FACT SHEET
DOUBLE GLAZING
Double glazing is a proven technology for reducing heat loss by up to 80% in winter.
Double glazing Is partially effective for summer as well (but not as good as shading).
You can compare the effectiveness of different double glazing products by looking at their
technical specifications.
WHAT IS DOUBLE GLAZING? pass through the window in summer, so the
lower the better for keeping cool and avoiding
Double glazing works by trapping a still layer of the need for air conditioning. SHGC range
air between two panes of glass. Essentially it’s between about 0.3 for a very low amount of
the layer of air that does the job, not the glass heat gain, and 0.9, being a large amount of
itself. Similar to a doona on the bed in winter heat gain.
time, the thicker the still layer of air the more it
reduces heat loss and keeps you warm. This is 2. VT tells you how much daylight can
the same principle that insulation in the ceiling enter through a window. There’s always some
or walls works as well. The more still, trapped reflection off a pane of glass, so VT tends to be
air in a wall or window, the better resistance to between 0.85 (large amounts of daylight) and
heat transfer. as low as 0.3 (low amounts of daylight).
Contrary to a popular belief, double glazing
does not reduce heat gain in summer
particularly well. If you want to reduce heat
gain in summer time, shading is more effective
and often a more economical option.
TECH SPECS
Heat transfer through a window (or any part of
a building) is measured using a “U value.” The
lower the U value is, the lower the rate of heat
transfer. Double glazing typically has a much
lower level of heat transfer than a single glazed
window. A typical single glazed window has a It’s good practice to consider the VT at the
U value of 5 or 6. Double glazed windows will same time as considering the SGHC, as
have U values in a range between about 3.5 typically a tinted glazing product that blocks
and 1.5. The lower the U value the better for out summer heat will also reduce the amount
reducing winter heat loss. Popular alternatives of daylight into a building. Tinted glass with
to double glazing such as low-e single low SHGC and VT may work well for some
glazed windows are often seen as a cheaper commercial buildings, but is generally not
substitute, but the U value of a low-e window is suitable for a home, as it will block the natural
still as high as 4 or 5, and is not comparable in light and require more artificial lighting. Often
performance to double glazing. it is better to specify clear double glazing with
There are two other critical technical a separate shading device such as louvres
specifications when choosing a double glazed or retractable canvas awnings for an optimal
window: the Solar Heat Gain Coefficient result.
(SHGC) and the Visual Transmittance (VT).
Technical specifications of double glazing will
1. SHGC tells you how much heat gain can tend to state the U value, the SHGC and VT,
MORELAND LEADING THE WAY IN ENERGY EFFICIENCY
FACT SHEET
as well as the thicknesses of the glass panes double glazing include:
and the air gap. For example, a 6/12/6 double •Reduce noise pollution into buildings
glazing unit refers to 6mm thick exterior glass, •Reduce condensation build up on the inside
a 12mm air gap and 6mm thick internal glass. of windows
This tells builders and designers how wide a •Improved comfort levels
frame needs to be and helps estimate the •Reduce greenhouse gas emissions
weight of the window. Some double glazed •Reduce running costs.
windows use a gas like argon or a vaccum to
improve the heatloss even further. THINGS TO BE AWARE OF:
There is no one perfect glazing solution for •Low-e glazing does not generally perform as
every building, or every orientation, hence well as double glazing, and is not normally a
the large array of products available! You reasonable substitute
can find most reputable windows rated on •Choosing low SGHC can dramatically reduce
the Window Energy Rating Scheme (WERS) the VT and the natural daylight in a building
website, including U values, SGHC, VT and •Weight of larger DG panes of glass can prove
profile thicknesses. It can sometimes get a bit a challenge during installation.
complex, but when in doubt remember:
• The lower the U value the better for reducing In Action at Moreland City Council Facilities
winter heat loss
• The lower the SGHC the better for reducing Double glazing has been retrofitted to the
heat gain in summer existing pool hall windows of both Coburg and
• The higher the VT the better for natural Fawkner Leisure Centres. The aim of the project
daylight was to reduce the heat loss from the pool
• Compare different products on WERS website halls as they are both large energy users and
• Refer to Your Home Technical Manual for more key targets for Council’s Community Energy
detail. Efficiency Program (CEEP). Council estimates
that the double glazing will reduce the heating
BENEFITS consumption by approximately $5,000 per
year at Coburg Leisure Centre and $3,000 per
The benefits of double glazing are well year at Fawkner. See case studies for more
documented and are not just about reducing information.
energy consumption. The main benefits of
In Action at FAWKNER LEISURE CENTRE
BEFORE DOUBLE GLAZING AFTER DOUBLE GLAZING
This activity received funding from Australian Government as part of the
Community Energy Efficiency Program. This was matched by Council Carbon
Management Strategy (CMS) funds. The views expressed herein are not nec-
essarily the views of the Commonwealth of Australia, and the Commonwealth
does not accept responsibility for any information or advice contained herein.
MORELAND LEADING THE WAY IN ENERGY EFFICIENCY
