The Office of Zoning Administrator measures both building height and the penthouse height from the roof slab level and not the surface of the roof assembly or membrane.
In addition, the penthouse setback is measured at the intersection of the vertical plane (the building façade) defining the exterior wall of the roof upon which the penthouse sits and the horizontal plane (the top of the reinforced concrete slab) defining the top of the structural roof shown on the below section as TOS (Top of Slab). The measuring of the height of penthouses from the roof level is NOT taken from the top of the surface membrane of the roof assembly as a whole where it meets the parapet wall. The Measuring Point for all Penthouse Setbacks:
The penthouse setback is measured on a diagonal line moving into the building from the point of intersection common to the vertical plane defining the exterior building wall and the horizontal plane defining the structural top of the roof.