT 70 fixed: rating ID | Uw | SHGC | Tvw | CT 70 tilt and turn: rating ID | Uw | SHGC |
|---|---|---|---|---|---|---|---|
| CLASSIC Clr (no low-E) | SCH-001-302 | 2.4 | 0.60 | 0.65 | SCH-002-303 | 2.1 | 0.38 |
| PLUS Clr | SCH-001-310 | 1.5 | 0.47 | 0.63 | SCH-002-313 | 1.6 | 0.30 |
| ADVANCE Clr | SCH-001-317 | 1.5 | 0.28 | 0.55 | SCH-002-321 | 1.6 | 0.18 |
| MAX Clr | SCH-001-323 | 1.5 | 0.22 | 0.53 | SCH-002-327 | 1.6 | 0.14 |
| MAX Gy (grey tint) | SCH-001-326 | 1.5 | 0.18 | 0.26 | SCH-002-330 | 1.6 | 0.12 |
Source: WERS (werslink.com.au), manufacturer Sustainable Windows, all "- WE" (warm edge spacer) units, checked 1 October 2026. Uw in W/(m²K). Tvw is visible light transmittance. The tilt and turn SHGC is lower than the fixed window's with the same glass because the opening sash adds frame area.
What the table shows
- Going from CLASSIC to any low-E unit is the big step for Uw: 2.4 to 1.5 on the fixed window. After that, PLUS, ADVANCE and MAX barely change Uw. They change SHGC.
- SHGC is the lever by orientation. On the fixed window it runs from 0.47 (PLUS) to 0.22 (MAX) at the same Uw.
- Tint costs daylight. MAX Gy drops Tvw to 0.26 against 0.53 for MAX Clr, for a small SHGC gain. Clear low-E usually gets there with more light.
- Triple glazing lowers Uw further. Fixed CT 70 reaches 0.9 with AGG PLUS + PLUS Clr 6/12/6/12/6 (SCH-008-007, SHGC 0.38) or 0.9 with MAX + PLUS (SCH-008-013, SHGC 0.20). Tilt and turn reaches 1.2.
Starting points by orientation
General principles to discuss with your assessor. The model decides the final selection.
- North, with eaves sized for summer shade: a higher-SHGC low-E unit such as PLUS, to keep winter solar gain.
- East and west: a low-SHGC unit such as ADVANCE or MAX, especially on large glazing and upper floors with little shading.
- South: little direct sun, so Uw counts most. Low-E double glazing, or triple glazing in cold climates.
- Cold climates (Blue Mountains, Southern Highlands): model triple glazing on living areas and large fixed lights first.
Workflow
What to send us, and what we send back
Send us
- The window and door schedule: opening sizes, opening types and the elevation or orientation of each.
- The NatHERS or BASIX assessment if one exists, or the glazing the assessor has assumed so far.
- Any acoustic report, so one glass unit can meet both targets.
- Frame colours inside and out, since colour changes Schueco's size limits.
We send back
- For each window type, the WERS rating ID, the AGG glass description, Uw, SHGC, Tvw and air infiltration of the unit we'd supply.
- Alternatives with a lower Uw or a different SHGC for the openings that limit the rating.
- For EasySlide lift and slide doors, which have no WERS listing yet, Schueco's Uf data, so the assessor can decide how to model them.
- A quote priced on the glass units that end up on the certificate.
Before the assessment
Ask us for rating IDs early, so the assessor models custom windows rather than defaults.
During the assessment
If the design misses 7 stars, change glass on the openings that drive the result, often large west and north glazing, before touching insulation or the floor plan.
Certificate issued
Send it to us. We check every window type against the listed U-value and SHGC range before we order glass.
Delivery and inspection
Each window matches the certificate, and we can supply the WERS details the certifier asks for.
Avoid a re-assessment
Common mistakes
- Assessing with defaults, then ordering something else. The NatHERS certificate lists each window type with a maximum U-value and an SHGC range. A product outside those limits means the assessment has to be redone.
- Treating a lower SHGC as always better. The U-value can always be lower than the certificate, but SHGC has a lower limit as well as an upper one. A darker, lower-SHGC glass than assessed can fail the substitution check and cost winter heating in the model.
- Mixing up frame materials. If the assessor modelled aluminium windows and you then switch to uPVC, or the reverse, the values change. Tell the assessor the frame is Schueco uPVC from the start.
- Swapping door types late. A SoftSlide slider (air infiltration 0.64 L/s·m²) is not a like-for-like swap for a hinged CT 70 door (0.04), and EasySlide has no WERS rating to substitute in.
- Using the wrong number. Uf, Ug and centre-of-glass figures aren't Uw. Only the WERS Uw and SHGC belong in the model.
- Forgetting acoustic glass. If the acoustic report changes a glass unit after the BASIX certificate is issued, check the new unit's WERS values against the certificate too.
| CT 70 tilt and turn | Uw 1.2–2.1, SHGC 0.12–0.3957 ratings, double and triple |
|---|---|
| CT 70 fixed | Uw 0.9–2.4, SHGC 0.18–0.6257 ratings, double and triple |
| CT 70 casement | Uw 1.6–2.2, SHGC 0.12–0.3943 ratings |
| CT 70 awning | Uw 1.6–2.2, SHGC 0.12–0.3943 ratings |
| CT 70 hinged door | Uw 1.1–2.2, SHGC 0.14–0.4857 ratings, double and triple |
| SoftSlide sliding door | Uw 1.6–2.5, SHGC 0.17–0.5641 ratings, double |
| SoftSlide sliding window | Uw 1.8–2.5, SHGC 0.14–0.4742 ratings, double |
| EasySlide lift and slide | No WERS listing yetUf from 1.47 W/(m²K), Schueco |
Full table with the lowest-Uw glass for each product: energy efficiency. Sources for the rules on this page: NSW Department of Planning (BASIX standards, 1 October 2023), NSW Planning Portal (BASIX DIY method, alterations and additions), Australian Building Codes Board (NCC 2022), NatHERS certificate guidance on window substitution.
Need WERS rating IDs for a 7-star assessment? Send the schedule.
FAQ
Questions from builders and architects
Do windows need to be BASIX approved?
No. There's no BASIX approval for a window product. BASIX assesses the whole dwelling, and each window is an input with a size, orientation, Uw and SHGC. What has to match is the installed window and the values on the BASIX or NatHERS certificate.
What changed for windows on 1 October 2023?
NSW raised the BASIX thermal performance standard for most new homes from an average of 5.5 to 6 NatHERS stars to 7 stars, and raised the energy standard. Apartments need an average of 7 stars with no unit below 6. NSW Planning lists homes in climate zones 9, 10 and 11 and apartment buildings up to five storeys as exceptions to the increase. Windows carry more of the load at 7 stars, so real WERS values matter more than they did.
What is a WERS rating ID?
It's the identifier for one rated combination of frame and glass in the Window Energy Rating Scheme, for example SCH-002-313 for our CT 70 tilt and turn window with AGG PLUS Clr 6/16/6 glass. It carries the Uw, SHGC and visible transmittance the assessor enters into NatHERS software as a custom window.
Can I change windows after the certificate is issued?
Only within the substitution tolerances on the NatHERS certificate: the replacement's U-value must be no higher than the value listed, and its SHGC must fall within the listed range. Outside those limits, the assessment has to be redone. Check with us before swapping glass or frame type.
Do I need triple glazing to reach 7 stars?
Not necessarily. In Sydney and coastal NSW, low-E double glazing can be enough, but the assessor's model decides. Triple glazing is worth modelling in cold climates and on large glazed areas. Our best triple glazed WERS ratings are Uw 0.9 for fixed windows and 1.2 for tilt and turn.
Does BASIX apply to renovations?
Yes, to alterations and additions valued at $50,000 or more, or with a pool or spa over 40,000 litres, according to the NSW Planning Portal. There are no set energy or water reductions for alterations, but new windows still go into the thermal assessment.