Sustainable approaches to future construction will need to consider the benefits of energy efficient glazing to both thermal performance and occupier wellbeing, as well as creating the initiative to rapidly increase their uptake in new buildings.

Up to 87 per cent of heat gain during summer in Australian homes – and up to 40 per cent of heat loss in winter – through the windows, leading to the average Australian home devoting about 40 per cent of its household energy use to heating and cooling.

While long-existing energy-efficient window designs are increasingly prevalent in commercial and office buildings, most residential windows in Australia have only single glazed windows.

Double or triple-glazed windows, along with other innovative technologies and methods, can offer much better performance, greater thermal comfort, and result in better physical and mental health. They also provide increased control of ventilation and natural light, and reduced noise from outside.

These window systems have insulating layers of air or gas between the glass panes, while other elements such as thermal breaks and films can be applied to improve performance. Importantly, these approaches can be used in new window units, or as retrofit options such as secondary glazing, which involves installing a glazed panel inside a frame with an existing window.

A study published in Energy and Buildings investigated the impact of different window designs on the annual energy loads of a house for all eight Australian capital cities, covering diverse climate zones. The analysis focused on two types of double glazing: uncoated, and coated with low-emittance films for improved thermal insulation or lower solar heat gain.

The results showed that while low-emittance double glazing provided superior performance, the low solar gain option was only effective in sunnier climate zones.

Research from last year, which evaluated commercially available window glazing for an office building in Darwin’s tropical climate, indicated double glazed variants provided a 5 per cent reduction in cooling loads, but that triple glazed or aerogel-based windows were a more viable, effective alternative.

A tripled glazed window filled with krypton provided the highest energy saving, demonstrating a 12 per cent saving when changing the window type from single to triple glazed glass. The environmental benefits of using double or triple glazed windows can also be maximised by the use of recycled materials in their production.

Materials that can be recycled include glass, aluminium and steel frames, wooden frames, and recycled PVC and composite frames.

For example, recycling aluminium uses only about 5 per cent of the energy needed to produce virgin aluminium, so incorporating recycled aluminium into frame manufacturing processes can substantially reduce energy consumption. The use of recycled materials also helps conserve natural resources such as metals, minerals, and timber, as well as slowing down the rate at which landfills reach capacity. Notably, recycling can also offer opportunities for waste-to- energy initiatives, which convert waste into energy sources such as biofuels, biogas, and heat energy.

A report prepared by RMIT University researchers for Sustainability Victoria found that Australia was trailing far behind other countries in installing high-performance windows.

A little more than 10 per cent of windows in new housing in Australia are high performance, compared to about 80 per cent in the United Kingdom, the United States, and New Zealand.

This is in part due to inadequate policies and a scarcity of research on optimal designs for Australia’s different climate zones, as well as lagging construction standards for new homes when compared to other developed nations.

The RMIT researchers noted that the industry was complex, and a range of measures would likely be needed to encourage the uptake and delivery of more high-performance windows.

They said: “The builders we spoke to identified some issues around understanding the various window products, such as the relative benefits of different frame materials.

“For example, uPVC and timber frames typically conduct less heat than aluminium; however, a thermal break can greatly improve aluminium frame performance.

“They also noted that high-performance windows cost more – this can be a challenge in an industry already struggling to provide housing at affordable prices.”

The report, Upscaling high-performance windows in Victoria, recommended improvements in policy and regulations, such as setting minimum performance requirements for windows similar to New Zealand, and better education for buildings and consumers to bust myths about high-performance windows. It also recommended financing, such as rebates for homeowners, and quality assurance so energy assessors are provided with well-informed advice and installation practices are properly regulated.

The researchers added: “Given the key role of windows in housing quality, performance and emissions, installing high- performance windows needs to become business as usual.

“In many other countries, double or tripled-glazed windows are now standard – if we don’t do the same, we will lock households into lower-quality, poorly performing housing for decades.

“Making high-performance windows standard building practice in Australia is achievable; however, some support for the window industry, builders and households will be needed.”