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How green is your renovation? The life cycle of homes

March 2012

  • John Thwaites

Home renovation is a national pastime for Australians. Whether it is TV shows like The Renovators and The Block or whether we just like to keep up with our neighbours, something is leading us to spend a fortune on extensions out the back, en suites and new kitchens. Australians spend about as much each year on upgrading existing homes as we do on building new ones.

When our family decided to do the standard back extension to an existing Edwardian home, I was surprised at the size of the builder’s quote.

“But I could buy a whole house for this,” I said. “Well you are, and there is a lot of demolition involved as well,” the builder not unreasonably replied.

At the same time that we are adding on rooms to existing houses, new houses are getting bigger and bigger. The average size of new houses has grown by about 40 percent over the last twenty years. This not only has a financial cost but an environmental cost as well in the energy, water and materials used in construction and in the energy needed to heat and cool our larger homes.

Last month I wrote about the life cycle of clothes and their impact on the environment. It turns out that most of the environmental impact comes not from production of clothes but from consumer use: washing, ironing and drying them.

But what about buildings? How much of their environmental impact comes from building construction and materials? And how much comes from their occupation?

Traditionally sustainability experts have focused on energy use in buildings: the energy used to heat and cool them and to run lights and appliances. This is understandable as buildings use around 40 percent of Australia’s energy and produce around 20 percent of our greenhouse gas emissions. Building regulations have been introduced to improve design and thermal efficiency and new buildings must now be built to a six star standard. As well, more efficient heating and cooling systems and appliances are available that can slash energy use and greenhouse emissions.

Just as life cycle assessment (LCA) enables us to better understand the environmental impact of clothing, so also it can help with buildings. In Melbourne we have experts in this life cycle assessment including Professor Ralph Horne and his team at the Centre for Design at RMIT.

Professor Horne has carried out a case study of housing in Victoria that compares the energy required for the whole building life cycle: the materials used in construction, the operational energy required to heat and cool it, and maintenance over a fifty year life of the house. The study reviewed four housing types: brick veneer with a concrete slab, mud brick with a concrete slab, weatherboard with a concrete slab and weatherboard with a timber sub-floor.

In the construction phase, the mud brick house with a concrete slab had the lowest emissions, because the production of mud bricks was far less energy intensive than producing commercial bricks or timber. The weatherboard with a timber sub-floor had less energy demand than the houses with a concrete slab because of the high energy and greenhouse gas emissions associated with the production of cement: approximately one kilogram of carbon dioxide for each kilogram of cement produced.

However, a different story emerged when Professor Horne investigated the operational energy demand for heating and cooling of the different housing types over a fifty year life. Here the brick veneer on a concrete slab performed best and the mud brick house used 70 percent more energy. Essentially this is because the mud brick house had no cavity wall or insulation and so required a lot of heating in the Victorian winter.

So which is more important – the embodied energy in the construction phase (where the mud brick performed best) or the energy used in operating the house over its lifespan (where the brick veneer did better)?

Professor Horne found that taking the whole life cycle into account including construction, operation and maintenance, the brick veneer used about 30 percent less energy than the mud brick. He found that in all cases the lifetime operational energy used was much greater than the embodied energy. In the mud brick house the operational energy represented nearly 90 percent of total energy and in the brick veneer it was around 70 percent.

However, Professor Horne also found that in very energy efficient housing, embodied energy comprises a greater proportion of lifecycle energy: up to 60 percent. As energy efficiency standards improve, embodied energy will become increasingly important. This is an important finding because our building regulations currently only cover operational performance and not the whole life cycle.

Embodied energy becomes increasingly important when we renovate our homes regularly. As part of the house is demolished and replaced, a lot of the building fabric becomes waste. New materials represent considerable extra embodied energy in our homes. The more frequently we renovate the greater the proportion of embodied energy.

Last month I pointed to Tullia Jack’s research that indicated we could cut down our environmental impact by reducing unnecessary washing of clothes. Perhaps we also need to make our home renovations a little more modest, or at least recycle as many of the building materials as possible.

John Thwaites, former Deputy Premier of Victoria, is Professorial Fellow Monash University and Chair of the Monash Sustainability Institute.





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