Bamboo - Structural

Bamboo, a giant grass, can grow up to four feet in one day. And, like grass, the bamboo stalk can be cut, leaving the roots intact to grow another lawn. This habit leaves the 1,500 or so species of bamboo that grow in the world to reproduce at a quick pace with very little human intervention required. Each plant lasts for about 75 years and bamboo reaches harvesting maturity in three to six years. The largest bamboo, known as timber bamboo, can grow to 120 feet with a 13-inch diameter in three years, and is so named because it is at least two times stronger than lumber of similar dimension. As a basis for comparison for bamboo's growth rate, consider Weyerhaeuser’s predicted 25-35 years for southern grown Spruce/Pine/Fir forests, the fastest growing species used for small dimension lumber in the United States.¹ Plus, bamboo will grow when more densely planted than timber, allowing greater yield per acre.

Bamboo has been tested to perform under compressive and tensile strengths comparable to traditional dimensional lumber wood species and its light weight means that it performs better in shear than materials of greater mass, like concrete. Shear forces are in play during adverse events like high winds and seismic activity.

Footnotes

¹http://www.weyerhaeuser.com/aboutus/facts/7.4_HarvestRegeneration.pdf

	Bamboo grows without a lot of human investment and is rapidly renewable, so it has long been a source of material for housing in developing nations. Designs and accessories are under development to make the building process simpler.
	In addition to its quick- and re-growth habits, bamboo has a dense root structure that serves as a bio-filter for storm water runoff, at the same time producing 30% more oxygen than a like-sized forested area. These features and the minor investment in energy that is needed to grow and harvest bamboo, when compared to other building materials, including wood, promote it as a very sustainable building material, particularly in the tropical climates where it grows best.
	Bamboo houses can be designed to exceed seismic and hurricane requirements of International Residential Code (IRC).2 Because of bamboo's ductility and light weight, houses built with the material have survived earthquakes of 6.7 magnitude. Footnotes 2http://illumin.usc.edu/article.php?articleID=114&page=4

Initial Cost  

Structural bamboo homes have been widely built in tropical and developing countries, where the product’s attributes and availability make it a construction method of choice.

In the United States, however, an importer of bamboo house packages indicates that the rough frame for a 960 sq. ft. home with 912 sq. ft. of covered porch would cost $68 per square foot (including porch area and $11,500 in shipping fees). This is about three times the cost of traditional building materials.

Operational Cost  

Not Applicable

One species of bamboo, bambusa stenostachya, or tre gai, harvested in 29 provinces in Viet Nam, has been ICC-ES approved³ as a structural material by the distributor, Bamboo Technologies. The report indicates that the International Code Conference recognizes the merits of the product established by test results contained in the report and promotes the material as an alternative to those prescribed in the International Residential Codes (IRC).

The International Network of Bamboo and Rattan, an organization that was established by treaty in 1997, represents a 50-country consortium of public, private, and not-for-profit sector partners. The Network has drafted international standards for bamboo structural performance that are currently under review.

Footnotes

³The report can be referenced at http://www.bambootechnologies.com/PDF.cfm/BambooICCESR1636.pdf

Not Applicable

Homes designed with structural bamboo are most often custom designs of post-and-beam configuration. In dry climates, like the U.S. southwest, straw bale construction can be used for walls between the bamboo posts. Many homes of structural bamboo are erected in high wind and earthquake prone areas so tie down hardware and designs that include continuous load paths are necessary. Available bamboo hardware includes steel reinforced joints and mortise and tenon joints.

Much like structural wood, bamboo is not warranted. The tre gai bamboo marketed by Bamboo Technologies is treated with borates and anti-mold fungicides and finished with an acrylic coating to further its durability.

The cylindrical, hollow, inner portion of bamboo provides some of the material’s strength while it remains light weight for handling.

Bamboo that has been overly wet will rot within weeks. Designs for bamboo need to include large roof overhangs to protect the material from saturation by rain. Because it is hollow, bamboo will burn quickly, so bamboo is predominantly used in one-story structures. The cylindrical shape of bamboo makes joining pieces a challenge - splines and hardware details are under development.