Two Union Square

The Two Union Square is a Modern Style skyscraper designed in 1984 by NBBJ, and built between 1987 and 1989 in Seattle, WA.

Two Union Square is not the only name you might know this building by though. The building is, or has also been known as Zippo Building.

Its precise street address is 601 Union Street, Seattle, WA. You can also find it on the map here.

The Two Union Square has received multiple architecture awards for its architectural design since 1989. The following is a list of such prizes and awards:

• AIA National Honor Award for Interior Architecture
• IIDA PNW INawards, INworkplace Macro Winner
• Interior Design Magazine Best of Year Award
• BOMA Building of the Year in 1999

The Two Union Square building is the tallest of the two skyscrapers that make up the Union Square complex in downtown Seattle.

The complex features 1,100 parking spaces, a three-story shopping center, a public courtyard, and an underground plaza that connects to several buildings on Fifth Avenue..

At the time of its completion in 1989 the Two Union Square incorporated solutions that were quite advanced at the time, these included being the first building to use high-strength concrete-filled steel tubes (19,000 PSI) for it's structure and hyper-efficient viscoelastic dampers for stability.

The building underwent a major restoration in 2019. The architect commissioned to undertake this restoration was NBBJ.

NBBJ was the architecture firm in charge of the architectural design.

That being said, architecture is a complex discipline involving many professionals from different fields, without whom this building would have not been possible. We will surely be leaving out a lot of names here, but here is a list of the people we do know also played their part in making the Two Union Square a reality:

• Magnusson Klemencic Associates in charge of Structural Engineering
• Turner Construction Company as the Main Contractor

The Two Union Square can be categorized as a Modern Style building.

By their own nature, the Modern and International Styles can still look current, even in contemporary buildings. So that's not to say the Two Union Square appeared old or outdated when it was completed, but NBBJ certainly did not take many risks when it came to choosing the design style. This made the building look more "classic" and integrated within the city's architecture.

The Two Union Square uses a framed tube-in-tube structure , with steel and reinforced concrete columns and reinforced concrete slabs.

A framed tube-in-tube structure uses a central core, known as inner tube, which usually holds stairs, lifts and installations, and a perimeter of columns around it, which form the exterior tube. The interior tube is tipically more massive (often made of reinforced concrete), and the exterior tube is "lighter" (made of steel or concrete columns). Both tubes are conencted via horizontal elements which make up the floors and also transmit any horizontal froces from the facade to the core.

The facade employs a non-load bearing curtain wall system. This means the curtain wall modules are anchored to the building's structural frame at the edges of the floor slabs. The perimeter columns are set back slightly from the facade, allowing them to remain independent of the curtain wall system.

This configuration enables a completely free design of the curtain wall, unencumbered by structural elements, thus providing greater flexibility in aesthetic choices and maximizing the visual impact of the exterior.

The structure uses a reinforced concrete core system combined with steel columns, which enhances structural stability and allows for large, unobstructed interior spaces.

The four central pillars, which form the core that provides rigidity to the structure, were built using hollow metal tubes with a diameter of 3 meters and a thickness of 10 mm.

From an aesthetic point of view, the facade features high-performance glass combined with light-toned granite panels.