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Embodied Energy
In the face of climate change, the great challenge for the construction industry is to reduce the energy used by buildings. When that energy comes from fossil fuel (as most electricity in Australia does) it produces greenhouse gas emissions, which cause global warming.
The energy associated with a building can be divided into two types. One is the ongoing energy used by the people living and working in that building. Good energy-efficient design - including adequate insulation, proper use of thermal mass and passive solar design - can reduce the energy needed to cool and heat a building, while features such as solar panels and solar hot water can power appliances and lighting without using fossil fuels.
But while most of us are aware of this sort of energy use, the other key component of a building’s energy use is often overlooked. This is the building’s “embodied energy” – the energy used during construction.
Embodied energy includes the energy used to extract the raw materials, for instance by mining or logging; to turn those raw materials into building products such as timber, bricks, aluminium, concrete or steel; to transport those materials and products to your property; and to power construction tools and machinery.
A third factor affecting a building’s overall energy use is how long it lasts. Each time a home is demolished and rebuilt – or, to a lesser extent, renovated - it requires more energy and raw materials. So by building a quality home that will last longer, you will reduce the embodied energy used over the years.
Calculating the overall energy use of a building (or any other product) by taking all these elements into account is known as life-cycle assessment (LCA). The Australian Government’s scientific research organisation, CSIRO, has calculated that the embodied energy of the average Australian home is about 1,000 gigajoules – equal to about 15 years of energy use in a typical Australian household. That makes it a significant proportion of a building’s overall energy consumption.
But while it is good in principle to reduce embodied energy, it might sometimes be better to use construction materials with a higher embodied energy if it makes your home more energy efficient or longer lasting. For instance, double-brick obviously uses more bricks than a brick veneer house, which means more energy is needed to make the extra bricks. But this should result in a better insulated home, saving energy to heat and cool the building. Or, to take another example, steel has high embodied energy but can last twice as long as brick.
The optimum solution will depend on your climate. Regions with more extreme climates will need better insulation. This might justify using materials with higher embodied energy because the likely energy savings on heating and cooling will be more significant.
Issues affecting a home’s embodied energy
• The energy used to get raw materials out of the environment, such as mining or logging.
• Transport costs, whether transporting raw materials or manufactured components. Locally-sourced materials will require less energy to transport them, as will more lightweight materials.
• Building practices can make a big difference to the amount of energy used. Look for an energy-conscious builder.
• The complexity of the manufacturing process; generally, the more complex something is to make, the more energy is used to make it.
• The size of your home; the larger a home, the more material is needed to build it and therefore the higher its embodied energy. (Not to mention that larger homes also require more energy to heat and cool.)
• The amount of wastage during construction; less waste means less material is used, which means less embodied energy. Reduce waste by specifying standard sizes.
Embodied energy of different materials
Making some building materials requires more energy than making others. For instance, mud bricks made from clay from your own property require almost no energy other than human labour and sunlight. Making aluminium, on the other hand, is an extremely energy-intensive process.
• Low embodied energy
Mud brick, stabilised earth, air dried timber, concrete blocks, precast concrete, AAC.
• Medium embodied energy
Kiln dried timber, bricks.
• High embodied energy
Steel, aluminium, hardboard, particleboard, MDF, plywood, cement.
Recycled building materials
One way to reduce your home’s embodied energy is to use recycled building materials. It takes far less energy to recycle a material than to mine and/or manufacture it from scratch – for instance, recycled aluminium has only 10 per cent of the embodied energy of new aluminium. Recycled materials that can be used with hardly any modification, such as timber floorboards, doors or window frames, require no extra energy apart from the energy used to transport them to your property.
Similarly, by building with materials that can be easily recycled and reused, you are helping reduce embodied energy use of another building in the future.
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