Submitted by: Andersen Construction

This highly complex renovation in downtown Seattle called for replacing the existing window washing equipment on top of the 64-story Seattle Municipal Tower.


Placing the equipment on top of such a tall and uniquely shaped building proved especially difficult. The team first examined the use of a tower crane, then helicopter, before deciding a derrick crane would cause the least tenant disruption and most schedule certainty. The design team responded by working diligently to overcome the challenges that came along with placing large, heavy equipment on the roof of the building, while also identifying necessary modifications to the building structure to accommodate its weight.

Weighing 2,000 lbs more than a fully loaded Boeing 737, the window washing equipment was brought up in pieces and assembled on a miniscule flat space on the roof.

Interior renovations included placing 65 tons of new steel members inside the building for added structure to support the equipment. The contractor used BIM and 4D modeling to enhance logistics and solve constructability issues before starting construction.

As if the project wasn’t challenging enough, all the work took place at night and on weekends to avoid disturbing tenants.

Owner: City of Seattle
Architect: ZGF Architects LLP
General Contractor: Andersen Construction
Engineers: Magnusson Klemencic Associates; Rushing Co.
Subcontractors: Hermanson Co.; Nuprecon; Snyder Roofing of Washington; SASCO Electric; Kent Engineering; Vertigo High Access Services