I was driving to a meeting the other day and I went past a construction site for a new house. I gasped! I was shocked! The house was…well basically, a black cube.
Why was I shocked? In subtropical Queensland, your key house design should be focused on keeping your house cool, and some of the best ways to do that without using air conditioners, is to create plenty of crossflow ventilation, provide shade for your windows (as a minimum), and choose a light colour for your walls and roof.
But then I had to stop myself! “Hang on a minute”, I thought – my house is also a dark colour (charcoal grey). So why does my place stay cool in summer and why does it look like this house wouldn’t without a whole lot of energy?
Let’s examine some basic design features of each house.
My house is a single storey, long rectangle.
The new house is a two-storey, almost cube shape, with a flat roof. Hot air rises so upper storeys are always warmer than the bottom level. In summer if there is no way for the heat to escape, the upper storey can become a hot box. In winter, if you are heating up your downstairs area because that’s where you are spending your time, all the heat flows upstairs unless you can trap it.
The external walls of my house are painted in a dark colour but our roof is cream coloured (we had the roof replaced just a few months ago from the dark grey flat concrete tiles to corrugated iron of a low solar absorptance colour).
As mentioned already the new house has black walls (or very dark grey). I admit I couldn’t see the roof colour but my guess was one that matched the walls. When you realise that the difference between a white roof and a black one is almost 20 degrees Celsius inside the house, you can appreciate that black is good for cold climates, but it doesn’t really cut it for Brisbane.
[Colorbond colours, http://colorbond.com/colour]
Of the colours in the palette above, only one is rated to have low solar asbsorptance according to the Building Code of Australia – can you pick which one it is?
[Visit http://www.steel.com.au/products/coated-steel/colorbond-steel/basix-and-bca-classification if you want to learn more]
Although bringing in daylight is good all year long, the trick in summer is not to let the light enter the house. There is plenty of ambient light outside to make it bright inside without letting the sun come right in. One of the basic design features of a house which controls that are the eaves. Yes, the simple eave has more than one role to play in a house. Besides protecting your windows and walls from the rain, keeping moisture away from the house and providing you with a dry place to walk around the house, eaves also play a part in shading your house. An eave properly designed for the latitude you live in, will let sun in during winter and will keep it out during summer. The width of the eaves at my house are 900mm which is just right for the full length windows I have on the eastern side and is plenty for the 600mm high windows on the western side.
The new house has no eaves. Walls and windows are completely exposed to the weather (rain, sun, etc.). As far as I could see there are no other external design features to shade the windows or walls – for the moment. No awnings, pergolas, verandahs, etc. Trees seemed to be lacking as well with the house taking up most of the block (except maybe at the rear). My house is surrounded by trees but even so, the western wall was not getting shaded in summer and I had to install a retractable awning to keep the afternoon sun off my kitchen wall. I chose a retractable one because in winter I want all the sunlight I can get!
[Visit http://www.yourhome.gov.au/passive-design/shading to see how to calculate the right size eaves for your windows and latitude]
Without knowing if there are other internal design features which will assist in the climate control of the house, I suspect that a fairly powerful air conditioning system will be required to keep the occupants of this house comfortable in summer. In the meantime, I better get started with stacking up some wood for winter.
If you want to learn more about how to make your house comfortable all year long and keep you bills low, then check out our workshop: Buyers Guide to Builders – Sustainability Series. There is a lot of information out there already if you are willing to spend the time looking. With our workshop we give you all the best hints and tips to get you started. We cover more than just energy saving measures: water, waste, materials, environment and community are all considered. Visit https://www.buyersguidetobuilders.com.au for more.