A green building is any building that has been constructed under principles that minimize the ecological impact of the structure, often through the use of environmentally friendly construction materials and increased energy efficiency. This can be achieved using different tactics, including utilizing recycled materials and sustainably harvested forest products in construction, and decreasing energy consumption through the use of efficient heating and cooling systems. Green buildings often incorporate renewable energy sources in their design, supplementing on-the-grid power supply with energy obtained from small-scale solar, wind and biofuel sources. They are generally created under the theory of sustainable development, and have been used as key components in some developments that are part of the New Urbanism movement in urban design.


In the United States, the most common standard for green building is the Leadership in Energy and Environmental Design (LEED) rating system, as defined by the U.S. Green Building Council. LEED standards were developed to create a holistic environmental design approach that addresses sustainable site development, water savings, energy efficiency, materials selection and indoor environmental quality. The LEED rating system is on a 69-point scale and has four different levels of certification: certified (26-32 points), silver (33-38 points), gold (39-51 points) and platinum (52-69 points).


Source:
http://www.usgbc.org/DisplayPage.aspx?CMSPageID=222