CONSIDERATIONS:
This technique for constructing walls has been recently revived as a low cost alternative for building highly insulating walls. The technique was practiced in the plains states in the latter 1800's and early 1900's. Many of the early structures are still standing and being used. The technique has been applied to homes, farm buildings, schools, commercial buildings, churches, community centers, government buildings, airplane hangars, well houses, and more.
Straw is also being used as a building material currently in sheet materials such as sheathing and wall panels. However, the approach of using bales directly, despite its history, is a new technique from a regulatory standpoint. The City of Austin recently passed a straw bale construction building code which is the fifth code enacted by a government body in the United States.
Building walls with straw bales can be accomplished with unskilled labor, and the low costs of the bales make this technique economically attractive. However, it is important to realize that the cost of straw bales will differ depending on what time of year they are harvested and how far they need to be transported. They are cheaper at the time of harvest rather than after they have been stored from the previous season and, of course, cheaper if they are transported shorter distances. Bales must also be protected from getting wet. Costs also begin to rise when one considers the type of stucco and its application. A mud plaster taken from site soil, applied by the owner/builder, and maintained by the owner is quite inexpensive, but may take a long time to apply. A cement stucco applied by a contractor is accomplished quickly and lasts a very long time without any maintenance, but also costs money. As with any style of construction, the more labor input by the owner and the less by the contractor, the less costly it will be.
Two basic styles of straw bale construction have been used: post and beam construction with straw bale infill, and structural straw bale construction or "Nebraska" style (the weight of the roof is supported by the bales). There are a number of straw bale buildings now located in the Austin area and local expert consultation and construction is readily available. (See Resources) (See Resources)
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In the case of straw bale construction, there are precedents of approval in other jurisdictions. Anyone wishing to receive approval in Austin should follow the local straw bale construction code. The inspections department in other areas can refer to the Green Building Program for locations of precedents from our as well as other building inspection departments.
There are numerous examples of this construction in the Austin regulatory jurisdiction and in the greater Austin area at this time. If test data is needed, the building inspection officials will indicate what is needed. Testing is currently being done in Arizona, California and New Mexico.
At this time, there are also a number of insurance companies and lending institutions in the Austin area that have given their approval to straw bale construction.
GUIDELINES
1.0 Summary Recommendations and Brief Overview
The bales are typically covered with concrete mortar/stucco, achieving a high degree of fire resistance.
Two hundred million tons of straw are burned annually in the US. The stability and lack of weathering in straw is not desirable in agriculture but quite desirable in construction.
Straw in straw bale structures has not shown evidence of termite infestations.
Dry bales should be used. Moisture levels in use and in storage should be below 14%. The bales should be kept dry after construction.
Bales are anchored to each other when stacked by stakes of wood (1x2x36), rebar (#3 or #4) or bamboo that penetrate at least two bales. Another less popular method uses mortar between bales. A new method uses 4" wide circular columns of concrete bored through the entire hight of the wall.
Bales can be used flat or on edge. They are best used flat for structural purposes.
Bales come with two-wires or three-wires holding them together. Two-wire bales weigh about 50 pounds and three-wire bales, 75-100 pounds. Two-wire bales are usually 14 inches high, 18 inches wide, and 32-40 inches long (typical in Texas). Three-wire bales are 16-17 inches high, 23-24 inches wide, and 42-47 inches long (typical in western states).
Bales should be firm and strung tightly with either baling wire or twine. Half bales and whole bales are needed so the bales are staggered when stacked.
A timber frame construction (or steel or concrete) can use bales as infill. The frame adds to the expense in materials and in labor for constructing it and then working around the frame with the bales. However, this approach will be more readily received by building officials.
Window and door frames and headers can be made from wood. Windows and doors are typically accentuated towards the interior or exterior of the opening creating a deep well. Care is needed to avoid water entering or collecting in these areas.
A wood plate or concrete beam (or bond beam) is placed on top of the wall. Trusses or roof framing can be set on this. A threaded bar can penetrate through the top bales and be fastened to the plate or beam for added roof stability
Poultry netting is mounted on both sides of the walls for plastering. Stucco lath is used around windows, doors, and corners for added strength. The wire netting and lathe are typically held against the bales by wire ties through the bales or pins into the bales.
Utilities can be laid in the walls as they are built, laid against the bales after the walls are built or run in moldings, interior walls, under floors, or in the attic.
Structural, or "Nebraska Style," straw bale construction requires that the bales sit for a short period of time to complete any settling before stucco is added. If the bales are firm, there will be very little settling (typically less than 1 inch). Threaded rods through the bales or a wire tie-down system which is connected to the foundation and the top plate have the ability to firm up the wall and compress it to compensate for any settling concerns.
Approximately 10,000 acres of wheat and oats are harvested in the Travis County region each year. Eight to ten acres can supply sufficient straw to build a small house.
The best time to obtain straw is at harvest time, May through June in our area.
More details are becoming available for working with straw bales. See the General Interest section of Resources. Thorough research is recommended prior to using straw bales for construction.
Green Building Program
City of Austin
Marc Richmond-Powers
(512) 499-7827
DAWN/Out On Bale By Mail
1039 E. Linden St.
Tucson, AZ 85719
(520) 624 1673
dawnaz@earthlink.net
Development Center for Appropriate Technology
David Eisenberg
P.O.Box 41144
Tucson, AZ 85717
(520) 624-6628
consulting, codes, regulation , advocacy
Sustainable Systems Support
P. O. Box 318
Bisbee, AZ 85603
(602) 432-4292
sssalive@primenet.com
consulting, workshops, videos
Burklund Family Enterprises
8223 S. Hwy. 183
Austin, TX 78719
(512) 243-1889
supplies baling services and bales
Bale-Block System
Santa Fe, NM
Texas Distributor: Ken Long
24315 Pedernales Drive
Spicewood, TX 78669
(512) 264-2416
structural building system using concrete columns through the bales
Agriboard Industries
Post Office Box 645
Fairfield, Iowa 52556
Tel: 800-696-2523
Tel: 515-472-0363
Fax: 515-472-0018
agriboard@lisco.com
structural insulated panel with straw core
"Baling Out - The Essential Straw Bale Newletter", has been launched in the UK. It will be published three times a year & is available from:
Baling Out
7 South View Street
Cornholme, Todmorden, OL14 8LE
UK
HOW TO BUILD YOUR ELEGANT HOME WITH STRAW BALES
"The Elegant Solution"
Carol Escott
P. O. Box 318
Bisbee, AZ 85603
(602) 432-4292
The Hay Exchange is a free internet database of hay and straw for sale classifieds and more. See what's available in your area.
A Strawbale Webring has been established. Click on the links below to move to other sites on Strawbale construction:
You may also want to read an article from The Last Straw newsletter explaining the ins and outs of Breathing Wall theory.
To subscribe to the Strawbale Listserv, send e-mail to
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Sustainable Building Sourcebook web version copyright Sustainable Sources 1994-1999.