Today, let us grasp at straw. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.
"If you don't let me in," snarled the Big Bad Wolf, "I shall huff and puff and blow your house in." We imagine that was no idle threat, for the First Little Pig's house was made of straw. (Do parents still tell children about the Three Little Pigs?)
Straw is a universal symbol of triviality. Yet when modern city dwellers speak of straw, they aren't sure what it really is. It's what's left of wheat or barley after the edible seeds are gone. Hay is animal fodder -- dried alfalfa or grass. Hay still has seeds for food value. Straw is empty and useless. Or is it!
Two friends recently went to Minnesota. "Vacation?" I asked. "Well, sort of. It's a workshop on building houses of straw." I thought they were joking -- but they weren't.
The trick is to pour a concrete foundation and embed vertical reinforcing bars in it. Then you impale bales of straw on the steel. You build a whole house out of straw Lego blocks.
You layer stucco on the outside and plaster on the inside. It reminds you of adobe, but adobe is a true composite material -- an earthen matrix strengthened with plant fiber. This straw house is a laminated composite -- a kind of straw-bale sandwich.
The bales are from three to four feet long. Their width can vary from just over a foot to almost two feet. You get a very thick wall regardless of how you put it together.
Those thick straw walls make remarkable thermal insulators. The rating is something like R46. You might as well live in a cave, but for doors and windows. The construction I've described will carry a light roof, but no more. If you want a two-story house, you build wooden truss-work around the bales.
Straw walls are cheap, but walls are only a fraction of the cost of a house. You save more because you can build so much of it yourself. Straw-bale houses also offer variety. A passive solar house of baled straw in California's Owens Valley shows up in a solar energy magazine. A two-story, 2100-square-foot house in Iowa has 5 bedrooms and 3 baths as well as energy efficiency.
Like any new technology, this one leaves us asking what the hidden flaw will be. When we first hear of straw houses, we ask about fire, and we mention the Big Bad Wolf. But water, not fire, is the straw house's enemy. The walls must be kept dry.
While we voice our doubts, houses go up. Their owners are enthusiastic. Some straw-bale houses have lasted almost a century. Straw is an ancient byproduct. We've made everything from bricks to paper from it. Yet we remember the First Little Pig. And I'll bet that nursery story does as much to keep us from making straw houses as any frailty of straw itself.
I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.
Myhrman, M., and Knox, J., First Aid Kit for Plastered Straw-Bale Construction. 1037 E. Linden St., Tuscon, AZ 87519: Out on Bale, (un)Ltd. 1993(?).
The Last Straw. Vol. 1, No. 3, Spring 1993.
Haggard, K., and McMillan, G., "Straw Bale Passive Solar Construction. Solar Today, May/June 1993, pp. 17-20.
Strang, G., Straw-Bale Studio, A Cheap, Sturdy Structure with Good Thermal Performanace. Fine Homebuilding, No. 24, December 1984/January 1985, pp. 70-72.
Glick, T.F., Cob Walls revisited: The Diffusion of Tabby Construction in the Western Mediterranean World. Humana Civilitas: Sources and Studies Relating to the Middle Ages and the Renaissance. Vol. I, On Pre-Modern Technology and Science. (B.S. Hall, D.C. West, eds.) Malibu: Undena Publications, 1976.
I am grateful to Karen and Donald Hall for relating their experience in the straw bale workshop and for providing the first two sources above. I am grateful to Jean Krchnak, UH Architecture Department, and Margaret Culbertson and Pat Bozeman, UH Library, for providing the additional materials.