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Straw-bale construction is not a new technology. It is merely getting more recognition today as consumers and builders look for more efficient and economic forms of construction. Straw-bale construction has been around in the United States since the turn of the century. Straw is a renewable resource in plentiful supply that can offer simple construction and great versatility.
There is approximately 200 million tons of straw available each year for use in construction that would otherwise go to waste. This waste straw is left over from crops such as wheat, oats, barley, rye, rice and flax, after all the food has been extracted. The straw is gathered and baled using a baling machine. Sizes of straw bales vary from 18"x14"x36" to 24"x18"x48" and weigh between 50 to 90 pounds. The straw is compressed by the baler and tied together with wire or string. A typical 2000 square feet house requires about 300 medium sized bales.
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Straw is an inexpensive building material.
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Studies have shown that straw bales have an average R-value of about 28.
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Straw is a plentiful renewable resource.
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Straw is available just about everywhere in the United States and in plentiful supply.
Once the straw is baled it must be kept dry until it has had a final protective finish coat applied. Straw compresses under pressure so it is important to wait until the straw is compressed before the stucco finish is applied.
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Very few states have granted approval for straw bale construction. Where approval has been given, it has been for the in-fill type of construction and not the load-bearing type. Many local authorities are dealing with applications for building straw-bale homes on a case by case basis.
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There are two ways to build with straw bales. Load-bearing is where the bales act as structural members and distribute the load. In-fill is where a frame is incorporated into the structure to carry the loads and the bales are used to fill in the between the structural members. The straw bales are built on a foundation, end to end and with overlapping joints on consecutive rows. The bales are secured with a suitable reinforcing material to provide stability. Openings for windows and doors are incorporated into the structure where required. Openings require lintels to distribute the loads imposed by the roof and narrow walls are kept to a minimum so that imposed load can be distributed evenly. A stiff roof plate is placed on top of the wall, which provides a connection for the roof to the foundation as well helping to distribute the loads. The straw will compress when the full weight of the roof is applied. When the straw is compressed the walls are sealed, covered with wire mesh and stucco applied to provide a weather-tight finish. The straw will be ruined if it gets wet, therefore it is important to cover the straw before the rain starts.
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Straw is an annually renewable material, which is often wasted. Straw-bale walls provide excellent thermal insulation, typically around R50. (R50 is a measure of the resistance to heat loss). Straw-bale construction provides a weatherproof, fire resistant and pest free wall with a stucco finish applied. The building process can be quite easy, requiring only a low level of technical ability. Straw-bale allows for a great deal of flexibility and creativity on the part of the designer and builder. Straw is available everywhere, thus making it available to everyone.
Costs vary are in the region of $2.00 to $4.00 per bale. Distribution costs are kept low because of the widespread availability of straw.
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