2023 New York Laws › MDW - Multiple Dwelling › Article 5 - Non-Fireproof Multiple Dwellings › Title 1 - Fire Protection › 150 - Cellar and Basement Stairs.

§  150. Cellar and basement stairs. 1. Except as otherwise provided in
  this section, there shall be no inside stair communicating  between  the
  lowest  cellar or the lowest story, if there be no cellar, and the floor
  next above, but any stair communicating between  such  floors  shall  be
  located  outside  the  dwelling  and if enclosed shall be fireproof in a
  fireproof enclosure with fireproof doors and door assemblies,  with  the
  doors self-closing, at all openings.
2. This provision, however, shall not apply to any stair not extending
  through  more  than  one  story and leading from an entrance hall to the
  upper stories where the walls enclosing  such  hall  are  fireproof  and
  unpierced  except  for openings to stairs, elevators, apartments, public
  reception rooms, professional offices and the outer  air.  In  no  event
  shall  there  be  any  other opening from such an entrance hall, and all
  apartments and such professional  offices  opening  therefrom  shall  be
  entirely  separated  from  any  space  within such dwelling used for any
  other purposes by fireproof walls which shall be  unpierced  except  for
  means  of  egress  into  the  entrance  hall.  The  provisions  of  this
  subdivision shall  not  apply  to  openings  which  are  protected  with
  fireproof   vestibules.   Any   such  vestibule  shall  have  a  minimum
  superficial floor area of fifty square feet and its maximum  area  shall
  not   exceed  seventy-five  square  feet.  It  shall  be  enclosed  with
  incombustible partitions having a fire-resistive rating of three  hours.
  The  floor  and ceiling of such vestibule shall also be of incombustible
  material having a fire-resistive rating of at least three  hours.  There
  shall  be  two  doors  to  provide access from the entrance hall and any
  other space not used for  openings  to  stairs,  elevators,  apartments,
  public  reception  rooms  and the outer air. Each such door shall have a
  fire-resistive rating of one and one-half hours and  shall  be  provided
  with a device to prevent the opening of one door until the other door is
  entirely  closed. One of these doors shall swing into the vestibule from
  the entrance hall and the other shall  swing  from  the  vestibule  into
  space  which  it  serves.    Such  vestibule shall also be equipped with
  sprinklers and  with  an  independent  exhaust  duct  having  a  minimum
  cross-sectional  area  of  one hundred forty-four square inches for each
  one thousand cubic feet, or fraction thereof, of air content,  and  such
  exhaust duct shall not be connected with any other ventilating system.
3.  In dwellings three stories or less in height which are occupied by
  two families or less on every story, any stair leading to the cellar may
  be located inside the dwelling provided it  is  entirely  enclosed  with
  fireproof walls and with fireproof doors and door assemblies at both the
  cellar level and the story above, with the doors self-closing.
4. The provisions of subdivision one shall not prohibit or apply to an
  inside  stair extending from a space used for commercial purposes in the
  cellar or lowest story to a store on the story next above, provided such
  stair is of incombustible materials,  has  closed  risers,  is  enclosed
  between  the  two  lowest  floors  with  walls  having a three-hour fire
  resistive rating and has fireproof doors and door assemblies at top  and
  bottom,  with the doors self-closing, and provided such commercial space
  in the cellar or lowest story is  completely  enclosed  with  partitions
  having  a  fire-resistive  rating  of at least two hours and there is no
  opening between the store on the story next above and any entrance  hall
  or other public hall or public portion of the dwelling.