Section 52. Stairs

1.  In  every  multiple  dwelling erected after April
  eighteenth,  nineteen  hundred  twenty-nine,   every   interior   stair,
  fire-stair  and  fire-tower  and every exterior stair in connection with
  any dwelling altered or erected after January  first,  nineteen  hundred
  fifty-one, shall be provided with proper balustrades or railings and all
  such  interior and exterior stairs shall be kept in good repair and free
  from any encumbrance. Every such stair, fire-stair and  fire-tower  more
  than  three  feet eight inches wide shall be provided with a handrail on
  each side.
    2. The upper surface of every balustrade  or  railing  placed  in  any
  stair  after April eighteenth, nineteen hundred twenty-nine, shall be at
  least two feet six inches and at most two feet eight  inches  above  the
  front  edge  of  the  stair treads, and at any stair landing shall be at
  least two feet eight inches and at most three feet above  the  level  of
  such landing.
    3.  The  treads  and  risers of every stair, fire-stair and fire-tower
  constructed after April eighteenth, nineteen hundred twenty-nine, in any
  multiple dwelling shall be of  uniform  height  and  width  in  any  one
  flight. Each tread, exclusive of nosing, shall be not less than nine and
  one-half   inches   wide;   each   riser  shall  not  exceed  seven  and
  three-quarters inches in height; and the product of the number of inches
  in the width of the tread and the number of inches in the height of  the
  riser shall be at least seventy and at most seventy-five.
    4. No winding stairs shall be constructed in any multiple dwelling.
    5. a. Except as otherwise provided in paragraph b of this subdivision,
  every   stair  constructed  after  April  eighteenth,  nineteen  hundred
  twenty-nine, leading to a cellar or basement from the first story  above
  shall  be  entirely  enclosed  with fireproof walls and be provided with
  fireproof doors and assemblies at both top and bottom,  with  the  doors
  self-closing;  except that, in a non-fireproof multiple dwelling erected
  before such date, where such a stair is permitted such  enclosing  walls
  may be fire-retarded.
    b.  When  the  first  floor or a part thereof, in a fireproof multiple
  dwelling, is used for business purposes, a stair leading to a cellar  or
  basement  from  such business space shall be enclosed in fireproof walls
  having a fire-resistive rating of at least three hours and  be  provided
  with  a  fireproof  door  and  assembly  at  the  bottom,  with the door
  self-closing. No opening shall be permitted between such business  space
  and the remainder of the dwelling.
    6.   The  department  shall  have  the  power  to  make  supplementary
  regulations relating to fire-towers.
    7. In every multiple dwelling  erected  under  plans  filed  with  the
  department  after  January first, nineteen hundred sixty, on every story
  above the entrance story every door opening into such stair shall be  so
  hung  and  arranged that in opening and when opened it shall at no point
  reduce the clear and unobstructed required width of the stair  or  stair
  landing.
    8. The provisions of this section shall not apply to a stair within an
  apartment  provided  that  each  level of the apartment is provided with
  required means of egress complying with the provisions of this article.