In 2006, Deutsche Bank decided that the towers would undergo a major renovation after 22 years due to changes in fire regulations. The renovation took place from 2007 until 2011. The work improved the fire protection systems and replaced the entire climate, water and lighting technology. This reduced energy consumption and CO2 emissions in the building at least 50 percent. A re-glazing with opening windows improved the energy balance further. The goal was to certify the building as a green building according to American standard LEED certification with the highest platinum for existing buildings, and the German seal of approval DGNB. The towers were the first high-rises to be given this certification by the U.S. Green Building Council. For the interior, the Bank chose Milanese architect Mario Bellini. During the work, approximately 2,500 employees were relocated to three other sites in Frankfurt, including the Investment Banking Center near the trade fair.