On Mar. 2, 1988, the Landmarks Preservation Board officially designated the Seattle City Light Steam Plant building and Hydro House as Historical Landmarks.

In May 1993, ZymoGenetics began the $25 million dollar renovation of the Steam Plant which was completed in Jun. 1994. The Steam Plant building has a total of 107,000 square feet spread over seven floors. Following the Historical Landmarks Preservation Board’s guidelines, the building exterior maintains its original character and features.

The seven original smokestacks were replaced with six stacks that serve as exhaust for laboratory ventilation systems. Two full height terra cotta panels have been restored to their original grandeur with exterior colors selected to compliment them.