1 United Nations Plaza, New York, NY

Main Roof Replacement

1 United Nations Plaza is a 40-story high glass and curtain wall office building constructed in 1975.  The main roof is located above the 39th floor and is rectangular and trapezoidal shaped. Within the field of the high roof is a window washing rig track which runs along the entire perimeter of the roof.  The main roof is surrounded on all sides by a low curb with metal railings and inboard of the window washing track rails there is a second line of railings that encircles the track.  At the west end, there is an open well down to a separate 39th floor mezzanine roof where cooling towers, water tanks and other mechanical equipment are located.

Due to localized water infiltration, DAA was retained to investigate and assess the overall roof condition, evaluate leak locations as to severity of deterioration, determine present conditions within the construction assemblies and to make recommendations as to appropriate remedial work.   DAA determined that the roof was at the end of its useful life and recommended complete removal and replacement of the roofing and its flashings. With the main roofs height and exposure to the wind, a ballasted roofing system was ruled out and a two-ply modified bitumen adhered system was selected.

Four basic repair conditions were developed. Before starting the overall roofing removal, all the horizontal window washing track rails, cleaned them to bare metal, refinished them and provided new nuts, bolts and related hardware and effected the structural repairs, some involving additional steel plates and on-site welding.