Straw Bale Test Program
Supported primarily by a grant from the California Department of Food & Agriculture, EBNet has completed an extensive series of tests and research on the material properties of straw bale structures. Each individual test is available as a downloadable PDF document on this web page. These program results have also been combined into a book edited by Bruce King, "Design of Straw Bale Buildings", available now from Green Building Press.
You are welcome to download any and all of the test reports and research summaries listed below (they are not copyrighted and forever in the public domain), and we hope you find them useful. Please be aware, however, that these reports--despite having been supported by grant funding--were generated only with an enormous outpouring of unpaid effort by EBNet and the project participants. We intend to improve and expand upon the tests, but can only do so with continued support. We ask that you make a donation to EBNet in proportion to the value you receive from this work, and suggest at least $5 per document.
Be extremely cautious about using this information in the design of building structures. Some of these tests can only be fully understood and applied to a specific project in a specific location by a qualified design professional. Please contact the test's author if you have questions.
List of Tests Available for Download and Test Descriptions
Load-Bearing Straw Bale Construction
A summary of worldwide testing and experience
Bruce King, PE
Properties of Earth, Lime, and Lime-cement Plasters
Compressive strength, Modulus of Rupture, shrinkage, erosion, and Modulus of Elasticity.
Load-bearing and Creep
Long-term deflection on walls with different combinations of plaster and load.
Out of Plane Load on Wall
Capacity of walls with different combinations of plaster and mesh to resist load perpendicular to the face.
In-Plane Cyclic Tests of Plastered Straw Bale Wall Assemblies
Capacity of walls with different combinations of plaster and mesh to resist load parallel to the face. A small version of this file is available for those with slower connections. Click either one of these links: Smaller File (1.4mb) or Larger File (4mb - better graphics...)
Monitoring Ridge Winery
The Ridge Winery building near Healdsburg, California is probably the largest straw bale structure in the world. It has rice bale walls up to 23 feet high, coatings of many different types of earthen and lime plasters, and many different moisture loading conditions (such as barrel rooms maintained at a high humidity and cool temperature next to hot, dry outside air). We installed temperature & moisture sensors in 60 wall locations which are wired to a microprocessor accessible by Dr. John Straube via modem. Dr. Straube is monitoring conditions in the wall, and will issue an interim report and analysis in June.
Moisture and Thermal Conditions for Degradation of Rice Straw
Matt Summers at the University of California Davis School of Agricultural Engineering is completing a Ph.D thesis on straw degradation. This work consists of isolating identical samples of rice and wheat straw under controlled conditions of temperature and humidity, then monitoring decay as evidenced by carbon dioxide production. This gives us baseline information about conditions under which straw will "go off", in the parlance of straw bale building. Wheat straw data will be available in early 2004 for comparison against performance of rice straw and hay.
Future work at UC Davis will identify the specific biological organisms (e.g. mold spores) whose activity constitutes what we call decay. EBNet will also report that work as it is published.
Moisture properties of straw and plaster/straw assemblies
Tests individual bales of straw, or plastered samples of straw, for capillarity (tendency to wick water up or sideways), permeability (tendency to allow migration of water), and sorption isotherms (ability to hold quantities of water like a sponge).
Fire Test Results... Show Fire Test Video
In July 2006, the Ecological Building Network funded and oversaw the following ASTM E119-05a - Straw Bale Fire Tests. Both walls withstood the fire and hose stream tests, as described in these two documents.
1-Hour Fire Resistance of a Non-Loadbearing Wall w/ Earth-Plaster
A 12 ft x 14 ft non-loadbearing wall constructed with 7.5 pcf rectangular wheat straw bales stacked in a running bond pattern, clad on each surface with 1" of earthen-plaster, produced, assembled and tested herein, successfully met the conditions of acceptance as outlined in ASTM Method E119-05a Fire Tests of Building Construction and Materials for a fire endurance rating of 1-hour.
2-Hour Fire Resistance of a Non-Loadbearing Wall w/ Cement-Stucco
A 10 ft x 10 ft non-loadbearing wall constructed with 7.5 pcf rectangular wheat straw bales stacked in a running bond pattern, clad on each surface with 17 GA stucco netting and 1" of cement/stucco, produced, assembled and tested as described herein, successfully met the conditions of acceptance in ASTM Method E119-05a Fire Tests of Building Construction and Materials for a fire endurance rating of 2-hours.
Thermal Performance of Straw Bale Wall Systems
No new testing was done; results of previous thermal tests, particularly the most referenced one from Oak Ridge National Labs, are reviewed, analyzed, and discussed in a summary report.
The recently revised version of SB 332, aka the California Straw Bale Building Code, is now viewable on the California Senate website. Based on the information we have gained in the testing program, as well as field experience to date, we will develop a model building code useful for both seismic and non-seismic areas, and will publish it as an appendix in the textbook next year.