CHEAP houses built from straw bales could dramatically improve building safety in earthquake zones. That鈥檚 the conclusion from tests in the US in which a simple straw bale house withstood shaking equivalent to a major earthquake.
Originally developed a century ago in Nebraska, homes with straw-bale walls are enjoying a revival in the US and Europe because they use green materials and provide excellent insulation. But the technology could also provide protection in quakes.
Civil engineer Darcey Donovan was designing straw-bale houses in Truckee, California, when she heard of the quake that had just killed more than 75,000 people in the Kashmir region of northern Pakistan in October 2005. Most died when their homes collapsed. She volunteered to help with the recovery, and in May 2006 spent a month in the devastated area building a women鈥檚 community centre made of straw bales. She was struck by the number of people who were homeless or living in tents yet who were afraid to return to or rebuild traditional stone-and-mud homes. 鈥淚 had helped build one building, but I needed to do more,鈥� she says.
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Realising that straw-bale houses might help, Donovan came up with a design that could be built cheaply with local materials. The foundations are made with sacks of gravel, while the building鈥檚 base uses clay and sand mixed with cement. Straw bales form the walls, which can then be covered with a plaster made from clay, sand and chopped straw. The roof is made of corrugated sheet metal. In western designs, the bales serve as insulation while a wooden frame supports the load, but Donovan was able to use the straw walls for structural support by keeping the houses to a single storey. Not only are the buildings sturdier than stone, they are much lighter, so a collapse is less likely to kill anyone inside.
Donovan has since founded the organisation to promote the idea. PAKSBAB has already helped local workers build nine homes in Kashmir, all of which are now occupied.
To test how the houses would fare in an earthquake, Donovan built one on a quake simulation table at the University of Nevada in Reno. In tests late last month, it stood through a series of eight quakes of increasing intensity. The plaster cracked and flakes crumbled off in the final run, when the accelerations reached 0.82 times the force of gravity 鈥� stronger than the 7.6-magnitude Kashmir quake 鈥� but the house survived.
鈥淚n the final test, which was stronger than the Kashmir quake, the plaster cracked but the house survived鈥�
鈥淭he structure did exceptionally well,鈥� says , who runs the Reno test lab. Given refinements to speed up construction, he thinks the design has a great future in quake zones around the world.
