Glazing and NatHERS
Does Double Glazing Help You Get a 7 Star Rating?
Double glazing can help improve a NatHERS rating, but it is not a guaranteed solution on its own. Whether it helps a project reach 7 Stars depends on the climate, orientation, window size, shading, frame type and the rest of the building fabric.
In brief: Double glazing can reduce heat loss and improve thermal performance, especially in cooler climates or areas with high heating demand. But a 7 Star NatHERS rating is shaped by the whole design. Poor orientation, excessive unshaded glazing or weak insulation can still hold the rating back, even when double glazing is used.
How Windows Affect a NatHERS Rating
Windows can have a major effect on NatHERS outcomes because they influence heat loss, heat gain, daylight, ventilation and solar exposure. A window is not just an opening in the wall. In thermal modelling, its size, location, frame type, glass performance and shading all affect how the home performs across the year.
NatHERS modelling considers the home in its specific climate. That means the same glazing decision may perform differently in Sydney, Melbourne, Brisbane, Canberra, Perth, Adelaide or a regional climate zone. A glazing upgrade that helps one project may not be the most efficient upgrade for another.
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Does Double Glazing Automatically Achieve 7 Stars?
No. Double glazing can help a home achieve a better NatHERS result, but it does not automatically produce a 7 Star rating. NatHERS assesses the full thermal performance of the dwelling, not one product in isolation.
A project with large areas of unshaded west-facing glazing may still struggle, even with double glazing. A project with good orientation, sensible window placement, effective shading and well-detailed insulation may reach the required outcome with a more targeted glazing strategy. The right answer depends on the design.
When Double Glazing Usually Helps
Double glazing is often useful where heat loss through windows is a major issue. This is common in cooler climates, exposed locations or homes with large window areas. It can also help improve comfort by reducing the temperature difference near windows during colder periods.
Double glazing may be especially useful when:
- the home is in a cooler or mixed climate
- large windows are part of the design intent
- heating load is holding the NatHERS rating back
- single glazing is causing too much heat loss
- the project needs better comfort near glazed areas
- the glazing upgrade is targeted to the windows that matter most
When Double Glazing May Not Be Enough
Double glazing is not always the best first move. In some projects, the main issue is not heat loss through the glass. It may be excessive solar heat gain, poor shading, difficult orientation, dark roof colour, weak insulation or a complex building form with too many exposed surfaces.
Double glazing may not solve the rating problem if:
- large west-facing windows are not shaded
- cooling load is the main issue rather than heating load
- the window area is excessive for the design and climate
- the selected glazing has the wrong solar heat gain characteristics
- the rest of the building fabric is underperforming
- the project needs layout or shading changes, not only product upgrades
U-Value, SHGC and Why the Specification Matters
Not all double glazing performs the same way. Window performance is usually described using values such as U-value and Solar Heat Gain Coefficient, often shortened to SHGC. These values affect how the window manages heat transfer and solar gain.
A lower U-value generally means the window is better at reducing heat transfer. SHGC relates to how much solar heat passes through the glazing. Depending on the climate and orientation, a project may need to reduce solar heat gain, preserve useful winter sun or balance both.
This is why the exact window specification matters. Simply saying “double glazing” is not enough for accurate NatHERS modelling. The assessor needs the correct window and frame performance information to model the project properly.
Double Glazing Versus Better Shading
In some designs, shading may be more cost effective than upgrading every window. Eaves, awnings, pergolas, screens, balconies and external shading can reduce unwanted solar heat gain before it reaches the glass. This can be especially important for east and west-facing windows.
The best option depends on what the NatHERS model shows. Sometimes double glazing is the right move. Sometimes shading, window placement or glass selection is more important. Often the strongest result comes from a combination of targeted glazing upgrades and well-designed shading.
Is Double Glazing Required for 7 Star NatHERS?
Double glazing is not automatically required for every 7 Star NatHERS outcome. Some homes may achieve the required rating with carefully selected single glazing, good orientation, appropriate shading and strong building fabric. Other homes may need double glazing or higher performance glazing to reach the target.
The risk comes from assuming the answer before the project has been modelled. A NatHERS assessment can show whether double glazing is necessary, whether it should be used only in certain areas or whether other design changes would be more effective.
How to Use Double Glazing Cost Effectively
A cost effective glazing strategy is usually targeted. Instead of upgrading all windows by default, the project team can use NatHERS feedback to understand which parts of the home are creating the greatest heating or cooling demand.
A targeted approach may include:
- using higher performance glazing only where it has the most impact
- combining glazing upgrades with external shading
- reducing excessive glazing where it is not essential
- improving frame performance as well as glass performance
- matching the SHGC to orientation and climate
- reviewing glazing before the design is fully locked in
Why Early NatHERS Advice Matters
Glazing decisions can affect cost, comfort, aesthetics and compliance. If the NatHERS assessment happens late, the project team may feel pressured to choose expensive upgrades quickly. If the assessment happens earlier, there is usually more time to compare options.
Early advice can help determine whether double glazing is genuinely needed, whether a different glazing specification would be better or whether the project would benefit more from shading, insulation or orientation changes.
Need Glazing Advice for a NatHERS Assessment?
Certified Energy can review your residential project documents and advise whether glazing, shading, insulation or other design changes are likely to affect the NatHERS outcome.
Related Guides
- 7 Star NatHERS Rating
- NatHERS Knowledge Hub
- Designing for 7 Star NatHERS on a Budget
- What a 7 Star Energy Rating Means for Your Project
- What Is a 7 Star Energy Rating?
FAQ
Does double glazing help with a 7 Star NatHERS rating?
Yes, double glazing can help improve a NatHERS rating, especially where heat loss through windows is a major issue. However, it does not guarantee a 7 Star result on its own.
Is double glazing required for 7 Star NatHERS?
Not always. Some homes may reach 7 Stars without double glazing, while others may need double glazing or higher performance glazing. The result depends on climate, orientation, window size, shading, insulation and the whole building fabric.
Is double glazing better than shading?
It depends on the project. Double glazing can reduce heat transfer through the window, while shading can reduce unwanted solar heat before it reaches the glass. Many projects benefit from both, but the most cost effective option depends on the NatHERS model.
Does all double glazing perform the same?
No. Window performance depends on the glass, frame, U-value, SHGC and installation context. Two double glazed products can perform differently in NatHERS modelling.
When should glazing be reviewed for NatHERS?
Glazing should be reviewed before the design is fully locked in. Early review gives the project team more flexibility to adjust window size, placement, shading or specification before late-stage upgrades become harder to manage.
