Energy Smart Homes - House Design

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Your choice of building materials can make a significant difference to the performance and comfort of your home. Dense materials such as brick, stone, concrete and rammed earth heat up and cool down slowly - they have what is called a high 'thermal mass'. Lightweight materials such as weatherboard and fibre cement allow the home to heat up and cool down quickly. These materials have a low thermal mass.

Thermal mass is simply the ability of a material to store heat. A 200 square metre home in the south west with good solar access to the north needs about 20 cubic metres of concrete and 20 to 30 cubic metres of internal brick or equivalent depending on your location (20 cubic metres for Geraldton and 30 cubic metres for Perth to Albany) to adequately store winter daytime warmth and gradually release it at night.

Thermal mass is most beneficial in homes which have good solar access to north facing windows. If solar access is limited, large amounts of thermal mass can increase your home's heating requirements during winter.

In summer, thermal mass can also help keep your home cooler during the day, provided you properly ventilate your home overnight. The aim is to allow the night air to cool down the mass inside your home, resulting in more comfortable conditions the next day.

Brick walls
Double brick walls heat up slowly and stay warm for long periods. This is an advantage during short periods of hot weather, but can make your home uncomfortable over extended hot spells. Insulating double brick walls will add to initial costs, but will help to prevent heat transfer to the interior of the home during summer and help to retain heat during winter.

Brick veneer walls consist of a single external layer of brickwork, with a lined stud frame inside. These walls have less thermal mass than double brick walls and therefore respond more quickly to temperature changes. Homes with brick veneer walls are better at cooling down during extended periods of hot weather - making conditions more comfortable at night during summer. Brick veneer walls are also easier to insulate.

Reverse brick veneer walls have the brickwork inside and lightweight frame and cladding outside. This has the advantage of providing the thermal mass on the inside of your home.

With both double brick and brick veneer walls (or any type of wall for that matter), it is important to ventilate your home in summer once the temperature outside becomes cooler than the temperature inside. This will help cool your home down and make conditions more comfortable. Retained night time coolness achieved through ventilation can also keep your home cooler during the day.

Lightweight walls
Weatherboard, fibre cement and other lightweight walls get hot quickly in the sun, but also cool down quickly once shaded and after sunset. During winter, they lose heat far more quickly than brick walls. The thermal performance of lightweight walls will improve significantly with insulation, which is cheaper and easier to install at the building stage.

Floors
Concrete floors store heat from the sun shining through northern windows in winter and return some of that heat during the evening. Laying dark tiles where the low angle winter sun hits the floor will maximise the absorption of heat to be re-radiated. It is important that this thermal mass is not exposed to direct solar energy during summer, as this can lead to uncomfortably warm internal conditions.

Timber floors do not have the high thermal mass of concrete floors. This means that a home with a timber floor will lose far more heat than one with a concrete floor. For homes on stumps which are open at the sides, it is recommended that insulation be installed to the underside of all exposed floorboards. Another solution is to fully enclose the area between the ground and the floor with a solid material like brick, but this will not be as effective as using insulation. An enclosed space under the floor will also require some permanent ventilation to control subfloor dampness.

Colour of external building materials
As a general rule, light colours tend to reflect the sun's heat while darker colours absorb it. You can take advantage of this fact when selecting the colour of your roof and wall materials. In summer, lighter coloured materials will help to keep your home cooler by reflecting heat from the sun. However if your home is properly insulated, which is a much more effective method of controlling heat transfer, the effect of external building colour on your comfort will be greatly reduced.