To make construction practices more sustainable, many architects have begun specifying "rapidly renewable materials." Unlike products made from petroleum, which is nonrenewable, or old-growth timber, which takes centuries to renew, these raw materials have very short harvest cycles. The LEED system of building certification from the U.S. Green Building Council (USGBC) offers points for rapidly renewable materials that regenerate in 10 years or less, such as bamboo, cork, wool, and straw. To qualify for the credit in a new construction project, the value of these materials must represent at least 2.5 percent of the cost of the products used in the building.

The council is continually considering adjustments to these and other credits that are part of the rating system. "People who have been doing LEED for six or seven years probably think some credit achievement percentages are a bit on the easy side," says Brendan Owens, USGBC vice president of technical development. "But we try to maintain a balance between technical rigor and market accessibility to encourage participation."

But probe beyond the concept of quick regeneration and you'll find caveats that make some rapidly renewable materials more green than others. The circumstances of production may cast a shadow on the sustainability of an agricultural product: Are fossil fuels, irrigation, or harmful chemicals used in its cultivation or manufacturing? Is the crop diverting acreage from food production? Are natural forests being destroyed to produce raw materials for construction? Does transportation consume inordinate amounts of fossil fuel?

Bamboo is a case in point. This fast-growing grass is hard enough to be used as a replacement for wood in applications such as flooring and furniture. However, most bamboo is grown and processed in China, and there are concerns about forestry practices, the toxicity of binders, and worker safety. A few bamboo plantations have earned certification from the Forest Stewardship Council (FSC), which accredits forests managed "to meet the social, economic, ecological, cultural, and spiritual needs of present and future generations." However, certified bamboo products are still not widely available in the U.S. And even though bamboo plantations sequester as much carbon as native forests, they do not support the same wildlife. What is more, while ocean shipping consumes less fuel per mile than overland trucking, the fuel used in shipping is more polluting. Clearly, the environmental balance is more difficult to calculate than by simply examining the length of a harvest cycle.

 

Siegel & Strain's Oak Lodge is built with highly insulating straw bales. Photo © J.D. Peterson