It’s not clear if the problem is one of economics or one of spin, but either way, environmentally conscious building design is a concept that hasn’t quite caught on. The technology and expertise to build “green” structures have been around for decades; now, a movement is underway to sell developers on the economic benefits of green building. In an effort to create brand-recognition among building styles, the U.S. Green Building Council, a private group, is certifying structures as sustainable if they meet a number of energy-efficient and eco-friendly criteria. Simultaneously, governments are beginning to encourage green building: In 2000, New York established a tax credit for sustainable development projects, and other states have since followed suit. But momentum is building slowly, at best. Only 2.3 percent of the 1.6 billion feet of nonresidential construction projects initiated last year applied for certification from the Green Building Council.