New York Consolidated Laws, Multiple Dwelling Law - MDW § 237. Stair construction

1. Every stair in a tenement erected after April twelfth, nineteen hundred one, shall be accessible on the entrance story from a street or street court, or from an inner court which connects directly with a street.

2. All such stairs shall have risers of eight inches or less and treads at least ten inches in clear width and three feet in clear length.

3. Winding stairs shall be unlawful except in a tenement provided with a passenger elevator.  When winding stairs or radial steps are installed or used, the strings from which the risers radiate shall be curved on a circle of at least one foot diameter, the treads shall be at least four inches wide at the string, not including the nosing, and the angle formed by the face of each riser and the string shall not diverge more than forty degrees from a line normal to the string at the intersection of such riser.  It shall be unlawful to construct new winding stairs.

4. Stairs constructed after April eighteenth, nineteen hundred twenty-nine, shall comply with the provisions of subdivisions two to six inclusive of section fifty-two.