When you’re ready to go shopping for building materials for your next home, you may not need to go any further than the nearest hay field. Straw-bale houses are becoming increasing popular and accepted in many areas of the West and Southwest, and this method of construction can offer an interesting alternative to conventional building.
There are a number of methods employed when constructing a straw-bale house, depending on the size and design of the house, local building codes, and a variety of other factors. Essentially, though, the house is constructed by using bales of straw for the exterior walls, which are then typically covered with stucco on the outside and plaster on the inside. Construction usually begins with a poured concrete footing, and the bales are then stacked up in courses with a running bond, similar to the laying of bricks, so that the mid-point of the bales on one course fall over the butt joints between the bales in the row below.
The tightly bound bales of straw have a good amount of compressive strength, meaning that they will support quite a bit of the weight of the roof. However, some sort of wooden or metal plate is used on top of the bales around the perimeter of the house in order to equalize and spread the roof load, and wood or metal posts are usually employed at set intervals between the bales for additional support.
At window and door openings, wood or metal support framing — called bucks — are installed first, then the bales are cut out and conventional windows are doors are installed. The thick bales result in some very deep window sills, and some builders will "splay" or angle the interior wood or plaster interior window openings to allow even more natural light to enter the rooms.
Once the bales are in place, conventional hand- or machine-applied stucco is used over the exterior. The stucco can be colored by painting or by adding cement dyes to the raw material prior to application. The interior of the bales is covered with plaster, again hand- or machine-applied. Interior walls are typically built with conventional framing methods, and finished with drywall or plaster to blend with the plaster finish on the exterior walls.
Being a relatively new and different construction process, one hurdle for the straw-home builder may come in the form of building code compliance. In the Southwest, for example, where this type of construction originated, many local codes have provisions that allow straw-bale homes and set the standards for their construction. Other jurisdictions may not have them in place as yet, so some solid research and communication with your local building department will be required before the first bale is ever set in place.
Two of the most common questions regarding straw-bale construction are how well the home will resist fire, and whether it is an invitation to insects and other pests. However, numerous studies and test homes built in a variety of locations have shown that once the bales are stuccoed and plastered, they are extremely resistant to both fires and pests. The U.S. Department of Energy quotes tests showing that straw-bale homes actually outperform conventionally framed homes when exposed to fire, and that the plastered walls so limited access to pests that they again outperformed conventional framing.
Another concern is rot, and this is something that needs to be addressed throughout the construction process. Straw-home builders look for bales of straw made up from thick, long-stemmed straw that is free of seeds, typically from the harvesting of wheat, oats, rye, barley, rice or flax. The straw needs to have been baled dry and then protected from the weather while stored at the construction site and also during construction. Moisture meters are typically employed to test and monitor how dry the bales are.
So why build a straw-bale house? Advocates of this form of construction cite a number of reasons, including increased energy efficiency; the use of a cheap, recycled material that lessens dependence on wood; and the relative ease with which an ambitious do-it-yourselfer can undertake much of the work. Construction cost estimates from the Department of Energy show a range from as little as $5 to $20 per square foot for a very modest home with lots of salvaged, recycled materials, to as high as $80 to $120 per square foot for a high-end home with lots of custom features.
For more information on the basics of straw-bale construction and testing, check out the U.S. Department of Energy’s Energy Efficient and Renewable Energy Network Web site. You can also get plans and tips by visiting www.balewatch.com.
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