You are building a home, possibly your first, equal parts excitement and stress gurgle around in your stomach. It seems like there are a million things to do, and you can’t help but look at your bank balance four times a day. Have you chosen the right neighbourhood? Do you really like those downstairs tiles? Will it be big enough, and where will guests sleep? Energy efficiency might sound like a bit of a non-issue amongst all that needs to be done, but you only get one chance to do it properly. An energy efficient home will save you money, benefit the environment, and most importantly improve your living space.
Consider these four major points of Energy Efficient Home Design:
Building an energy efficient home is all about orientating the house design to align with the natural process of your environment and save energy.
Using principles like passive solar heating and cooling and an understanding of your climate, you can use the predictability of your environment to save on, or do away with, auxiliary heating and cooling.
Local Climate Research
Before you start designing an energy efficient home, you need to research the location. Australia’s climate varies a lot depending on where you are building, and therefore some research will best inform your energy efficient housing design.
Climate Research Checklist:
Angle of the sun: You need to know this to work out how much light will get through your windows in different seasons. If you are building in Rockhampton, you need a completely different approach to window and wall orientation than if you are building an energy home in Perth.
Temperature: You how cold does it get in winter and how warm in summer. What is the difference between daytime and nighttime temperature? You will need to know this so that your energy efficient home design accounts for changes in temperature
Direction of the wind: A good breeze will cool your house and give it a fresh feeling.
Passive Solar Heating for Energy Efficiency
Let’s start with the basics. If you want to heat your house in winter but keep it cool in the summer, you need to orientate your house to the north. This is due to the movement of the sun. If you are south of the Tropic of Capricorn, the sun sits in the north of the sky. It still tracks east to west, but shines down at an angle. Energy efficient homes take advantage of that angle and build north facing walls. Because the sun is at a higher angle in summer, an eve or a sail can cast a shadow over a wall that will get direct sunlight in winter. Focus on building long north facing walls but remember that solar north is different from magnetic north in most of Australia.
A single pane window can lose 10 times the heat of an insulated wall in an hour. This makes windows your biggest liability, and your biggest asset when designing an environmentally friendly house. Most people will agree that you need windows, so it quickly becomes a question of where to put them. Just like you want a lot of wall facing north, to catch winter sun, you want a lot of windows pointing in that direction. They will let the sun in all winter, and if you shade them in summer, with a pergola or adjustable shade, the sunlight, cast from a higher angle, won’t get to them.
You can’t just have windows on one side of your house. What you would save by cooling the house, you would spend running lights on the side without windows. What you can do is shade these windows properly to mediate the day’s temperature extreme. If windows face to the east or west, you should shade with an awning or a blind. An east window will warm in the morning, and a west window will warm in the evening. In winter a thick set of blinds or curtains will keep the heat in by creating a pocket of warm air. Double glazed windows are another great way to keep heat in, but they still need to be shaded in hot climates.
Placing windows isn’t just about the sun. A breeze, and air flow, can make a house feel colder in summer, and who doesn’t feel like a space that is fresher/cleaner because a breeze is moving through it? Building windows across from one another is an effective way to create a breeze in your energy efficient home.
The Australian Bureau of Meteorology takes daily measurements of wind speed and direction. It is a great resource, but it doesn’t record the night time and late afternoon winds that make or break a good night’s sleep. On the East Coast, the wind is predominantly north-easterly to south-easterly, while on the West Coast south-westerly breezes are common. Talk to the landowner, do some research, and chat with neighbours to learn more about the breeze flow.
Think about other ways to shade a window. Trees are an effective way to block the sun. You should plant evergreen trees in hot climates, and deciduous trees in cold climates. If you do this, the trees won’t block the sun when you need it. You should also consider the site. If there is a double story house blocking all your northern sun, well you might want to orientate differently.
Colour and its Effect on House Temperature
Just slapping on a lighter or darker coat of paint can be the difference between a hot box and an energy efficient house. Light coloured roofs, for example, can reflect up to 70% of the sun’s energy, but it is a double-edged sword. A lighter roof will lead to a house that is colder in both summer and in winter. Think of it like wearing a black or a white shirt, but your house has to wear that shirt all year round. It’s best to just stay away from black and white roofs unless you live in a very hot or very cold climate.
Open plan living is modern and welcoming, but it is also very expensive to heat and cool. If you are planning to invest in an air con or a heater, you should make sure you can partition the space. You can do this with good old fashioned doors. This isn’t always practical or the best design choice. Look into French and rolling doors if you want open plan living that you can close off to heat or cool.
Downstairs is cooler than upstairs. Heat rises, and the top floor shades the bottom from all that energy that hits the roof and heats the air. In a warm climate, you should put living areas down stairs and reserve upstairs for rooms that you don’t have to spend that much time in. In a colder climate, do the opposite. Either way you are saving on cooling or heating by planning your energy efficient home in accordance with how you are going to use it.
Thermal Mass and Insulation
People confuse thermal mass with insulation, but they are two really different things. Think of thermal mass like a battery that stores heat. Materials have something called heat capacity. Basically different materials are better or worse at retaining heat.
Insulation is intended to stop heat moving from place to place. In a way, it is kind of the opposite of thermal mass. Both of these techniques have pros and cons, and they are both applicable to different energy conservation applications.
The mass will start to warm when the sun first shines on it. This mass can be a concrete wall or floor on the other side of a window. If the thermal mass is well thought out, it will reach its heat capacity from the heat of the day. In the afternoon, the mass will start to cool as it gives off heat, and this will warm the inside of the house. Thermal mass will work better in some climates than others. The technique is best for places that are uncomfortably warm in the heat of the day and uncomfortably cold at night. It evens out the extremes in temperature.
In climates where the nights are uncomfortably hot, or the days uncomfortably cold, thermal mass is going to enhance these unpleasant temperature extremes. In the heat of far North Queensland, houses are built out of wood because it is a material that doesn’t store much thermal energy. This doesn’t cool the days, but it also won’t heat the nights.
Insulation works by slowing conductive heat flow. Conductive heat is when you place a spoon in a warm cup of tea, and the hot water heats the spoon. Heat moves from hot to cold, and Insulation works by building a barrier between the two. When it is cold, the excess heat in your house moves outside, and when it is hot, the heat moves inside to warm your cold house. Insulation can’t warm or cool anything by itself, but it is great for keeping things at their current temperature. This makes it perfect for hot and cold climates.
This is intended as just a quick overview and some things to consider when you are designing an energy efficient home. There is no substitute for a floor plan designed by a professional, and this should only be the beginning of your research. Take the time to design an energy efficient home, and you will save money in the long run. You only get to build this house once do it properly the first time around.