In a city famously full of cranes and new glassy towers, one has risen faster and higher than nearly all of the rest. For the last two years Rainier Square Tower has been rapidly climbing out of the center of Seattle’s skyline like a giant erector set. Last week it passed a major milestone: it became the second tallest tower in the city.

On Friday, as construction crews added another layer of steel to the building, the skyscraper passed 772 feet, the height of Seattle’s former second tallest building, 1201 Third Avenue. Construction crews are expected to top out Rainier Square Tower at 850 feet later this month, according to a spokesperson for Wright Runstad, the building’s developer. Columbia Center, at 937 feet, is the only building taller in Seattle.

The 1.7-million-square-foot Rainier Square Tower (not to be confused with Rainier Tower, which stands right next to it) is a mix of ground-floor retail, underground parking, 722,000 square feet of office space, and 200 luxury apartments on its upper floors. The property will also include an adjacent, 12-story, 150-room hotel. When it’s completed, the 58-story tower at the corner of Union Street and 5th Avenue will be the seventh-tallest building on the west coast, with the highest residential apartments in the city.

The tower has a wide base that narrows as it climbs, an inverse reflection of the curved base of the Rainier Tower next door. The building was designed by NBBJ, a global architecture firm based in Seattle, and is owned by the University of Washington. The university selected Wright Runstad to develop the property.

You're not imagining things if it's felt like Rainier Square Tower has been growing especially fast. Construction crews are using a new technique that is expected to reduce construction time by 40 percent.

Most skyscrapers are built by pouring concrete into a core at the center of the building that is reinforced with steel rebar. Rainier Square Tower’s core is instead being built with composite steel plates that are then sandwiched together with concrete. This building technique allows crews to forgo the rebar and build faster, completing the tower nine months faster than a building of comparable size. Engineering News-Record, an industry magazine, called the building’s construction technique a “potential game changer.”

At least in terms of its height, Rainier Square Tower is already a game changer for our city's skyline.