ConstructionPro Week, Volume: Construction Advisor Today - Issue: 15 - 08/05/2009

Straw Bale Construction

In the familiar children's story The Three Little Pigs, the smart pig was the one who built his house of bricks. The foolish pig built his house of sticks. The lazy and stupid pig built his house of straw.  As it turns out -- assuming a home is more than just a fortress against attacking wolves -- straw may be the most intelligent choice after all.  Straw bale construction is an increasingly popular way of making homes cheaper, more energy efficient, safer and more sustainable in the consumption of building materials.

 

Energy Efficient Numbers
Straw bale is more energy efficient, because with all the air, and heat, trapped between the strands of straw, straw bales "resist the flow of heat two to three times better than conventional building materials," according to a 2004 paper by Lihn Vuong of the University of Puget Sound. "The insulating performance of straw bale walls is between R35 and R50, almost three times the insulation of typical wood-frame wall systems. The insulating capabilities of straw bale substantially reduce heating costs, as much as 50 percent."
Straw bale is more sustainable because "one sixth to one half of the world's wood, minerals, water and energy are used in the manufacturing and transport of construction materials," according to Vuong, and 45 percent "of all the energy consumed in the world is used in the manufacturing and transportation of building and construction materials."

 

Straw bales are at least 30 times "less energy intensive than a wood frame or equivalent fiberglass insulation," according to Vuong's sources. "It takes 120 thousand KJ of energy to produce a ton of straw and 6.16 million KJ to produce a ton of steel, according to calculations performed by Richard Hoffmeister at the Lloyd Write School of Architecture."

 

Straw Bale Make-Up
Straw bale construction uses straw from crops such as wheat, oats, barley, rye and rice. Compressed and tied into bales and used as building blocks, "it offers numerous benefits including energy efficiency, affordability, resistance to earthquakes and fire, and high indoor air quality," according to PAKSBAB, or Pakistan Straw Bale and Appropriate Building, which describes itself as "an international group teaching and promoting straw bale and other appropriate building methods in Pakistan."

 

The classic straw bale wall assembly, according to the Natural Building Network, is straw bales stacked with "thick metal mesh reinforced cement and/or lime stucco skin applied directly to each face. Earth plasters, usually somewhat thicker, have also been widely used."

 

The mesh binding has two purposes: structural strength and temporary bracing during the construction process. Without proper binding and bracing, wind could topple the stacked blocks, said Jeff Ruppert, principal in Odisea LLC, a structural and civil engineering company in Colorado. To avoid this, he said bales can be stacked between posts and attached to framing members with mesh, such as an expanded metal lath. Another option, more popular in times past, are pin braces, such as rebar or bamboo stakes, which are driven through the center of the bales.

 

Carbon Benefits
"Another advantage of straw bale buildings is that you're sequestering carbon," said Catherine Wanek, co-director of Builders Without Borders, an international network of ecological builders who advocate the use of straw, earth and other local, affordable construction materials. Author of The Straw Bale Home and The Hybrid House (to be released early next year), both published by Gibbs Smith, Wanek points out that straw is typically regarded as a waste product and burned, releasing carbon into the atmosphere. In the United States alone, 200 million tons of straw are produced annually.

 

Global Build-Up
Currently, according to the International Straw Bale Registry Project, 1,444 straw bale structures were registered worldwide as of July 2009 (http://sbregistry.greenbuilder.com/search.straw). Registered straw bale structures are just a fraction of those that have been built so far, however, said Ruppert, whose company has offices in Boulder and Carbondale, Colo. Though 639 straw bale structures are registered in the United States, Ruppert said he's had contact with about 500 projects just in Colorado over the past 10 years.

 

"So I'm guessing there's probably at least 1,000 in Colorado alone," he said. "California has a lot of them. So do Texas, Arizona and New Mexico."

 

Ruppert works with the Altai Project, which promotes straw bale construction in Siberia, where his group worked with local supporters in 2008, for example, to build a straw bale gallery/conference building for the Institute of Architecture and Design near Barnaul, Russia.

 

Of the many countries where straw bale construction is being pursued, China stands out with 597 buildings on the registry, most concentrated in Mongolia. The impact on global air quality from Chinese buildings is high, considering that production and consumption of coal in that country is highest in the world and that some "four tons of carbon dioxide per year [are] released from each coal-burning conventional household in China," according to Vuong.

 

Straw bale homes built in China have shown a reduction of between one and two tons of coal consumed per year, and for each straw bale house, it is estimated that carbon dioxide emissions will be reduced by 125 tons over a 30-year span. For the world's most populous country, in other words, the potential benefits both the home owner and the environment.

 

On one Chinese project, analysis of energy saved by straw bale construction determined that a straw bale house uses 65 percent less energy than its brick or adobe counterpart, meaning 65 percent less use of coal and the mitigation of 353 tons of carbon over a 30-year period.

 

Short and Long-Term Benefits
For the home owner, new homes are more affordable, warmer, more comfortable and, according to one researcher, the higher moisture content in straw even promises to help reduce respiratory disease.

 

For the environment, straw bale reduces air pollution -- heating needs go down, straw is not burned as waste and its use reduces deforestation for lumber.

 

And unlike the image of the flimsy house built by the lazy and stupid pig, straw bales can provide a stable and lasting structure. "The oldest straw bale buildings we know of are over 100 years old," said Catherine Wanek. "They've found straw in the pyramids carbon dated at over 7,000 years old, so these buildings could potentially last indefinitely."

 

Building Blocks, Building Dreams
Straw bales can be applied as infill in post-and-beam construction or stacked and stabilized by wire mesh in a wall or ceiling. In Pakistan, PAKSBAB has been using the more locally available material of fishing net.

 

"Similar to modern conventional building methods, typical straw bale construction has largely been reliant on energy intensive materials, skilled labor and complex machinery, making it unaffordable for the poor," according to PAKSBAB. "In response, PAKSBAB is developing unique systems that utilize unskilled labor, locally-resourced materials and adapt traditional building techniques."

 

"They don't have straw bales available in Pakistan, so they have to make their own bales," said PAKSBAB founder and CEO Darcey Donovan, who lives in a straw bale home in Truckee, Calif. "We have a compression mold that we fabricated locally and use a farm jack to fabricate the bales. It's something they can borrow from us if they need to use it, and if somebody wanted to go into a larger scale business, it's quite affordable for them to make."

 

PAKSBAB's structures in Pakistan are 80 percent more energy efficient than the conventional buildings at 50 percent of the cost, according to the organization. "Because the necessary materials are indigenous and affordable, viable local industries are created to serve the needs of those without homes and empower those who provide them."

 

Withstanding Mother Nature
Among the benefits of straw bale construction, according to Donovan, and of particular importance in Pakistan, is its resistance to earthquake. The 7.6 magnitude Pakistani earthquake of October 2005 caused 74,000 deaths according to official government figures, but a consensus of opinion in the local population suggests the figure may be closer to 100,000. A primary cause of fatalities, all too familiar from video images seen around the world, was the heaps of rubble that once were buildings. Traditional construction is stone and mud mortar with heavy timbers in the clay-insulated roof. When these heavy structures collapsed, they also left some 3 million people homeless.

 

To confirm the greater safety of straw bale homes, working under a 2007 research grant from the Earthquake Engineering Research Institute's Endowment Fund, PAKSBAB studied the performance of earth-plastered, load-bearing straw bale "wall assemblies under in-plane cyclic loading, and the performance of a small, full-scale straw bale house using shake-table simulation."

 

A full-scale, 14-by-14-foot straw bale building, similar to small homes PAKSBAB is constructing in Pakistan, was rolled into the Network for Earthquake Engineering Simulation (NEES) facilities at the University of Nevada Reno and loaded onto a shake table. The building was subjected to simulated earthquakes of up to 0.82 Gs acceleration, as compared to estimates of between 0.3 and 0.6 Gs for the Pakistan earthquake.

 

"It went through eight earthquakes that day, and at the end of the day it was still standing," Donovan said, not to mention the fact that a collapsing structure of straw bales is a less daunting prospect than a collapsing structure of stone and mortar.

 

In 2007, PAKSBAB collaborated with the Pakistani organization Salamat-e-Hazara to build a residence and conduct a training course in Qalandarabad, and subsequently three houses in Mansehra and Shinkiari. PAKSBAB, which is currently working on its 11th straw bale structure in Pakistan, has conducted two training courses in that country to date.

 

Most of the designs being built now in the earthquake zone, however, are concrete and quite expensive, said Donovan. They are too expensive for people who are struggling just to feed themselves. Many are simply rebuilding with rock, brick and clay mortar, often salvaged from the rubble.

 

"They can pick up the stones, scrounge around and come up with materials to build shelter, but they're not earthquake safe," Donovan said, "and not necessarily comfortable homes to live in."

 

That more straw bale structures have not been built in Pakistan is a matter of funding at this point, Donovan said. "To date, we've had donations from family and friends and a few small donations from organizations, but we need to get funding on a large scale to make it happen. The people we're focusing on are extremely poor and cannot afford to build their own houses, so they need financial assistance. Our goal is to involve them in projects by contributing their labor. We want to make sure we're not just giving away houses to people."

 

The other obstacle to widespread use of straw bale in Pakistan is unfamiliarity with a novel approach. "You can do a training course for a month, but they really need more training than that to build their own house," Donovan said. "[We need to train] people to understand what is important as they build a house so they know what is well built and safe. The hurdle that we have to overcome is that this is a new building method for people who have been familiar with stone and mortar their whole lives."

 

Why Straw?
Straw bale is especially appropriate for poorer countries, however, as materials cost only about one-third of the system budget as opposed to about one-half for a wood building, and the rest is labor, Jeff Ruppert said. But, labor is not a cost at all in terms of money if one does not pay somebody else to do the work. "So for the owner/builder, it makes sense to choose a material like this," Ruppert said.

 

And with straw bale, the work is easier for the average person to accomplish. The resulting structures may not have the clean lines of a conventional structure, but "the coolest buildings I've seen, the most attractive to me, have been the free-form buildings that people have done with straw bale and cob and these fiber and clay type materials, where they're not building something exact but letting things flow and get really artistic with it," Ruppert said. "And then there are people who want the walls super straight exactly like a frame building. The walls undulate naturally with straw bale, so you have to fill in with more plaster to make the walls perfectly straight."

 

Getting Building Code Recognition
Where building codes and other regulation are lax or nonexistent, it is easier for people to do what they want at their own pace with the materials they want and save money by doing most of the labor themselves, Ruppert said. Where regulations are tighter, straw bale can meet with roadblocks. Regulatory barriers exist in Russia, for example, where building materials have to be approved by the government. Straw bale is not on the list of approved materials, although the Institute of Architecture and Design is working to change that.

 

"Before we started the project, we had a conference and they invited powerful people who should be exposed to this," Ruppert said. "This project was run by the deans of the architectural school, so they pulled strings and got it approved as a demo project. Hopefully that will lead to higher acceptance of it and eventually place it on the list of approved materials."

 

In the United States, most building officials have been exposed to straw bale and getting a permit for a straw bale building is not difficult, he said.

 

"At the ICBO International Conference of Building Officials in '96 or '97, we had a couple of high-profile allies in the ICBO and they were able to get us into these conferences and let us introduce it," he said. "Since then, it's been slowly disseminating. Through those outreach efforts, most building officials know about it now."

 

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