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Build With Straw 

Straw-bale construction is not a new technology, but it is getting more recognition as consumers and builders look for more efficient and economic forms of construction. 

Straw is a renewable resource in plentiful supply that can offer simple construction and great versatility. Approximately 200 million tons of straw that would otherwise go to waste is available each year for use in construction. 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.

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.

Straw Bale House by Alan Sirulnikoff

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.

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.



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.

A typical 2,000-square-foot house requires about 300 medium sized bales. Costs range from $2.00 to $4.00 per bale. 

Source: 
NAHB Research Center, Inc.
400 Prince Georges Blvd.
Upper Marlboro, MD 20774
800-898-2842


 

Straw Bale Details
A Manual for Designers and Builders
New Society Publishers, 2003

The architectural drawings offered in this volume cover a range of straw bale building choices, including load-bearing and post-and-beam structures, stem and pier and frost-protected shallow foundations, plasters and finishes, flooring and roof overhangs.

Presented in a large, easy-reading format, the manual offers an overview of the latest scientific test results that offer an understanding of the strengths and limitations of straw bale walls.

The authors do not comment on or critique straw bale designs in this book. Instead, their state aim is to provide the detailing for bale  projects so that they will be "well built and will stand the test of time.

"It is not difficult to design and construct a well detailed bale building," they point out, "but the details are not always obvious at the paper stage, and it often becomes time consuming and bothersome to fix things once they've been built according to plans without proper detailing."






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