in Greener Homes on 26 April 2009
Heal your eco-unfriendly windows.
In a typical home, windows cause more heat gain or loss than any other part of the building fabric. “Standard windows are like a thermal wound in the building envelope,” says Gary Smith, from the Australian Window Association.
You can heal the wound, but it will take good advice and careful thought. “There are hundreds and hundreds of options,” Mr Smith says. As well as cost and style, you need to consider the best fit for the window’s orientation.
When you make your choice, be aware of both the warmth that passes through the window and the frame (conduction), and the radiant heat caused when sunlight hits the glass directly (radiation).
A window’s conduction is measured by its U-value. The lower the U-value, the better its insulating qualities, and the better for your home. For insulation, double-glazing is best – or you can improve existing panes by retrofitting with (much cheaper) secondary window systems. Remember that the frames also conduct heat; preferred options are wood, high-performance or thermally broken aluminium, fibreglass or uPVC.
In Victoria, we spend more time heating our houses than cooling them – with a bit of planning the sun can help you do it for free. Make sure north-facing windows get direct sun in winter, but are shaded during summer. For these windows, choose products with a high ‘solar heat gain coefficient’, but at the east and west cut the solar heat by installing glass or films that are tinted, reflective or coated (‘low e’ glass).
Good windows are expensive up front, but will add to resale value and more than pay back over the life of the home. For the budget-conscious, Mr Smith suggests starting with living areas. “Begin fixing the main places where you spend your time. Better windows and glasses give you a huge improvement in comfort.”
Windows might be transparent, but they’re complex. This information is only part of the story so research thoroughly, seek expert advice and shop around. The Window Energy Rating Scheme website is a good place to start.