The modern Australian home is filled with light, mostly due to the trend towards large windows and external doors, which connect the inside with alfresco areas and create a sense of space throughout.

However, while the use of glass brings light, air and sunshine into homes, it can also make it challenging to ensure thermal comfort and energy efficiency.

The secret is choosing the right type of glazing in new windows and doors – one that manages thermal performance, saves money on energy bills, and reduces the long-term carbon footprint of a building.

Specifiers might be surprised to realise the type of glass used in windows and doors has a significant effect on ensuring a comfortable indoor climate. Up to 40% of a home’s heating energy can be lost and up to 87% of its heat gained through windows.

Investing in energy-efficient windows and doors can greatly reduce annual heating and cooling costs. For example, energy-efficient glazing can reduce the required size of an air-conditioning system by 30%, leading to significant cost savings.

The Australian Glass and Window Association (AGWA) has an informative YouTube video detailing the energy requirements for new homes and how to select the right type of glazing to maximise energy efficiency.

Energy requirements for new homes

New homes need to meet mandated energy requirements. Terms used to describe energy efficiency include the Solar Heat Gain Co-efficient (SHGC) and the U-value.

The SHGC measures the amount of heat that passes through a window, resulting in a number between zero and one. Zero SHGC means that no heat passes through the window, while one SHGC means that 100% of the heat passes through. For example, 0.7 SHGC means that 70% of the heat is passing through the window.

U-value relates to the movement between heat and cold via a window through conduction, radiation, and convection. A lower U-value means that a window is a good insulator and therefore, more efficient with energy usage, and ensures that the internal temperature is more stable and comfortable.

Double glazing Vs Low E glass

When looking for energy-efficient glass, the most common choices are between double glazing and Low E glass.

The ‘E’ in Low E glass stands for ‘emissivity’, or the amount of radiant energy emitted or absorbed through a surface such as a pane of glass. It has a microscopically thin, transparent metal coating that reflects long-wave infrared energy or heat. This reduces the rate that heat enters or leaves a building and is a cost effective choice when trying to improve energy efficiency.

An untreated glass window has an emissivity rating of about 0.84, while a Low E window or window with Low E window treatment has an emissivity rating of just 0.02. It requires no special cleaning, and it improves the U-value and SHGC of the window or door.

Double glazing involves forming two pieces of glass into a unit, connected with a piece of metal or plastic called a spacer bar. The unit is then filled with argon gas and sealed off – ready to be installed into the window frame. Double glazing works by reducing a window's ability to conduct heat.

The double stacking of glass and argon gas in between provides a layer of insulation, which slows the rate of heat or cold flowing in and out of the home, resulting in up to three times better thermal insulation compared to standard single glazing.

It is a great choice if a home is in an area that includes extremes of heat and/or cold and can significantly reduce your heating and cooling costs over the longer term.

In some instances, double glazed windows and doors can be made with Low E glass.

How to improve the overall performance of the building

Energy efficiency starts at the design stage, especially if the building’s orientation is considered. The orientation is the direction the house faces and can assist in providing energy efficiency in summer and winter– resulting in higher comfort levels and lower energy costs.  

The key is to maximise north-facing windows, which allows the sun to stream in during winter but, when combined with appropriate shading, keeps it out during the hotter months. The design should position the building on the site to take advantage of its orientation.

Additionally, it’s important to make sure the installation of new windows is of high quality. Even the best windows can have their thermal properties compromised if they are not installed correctly.

Why timber is a better insulator

The energy performance of timber frames is significantly better when compared to aluminium because wood is a natural thermal insulator thanks to the air pockets within its cellular structure.

This natural insulation means less energy is required within a completed building, which, in turn, reduces costs and future demands on energy usage. It can even be part of a solution for meeting Passive House design standards, which measure the rate of internal thermal comfort without the need for additional recirculation of air.

Additionally, timber frames use much less fossil fuel in their production than any other alternatives.

Navigating glass choices

Windows and doors are amongst the chief architectural elements that have the greatest impact on thermal comfort and the overall energy footprint of a building.

NICCO has been designing and manufacturing custom-made timber windows and doors for more than 20 years and can assist architects, designers, and builders navigate how they can use them for optimal performance.

Image credits

Architecture: Carter Williamson

Build: SFN Constructions

Photography: Katherine Lu

Location: Bondi, Sydney NSW