Cusack, Victor Bamboo Rediscovered [book] Earth Garden Books, 1997 www.goodlifebookclub.com Janssen, Dr. Jules J. A. Building with Bamboo [book] Intermediate Technology Publications, 1995 www.itdg.org

Bamboo Tower

Janssen, Dr. Jules J. A.
Laboratory Manual on Testing of Bamboo for Determination of Mechanical Properties
[book]
International Network on Bamboo and Rattan (INBAR), 2nd draft, 1998

Bamboo Pavilion

 

King, Bruce and 11 contributing authors
Design of Straw Bale Buildings / The State of the Art
[book]
Green Building Press, 2006
The most comprehensive and up-to-date guide to design and detailing.

California Straw Building Association (CASBA) [website] www.strawbuilding.org Myhrman, Matts, and MacDonald, Steve Build It with Bales [book] Out On Bale, version 2.0, 1997 The best how-to guide for building and detailing www.chelseagreen.com Roulac, John Hemp Horizons [book] Chelsea Green Publishing, 1997 www.chelseagreen.com

The proposed Public Library has a domed, photovoltaic roof and four foot thick gunited straw-bale walls. Watercolor and design by Henry Lenny

Steen, Bill and Athena
The Beauty of Straw Bale Homes
[book]
Chelsea Green Publishing, 2000
A wealth of photographs, plus useful building information
www.chelseagreen.com

Steen, Athena and Bill, Bainbridge, David, and Eisenberg, David
The Straw Bale House
[book]
Chelsea Green Publishing, 1996
www.chelseagreen.com

The Last Straw Journal
[magazine]
The International Journal of Straw Bale and Natural Building
www.thelaststraw.org


Network Productions, Inc.
[videos]
The Straw-Bale Solution, 1999
Building with Straw / vol. 2 / a Straw Bale Home Tour, 1995
Building with Straw / vol. 3 / Straw Bale Code testing, 1996
Proceedings from the International Straw Bale Building Conference, 1999

A brief introduction to Straw-Bale Construction ( a paper, shown below...)

The Real Goods Solar Living Center in Hopland, California is heated and cooled by sun and wind, uses fly ash concrete, sustainably-harvested lumber, and straw- bale walls coated with gunearth (Pisé). Designed by Sim Van der Ryn Photo by Richard Barnes

 

Forest Stewardship Council (FSC)
[website]
a primary resource for sustainably harvested, certified lumber
www.fscus.org

Edminster, Ann and Yassa, Sami
Efficient Wood Use in Residential Construction
[book]
Natural Resources Defense Council, 1998
www.nrdc.org

Many additional resources can be found in the bibliographies and websites of the referenced sources - this is by no means a comprehensive list.

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A brief introduction to Straw-Bale Construction
by Bruce King
exerpted in part from
Alternative Construction - Contemporary Natural Building Methods
edited by Lynne Elizabeth and Cassandra Adams
John Wiley & Sons, 2000
Reproduced with permission

The first straw-bale buildings were erected 100 years ago in western Nebraska (USA), and many of those structures are still there and in good shape. Over the past ten years, an ever growing number of people have been building and experimenting anew with straw bales as construction materials, and there now exists a body of testing and anecdotal knowledge about straw bale structures that, while modest and inexact, gives us some basis for understanding how these buildings work. Specifically, builders and designers have learned the following:

1. The type of grain (eg wheat, rice, barley, etc.) may not matter, though the wet-farmed crops such as rice are higher in silica content, making them harder on tools but more resistant to decay.

2. The moisture content of the bales should be kept below 20 or even 15%, ideally for the entire life of the bale before installation and plastering.

3. The denser the bale, the better for building. Seven pounds per cubic foot (dry density) is considered minimal for load-bearing bale walls.

4. Stacked straw bales will settle in the first few weeks, though less so if pounded heavily into place. Builders will either allow time to settle the wall, or apply precompression with strapping that can also serve to stiffen the entire structure.

5. The stacked bales need to be pinned for stability during construction, usually with rebar or bamboo. Though extensive pinning has been mandated in the first straw-bale building codes, and is useful for jobsite stability, the value of the pins in the completed structure is uncertain and untested.

6. As is the case with most earth walls, straw-bale walls are inherently massive, and derive much of their enormous stability and strength from simple geometry. This author knows of no case of a wind loading failure in a straw-bale structure, including two cases in which hurricane force winds struck unplastered walls. The various straw-bale building codes provide empirical guidelines for geometry, restricting height to width and height to length ratios, and establishing minimum thicknesses.

7. Post and beam (ie not load-bearing) straw-bale walls require virtually no engineering, other than appropriate support for their selfweight and out of plane loading. Tests conducted in Albuquerque [King, Buildings of Earth and Straw, 1996] verified what many had already suspected: that plastered straw-bale walls are inherently sturdy under out of plane load, and only require secure fastening at panel perimeters for stability in wind or seismic events.

8. Perhaps the most important lesson learned to date is that straw-bale walls need to breathe, ie have vapor permeable surfaces. The only places on a bale wall where building paper, or any sort of moisture membrane, is both needed and appropriate are: the very bottom, the top, exposed windowsills (and other horizontal surfaces), possibly the outside of the first course or two, and on the inside adjacent to plumbing fixtures. Straw-bale walls are vulnerable to moisture decay, but all failures or problems to date can be traced to outright leaks of water—not from water vapor. Also, as discussed below, plaster applied directly into the straw is the primary structure, (not just deadweight as engineers have historically treated it), which can and should be used in design. Separating the plaster from the straw-bale substrate is difficult, a potential moisture trap, and destroys the holistic strength of the wall assembly.

Tests done to date show that unplastered straw-bale walls, particularly when pinned and/or compressed, are an effective load-bearing system, but generally too elastic for the standard materials used for doors, windows, and weatherproofing. Typical strength values for a single straw bale are: up to 70 psi in compression, and an Elastic Modulus of about 200 psi. (King, Buildings of Earth and Straw, 1996). These tests do tell us that the straw bales alone provide useful reserve strength and ductility, particularly under gravity and in-plane loading. However, the addition of any plaster to the walls—regardless of whether we can know and quantify the plaster strength—transforms the walls into hybrid straw/plaster structural elements; the rigid plaster becomes the primary load-carrying element, and the straw serves as a structural insulating substrate.

Design can be based on the conservative, empirical guidelines given in the first straw-bale codes. Alternatively, the plaster skins (very thin, reinforced concrete walls) and straw-bale substrate (a soft but useful shear transfer mechanism) can be recognized and designed to behave as a structural sandwich panel. UBC defined scratch and brown coat stucco, with normal stucco mesh or heavier wire fabric, can be used for gravity and in-plane loads, and the sandwich mechanism is clearly active both for out-of-plane loading and for vertical load stability. The UBC allows 180 pounds per linear foot for 7/8" 3-coat stucco under in-plane shear, which engineers in California have adopted for straw-bale construction, but recent tests resulted in a 769 plf failure load for UBC stucco on straw bales (White and Iwanicha, 1997). Load-bearing capacity of plastered straw-bale walls was established in tests in Colorado (Ruppert and Grandsaert, 1999), giving ultimate failure loads of from 3200 to 6100 pounds per lineal foot. Lateral design in seismic risk areas, given the current imperfect understanding of the straw/stucco assembly, would typically call for a supplemental bracing system except in the smallest and simplest structures.

It bears emphasizing that there exist many load-bearing straw bale homes in Nebraska and Wyoming that have peacefully endured nearly a century of snowstorms, high winds, temperature extremes, and human occupancy without ever having had the backup of rebar pins, precompressing, engineered foundations, and other features that are now deemed crucial. Those houses are out there, uncracked, unrotted, unburnt, possibly as much a testament to the value of common sense in construction and maintenance as to the strength of straw bales. In any case, they're there, and they quietly remind us that straw bale construction can easily be strong and durable. As a methodology for engineered design of plastered straw bale buildings evolves over the years to come, it should continually reflect back on these impressive examples.