2006 New York Code - Stair Construction.

 
    §  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.