Washington, D.C., the home of many of the federal agencies that oversee green building initiatives in the United States, is also home to a remarkable amount of green construction. From 2003 to 2009, Washington, D.C., and the surrounding region added 23 million square feet (2,136,730 square meters) of LEED-certified space, according to the Metropolitan Washington Council of Governments [source: Aratani]. In 2006, the District of Columbia passed the Green Building Act, a law requiring, among other things, LEED certification for new public buildings.
According to 2012 reports from the U.S. Green Building Council, Washington, D.C., had the second largest number of LEED projects in the country with 884 [source: USGBC]. There's also 31.5 square feet (2.9 square meters) of LEED-certified space per resident -- more than any other state, and more than 10 times as much as runner-up Colorado [source: USGBC]. The city also lays claim to a green-building superlative: The 143-year-old Treasury Department headquarters is the oldest LEED-certified building in the world [source: O'Keefe].