Which type of glass is best for energy efficiency?

There are so many things to consider when you’re choosing which glass or window to use in a home. Beyond cost, builders also typically factor for state-based legislation, the geography of where a home is located, weather conditions in your area, and more. One thing’s for sure though: everyone’s interested in saving on energy leakages, and therefore heating and cooling costs.

Whether you’re motivated by environmental or economic reasons, it’s increasingly common for architects, builders and homeowners alike to focus on energy efficiency.

While it sounds straightforward, ‘energy efficiency’ is a sophisticated concept. Many different elements of a home’s design can impact upon your overall rating, and windows are just one of many categories. Even within the category of ‘thermal performance’—which broadly refers to how well your windows protect against the effect of hot or cold weather—there are considerations around:

• The typical weather in your area: including how humid it gets, whether it’s a hot or cold climate, how much sunshine your home receives throughout the day, and the impact of wind.
• Building design: including which direction your home faces, the size of the rooms, how many stories in your home, and more.
• Building materials: including the type of insulation you use, and the materials used to build the home.
• The size and configuration of your windows: including whether your windows are in full sunlight, or partially covered by trees or other buildings.

Despite all of those considerations, the Australian Government’s guide to environmentally sustainable homes suggests that up to 40% of a home’s heating energy can be lost and up to 87% of its heat gained through windows.

 

Did you know: the thickness of glass only relates to the strength or resilience of a window and has virtually no impact on performance in energy efficiency. Thicker glass is typically used to protect against high wind loadings; it’s most commonly used in the upper levels of high-rise apartments or office buildings.

 

So, which glass type and window configuration is the best for energy efficiency performance?

Before we can answer that, we need to understand the different types of glass commonly used throughout Australia, and where—and why—they’re used.

Common glass types and window configurations.

Annealed glass (or ‘float’ glass)

Annealed glass is used in many windows. ‘Annealing’ refers to a process used to cool the glass in production. While it is excellent for cutting and polishing, annealed glass is not heat-treated and is therefore not as durable as other types of glass.

Toughened glass

Toughened glass is produced using a process where the panes are heated in a certain way to make them stronger. This process also makes the glass shatter into small, chunky squares—rather than long, thin shards—which are safer to handle than cracked or smashed annealed glass panes.

Laminated glass

Like toughened glass, laminated glass is commonly used in situations where safety is a consideration, but it also offers a high level of acoustic performance to protect against the impact of noise. Laminated glass features a soft vinyl layer between two pieces of glass, which minimises the transmission of noise through the window.

Low emissivity glass (often called ‘low e glass’)

Low emissivity glass can prevent the sun’s heat from escaping a room. Or, it can rebound the sun’s rays from the outside and stop the associated heat from coming into the home. There are two types of low emissivity glass, being ‘low e hard coat’ and ‘low e soft coat’:

• Low e hard coat: The hard coating is applied when a manufacturer is making the glass. While the glass is very hot—and still ‘flexible’—it is sprayed with a coating which is then chemically bonded into the surface of the glass. Low e hard coat can be used as a single pane of glass within a home or building (a configuration referred to as ‘single glaze’) because it is more robust. Low e soft coat, on the other hand, cannot be used as a single glaze window and usually features within a double glaze configuration.
• Low e soft coat: Soft coating is sprayed onto the glass after the production process, once the pane has cooled down. Low e soft coat typically offers better energy efficiency performance, but it’s not robust. For example, scratching the surface with your finger can remove the soft coating. As a result, low e soft coat glass is only ever used inside a double-glaze unit, on the inside pane of the window configuration.

Single glazed windows

Single glazed refers to a window with only one layer of glass, or one single pane within the window; most windows in a standard home are single glaze. Single glazed windows can come in a variety of glass types, including annealed glass, toughened glass, or low e.

Double glazed windows

Double glazed windows use two separate pieces of glass which are separated by a central air gap, usually filled with Argon gas. The layer of Argon acts as an insulating barrier and reduces the conductive properties of each piece of glass (how easily cold air, sunlight or humidity can pass through the glass).

The best type of glass and windows to choose for energy efficiency depends on your climate zone.

There are eight different climate zones in Australia, as implemented by the Australian Building Codes Board.

Broadly speaking, the climate zones are either ‘heating climates’ or ‘cooling climates’.

• Heating climates are areas where the majority of energy and design considerations are geared towards heating a house and keeping it warm throughout cold weather. For example, Melbourne is deemed climate zone 7 (cold temperature), while parts of country Victoria and Tasmania are considered climate zone 8 (alpine conditions). Climate zone 8 is the maximum rating for a heating climate.
• Cooling climates are areas where the majority of energy and design considerations are geared towards keeping a house cool, because the weather in these areas is usually hot or humid. Southern Queensland, near the Gold Coast, is considered climate zone 3 (hot dry summer). As you continue up the coast into Far North Queensland, we reach climate zone 1 (high humidity in summer with warm winters).

With climate zones in mind, the concept of energy efficiency changes depending on where you are in Australia:

1. In a heating climate—like Victoria and Tasmania—energy efficiency is largely about getting as much heat into your house as possible, then stopping it from getting out.
2. In a cooling climate—like Queensland—energy efficiency is largely about stopping any heat from getting in through your windows.

With that in mind, the best type of glass and windows for energy efficiency are…

If you live in a heating climate, like Victoria or Tasmania, then the best glass type or window specification for energy efficiency is:

Double-glazed windows with low e glass configured on face three of the insulated glass unit.

This configuration is optimised to allow heat into your home, before trapping that heat on the inside of the building.

Find out more about our range of double glazed products, including double-glazed sliding windows and double-glazed corner windows.

If you live in a cooling climate, like Queensland, then the optimum glass type or window configuration for energy efficiency is:

Single glazed windows with tint —or super tint— glass on the outside face of the window.

The tint on the outside face of the window essentially reduces the amount of solar radiation and ultraviolet rays passing through the window, reducing glare and increasing comfort.

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Looking for more specific recommendations for your home?

While these recommendations are useful as a general guide to energy efficient products based on climate, the reality is that energy efficient design is rarely ‘one-size-fits-all’.

Whatever your specific energy goals—wherever you are in Victoria, New South Wales or Queensland —our experienced team is always available to help you achieve the best result possible.

Get in contact today for more information on energy efficient windows in the home.