Now it's green grow the houses

In the future, we will live in homes made out of straw. If we're serious about minimising the carbon footprint of our homes, then straw bales, coated in plaster, are the way to go - and the Clark Government does seem serious.

If you thought the food miles debate was global warming moved too close to the sun, the Government's sudden focus on the embodied energy in our homes is even more esoteric. Embodied energy is the energy used to produce a final product from raw materials, from reinforced concrete to taps.

It's the front end of a bid to put a carbon footprint on our homes by calculating their whole-of-life energy output. It's a whole new way of looking at a plank of wood.
It promises much: lower greenhouse gas emissions, lower household energy bills, healthier homes and, some say, cheaper homes. Manufacturers will need to adapt products to minimise their carbon cost or face extinction. Our homes will be rated according to their lifetime carbon output - the more efficient, the higher the market value.

Sustainable housing is a path we're already some way down, and law changes require double glazing and more insulation in most areas, energy efficient lighting in new commercial buildings and incentives on offer for solar water hearing. Many homeowners and some property developers are voluntarily going further, aiming to reduce a building's operational energy output.


But lifecycle assessment goes the whole buffalo: considering the energy used in the manufacture of components, and the transporting of materials, through to the energy used in the building's eventual demolition.

What's envisaged is a time when houses will be rated according to their lifetime energy consumption, or carbon output. Architects will design to a carbon maximum, choosing long-lasting materials with low-embodied energy. Potential for end-use recycling will be factored in.

The manufacture of a cubic metre of baled, compressed straw consumes 31 megajoules. A cubic metre of ready mix concrete uses 2350 megajoules. Convert that to carbon-equivalent emissions and the obvious conclusion: concrete bad; straw bales good. But it's not that simple - what, for instance, if the concrete is recycled?

Last year, Scion looked at the energy required to build and run an average house for 50 years. The study concluded that operational energy use was more significant over the life of the house. But embodied energy is still significant and can be as high as 30 to 40 per cent of carbon equivalent emissions over the 50 years, says Nebel
"The more insulation you put into the house, obviously the higher the embodied energy will be. So it's not necessarily a bad thing to have high embodied energy. You have to take the two in combination - you need quite a lot of insulation before you reach the tipping point."
"Designers and regulators will have to be particularly careful in their decision making in this area if they are not to push housing and material costs to higher levels and cause confusion in the marketplace.

"The key will be to ensure that regulators and policy makers adopt an approach based on proven methodologies, not unsubstantiated theories."

Green Building Council chief executive Jane Henley is worried the Government is too focused on emissions. "From a sustainability perspective we risk losing sight of other environmental impacts such as waste and water." The biggest issue seems to be where to draw the line.
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