Wednesday 18 Nov 2009
Smart shading can help heatproof your home, writes Michael Green.
If you shade your windows well, you'll be able to switch off your air-conditioner more often this summer, says David Hallett, the state manager of Archicentre.
“It can make you more comfortable on two fronts — it will keep your rooms cooler and ease the burden on your hip pocket as well.”
Archicentre is the advisory service of the Australian Institute of Architects. It runs free seminars on a variety of issues, including renovating and sustainable building.
Mr Hallett says the key to effective shading is to stop the sun from striking windows directly.
“Many people try to stay cool by drawing curtains or internal blinds, but the sun is still transmitting heat into the room. The trick is to stop it hitting the glass in the first place.”
Large structures such as verandas, pergolas and covered outdoor living areas can all do the job, but there's a catch.
“In Melbourne, you've got to balance keeping the sun out during the hot months with getting it in during a cold winter,” he says.
If you're planning to build or renovate, pay special attention to your eaves.
During summer, the sun tracks high in the northern sky and stays hot until late in the afternoon as it sets in the west. In winter, the sun is lower in the sky all day.
Because of this difference, it's possible to design eaves so they block sunshine in summer, but let it in throughout winter.
“If you design the building well, with living areas to the north, you will want the winter sun coming in. The calculation of eaves becomes very important,” Mr Hallett says.
Even so, you don't need to completely redesign your home just to improve its shading. Other cheap and effective tactics include installing shadecloth or outdoor blinds on your windows.
Mr Hallett warns DIYers to be cautious with shade sails. “Make sure they're designed and installed properly because they can come down in strong winds and take some of the building with them.”
Another simple strategy is to grow trees for shade. Robin Brimblecombe, a solar energy researcher at Monash University, says careful planting of deciduous trees to the north and west will help cool your home in summer while allowing sunlight in when they lose their leaves.
According to Dr Brimblecombe, US researchers recently found that houses with existing shade trees use an average of 5 per cent less electricity over summer. (For more information, see his article in the current issue of ReNew magazine.)
Before you decide on a tree variety, it's wise to contact a nursery for detailed advice.
“When you plant leafy trees you need to consider whether you've got enough water to sustain them through summer,” Dr Brimblecombe says.
Despite the extra shade, bigger isn't always better. Thirsty roots can damage pipes and foundations. Smaller trees can be very effective, especially to the west.
“For sustainability, deciduous fruit trees like apples and stone fruits are a great idea,” he says.
“You get the double benefit of shade and edible produce.” Dr Brimblecombe also suggests growing deciduous grape vines on a north-facing pergola.
“It's lovely to sit under their shade and you also get a cooling effect from the leaves as they transpire.”