Today most new houses and additions will require double glazing to comply with the New Zealand Building Code.
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 reduce heat loss, condensation on the glass, and heating and cooling costs.
The investment will be worthwhile — a warmer, healthier, quieter home with lower power bills. There’s a lot to consider — speak with your builder, designer or window supplier about the best options.
The right glazing choices can help make your home more comfortable in both hot and cool weather whether you are building a new home or renovating.
It is worth considering retrofitting double glazing by replacing existing windows with double glazed ones, or by choosing another option such as fitting secondary glazing to existing windows.
The amount and orientation of glazing for your home will depend to a large extent on the climate and microclimate of your site. Wind, temperature, sun angles and proximity to the coast will all influence decisions about the size, type and placement of glazed areas.
There is a range of glazing options available. Some keep heat inside your home, others keep heat, noise, light and glare out.
If you’re building new, or replacing window/door frames and the glazing, choosing the right frames will help you get the best performance out of your windows, skylights and glazed doors. The table on this page provides a basic comparison of the thermal performance of a small number of common glazing and frame combinations. The higher the R-value the higher the performance — less heat will transfer from one side to another.
GLASS OPTIONS
There are many different types of glass available for double (and triple) glazing other than standard clear glass, including:
• 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 light that can get in, so are good at keeping summer heat out. The type of glass treatment determines whether infrared light (radiant heat), visible light or ultraviolet light is filtered out — ultraviolet light causes fading.
• Laminated glass consists of two sheets of glass bonded with a plastic or resin layer. It absorbs ultraviolet light and some heat and is the best option for reducing noise. If it’s hit, the glass is held together by the resin layer.
• Toughened glass is much stronger than standard glass. It’s designed to withstand direct impacts and to shatter into small chunks if broken.
Building Code clause F2.3.3 requires that glass that people are likely to come into contact with shall either break safely, resist impact or be protected by a barrier.
This glass must have a stamp on it to show that it is safety glass which meets the required standard.
You can make sure you have safety glass through the Ministry of Business, Innovation and Employment’s Building Performance website, which has more information on how to check whether glass is safety glass.
WHAT IS DOUBLE GLAZING?
A double-glazed window uses two panes, separated by a gap which is filled with air or an insulating gas such as argon. It is also known as an insulating glass unit (IGU).
Although gaps can vary between 6mm and 12mm, a 12mm gap is most common as it has the optimal insulation performance.
Argon gas is a better insulator than air, though slightly more expensive and in combination with low-E glass and high-performance frames can give an excellent thermal performance.
You can vary the glass you use for the two panes in a double glazing unit, and you can choose two different types of glass for each pane.
If you are retrofitting double glazing to your existing windows, there are three main options:
• Replacing the whole window frame with new frames.
• Installing double glazed inserts into your existing window frames — this is a cheaper option if your window frames are still in good condition.
• Installing temporary or permanent secondary glazing.
Low-E and tinted glasses can be included in these retrofit options.
TRIPLE GLAZING
Triple glazing consists of three panes of glass separated by air gaps to provide comparatively high levels of heat retention and noise reduction. Triple glazing is an option for very noisy or very cold locations but is more expensive.
NOISE REDUCTION
Glass is usually the weakest barrier to noise in the building envelope.
Standard double glazing provides a little improvement on single glazing for most sound frequencies but not always for low frequency noise.
Triple glazing is better again. If noise is a problem, options include using thicker and/or laminated glass — some laminated glass comes with a thick acoustic inter-layer — and increasing the air gap in double glazing.
Opening the windows will increase noise levels, so you’ll need to consider the best way to manage ventilation if exterior noise is an issue.
Alternatively, consider secondary glazing. It can be a better option for blocking external noise — consult an acoustician for low frequency noise or traffic noise issues.
R-VALUE
Standard aluminium with clear double glazing 0.26
Thermally broken aluminium with clear double glazing 0.31
Thermally broken aluminium with low-E, argon-filled double glazing 0.43
Timber or uPVC with clear double glazing 0.36
Timber or uPVC with low-E, argon-filled double glazing 0.53
Standard insulated wall construction R-value1.9 — SmarterHomes
