NatHERS Design Factors
Windows can have a major influence on a NatHERS rating. Their size, orientation, glazing, frame type and shading all affect how much heat enters or leaves a home.
Window design affects NatHERS ratings because windows influence heat gain, heat loss, daylight, solar exposure and comfort. A well placed, well shaded and well specified window can support thermal performance. A poorly placed or poorly specified window can make a home harder to keep comfortable and may lower the NatHERS result.
Windows are one of the most sensitive parts of the building fabric. They connect the home to light, views and ventilation, but they can also create unwanted heat gain in summer and heat loss in winter.
A NatHERS assessment models the home in relation to its local climate and design. Because windows sit at the intersection of orientation, solar exposure, glazing performance and shading, they can strongly influence the predicted heating and cooling needs of the home.
This does not mean good NatHERS outcomes require small, dark or closed homes. It means window design needs to be intentional. The right window in the right place can support comfort. The wrong window in the wrong place can create a performance burden.
A window does not affect the NatHERS rating through glass alone. The assessment considers how the whole opening performs in the specific home and climate.
• Window size and total glazed area
• Orientation and exposure to sun
• Glazing type and performance values
• Frame material and frame performance
• Eaves, awnings, balconies and external shading
• Room use and internal zoning
• Local climate and seasonal heating or cooling needs
The impact of a window can change depending on the rest of the design. A large shaded north facing window may behave very differently from an unshaded west facing window, even if the glass specification appears similar.
Orientation is one of the most important parts of window design. The same window can have a different thermal impact depending on whether it faces north, east, south or west, and depending on the home’s climate zone.
In many Australian homes, north facing glazing can be useful when it is paired with appropriate shading. It may allow winter sun while limiting summer heat gain. East and west facing windows often need more careful treatment because low angle morning and afternoon sun can be harder to control.
South facing windows may have less direct solar gain, but they can still affect heat loss, daylight and comfort. NatHERS modelling considers these relationships rather than treating all windows as equal.
The aim is not simply to reduce windows. The aim is to place and specify windows so they support the climate response of the home.
Good window design balances daylight, views, solar control, insulation, ventilation and thermal comfort.
Glazing performance is not one single thing. In NatHERS, windows are influenced by values that describe heat transfer and solar heat gain. These values help model how much heat may move through the window and how much solar energy may enter the home.
Double glazing can be helpful, especially where heat loss or heat gain through windows is a performance issue. However, it is not automatically the best or only solution in every climate or every design. The specific glazing type, frame performance, window orientation and shading all matter.
Frames can also influence performance. A high performing glass unit can be weakened by a poor performing frame, while the right frame and glazing combination can support a stronger thermal result.
Shading is often one of the most practical ways to improve window performance. Eaves, awnings, balconies, pergolas, external screens and neighbouring structures can all affect how much sun reaches the glass.
Good shading is climate and orientation specific. In some situations, the goal is to block high summer sun while still allowing useful winter sun. In other locations, stronger year round solar control may be needed to manage cooling loads.
Because shading can be difficult to add elegantly at the end of design, it is best considered early. Window placement, façade depth, roof form and outdoor living areas can all help create shading that feels integrated rather than added later.
Yes, large windows can still be part of a strong NatHERS outcome, but they need to be coordinated carefully. Large glazing areas usually increase the importance of orientation, shading, glass selection, frame performance and the surrounding building fabric.
A home with generous glazing may need better performing windows, stronger solar control or higher performance in other parts of the building fabric. In some cases, reducing or redistributing glazing may be more effective than simply upgrading all glass.
The best solution depends on the actual design. A NatHERS assessment helps show whether the window strategy is helping the home or creating avoidable heating and cooling demand.
For many new homes, window design can influence whether the project reaches the required NatHERS star rating. This can be especially important for homes targeting or required to achieve 7 Star Rating outcomes.
In NSW, window specifications can also affect BASIX documentation because glazing and thermal performance commitments may need to align with the assessment result. If windows change after the assessment, the NatHERS and BASIX pathway may need to be reviewed.
Window decisions can also sit beside Whole of Home considerations, especially where heating and cooling system assumptions are affected by the thermal performance of the home.
• Large west facing glazing without enough shading
• High glazing areas in lightweight homes without enough fabric balance
• Window specifications that do not match the intended performance level
• Shading that is drawn architecturally but not resolved in enough detail
• Late window changes after the assessment has already been completed
Window design should respond to climate, not just appearance. In cooler climates, windows may need to support useful solar gain while reducing heat loss. In hot climates, solar control, shading and cooling load reduction may become more important.
In mixed climates, the balance can be more subtle. A window strategy may need to support winter comfort without creating summer overheating. This is where NatHERS modelling can help test the design rather than relying on assumptions.
The strongest outcomes usually come from early coordination between architectural design and energy assessment. When window size, placement, shading and glazing performance are considered together, the home is more likely to achieve a practical NatHERS pathway without last minute compromises.
Certified Energy provides NatHERS assessments for new homes, townhouses and multi residential projects. Our team reviews the design, models the thermal performance and helps identify how window decisions are influencing the rating.
Where needed, we can help project teams understand whether the pathway is affected by glazing area, orientation, frame type, shading or broader building fabric decisions. We can also help connect the assessment with related requirements such as NatHERS, BASIX and Whole of Home.
For a broader explanation of the rating framework, visit our NatHERS Knowledge Hub.
Yes. Window size, orientation, glazing performance, frame type and shading can all affect the NatHERS result because they influence heat gain, heat loss and thermal comfort.
Does double glazing always improve a NatHERS rating?Double glazing can help in many designs, but it does not automatically solve every rating issue. The result depends on climate, orientation, window size, frame performance, shading and the specific glazing values.
Are large windows bad for NatHERS?Large windows are not automatically bad, but they need to be carefully designed. Orientation, shading, glazing type, frame performance and climate all influence whether large windows help or hurt the rating.
Which window orientation is hardest for NatHERS?It depends on the climate and design, but unshaded east and west facing windows often need careful treatment because low angle morning and afternoon sun can be difficult to control.
Should window design be reviewed early?Yes. Window decisions are often harder to change late in the design process. Early NatHERS review can help identify whether window size, placement, glazing or shading is affecting the rating.