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Basics of Straw Bale Construction

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Straw Bales
Straw-bale construction burst on the home building scene in the 1990s, although variations on this type of construction have been around for nearly 100 years. Similar in theory to foam-block construction, straw-bale construction offers a less expensive building medium with a very high resultant R-value in the walls - up to R-50 depending on the size and quality of bales used. The method is also far cheaper than foam-block or balloon-framed construction, usually coming in about 10 to 20 percent under stick-built houses. To build with straw bales, a foundation must be poured with vertical, reinforcing steel bars extending eight to 10 feet above grade. The straw bales are then spiked down on these rebars in a staggered, brick-like manner. Where wide gaps are necessary, wooden planking is used to reinforce the bales above. After a truss-style roof is applied, the 18- to 24-inch-thick bales are plastered on the inside and stuccoed on the outside. Straw-bale construction has been most popular in areas where the climate is relatively dry. That's because it's imperative to keep the bales absolutely dry from the moment they come out of the field until the final coats of plaster and stucco are applied. Otherwise, mold, mildew and rot can set in. It's also essential to use only straw, not hay. Straw is left over when wheat, oats or other grain-bearing stalks are stripped of their seeds. Any seeds left in a bale have the potential to germinate and expand from the inside, cracking wall coatings on the outside. Hay is simply dried grass, which is chock full of seeds that are generally not removed, since unlike other grains, they are not used for food. In addition to the dampness and seed issues, many straw-bale homeowners report problems with rodents. When done properly, mice will not be able to penetrate stucco or plaster. But as the years go by, a crack here or a chip there may invite a furry critter inside the walls. Once in, their tunneling and home-building abilities are truly remarkable, though not desirable.

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