Seattle's skyline gained its most significant addition in decades when Rainier Square Tower was completed in 2020 - the tallest building constructed in the city since the Columbia Center went up in 1985. At 850 feet and 58 stories, it's now the second-tallest building in Seattle, standing at 401 Union Street in the heart of downtown, directly adjacent to the historic Rainier Tower.
A Modern Neighbor to a Seattle Icon
The tower sits on the Metropolitan Tract, land owned by the University of Washington, on the site of the former Rainier Square shopping mall that opened in 1978 and closed in 2017 to make way for the new project. Right next door stands the original Rainier Tower - the 1977 building designed by Minoru Yamasaki (also the architect of the original World Trade Center) that locals nicknamed the "Beaver Building" for its distinctive inverted-pyramid base, tapering down to a narrow pedestal at street level. Rainier Square Tower's design, by architecture firm NBBJ, was conceived as a modern counterpart to that landmark - a metal "prism" panel facade that shifts appearance throughout the day as sunlight moves across it, rather than competing directly with its older neighbor's unusual silhouette.
An Engineering Story Worth Telling
What sets Rainier Square Tower apart structurally is its use of SpeedCore - a composite steel-plate and concrete core system that had never been used at this scale in a US high-rise before. Instead of the usual rebar-and-formwork process for a concrete core, steel plates sandwich a concrete fill, allowing the entire central core to rise dramatically faster than conventional construction. The approach reportedly cut about nine months off the schedule - a genuinely significant engineering decision, not just a cosmetic one.
Office, Retail, and the City's Highest Homes
The building holds roughly 722,000 square feet of office space across floors 2 through 37 - space Amazon leased in its entirety shortly after the project was announced. Above the office floors, floors 39 through 58 hold residential units, giving Rainier Square's residents the highest homes in Seattle. The lower levels include retail space, continuing the site's decades-long role as a downtown shopping and dining destination.
Part of a Changing Downtown
Rainier Square Tower's arrival reflects a broader pattern in downtown Seattle - after decades where the tallest buildings mostly dated to the 1980s boom, a new generation of towers has started reshaping the skyline, with Rainier Square as the first major addition in over three decades and more mixed-use, high-rise projects following since. For a city known for its progressive, tech-driven growth, the tower stands as a genuine architectural landmark rather than just another glass box - a building that pushed a real construction innovation into practice while adding meaningfully to Seattle's skyline for the first time in a generation.
Not every project calls for a 58-story SpeedCore tower, but the same principle - letting real engineering constraints shape the design rather than fighting them - guides our own architecture work at any scale.
Not every Seattle tower is thriving the way Rainier Square is - for the other side of the story, see our piece on Seattle's office vacancy and conversion crisis.
