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April 24, 2003
Photo courtesy of Living Shelter Design
In post and beam construction, straw bales serve as infill to form walls and provide insulation. The bales are stacked like big bricks and covered with stucco or plaster. With proper detailing, the walls will resist moisture.
More AND MORE of our customers are getting savvy about sustainable design.
This is an encouraging trend, in which environmental stewardship and health issues join energy efficiency and personal comfort as valuable considerations in any construction project planned for humans to occupy.
Whether we are talking about a home or a public place, people like being part of something that does not waste resources either during construction or over the life of the building. And surveys repeatedly show they are willing to pay 10-15 percent more to make this happen.
As an architect involved primarily in home design, I have found this shift to be both a blessing and a challenge. We champion the ideals, do the research and educate our clients about their choices.
While it is true that certain aspects of detached housing are not as sustainable as other types of residential construction, the demand for single-family homes continues to be high. As long as these are being built, we have an opportunity and a responsibility to make them as close to a sustainable goal as possible. One method we like to use in doing this is straw bale construction.
Straw bales have a lot to offer to sustainable construction. They provide excellent insulation for both temperature and sound transmission. Straw is a nontoxic, natural material, which contributes to cleaner indoor air. A house built with straw bales typically uses less lumber, reducing the impact on our forests.
Straw is annually renewable and abundant wherever grain crops are grown, and is currently burned as a waste product in many areas. Baling the straw for construction can thus reduce air pollution and provide local farmers with an additional source of income.
From an emotional standpoint, the thick walls impart a sense of protection, create natural window seats, and are easy to carve into niches and curves to personalize the space. The uneven surface of the bales can create a sensual surface, imparting a feeling of warmth and comfort often missing from framed or concrete buildings.
Two wall systems
There are basically two types of bale wall systems, both using dry, dense bales stacked in a running bond, like big bricks, and covered with stucco or plaster. In load-bearing construction, the roof rests on a wood plate system set on top of the stacked wall, which is compressed and secured to the foundation. This can work well for simple structures, but has limitations.
Photo courtesy of Living Shelter Design
The thick walls of straw-bale-constructed homes create natural window seats, and can be carved into niches that personalize the space.
In post and beam construction, a frame carries the structural load of the building, while the bales serve as infill to form walls and provide insulation. The bales can be placed either inside, outside, or in between the posts. This can allow more design flexibility and initiate fairly straightforward permitting if you build in a jurisdiction that has allowed straw bale construction in the past.
There have been several laboratory tests on bale walls, establishing a two-hour fire rating and various gravity and lateral load values for specific applications. Test data is documented in “The Building Official’s Guide to Straw Bale Construction,” available online through the California Straw Bale Association Web site, www.strawbuilding.org.
Similar to wood, straw is a cellulose material and susceptible to moisture damage. As with any construction method, proper detailing at the roof, windows, doors and floor is required to stop liquid moisture from entering the walls. To ensure a bond from straw to stucco, no moisture barrier is used. It is therefore important to select a stucco material with proper permeability for the walls to allow moisture vapor to escape.
While most people now accept that bale buildings make sense in dry climates, many question the applicability west of the mountains. To that end, there are several straw bale structure moisture test sites in Western Washington and Oregon, all of which show encouraging results of levels remaining below 15 percent. (Degradation begins when moisture levels sit at 21 percent for two weeks or longer.)
For the past decade, straw bale home construction has been primarily an owner-builder phenomenon. This is due to the ability for the walls to go up in a short period of time with volunteer labor, and a perception that they are less expensive to build. (They can be, but sometimes cost more. They are typically comparable to other wall systems.)
We have been involved in 14 straw bale homes in Washington state, and as popularity increases, there is a growing interest to have building professionals involved. Two homes on Bainbridge Island will start work this summer, with contractors involved in both. One in Quincy is currently under contracted construction as well.
Sustainable building resources
If you would like to learn more about sustainable building methods, including straw bale construction, there are several workshops to choose from this summer. Check these Web sites to peruse some of the offerings.
The Bainbridge Island projects are also on the leading edge of green single-family home construction in other areas. They utilize rainwater catchment systems, low-impact pier foundations, local and sustainably harvested wood structures, composting toilets and natural finishes inside and out. One of these homes will be the site of a six-day natural construction workshop in September.
Straw bale technology is not limited to single-family structures. There are currently wineries, schools, dormitories, libraries and churches operating within bale walls. Plans are in the works for a future Natural History Center in Kittitas County and an expansion of the Carpenter Memorial Library in Cle Elum, and there are rumblings about a parks arena and a Catholic church in Ellensburg.
As knowledge and experience are key in winning a prospective project, learning the methods of building with this material now and putting it to use soon will open up doors in the future.
Terry K. Phelan is the owner of Living Shelter Design, an architectural firm in Issaquah specializing in green custom home design.