A new penthouse floor was added to the top of the building’s five-storey mansard roof, taking the total height from 19 to 20 storeys, and a spa and garden were created on two new levels above the historic Palm Court.
Design work began in April 2004 and the final phase of the 930,000ft² structure was completed in December 2007, on schedule and within budget.
WSP undertook extensive research to gain an insight into the hotel’s original design, going through city files to find old photos, sketches, blueprints and drawings of the building. However, it had to rely on old, incomplete building records, which meant the design had to continuously evolve to accommodate unanticipated existing conditions.
The WSP team installed 165-ton Vierendeel trusses over the Palm Court, which could support the new levels above without requiring additional columns in the landmark court itself, while at the same time creating an open space for the spa.
Getting these 165-ton trusses into the courtyard presented a challenge of its own. Crawler cranes were used to slide the top and bottom chords through the Plaza’s windows on 59th Street, where they were picked up by cables suspended from the ceiling framing, and then delivered to the courtyard and suspended while ironworkers connected them to the existing structure.
WSP also carried out the painstaking restoration of the magnificent stained-glass ceiling over the Palm Court, which has brought back the historic glamour of this landmark space.