Double glazing and glass options
The right glazing choices can help make your home more comfortable in hot and cool weather.
There are several glazing options available. Some keep heat inside your home. Others keep heat, noise, light and glare out.
Types of glass
Most New Zealand homes use clear glass in their windows and doors. Heat, light and noise can easily pass through this type of glass. When used as single glazing, it won't keep your home as comfortable or quiet and it won't keep your furniture from fading. If broken, standard glass shatters into sharp fragments which can be dangerous.
There are several other types of glass available:
- Low-emissivity glass (also known as ‘Low-E’ glass) lets light and heat in, but helps prevent heat from escaping.
- Reflective glass, tinted glass and spectrally selective glass reduce the amount of heat and ultraviolet light that can get in (ultraviolet light causes fading).
- Laminated glass is two sheets of glass bonded with a plastic or resin layer. It absorbs ultraviolet light and reduces noise. If it’s hit, the glass is held together by the resin layer.
- Toughened safety glass is much stronger than standard glass. It’s designed to withstand direct impacts or shatter into chunks if broken. Under the Building Code, safety glass has to be used in some areas.
Laminated glass is the best option for noise, as well as being safe and secure. Reflective, tinted and spectrally selective glass are options for keeping summer heat out.
All of these types of glass can be used with double glazing, which is the best option for winter comfort.
Double glazing
What is double glazing?
A double-glazed window uses two panes, separated by a 6-12mm gap which is filled with air or an insulating gas such as argon. It is also known as an Insulating Glass Unit (IGU).
- Typical double glazed aluminium window
How effective is double glazing?
Double glazing can make a big difference to comfort levels in your home. Combined with insulation in the walls, ceiling and floor, double glazing your windows and doors will help keep temperatures stable and reduce heating and cooling costs.
By double glazing a window with clear glass, you can halve the heat loss compared to a single-glazed window of the same size and shape. You can reduce the heat loss further by using different glass types (such as Low-E glass) and using argon gas to fill the space between the two panes of glass.
Double glazing also helps to reduce condensation.
Double glazing and noise reduction
Double glazing can also help to reduce noise levels, particularly in the medium to high frequency range (including voices). However, double glazing on its own won't filter out loud or low-frequency noise such as that from traffic.
More effective noise reduction can be achieved by using thicker glass or by using laminated glass (some laminated glass comes with a thick acoustic inter-layer). The gap between the panes can also be increased for more effective noise insulation, but this reduces the effectiveness of double glazing as a heat insulator.
Secondary glazing, solar film and other options
Secondary glazing
‘Secondary glazing’ means inserting a second pane of glass in or on to an existing window frame. This approach can help reduce heat loss and noise. It’s an alternative to retrofitting new double-glazed windows, especially for old wooden houses.
Generally, timber reveals and other structural features of the window can be kept. Check with a professional installer to see if this option is for you.
Solar films
An alternative to using tinted and reflective glass is to use a thin, flexible, transparent film to enhance a single pane. Film can be applied to almost any glazed fixture that has a frame.
Solar films can reduce glare, reduce solar heat gain, reduce fading, and reduce the likelihood of injury from breakage.
Check the cost and effectiveness of solar films for the comfort and safety level you want. If you need to keep your home warm in winter, some low-emissivity films could help reduce heat loss, but may not be the most effective option for thermal insulation. Films are an option for privacy, and for sun control in summer.
Glass blocks
Glass blocks can be used as an alternative to double glazing, for glazed areas that don’t need opening. The blocks are joined and mounted into strengthened frames.
Triple glazing
Three panes of glass are separated by air gaps to provide very high levels of heat retention and noise reduction. Triple glazing is an option for very noisy or cold locations.
More information
From Smarter Homes
From other sites
The Energywise website has information about window design and placement.
The New Zealand Window Association website has information on the Window Efficiency Rating System and window systems. You can buy a BRANZ Ltd bulletin on Window Efficiency Rating System from the BRANZ website (click on the link to the BRANZ bookshop).
