Straw-bale construction is a building method that uses straw bales as structural elements, insulation, or both. It is commonly used in natural building. It has advantages over some conventional building systems because of its low cost, easy availability, and high insulation value.
Although grasses and straw have been used for building around the world in a range of ways since prehistory, their incorporation in machine-manufactured modular bales seems to date back to the early 20th century in the midwestern United States, particularly the sandhills of Nebraska, where grass was plentiful while other building materials (even quality sods) were not.
Straw-bale construction project by John Cross, Willits, CA
Exterior view of straw-bale library in Mattawa, Washington, taken in 2008 (constructed around 2000)
"Straw bale construction is at once an American invention and a sustainable answer to housing needs on and off the reservation."
—Rick West, Director, Smithsonian Institution, National Museum of the American Indian
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Methodology
Straw-bale building typically consists of stacking rows of bales (often in running-bond) on a raised footing or foundation, with a moisture barrier between the bales and their supporting platform. Bale walls are often tied together with pins of bamboo, rebar, or wood (internal to the bales or on their faces), or with surface wire meshes. The walls are then stuccoed or plastered, either with a cement-based mix, lime-based formulation, or earth/clay render. Bale buildings can have a structural frame of other materials, with bales simply serving as insulation and stucco substrate. This type of straw-bale construction is know as the infill technique. It is most often used in northern regions, where the potential snow-loading can exceed the strength of the bales. Alternatively, the bales may actually provide the structural support for the building (load-bearing or Nebraska-style technique). A combination of framing and load-bearing techniques may also be employed, creating what is known as hybrid straw-bale construction.
Typically, bales created on farms with baling machines (field bales) have been used, but recently higher-density precompressed bales (or straw blocks) are increasing the loads that may be supported. Whereas field bales might support around 600 pounds per linear foot of wall, the high-density straw bales bear up to 4,000 lb/ linear ft and more. The basic bale-building method is now increasingly being used to bound modules of other, often recycled, materials, such as tires, cardboard, paper, plastics, carpeting, wood-chips, and rice hulls.
Further Reading
- Design of Straw Bale Buildings. Bruce King. Chelsea Green Publishing, 2007.
- More Straw Bale Building: A Complete Guide to Designing and Building with Straw. Chris Magwood. New Society Publishers, 2005.
- Straw Bale House, The. Steen, Steen, Bainbridge & Eisenberg. White River Junction, Vermont: Chelsea Green, 1994.
- Building a Straw Bale House. Nathaniel Corum. Princeton Architectural Press, 2005.
External Links
- California Straw Building Association
- DOE Building Technologies Program: House of Straw - Straw Bale Construction Comes of Age title
- GreenBuilder.com: International Straw Bale Registry Project - United States
- GreenHomeBuilding.com: Strawbale
- EarthAndStraw.com: Straw Bale Construction - Southeast US
- Straw-bale construction at the Open Directory Project
- Rawlinson, Linnie. Artist Gordon Smedt's straw-bale house, feature on CNN.com, 13 August, 2007. With image gallery.
- Long Branch Environmental Education Center: Possible concerns regarding mold and humidity, technical paper, 2002.