CHICAGO, Ill. (AP) — Chicago’s Willis Tower skyscraper has become the largest building in the U.S. to reach the highest level of energy efficiency.

The Chicago Tribune reports that the building’s owner announced Thursday that the 110-story skyscraper received the Leadership in Energy and Environmental Design Platinum certification. It’s the top designation for energy efficiency and sustainability under LEED guidelines. Willis Tower attained LEED Gold status in 2018.

Equity office said efficiency was improved via upgrades to heating and cooling systems, hot water generators, lighting, plumbing and ongoing elevator system overhauls. Willis Tower is the second-tallest building in the Americas. It was previously called the Sears Tower.