The vision was bold: Transform a 60-year-old stadium into the world’s first net-zero arena while also doubling its size. To get there, the team got creative—melding iconic architecture with eco-friendly infrastructure. And now the US$1.15 billion Climate Pledge Arena in Seattle is home to two professional sports teams and a host of concerts from Billie Eilish to Bruce Springsteen. Architectural firm Populous knew it had to preserve landmarked elements of the stadium, including the sloped roof designed for the 1962 World’s Fair. So construction contractors Mortenson� salvaged and temporarily suspended the 44 million-pound (20-million kilogram) topper. At the same time, the team used digital tools to simulate the built environment and then essentially constructed a brand-new arena underneath—a process project leaders likened to building a ship in a bottle. The original scope didn’t include a deep focus on sustainability, but 15 months into the project, the team made the pivot to zero...