The 2018 Stirling Prize has been awarded to Foster + Partners for the firm’s Bloomberg Headquarters in London.

“For many companies our size, building a new headquarters would have meant opting for a glass skyscraper,” said Bloomberg C.E.O and former New York Mayor, Michael Bloomberg, at the building’s opening almost a year ago to date.

Instead of glass, Bloomberg got sandstone—and lots of it. That’s not to say the building doesn’t shirk urban vistas: the office’s sixth floor features a fantastic panorama of Christopher Wren’s St. Paul’s cathedral, London’s finest and largest stone building.

The Bloomberg HQ’s selling point, however, is its sustainable qualities. The building has received a rating of 98.5 percent by BREEAM (the U.K. equivalent of LEED), one of the designation’s highest scores ever awarded.

“Bloomberg is a once-in-a-generation project which has pushed the boundaries of research and innovation in architecture,” remarked David Adjaye, who chaired this RIBA Stirling Prize judging panel, in the announcement. “The design process involved unprecedented levels of research, innovation and experimentation, with pioneering new details and techniques tested, prototyped—sometimes at 1:1 scale—and rigorously improved.”

In the same announcement, firm founder Norman Foster stated that, “From our first discussions to the final details of the project, Mike Bloomberg and I had a ‘meeting of minds’ on every aspect of the project—its sustainable focus, commitment to innovation and drive to create the best workplace for Bloomberg employees. The RIBA Stirling Prize is a testament to the incredible collaborative spirit that has underpinned the entire project from start to finish.”

This is the third time Foster + Partners has won the Stirling Prize—for the Imperial War Museum, Duxford in 1988, and 30 St Mary Axe (best known as “the Gherkin”) in 2004.