In March 2009, the City of Bloomington passed an ordinance establishing the Green Buildings Program. It requires that all new construction and major renovations of city buildings be built to achieve LEED Silver certification from the U.S. Green Building Council. Major renovations are defined as any alteration that affects more than 50% of the total floor area, or causes 50% of the building occupants to relocate, or involves replacing the HVAC systems. 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.