New York Consolidated Laws, Multiple Dwelling Law - MDW § 235. Stairs in non-fireproof tenements

1. Every non-fireproof tenement erected after May fifteen, nineteen hundred two, containing more than twenty-six apartments or suites of rooms above the entrance story shall have an additional stair for every additional twenty-six apartments or suites or fraction thereof;  except that if such tenement contains not more than thirty-six apartments above the entrance story, in lieu of an additional stair the stairs, stair halls and entrance halls throughout the entire tenement may each be at least one-half wider than is specified in sections two hundred thirty-four, two hundred thirty-seven and two hundred thirty-eight.

2. The number of apartments on any story in any non-fireproof tenement may be altered, if the number of living rooms on such story is not increased by more than twenty per centum.  If the number of living rooms on any story or section thereof above the entrance story exceeds twenty, there shall be an additional stair for each twenty rooms or fraction thereof on any such story or section thereof, except that if the number of living rooms on any such story or section does not exceed thirty, in lieu of an additional stair one stair and every public hall connected therewith may be at least one-half wider than is specified in sections two hundred thirty-four, two hundred thirty-seven and two hundred thirty-eight.

3. Whenever the total number of rooms, exclusive of bathrooms, water-closet compartments, and cooking spaces less than eighty square feet in area, in any non-fireproof tenement or section thereof is decreased through the process of an alteration, the number of apartments may be altered and the provisions of this section which relate to additional stairs shall not be applicable.