Anyone who has ever gone camping will be able to tell you the basics of cross-ventilation – opening up opposite windows (or tent flaps) to allow the air to flow from one side to another.
It’s the same thing that you would do if you have to sit in your car on a hot day. One window is simply not enough, but one open on each side of the car does the trick. Now apply this to your home and you’ll find substantial reductions in your energy costs for cooling.
Cameron Rosen, managing director of Australian Living, a Sydney construction company with a sustainable bent, says the first step in planning for cross-ventilation is working out where the breezes are on your own site.
There’s several ways to do this – the simple golfer’s trick of throwing some dry grass into the air when the breeze is blowing to see which direction it’s coming from; keeping a close eye on trees, flags, a weather vane or a windsock to see how it behaves; or lastly, taking a look at the observations on the Bureau of Meteorology’s website for an area near you.
You can either see it as a wind rose (the longer arms of the rose indicate where the wind is coming from), or view a map of Australia, which gives a good insight into just how different the afternoon breezes are across Australia. There’s also a second, clickable map.
“In a summer home, it’s very important to catch that breeze in the afternoon and be able to purge or remove the heat out of the home that’s gained during the day,” says Rosen.
“You might have really good insulation and what not, but it could be [by] just operating the home, opening and shutting doors, the heat comes in.
Rosen says rather than having windows directly opposite each other, it can be helpful to have them offset somewhat. Placing windows diagonally opposite allows you to “get more of the length of a room, because a diagonal is longer than the width or the breadth”, Rosen says.
Owners of existing homes with just one window in a room where a prevailing cooling breeze enters could consider installing an exhaust fan to act as the second window. “If you’re limited to only having one window, having an exhaust fan in the room, on the other side of the room, can help you drag that heat out, to act as the window,” says Rosen.
Rosen has lived for 14 months in his Sydney home, which incorporates cross-ventilation, and admits it has been a learning experience – it wasn’t until the home was built and the window treatments were up that Rosen’s wife realised just how annoying she found the blinds flapping overnight as the cool breeze entered the home.
“I don’t think I got my cross-ventilation 100 per cent,” he says. If Rosen had his time again, he would consider plantation shutters on the bedroom windows to cut out the noise factor at night.
As well as placing the windows in the right spots, Rosen says the type of windows are important. Some – such as louvres, casement and awning windows – can help to draw in a good amount of breeze, whereas traditional double-hung windows can struggle to allow adequate air flow because they can only open so far.
Something else to look out for is having too many windows open on all sides of your home when you are trying to cool it down. “If you have all the windows in the house open the energy actually swirls, it doesn’t get out because you’ve got the pressure coming [from all] directions, so opening the front door and the back door and keeping the east-west windows shut [in a house that has doors on the north and south] is also very good,” says Rosen.
Do you know where your prevailing breezes come from in the afternoons? What are your tips for ventilating your home? Have you found certain windows better than others?
Carolyn Boyd | domain.com.au