Using passive design to save on energy bills

How orienting your home can affect the cost of your power bills

Australia can be a climate of extremes, often requiring us to heat and cool our homes. Unfortunately, this can mean using costly appliances such as air conditioners and heaters. If like many Australians you’re reeling at the cost of your power bill, setting up your house to use the climate as natural source of heating and cooling can lower your bills and make your home more comfortable to live in all-year-round.

The good news is, with a little planning – known as passive design – you can get reduce or eliminate the need for auxiliary heating and cooling by taking advantage of the sun.

What is it?

Passive design involves orienting (positioning) your home to make the most of the sun’s direction and wind patterns. This means your home is more comfortable to live in as well as cheaper to run so it’s more energy efficient. It’s all about smart design – keep the warmth in during winter and out during summer.

A house built with ideal orientation takes into account positioning, seasonal variations, climate, and its surroundings. How the house is built also plays a part – this involves factors such as glazing; insulation; ventilation; shading; sealing (protecting against air leakage); window choice; and thermal mass (ability of a material to absorb and store heat) of the materials used for floor, walls and roof.

Why it’s important

It’s estimated that 40 per cent of energy used in the average Australian home comes from space heating and cooling. Good orientation can help reduce the reliance on external heating and cooling, assisting with the reduction of energy bills. This not only helps your bank account but the environment as well, thanks to less greenhouse gas emissions. 

Maintaining a more natural temperature range in the home tends to feel more comfortable, too – artificial heating can sometimes feel slightly suffocating and cooling, too icy.

So if these benefits sound appealing or you simply want to live more sustainably, you might want to consider your house’s orientation before you build.

What you need to know

According to Your Home – Australia's guide to environmentally sustainable homes, it’s recommended you choose a home or building site with potential for both passive heating and cooling, with the ability to adjust one or the other depending on the climate or regional conditions.

In hotter climates, good orientation for passive cooling is needed as west-facing walls and windows need shading in summer to prevent overheating.

For colder climates, the potential for passive solar heating is paramount. North-facing orientation of walls and windows is considered best as they get more solar radiation.

Unlike active solar heating that uses roof-mounted solar panels to convert sunlight into electricity, passive solar heating requires no external equipment – it gives free heating direct from the sun as it strikes through glass windows. How effectively the heat is absorbed and retained to warm up the house depends on factors such as orientation and the thermal mass of the walls.

Tips for the passive design of your home

If you’re interested in taking advantage of passive design, it’s best to start with a block of land that has good orientation or a house that can be easily adapted. Talking to a builder with experience in the field is the best way to make sure you consider all factors needed when planning, building, renovating or buying. Here are some factors that will need to be considered:

• What are your cooling and heating needs? Check your power bills to see how often you heat in winter and cool in summer.
• In winter, it’s worth ensuring the daytime living areas have passive solar access.
• You’ll need adequate glass in the north-facing areas to let in sun and warm the rooms.
• The size of your block and position of the homes around you can affect how much sun your home will be able to access.
• Smaller, shaded windows that can be opened will increase cross-ventilation to the south, east and west.
• Double-glazing helps retain heat in windows that don’t get a lot of sun.
• Utility areas such as laundries, bathrooms, garages and sheds are best positioned on the south or west side of the property.
• External structures such as pergolas with need louvres that can be opened and angled to allow for sun penetration.
• Landscaping of trees should allow for a ‘funnelling’ of cool breezes and protection against harsh winds.
• Deciduous trees are best for shading in summer while letting sun in during winter.  

If you’re already have a home that doesn't have optimum orientation, you can still apply some of these strategies to improve its thermal comfort. For instance, installing a skylight, planting trees, glazing or re-arranging living and sleeping areas can result in a big benefit!

For more info
To get assistance with passive design considerations, check local meteorological records, consult with a local energy authority, builder, architect or contact your state, territory or local government. The most thorough method is to have an accredited thermal performance assessor check your home’s thermal performance – you can find one through Australian Building Sustainability Association.