In March 2009, the City of Bloomington passed an ordinance establishing the Green Buildings Program. This ordinance directed the City of Bloomington to incorporate green building principles into municipal facilities by committing to the use of Leadership in Energy and Environmental Design (LEED) green building rating system, developed and awarded by the U.S. Green Building Council (USGBC), for projects involving city government buildings and facilities. Specifically, all new occupiable City of Bloomington buildings must be designed, contracted, and built to achieved LEED-NC Silver certification level at a minimum. The Green Buildings Program encourages certification beyond Silver (to Gold or Platinum) when possible. Furthermore, the ordinance establishes that the city's existing building stock be subjected to a two-phase evaluation to determine which city building should be brought up to LEED Silver. Only those buildings whose cost-benefit analysis and payback period of 10 years or less will be considered. At least one city building per year beginning in 2011 through 2020 will be subjected to a phase II analysis.