Windows of Opportunity: Your Guide to High-Performance Glazing
The right glazing can boost your home's energy efficiency and slash your bills – here's everything you need to know
At face value, windows appear to serve a simple function: they allow the occupants of a home to see outside, and let natural light and fresh air filter through. But there’s more to glazing than meets the eye; the windows you choose can have a significant impact on your home’s thermal performance and energy efficiency.
According to the Australian government’s Your Home website, up to 40 per cent of a home’s heating energy can be lost, and up to 87 per cent of its heat gained, through windows. So choosing the right windows can not only make your home more comfortable naturally, but can make a big difference to your energy bills too.
According to the Australian government’s Your Home website, up to 40 per cent of a home’s heating energy can be lost, and up to 87 per cent of its heat gained, through windows. So choosing the right windows can not only make your home more comfortable naturally, but can make a big difference to your energy bills too.
Measuring Heat and Solar Radiation Transfer
U-value: Conduction is measured with a U-value. U-value is the measure of how much heat is transferred through glass. A lower U-value indicates better insulation properties, which means reduced heat gain in summer and heat loss in winter.
Solar heat gain coefficient (SHGC): SHGC is the measure of how much heat from direct sunlight (solar radiation) passes through the window. A greater amount of solar radiation can pass through windows with a higher SHGC, enabling solar heating for the home. A window with a lower SHGC allows less solar heat to pass through. Glass selection has a big impact on the SHGC measure of a window or door.
U-value: Conduction is measured with a U-value. U-value is the measure of how much heat is transferred through glass. A lower U-value indicates better insulation properties, which means reduced heat gain in summer and heat loss in winter.
Solar heat gain coefficient (SHGC): SHGC is the measure of how much heat from direct sunlight (solar radiation) passes through the window. A greater amount of solar radiation can pass through windows with a higher SHGC, enabling solar heating for the home. A window with a lower SHGC allows less solar heat to pass through. Glass selection has a big impact on the SHGC measure of a window or door.
Types of Glazing
Energy-efficient windows come in a variety of forms, including double- and triple-glazed and those made with low-E glass. Various coatings can also improve their performance.
“Glass now has a major influence on home design. Advancements in glass technology mean Australians can choose from a selection of glass options that offer different performance features,” says Samantha Anderson, business development manager at Viridian. “Smart homeowners looking to future-proof their home will look to performance glass products to create a home that feels good, functions efficiently and offers truly personalised comfort.”
See more stunning modern homes
Energy-efficient windows come in a variety of forms, including double- and triple-glazed and those made with low-E glass. Various coatings can also improve their performance.
“Glass now has a major influence on home design. Advancements in glass technology mean Australians can choose from a selection of glass options that offer different performance features,” says Samantha Anderson, business development manager at Viridian. “Smart homeowners looking to future-proof their home will look to performance glass products to create a home that feels good, functions efficiently and offers truly personalised comfort.”
See more stunning modern homes
Double and triple glazing
Double- and triple-glazed windows have at least two sheets of glass with an inert gas such as argon (typically cheaper) or krypton between them. The gas, which is a poor thermal conductor, slows the passage of heat through the glass. The entire unit is sealed in the frame for lower heat exchange rates. These types of windows can also feature soundproofing qualities to reduce the impact of outside noise, as well as UV protection to prevent harmful rays from fading your furniture and finishes.
Windows such as Viridian’s LightBridge range can be tailored to address a variety of specific design needs, including noise reduction, privacy, security and UV-control. Stegbar’s thicker float glass, laminated glass, insulated glass units and secondary window units also significantly reduce noise levels.
Double- and triple-glazed windows have at least two sheets of glass with an inert gas such as argon (typically cheaper) or krypton between them. The gas, which is a poor thermal conductor, slows the passage of heat through the glass. The entire unit is sealed in the frame for lower heat exchange rates. These types of windows can also feature soundproofing qualities to reduce the impact of outside noise, as well as UV protection to prevent harmful rays from fading your furniture and finishes.
Windows such as Viridian’s LightBridge range can be tailored to address a variety of specific design needs, including noise reduction, privacy, security and UV-control. Stegbar’s thicker float glass, laminated glass, insulated glass units and secondary window units also significantly reduce noise levels.
Double-glazed windows can reduce heat loss or heat gain by almost 30 per cent in comparison with single-pane aluminium windows. Triple glazing performs even better and is ideal for colder environments and extreme northern climates. The extra pane of glass, however, does make them thicker, heavier and more expensive.
Low-E glass: Low-E (low emissivity) glass has a transparent coating – an invisible layer of metallic oxide – that minimises the amount of heat that passes through the glass while still allowing light to flow through. Low-E coatings add to the cost of a window, but they can cut your energy costs.
“In the past you would need to use dark tints and thick glass to achieve performance, but with today’s coating technology, clear-coated glass such as low-E provides the same solar protection as tinted glass,” says Stegbar glass expert Carley Armstrong.
“In the past you would need to use dark tints and thick glass to achieve performance, but with today’s coating technology, clear-coated glass such as low-E provides the same solar protection as tinted glass,” says Stegbar glass expert Carley Armstrong.
Low-E glass reduces solar gain in winter and summer. Therefore, homeowners in colder regions may choose coatings that maximise solar heat gain, particularly in winter, while those in warmer climates may choose coatings that reduce solar heat gain in summer.
Low-E coatings are often used to complement double glazing so as to provide even better thermal efficiency. They can be tailored to let the sun’s energy in or to block it out. In colder climates where sun control is not a priority, adding a low-E coating to the internal pane of glass can help keep a house warmer in winter.
Read about 9 energy-smart Australian homes
Low-E coatings are often used to complement double glazing so as to provide even better thermal efficiency. They can be tailored to let the sun’s energy in or to block it out. In colder climates where sun control is not a priority, adding a low-E coating to the internal pane of glass can help keep a house warmer in winter.
Read about 9 energy-smart Australian homes
Optimise your glazing
High-performance glazing costs more than single-pane windows. So if you’re building or renovating on a budget, which rooms of the home and orientations are worth splashing out and where might you use a cheaper alternative?
Climate and reliance on heating and cooling will influence which glazing will work best and where. For example, insulation is important in colder climates such as Victoria, whereas sun protection is a priority in hotter environments such as Queensland.
Energy-efficient glazing should ideally be used in every part of the house. But rather than taking a ‘one-type-fits-all’ approach, you can optimise thermal performance and keep the budget under control by choosing different glazing types based on room use, orientation and climate.
High-performance glazing costs more than single-pane windows. So if you’re building or renovating on a budget, which rooms of the home and orientations are worth splashing out and where might you use a cheaper alternative?
Climate and reliance on heating and cooling will influence which glazing will work best and where. For example, insulation is important in colder climates such as Victoria, whereas sun protection is a priority in hotter environments such as Queensland.
Energy-efficient glazing should ideally be used in every part of the house. But rather than taking a ‘one-type-fits-all’ approach, you can optimise thermal performance and keep the budget under control by choosing different glazing types based on room use, orientation and climate.
Room use: “If you are on a budget, a good starting point is to look at the places in your home where you will experience everyday benefits from performance glazing,“ Armstrong says.
Invest in the rooms that are used the most, such as living and family spaces, to increase the comfort level and reduce heating and cooling costs. For north-facing living spaces, which are exposed to direct sunlight, consider a glass that reduces UV exposure and glare.
Invest in the rooms that are used the most, such as living and family spaces, to increase the comfort level and reduce heating and cooling costs. For north-facing living spaces, which are exposed to direct sunlight, consider a glass that reduces UV exposure and glare.
Bedrooms that are used less frequently during the day have less need for energy-efficient glazing. However, other factors may be considered. “If bedrooms are at the front of the house near a busy road then noise may be an issue, in which case acoustic performance glass is helpful. If they are located upstairs, make sure to get windows that fully open to let out the rising hot air during summer days,” Anderson says.
She also notes that the National Construction Code has restrictions on upstairs window openings that can leave homeowners with limited options for airing their living spaces. “Choosing performance glass will therefore allow you to better control the flow of heat in and out of your windows to ensure cooler bedrooms in summer.”
Less-used areas, such as laundries and bathrooms, have less need for high-performance glass, however, they still contribute to the overall efficiency of a house, in which case low-E may be an appropriate choice.
She also notes that the National Construction Code has restrictions on upstairs window openings that can leave homeowners with limited options for airing their living spaces. “Choosing performance glass will therefore allow you to better control the flow of heat in and out of your windows to ensure cooler bedrooms in summer.”
Less-used areas, such as laundries and bathrooms, have less need for high-performance glass, however, they still contribute to the overall efficiency of a house, in which case low-E may be an appropriate choice.
Climate and orientation: In cooler climates, U-value is the driver of annual energy consumption, whereas SHGC is more influential in hotter climates,
For all orientations, a low U-value outperforms a high U-value, especially with north-facing windows, which is where homes collect the most solar heat. If budget is a consideration, then windows on northerly orientations should generally have a low U-value to increase insulation, thereby reducing solar heat gain in summer and increasing solar heat gain in winter. In contrast, south-facing windows can have a higher U-value because there is less solar heat gain from the south in winter and summer.
How to get more from your windows for less
For all orientations, a low U-value outperforms a high U-value, especially with north-facing windows, which is where homes collect the most solar heat. If budget is a consideration, then windows on northerly orientations should generally have a low U-value to increase insulation, thereby reducing solar heat gain in summer and increasing solar heat gain in winter. In contrast, south-facing windows can have a higher U-value because there is less solar heat gain from the south in winter and summer.
How to get more from your windows for less
In temperate and cooler climates, northerly glazing should have a higher SHGC to allow for more solar heat gain. In hot climates, glazing should have a low SHGC to reduce solar heat gain.
“Insulation in your windows is important all year round, regardless of orientation,” Armstrong says. “However, it’s the west you need to be concerned about in summer.” West- and east-facing windows with a low SHGC will reduce overheating in summer. Armstrong recommends double glazing or low-E coatings for optimum performance in all seasons, so as not to miss out on passive heat gain in winter.
“Insulation in your windows is important all year round, regardless of orientation,” Armstrong says. “However, it’s the west you need to be concerned about in summer.” West- and east-facing windows with a low SHGC will reduce overheating in summer. Armstrong recommends double glazing or low-E coatings for optimum performance in all seasons, so as not to miss out on passive heat gain in winter.
Retrofitting your glazing
There are several options if you’re looking to retrofit your existing windows to improve their insulation performance.
Secondary glazing: Secondary glazing can be retrofitted to existing windows by adding an extra pane of glass or clear acrylic. It can be attached through magnetic strips or built onto the existing frame and, depending on the product, may be able to mimic the properties of a double-glazed window.
Glazing films: Magnetic and transparent films, such as reflective coatings, can be fitted to the glass of an existing window to reduce heat gain and the amount of light in winter as well as in summer.
There are several options if you’re looking to retrofit your existing windows to improve their insulation performance.
Secondary glazing: Secondary glazing can be retrofitted to existing windows by adding an extra pane of glass or clear acrylic. It can be attached through magnetic strips or built onto the existing frame and, depending on the product, may be able to mimic the properties of a double-glazed window.
Glazing films: Magnetic and transparent films, such as reflective coatings, can be fitted to the glass of an existing window to reduce heat gain and the amount of light in winter as well as in summer.
Upgrade: Anderson suggests upgrading single-pane windows to a low-E single-glazed product. “This will improve insulation over ordinary glass by approximately a third,” she says. “Alternatively, installing high-performance double glazing will more than double the insulation performance compared to a low-E, single-glazed product.”
Similarly, Armstrong advises that improving the glass won’t solve the problem of draughty windows and doors. “If you have good solid windows, then replacing three-millimetre clear glass with energy-efficient glass appropriate for the elevation and climate is going to provide a good solution,” she says. “An acoustic laminate for sound reduction, or a low-E laminate for energy efficiency, will allow you to improve the overall thermal efficiency of your home.”
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Glass windows and doors can impact the thermal performance of a building, contributing to the energy efficiency and comfort of a home. Windows lose more heat in winter and gain more heat in summer than any other surface in the home.
In many parts of Australia, the priority is to reduce solar heat in summer in order to keep the house cooler, and maximise solar heat in the winter so it stays warmer. Quality glazing can help do this by improving the efficiency of glass windows and doors. Good glazing reduces heat gain and loss, thereby helping to minimise the use of artificial heating and cooling in a building.