N.Y.C. Admin. Code § EBC D502: D502 Maximum height (MDL 101, 141).

Such a dwelling shall not be increased in height greater than 75 feet (22 860 mm) above curb level or 6 stories.

Exception: Such a dwelling may be increased in height above 75 feet (22 860 mm) or 6 stories, provided such dwelling meets the requirements of Items 1 through 4, below. In such cases, notwithstanding any contrary requirements of this code or the New York City Building Code, any existing unenclosed stair needs to be enclosed and separated from the public halls only at the altered portions of the building.

1. The entire building shall comply with the height and area limitations of Chapter 5 of the New York City Building Code.

2. The entire building shall comply with Chapter 9 of the New York City Building Code as if hereafter erected.

3. The building shall comply with any applicable elevator requirements of Section D306.1.

4. Fire escapes shall not be utilized as a second means of egress from dwelling units unless the addition comprises a penthouse structure that is located upon the roof of a sixth story and that forms the upper level of a multi-story dwelling unit, and the building is deemed to be no more than 6 stories pursuant Section 504.3 of the New York City Building Code.