2006 New York Code - Parapets And Guard Railings.

 
    §  138.  Parapets  and  guard railings. Except as hereinafter provided
  every open area of a roof, terrace, areaway,  outside  stair,  retaining
  wall  or porch shall be protected by a parapet wall, a guard railing, or
  both, extending three feet six inches or more in height above the  level
  of  such area or, in the case of a stair landing, stair window or window
  in a public hall, above the level of  the  floor  adjacent  thereto.  In
  dwellings  two  stories  in  height, it shall be sufficient if the guard
  railing is erected at least five feet  distant  from  and  encloses  any
  required bulkhead or scuttle opening to the roof. This section shall not
  apply to dwellings one story in height.