Straw bale construction
in Greener Homes on 30 May 2010
The first little piggy had the right idea.
MARK Dearricott had worked for a decade as a bricklayer when he decided to help a friend with his straw bale construction business. “I thought it was pretty dodgy, building houses out of straw,” he admits. “But after the first few, I realised its potential was tremendous. It’s a brilliant material.”
Mr Dearricott now runs Professional Strawbale, and has built about 200 houses across Victoria. He’s flat out with projects and inquiries, often for the suburbs. “It’s a very versatile material. It suits any design, from a cute little cottage to a super-straight, ultra-modern house.”
He says a professionally built straw bale dwelling costs about 15 per cent more than standard brick-veneer, but makes for a much more comfortable home, with exceptional insulation and sound proofing.
Construction techniques vary: straw bales can be used in load bearing walls or as in-fill for a timber frame. In both cases, the bales are laid like giant bricks and then sealed with lime, cement or earthen render.
Mr Dearricott favours conventional post-and-beam frames for ease of construction and compliance with council regulations. He warns that while regional councils are now accustomed to straw bale homes, the planning process may not be so smooth with inner-city councils.
He says would-be clients have three main concerns: mice, water and fire. The render, usually about five centimetres thick, protects the bales against all three. “The straw is completely sealed,” he says. “Everything is rendered, including the tops of the walls.”
Nevertheless, it’s wise to include well-designed eaves to shelter the walls from the prevailing weather – they’re a must if you use earthen render.
Surprisingly, the bales don’t present an added bushfire risk. CSIRO testing, conducted in 2002, found that rendered bales are non-combustible under bushfire conditions. “The straw is compacted tightly and it won’t burn because there isn’t enough oxygen flow,” Mr Dearricott says.
Chris Rule and his family built their straw bale home near Bendigo five years ago. Mr Rule, a cartoonist and writer, has since designed and built another straw bale house and recently became a registered builder. “Straw bale enticed me into it,” he says. “It looks beautiful and its possibilities are so interesting.”
One of those possibilities is for householders to do some of the construction, and save on their costs. On a recent project, the owner and his friends spent a day laying the bales. “They had a lovely time learning how to do it,” Mr Rule says. “There was a real picnic atmosphere and they were building a house. It’s very low-tech, forgiving and fixable, so you can be involved. In the housing industry, people generally don’t get involved.”
He acknowledges that although the insulation provided by the bales is excellent, it’s just one part of good solar passive design. “If the house gets sun at the wrong time of the year and you haven’t designed your windows well, a straw bale home can shocking because the heat stays inside.”
As a building material, bales have many pluses. Straw is a waste product, often burned at season’s end; using it in construction stores carbon. It’s also renewable, biodegradable and non-toxic. When it’s sourced locally, Mr Rule says, it has very low embodied energy. “We got our straw from 2 kilometres down the road, opposite our family farm.”