Windows (and glass doors) are an essential part of any building. We need them to connect us to the outdoors for natural light, views, to create breezes for cooling, and many other aspects of occupant health and wellbeing. But windows are the weakest component of the building enclosure (or envelope).
"Up to 40% of a home’s heating energy can be lost and up to 87% of its heat gained through windows." (yourhome.gov.au)
What is double glazing?
The most common window in Australian homes of recent decades is the single glazed aluminium framed unit. These feature uncontrolled heat gain (in summer) or heat loss (in winter) through conduction = a high U-value (how readily a window system conducts heat - and the lower the U-value, the better). Combined with a typical aluminium frame, single glazed windows provide a direct path for the flow of heat between the indoors and exterior. You only have to touch one of these frames on a hot summer afternoon to realise how well they conduct heat! You may also have cleaned mould growth off them due to condensation repeatedly forming on the cold frame during winter mornings - not pleasant to see, touch or breathe!
So how do we combat this? Enter double glazing…
Double glazed insulated glass units (IGUs) feature 2 layers of glass separated by an air gap, and they restrict the flow of heat in or out of the building. Good quality units also come with thermally-broken frames: there is a layer of insulating material separating the interior and exterior frame components to control heat flow even further.
(Image source: AWS https://www.awsaustralia.com.au/thermalheart)
Why double glazing?
There are many benefits to selecting double glazed IGUs over standard single glazing for your home, including:
Increased insulation of building envelope
Reduced heating & cooling loads = ongoing running cost savings
Increased comfort, by reducing drafts caused by the contrasting temperatures of the glass surface to interior air temperature
Reduced noise entering from outside the home
Increased safety and security
Choosing double glazed IGUs will increase the initial construction cost - a cost that will reduce energy demand of the building for every year of its life.
What to look for when selecting windows?
Thermally-broken frames
WERS (Window Energy Rating Scheme) Certified products: these have been fully assessed for window energy performance
Can be combined with advanced coatings (low-e) for optimal performance
Site, window location and solar access, as well as gap width and other window specifications all need to be taken into consideration when selecting windows for your home, so consult a professional to make sure you are getting the right window for the right place
Not a magic bullet
Double glazing must be combined with other elements of passive design (effective shading, window coverings, insulation, orientation…). Working in tandem with the rest of the building envelope, they will help keep the heat where you want it, and increase the comfort and efficiency of your home.