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April 28, 2009

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Straw bale house survives earthquake tests

April 6, 2009
Courtesy University of Nevada, Reno
and World Science staff

It huffed and puffed, but an earth­quake-simula­t­ion ta­ble with a force re­port­ed as 82 tons could­n’t knock down a straw bale house de­signed and built by civ­il en­gi­neer Dar­cey Dono­van.

The 14-by-14-foot (4.3 me­ter) dwell­ing with clay plas­ter walls un­der­went twice the ac­celera­t­ion and shak­ing as recorded at the 1994 Northridge, Ca­lif. earth­quake, the larg­est meas­ured ground ac­celera­t­ion in the world, Dono­van said.

A straw bale house is test­ed for quake re­s­is­tance at the Uni­ver­sity of Ne­va­da, Re­no. (Cre­dit: Mike Wol­ter­beek, U. of Ne­va­da, Re­no)

In the last of sev­en in­creas­ingly vi­o­lent tests, the house cracked, swayed and sent out a small cloud of dust and straw — but stayed erect. Dono­van over­saw the tests March 27 at the Uni­ver­s­ity of Ne­vada, Re­no, where she is an alum­na. 

She has been build­ing si­m­i­lar homes since 2006 through­out the north­west fron­tier of Pa­ki­stan, in the Him­a­la­ya foothills be­tween the trib­al ar­eas and Kash­mir. A 2005 earth­quake in Kash­mir, meas­ured at mag­ni­tude 7.6, killed 100,000 peo­ple, most of whom per­ished af­ter their flim­sy homes fell on them as they slept.

Dono­van uses bales for struc­tur­al sup­port rath­er than just as in­sula­t­ion as in oth­er straw-bale de­signs. 

“Our goal is to get the larg­est num­ber of poor peo­ple in­to earth­quake-safe homes. We want to make it as af­ford­a­ble as pos­si­ble,” Dono­van said. “S­traw bale hous­es are used around the world, but those have posts and beams for sup­port and rely on en­er­gy-intensive ma­te­ri­als, skilled la­bor and com­plex ma­chin­ery, mak­ing it un­af­ford­a­ble for the poor.”

“Our de­sign is half the cost of con­ven­tion­al earth­quake-safe con­struc­tion in Pa­ki­stan,” she added. “The ma­te­ri­als we use — clay soil, straw and grav­el — are readily avail­a­ble; and we uti­lize un­skilled la­bor.”

Part of the trick to Dono­van’s de­sign, she said, is simply pack­ing the straw hard. “We build a small, steel com­pres­sion box, pack it with straw, which is readily avail­a­ble from the Pun­jab Dis­trict, lit­er­ally stomp on it to com­press it, add a lit­tle more, stomp on it a lit­tle more, and then fi­nally use stand­ard farm-type hand jacks to do the fi­nal com­pressing of the bales,” she ex­plained.

“We fill old vegeta­ble sacks with grav­el, like sand­bags, for the founda­t­ion. The bags are fully en­cased, or boxed, in a mor­tar made from clay soil and ce­ment. It’s as low-tech as pos­si­ble.” The build­ings are 80 per­cent more en­er­gy ef­fi­cient than mod­ern con­ven­tion­al build­ings, con­tin­ued Dono­van, whose group al­so trains lo­cal res­i­dents how to build the homes.

While the re­gion lacks build­ing codes, Dono­van and a group she founded, Pa­ki­stan Straw Bale and Ap­pro­pri­ate Build­ing or­gan­iz­a­tion (paksbab.org) are seek­ing an en­dorse­ment from Pa­ki­stan’s newly formed Earth­quake Recon­struc­tion and Re­ha­bilita­t­ion Au­thor­ity.

* * *

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It huffed and puffed, but an 82-ton-force earthquake-simulation table couldn’t knock down a straw bale house designed and built by civil engineer Darcey Donovan. The 14-by-14-foot (4.3 meter) dwelling with clay plaster walls underwent twice the acceleration and shaking as recorded at the 1994 Northridge, Calif. earthquake, the largest measured ground acceleration in the world, Donovan said. In the last of seven increasingly violent tests, the house cracked, swayed and sent out a small cloud of dust and straw — but stayed erect. Donovan oversaw the tests March 27 at the University of Nevada, Reno, where she is an alumna. She has been building similar homes since 2006 throughout the northwest frontier of Pakistan, in the Himalaya foothills between Pakistani tribal areas and Kashmir. A 2005 earthquake in Kashmir, measured at magnitude 7.6, killed 100,000 people, most of whom perished after their flimsy homes fell on them as they slept. Donovan uses bales for structural support rather than just as insulation as in other straw-bale designs. “Our goal is to get the largest number of poor people into earthquake-safe homes. We want to make it as affordable as possible,” Donovan said. “Straw bale houses are used around the world, but those have posts and beams for support and rely on energy-intensive materials, skilled labor and complex machinery, making it unaffordable for the poor.” “Our design is half the cost of conventional earthquake-safe construction in Pakistan,” she added. “The materials we use — clay soil, straw and gravel — are readily available; and we utilize unskilled labor.” Part of the trick to Donovan’s design, she said, is simply packing the straw hard. “We build a small, steel compression box, pack it with straw, which is readily available from the Punjab District, literally stomp on it to compress it, add a little more, stomp on it a little more, and then finally use standard farm-type hand jacks to do the final compressing of the bales,” she explained. “We fill old vegetable sacks with gravel, like sandbags, for the foundation. The bags are fully encased, or boxed, in a mortar made from clay soil and cement. It’s as low-tech as possible.” The buildings are 80 percent more energy efficient than modern conventional buildings, continued Donovan, whose group also trains local residents how to build the homes. While the region lacks building codes, Donovan and a group she founded, Pakistan Straw Bale and Appropriate Building organization (paksbab.org) are seeking an endorsement from Pakistan’s newly formed Earthquake Reconstruction and Rehabilitation Authority.