The Big Bad Wolf huffed, puffed and blew down a pig-built straw house, but the windy wolf might have met his match in a modern straw bale house. With some design specializations, a straw bale house might even be able to survive a tornado, like the one that recently killed 24 people in Oklahoma.
Straw bale construction uses plaster-coated bales anchored to a solid foundation and sturdy roof. The technique continues to grow in popularity as more builders seek environmentally-responsible, energy efficient, cost-effective architectural techniques. As straw structures become more common, more research focuses on their ability to survive disasters.
“Straw bale construction continues to prove itself across a wide range of climates and geographies,” said Colin MacDougall, civil engineering associate professor at Queen's College in Ontario, Canada. MacDougall's recent research has focused on the reaction of straw bales to physical stresses.
“It has been shown that properly designed, straw bale construction can resist wind, earthquake, fire, and insects at least as well, in some cases better, than conventional construction materials and techniques,” said MacDougall. “Our knowledge and understanding of how it works and how to best design with it, is certainly not complete, but grows every year.”
Architect Joseph Bilello's experiments using the “tornado cannon” at Texas Tech University suggested that straw bales could be used to make tornado-resistant homes. The tornado cannon shoots 2x4's at up to 100 mph at structures to test their resilience to projectiles flung by a tornado. At that speed wood beats rock. The blazing-fast boards shoot though brick walls and straw bales alike.
However, by shifting the way the straw bales were aligned, Bilello, now dean of the College of Architecture and Planning at Ball State, found that the 100 mph boards bounced off the bales. Normally, straw bales are laid lengthwise to form walls. When the bales are laid with their smaller ends facing out, they became tornado shields. Bilello explained to Discovery News that this has to do with the pattern formed by the straw when it is baled.
“Unless builders don't mind having three-foot-think walls, if people want to use straw bales to make tornado resistant structures, they will have to change the way balers bundle the straw,” said Bilello.
For now, there haven't been many real world tests of Bilello's observations.
When a tornado touched down near his southwest Missouri straw bale home, George Parsons slept soundly. Parsons is an environmental specialist for Joplin Regional Stockyard.
“I feel safer in a straw bale house than in a stick house, as I call your typical wooden house,” Parsons told Discovery News.
Despite Parsons' comfort during a close call with a tornado, the true test will come when a straw bale structure survives a direct hit from a tornado.
“Straw bale buildings do not have a good track record in tornadoes, because there is no track record,” said Michael Rakowski, design engineer with Kiewit Engineering and co-author with MacDougall on straw bale studies.
This lack of experiential evidence may make schools and home owners leery of straw bale structures as tornado shelters.
“The public probably does not see these as a viable shelter as there is no past experience,” said Rakowski. “They may work but require further research.”