The Three Little Pigs have given straw houses an undeserved bad name. It wasn't the straw that led to a huff-and-puffable home - it was the construction technique.
The Three Little Pigs have given straw houses an undeserved bad name. It wasn't the straw that led to a huff-and-puffable home - it was the construction technique.
As homeowners and builders across the country have discovered, the pigs should have baled their straw. This technique provides a cost-effective answer to the high cost of building materials and the need for low heating bills. It also boosts local farm economies by developing a market for agricultural waste products. And, it is a renewable resource - it gets produced with each crop.
Plentiful supplies
Each year, 200 millions tons of straw are wasted or under-used, according to the U.S. Department of Energy. The U.S. Department of Agriculture estimates that America's farmers harvest enough straw annually to build about 4 million 2,000-square-foot homes a year.
Straw is the byproduct of crops such as wheat, oats, barley, rice, rye, and flax. It is tough and fibrous, making it ideal for use in construction. It should not be confused with hay, which has a higher moisture content and contains seeds that could attract pests. And bales cost only 50 cents to $3.50 each, depending on the location. It takes about 300 standard three-wire bales of straw - a total expense of $1,000 - to build a 2,000-square-foot home.
Historic technique
As with many energy-efficient technologies, straw bale construction is not a new concept. In the early 20th century, farmers in Nebraska, Wyoming, and other states discovered the advantages of building their homes of straw. This technique developed shortly after hay balers became common farm implements in the 1890s. Since wood and other traditional building materials were scarce, residents assessed other resources and found that straw made an ideal building material for homes, farm buildings, churches, schools and stores.
Some of these houses still provide shelter to residents today, having withstood wind, snow, rain, and even earthquakes through the years. One Wyoming resident told Mother Earth News, "The earthquake was in the 1970s and it was either 5.3 or 5.8 (on the Richter scale). There wasn't a single crack in the house. You can live in this house comfortably during the summer. It stays nice and cool. We have never needed any air conditioning, and in summer we get days up in the 90s. Also, last winter, I only turned on our small bedroom heater twice. If I had to guess how our utility bills compare to those of our neighbors, I'd have to say our bill is about half."
Two categories
Straw-bale construction techniques fall into two main categories: Load-bearing and nonload-bearing.
In load-bearing straw-bale, or "Nebraska-style" construction, the walls support the weight of the roof without wood structural supports. This technique requires careful planning to ensure the walls can support the weight of the roof. In most cases, this means using a hip roof that distributes weight evenly along the walls.
Typically, bales are stacked on a poured concrete stem wall. Either three-wire (23 inches by 16 inches by 42 inches) or two-wire (18 inches by 14 inches by 36 inches) bales may be used. They are joined and reinforced by steel, wood, or bamboo pins and frequently covered with chicken wire, which helps hold the finish.
Upon completion, the exterior is usually covered with adobe and the interior walls are usually plastered, creating flat, attractive surfaces. Nebraska-style construction can be used on fairly small, one-story structures, but is not useful for homes with more intricate designs and large square footage.
That's why many designers have turned to nonload-bearing construction, which uses a wood or other frame to support the roof. The bales fill the space between the framing. This technique allows the building to use smaller framing components, because the bales provide additional support. It also offers more flexibility of design, multistory construction, and more complex floor plans.
Energy savings
With either construction method, the straw bale home provides significant energy savings through R factors of between 36 to 50. This superinsulated rating would cost significantly more if achieved with traditional insulation. And, the amount of infiltration depends to some extent on the way the bales are stacked.
Besides energy efficiency, straw-bale construction offers a number of safety and comfort features not offered by other homes. The thick walls create a soundproof, secure environment. And while many people think straw bales would pose a fire hazard, in fact the opposite is true. Fire hazard tests performed by the National Research Council of Canada found that plastered straw bales resist fire better than more conventional building materials. Bale walls are dense, making them difficult to burn. Instead of flaming, bales smolder and burn slowly. The only drawback is that straw-bale fires may be more difficult to extinguish.
Many people also think that infestations of pests would be a problem in a home made of straw bales. Once again, the opposite is true. Unlike hay, straw does not contain seeds or other nutrients that would make it appetizing to vermin. In addition, straw-bale construction makes solid walls, not hollow walls where insects and rodents can hide. The interior and exterior coatings on the bales keep them away from the elements and the pests.
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