Section 27-2065. Light and ventilation of water closet compartments

a. In
  every water closet compartment, bathroom and general toilet room one  of
  the following requirements for light and ventilation shall be met:
    (1)  There  shall  be  a  window  opening  upon a street, yard, court,
  partially enclosed balcony or space above a setback,  on  an  offset  or
  recess which may be less than six feet in width. Every such window shall
  be  at  least  three  square feet in area and one-half of its area shall
  open.
    (2) If the water closet compartment, bathroom or general  toilet  room
  is  either  located  on  the  top story or is underneath the bottom of a
  lawful shaft or court, it may be lighted and ventilated by a skylight in
  the roof. Such skylight shall contain three square feet of  glazed  area
  and shall open.
    (3)  There  shall  be a system of mechanical ventilation, approved for
  construction and arrangement by the department. In a  multiple  dwelling
  such system of ventilation shall be maintained and operated continuously
  to  provide  at  least  four  changes per hour of the air volume of each
  water closet, bathroom or general toilet room daily from six o'clock  in
  the  morning  until  midnight in all residential parts of a dwelling and
  from seven o'clock in the morning until seven o'clock at  night  in  any
  nonresidental  parts  of  a dwelling. In a private dwelling the approved
  system of mechanical ventilation may be switch-operated.
    b. Nothing in this section shall require any change to be made in  the
  lighting  or  ventilation of water closets, bathrooms, or general toilet
  rooms in any portion of any old law tenement or any  converted  dwelling
  if  such  lighting  or  ventilation  was  lawful on July first, nineteen
  hundred sixty-one and in one or two family dwellings if such lighting or
  ventilation was lawful on August second, nineteen hundred sixty-seven.