Austin's largest high-rise office building has grabbed one of the most prominent green building ratings in the U.S., officials announced Tuesday. The Frost Bank Tower downtown received The U.S. Green Building Council's Leadership in Energy and Environmental Design Gold certification, the second-highest tier on the LEED scale. The national organization rates buildings according to their design, construction and energy and water use. Frost earned the certification under the council's "Existing Buildings Operations and Maintenance" category. The building is the second in owner Thomas Properties Group's (Nasdaq: TPGI) portfolio to achieve Gold-level certification. â¿¿Achieving the USGBCâ¿¿s Existing Building certification is a challenging and time-consuming process that requires a great deal of historical property performance information. Our LEED Gold certification was well worth the effort and gives the building a competitive edge as more and more companies are looking for sustainable offices from both a cost-saving and environmental perspective,â¿ said John Kelley, vice president of property management with Thomas Properties. The LEED rating was credited in part to the tower's 92 out of 100 EPA Energy Star rating granted for water conservation features, waste minimization, green janitorial practices and innovative, corporate-driven sustainability policies and operating procedures. Built in 2003, the 33-story Frost Bank Tower houses 530,000 square feet of office space at the corner of Congress Avenue and Fourth Street. The project is one of many in Austin that have or are striving for LEED certification. As of July last year, the number of LEED-certified, high-performance buildings in this area more than tripled from 24 in 2008 to 76 in 2010, as reported in the Austin Business Journal. Central Texas has about 1,000 LEED accredited professionals, a designation that signifies a person is qualified to lead a project toward certification.