San Francisco would have the most stringent green-building standards in the U.S. if the city Board of Supervisors adopts a new measure proposed yesterday by Mayor Gavin Newsom. By 2012, Newsom wants all new residential buildings over 75 feet tall, commercial buildings of more than 5,000 square feet, and renovations on buildings of more than 25,000 square feet to be certified by the U.S. Green Building Council. City government buildings are already required to meet the council’s internationally recognized LEED standards. Newsom proposed a carbon tax last week, and he’s not done yet; he promises, “We’re going to be making a lot more announcements about reorganization around this priority [of greening] in the new term as well.”