Straw used for construction in Southwest

Due to a high demand nationwide for building products such as cement, steel and plywood, a few contractors in the Southwest are building with unusual materials — including two-foot-thick rice straw bales.

At a 20,000-square-foot office building being built in Santa Clarita, Calif., straw bales are being stacked like blocks on top of steel rebar. The blocks, which are held together by the rebar, will be tied down with steel cables and then covered with stucco. When completed, city leaders hope to get the building certified as a “green building” by the U.S. Green Building Council, an association of contractors who promote environmentally friendly construction.

Jim Ament, the project’s construction manager, said the method is friendly to the environment because it uses a product that is readily available and renewable.

“You take something that’s basically trash and you’re reusing it,” Ament told the Los Angeles Daily News.

City officials were hesitant about the building method when the project architect first proposed it, said Tom Nelson of HOK Sustainable Design. But after comparing pricing with more traditional construction methods, the city adopted the straw technique. The city’s $15.9 million Transit Maintenance Facility is to be completed by early 2005.

According to the California Straw Building Association, straw buildings have existed since the 1800s, but have not been used in construction in California since 1995, when building codes for the method were adopted. Codes for straw construction also exist in Arizona, Texas, Colorado and New Mexico.

Part of the reason for the popularity of straw building in the Southwest is their insulation rating — up to R58. An insulation rating of R19 is most common in traditional wood or brick buildings. Straw structures also do well in the dry heat, according to the CSBA. While straw, once covered with plaster, is longer lasting and can withstand decades of rain, the CSBA’s website states that straw construction does better in the low-humidity climate of the Southwest because the straw walls quickly dry out after rain. The more humidity in the air, the higher the chances of the straw decomposing.

Heather Merenda, the sustainability planner for Santa Clarita, told the Los Angeles Daily one concern city officials had about the construction method was its fire safety. Once covered with stucco, however, the bales have a fire resistance of about two hours. Without stucco, that resistance is reduced to 30 minutes.

What about pipes and electrical wiring? According to the CSBA, straw construction contractors often take the precaution of installing pipes that will not sweat or leak inside continuous sleeves within bale walls. Ordinary Romex is often used in bale walls, and UF cable, rated for direct burial, is sometimes used where extra caution is needed. The Romex or cable is set three inches into the bale walls, safe from punctures.

Because straw bale construction is used in areas prone to earthquakes, a conventional wood post-and-beam system carries vertical loads.

To find out more about straw bale construction, click on the link to the right.