Glazing refers to the layers of glass that are sealed in a frame to make up a window. Traditionally, single glazing, with just one pane of glass in the frame, was used.
Today, double glazing, with two layers of glass – or even triple glazing, with three layers – is increasingly popular because it reduces the amount of heat lost through windows and helps increase the energy efficiency of your home.
A single pane of glass provides very poor insulation because glass is a good conductor of heat. Much of the heat in your room literally goes out the window.
Install double glazing and you have a layer of air trapped between two panes of glass. Because air is a poor conductor of heat, much less heat is lost through the window.
If the inside of one pane has Low E coating, even less heat is lost, because the coating reflects heat back into the room.
Single, double or triple glazing refers to the number of panes of glass that are sealed in a frame to make up a window.
Double or triple glazing has a layer of insulating air, or other gas, between panes that acts in a similar way to a fibreglass batt in a wall. It reduces heat loss from windows and increases comfort and warmth.
Other benefits of double or triple glazing can include lower energy bills and reduced noise.
A Low E glass coating can further boost the benefits of double or triple glazing.
Thermal performance measures effectiveness of glazing and shows the difference double and triple glazing can make to improving the energy efficiency of your home.
keeps you warm in winter, cool in summer
reduces energy bills
replaces thermal drapes
reduces noise
reduces condensation
requires minimal maintenance
improves security
upgrades and adds value to your home
For new builds, double or triple glazing can help you meet the requirements for energy efficiency in line with The New Zealand Building Code requirement for new residential construction. (Internal link to the Energy Efficiency section of this Guide)
A single pane of glass offers very poor insulation, leading to a lot of heat lost through the glass in winter. Double – or triple – glazing traps air between two (or three) panes of glass, which by comparison to single glazing has twice the heat loss of double glazing.
Heat loss can be further reduced by coating one or more panes with transparent Low Emissivity (Low E) coating, which reflects the heat back into the room.
Thermally efficient window frames also help prevent heat loss and are ideally teamed with double or triple glazing. Other special glass treatments can be used in double or triple glazing for safety, security or fire resistance, or to match your decor.
Thermal performance measures the effectiveness of glazing in reducing heat loss. This measure is called a U value and can provide a useful guide to the difference double or triple glazing could make in your home.
The higher the U value, the less energy efficient the window is, meaning more heat is lost. The U value of a single-glazed window can be 5 or higher, while a triple-glazed window could have a U value of less than 1.
A useful measure of energy efficiency is our WEERS (Window Energy Efficiency Rating System) which rates the actual energy efficiency of the windows you purchase for your home.
Window and glazing combinations are usually referred to by R value, which is the reciprocal of the U value. This makes it easier to relate to roof, wall, and floor insulation values as they are described in the Building Code. In opposition to U values, with R values the higher the number the better the performance.
The following Table has been extracted from H1/AS1 – 5th Edition and describes the Construction R values of a range of generic frame and glazing combinations. These values represent the weighted average of a typical houselot of windows and doors. Large and complex housing projects may require the calculation of the R values specific to the project selections.
For most homes in New Zealand, double glazing will be enough to significantly improve comfort and warmth and increase energy efficiency. Triple glazing is likely to be of most benefit to people in the coldest parts of the country or where noise pollution is an issue.
A pane of double (and triple) glazing is referred to as an IGU (Insulating Glass Unit) within the Window & Glass industry.
As with all manufactured products, IGU’s have a foreseeable lifespan. When, under normal use conditions, condensation (fogging) occurs within the space between the panes, the unit is deemed to have reached the end of its useful life. IGU’s typically carry a 10-year warranty and as the purchaser you will expect your glazing to last longer than the warranty period, but you do not, or should not, believe it will last forever, even if well maintained.
With NZ’s diverse climatic conditions, during its life, your IGU is exposed to a range of environmental influences, including temperature and atmospheric pressure fluctuations, wind loads, sunlight / UV light, water, and water vapour and in coastal locations salt laden sea air. In service history both internationally and within in NZ has shown a variety of IGU life expectancies depending not only on these environmental factors, but also on the design of the unit, its installation and how well it is maintained. To ensure the highest probability of a long life for your IGU’s, we recommend you use units supplied by a member of the IGUMA (Insulated Glass Unit Manufacturers Association) and installed in accordance with industry guidelines.