“Existence is beyond the power of words to describe,” said the Chinese monk Lao Tzu in his classic poem “The Way of Life.” “Terms may be used, but none are absolute.” Were the old sage alive today, he could say the same about green building: Yes, it's real, but it's tough to define. Or he might fall back on the late Justice Potter Stewart's 1964 definition of obscenity: “I know it when I see it.”

For sure, houses have a huge environmental impact and a major affect on quality of life. So “greening” homes is clearly an idea with practical merit for the planet and for people. But “green” is also the hot new marketing fad—which makes a lot of people eager to jump on the bandwagon with green claims based on sketchy rationales.

Environmental Building News editor Alex Wilson has seen a lot of that: With a Web site at www.buildinggreen.com, Wilson's organization produces the GreenSpec Directory of green building products. Says Wilson, “We get products pitched to us daily as green: ‘This should be in your directory.' And we reject most of those, because they don't meet our criteria.”

But products, Wilson points out, are just part of green building's big picture. “Don't overemphasize materials,” he argues. “Far more important are energy efficiency, location, land-use strategies, building size, indoor environmental quality. ... [Y]ou can build a green home without using many green products, just by building with more insulation or a tighter envelope, or building in a particular location or [building] a smaller house.”

But those qualities, too, involve subjective judgments. And while consumers may want green houses, few have the time or the knowledge to evaluate buildings themselves. That's where green-building rating schemes come in—systems that take some of the work out of shopping for an earth-friendly home, such as Energy Star energy-efficiency labels.

Today's top players in the green rating game are the NAHB's Green Building Guidelines, developed by the NAHB Research Center, and the Leadership in Energy and Environmental Design for Homes (or LEED-H) program, a pilot project of the U.S. Green Building Council (USGBC). Both came about through similar processes: Each organization reviewed dozens of local green building programs, boiled down their requirements into categories, held a dialogue among stakeholders, and published draft guidelines for comment and review before issuing a checklist and a “good, better, best” ranking system. But they target different market sectors: The NAHB aims to foster incremental improvement among mainstream builders using mostly conventional practices, while the USGBC wants to reward peak performance among pioneers who go green in a big way.

Jay Hall of BuildingKnowledge.com, lead consultant on the LEED-H project, says he carefully compared the two systems' ranking thresholds. “[The] NAHB's top tier aligns almost perfectly with our entry-level tier,” Hall says. “They have their Bronze, Silver, and Gold; their Gold aligns with our Certified, and then we have our Silver, Gold, and Platinum above that.” But the criteria are consistent, he says: “I think our programs work together well, and over time I think they can work together even better. We are really anxious to work with them.”

Green building is in a growth phase now, and green guidelines are hot. But as the whole market moves in the green direction, specific guidelines may eventually become less relevant, overtaken by builders and consumers practicing random acts of sustainability. Says Wilson, “There is an increase in awareness and demand that is fueling change. I think in 15 or 20 years we will look back at this period right now as a fundamental watershed in the building industry. I think it's just beginning.”