93-569 Tower Top Articulation
All towers that exceed a height of 350 feet shall provide articulation in accordance with this Section.
For the purposes of this Section, a minimum of the uppermost 15 percent of the height of a building or other structure, including all rooftop mechanical structures and their required enclosures pursuant to the regulations of paragraph (b) of Section 93-41 (Rooftop Regulations), shall henceforth be referred to as the "Tower Top Zone". However, chimneys, antennae or decorative spires shall not be considered part of the Tower Top Zone, provided no such structures contain floor area.
The height of such building or other structure shall be measured from the highest level of the public sidewalk or finished grade located nearest such building or other structure.
The Tower Top Zone shall contain an "Upper Zone" and a "Lower Zone." The Lower Zone shall be a minimum of 50 percent of the height of the Tower Top Zone and shall contain tower stories. The Upper Zone shall contain the highest tower story where floor area occupies more than 75 percent of the gross area of such story, and any enclosed rooftop mechanical equipment.
For the purposes of this Section, each tower of a building or other structure shall be comprised of four separate tower top elevation views that shall be used to measure compliance with the regulations of this Section. Each elevation view shall have an angle of 90 degrees from another such view.
Each tower top shall provide the following forms of articulation:
(a) Change in the building or other structure profile
(1) Constructing the profile change boundary
To comply with the provisions of this paragraph (a)(1), a rectilinear boundary within the Tower Top Zone shall be created in each elevation view to determine the required amount of profile change. In order to construct such boundary, two datum lines shall first be drawn in each elevation view. Such datum lines shall begin at the average outermost edges of those portions of tower floor plates above a height of 350 feet containing floor area below the Tower Top Zone, and shall extend upward for the entirety of the height of the building or other structure. The rectilinear profile change boundary shall include the portion of these two datum lines within the Tower Top Zone, as well as their intersection with two datum lines indicating the uppermost elevation and the lowermost elevation of the Tower Top Zone. In addition, a datum line shall indicate the boundary between the Upper and Lower Zone, creating a boundary for both the Upper Zone and Lower Zone.
(2) Required profile change
A minimum of 10 percent of the area of the profile change boundary within the Lower Zone shall remain open to the sky in each required elevation view. Such profile change shall begin upward at the lowermost datum line of the Tower Top Zone. In addition, a minimum of 20 percent of the area of the profile change boundary within the Upper Zone shall remain open to the sky in each required elevation view.
However, for portions of a building or other structure providing enclosed rooftop mechanical equipment within the Upper Zone, the width (as viewed in elevation) of the lowermost portion of enclosed rooftop mechanical space at that point in elevation which coincides with the uppermost portion of the highest tower story shall in no event be reduced beyond 50 percent of the width of such highest tower story. Upwards of such a point in elevation, no restriction on maximum width reduction for enclosed rooftop mechanical spaces shall apply.
(b) Change in the building or other structure lot coverage
For portions of a building or other structure within the Lower Zone, the average lot coverage for all tower stories within such zone shall not exceed 80 percent of the lot coverage of the tower story with the largest lot coverage below the Tower Top Zone and above a height of 350 feet.
(c) Material continuity
A minimum of 10 percent of the surface area of the exterior portion of the facade of the building or other structure within the Tower Top Zone, as viewed in elevation, shall be composed of a single material. Such material shall be continuously visible (in each elevation view) from the lowermost datum line of the Tower Top Zone to the uppermost datum line of the Tower Top Zone. However, within each story of the Lower Zone, a break in the vertical continuity of the material shall be permitted, provided that the vertical break does not exceed 12 inches.