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Housing : June 2009
Timber Feature energy efficient timber Timber has a low embodied energy. But what does it mean? Housing takes a look. E nergy efficiency in building is about – in part – ensuring that as little energy as possible is required to heat or cool a building over its lifetime and so reduce greenhouse gas emissions. The key term here for the consumer is ‘thermal comfort’. Obviously heating and cooling will have entirely different demands depending on where you live in Australia. [See box at right.] For example, Darwin and Hobart have entirely different ways of achieving thermal comfort. The issue here is that energy efficiency (read thermal comfort) must be provided, irrespective of where we build inAustralia. This has been mandated in the Building Code of Australia (BCA) since 1 January 2003. Timber can and does play a very important role here because when used in combination with other materials, for example, glassfibre insulation and/or foil, it can provide this thermal comfort using minimal energy. The connection between energy efficient buildings and energy efficient timber lies partially in discovering what timber’s embodied energy is.And it so happens that timber has a low embodied energy. Embodied energy is the energy consumed by all the processes associated with the production of a material from harvesting to product delivery. It does not include the operation nor the disposal of the product. These two relate to the lifecycle impact of a building and, along with ‘operational energy’, are concepts which demand an article in their own right and are not covered here. Embodied energy is expressed as an amount of energy per either a unit volume or mass or area. Energy is expressed in joules, which are very small units, like millimeters, and to stop the numbers from becoming very big we use mega (1 million) joules per, say, volume (m3), area (m2) or mass (kg), and written, for example, asMj/kg.A further example is Ice = 0.335Mj/kg. Embodied energy is the energy consumed by all the processes associated with the production of a material Studies have shown that the embodied energy of softwood timber framing products is in the range of 4.4Mj/kg to 9.2Mj/kg. (Table 2 refers to some other common building products and provides a frame of reference.) The point to emphasise here is that the embodied energy includes all energy expended – from the timber growing stage through to the delivery of the finished product – to a supplier. Embodied energy allows us to calculate what the energy output costs are when we take into consideration the harvesting, refining, distributing and, for example, dealing with pollution, which all use energy. In other words, if these What’s your climate classification? Cooling climate cities include: Darwin, Cairns, Mackay, Broome, Rockhampton, and Brisbane. Heating climate cities include: Hobart, Canberra, Bathurst and alpine regions of Australia. Cooling and heating climate cities include: Melbourne, Geelong, Sydney, Newcastle, Alice Springs, Perth, Adelaide, Albany, and Bunbury. Photo courtesy Boral Timber 44 HOUSING JUNE 2009