§ 150.18  LIGHT AND VENTILATION.
   No person shall occupy as owner-occupant, or let to another for occupancy, any dwelling or dwelling unit, for the purpose of living therein which does not comply with the following requirements.
   (A)   Every existing habitable room shall have at least one window or skylight facing directly to the outdoors which shall provide adequate light and ventilation but the maximum total window area that can be required shall not exceed 10% of the floor area of the room, except for all newly constructed houses, the minimum total window area, measured between stops for every habitable room shall be 10% of the floor area of the room. Whenever walls or other portions of structures face a window of any like room and the light-obstructive structures are located less than three feet from the window and extend to a level above that of the ceiling of the room, the window shall not be deemed to face directly to the outdoors and shall not be included as contributing to the required minimum total window area. Whenever the only window in a room is a skylight type window in the top of the room, the total window area of the skylight shall equal at least 5% of the total floor area of the room, provided that this division (A) and division (B) below shall not apply to recreation rooms, utility rooms and workshops in basements or cellars if properly lighted by electricity and ventilated by mechanical or other means approved by the Building Inspector.
   (B)   Every habitable room shall have at least one window or skylight which can easily be opened directly to the outside, or other device as will adequately ventilate the room. The total of openable window area in every habitable room shall be equal to at least 45% of the minimum window area size or skylight-type window size, as required in division (A) above, except where there is supplied some other device affording adequate ventilation and approved by the Inspector.
   (C)   Every bathroom and water closet compartment shall comply with the light and ventilation requirements for habitable rooms contained in divisions (A) and (B) above, except, that no window or skylight shall be required in adequately ventilated bathrooms and water closet compartments equipped with a gravity or mechanical ventilation system which is approved by the Inspector.
   (D)   Every habitable room of every dwelling shall contain at least two separate floor or wall-type electric convenience outlets, or one like convenience outlet and one supplied ceiling-type electric light fixture; and every water closet compartment, bathroom, laundry, furnace room and public hall shall contain at least one supplied ceiling or wall-type electric light fixture. Every like outlet and fixture shall be properly installed, shall be maintained in good and safe working conditions, and shall be connected to the source of electric power in a safe manner.
   (E)   Every public hall and stairway in every multiple dwelling serving five or more dwelling units shall be adequately lighted at all times. Every public hall and stairway in structures devoted solely to dwelling occupancy and containing not more than four dwelling units may be supplied with conveniently located light switches, controlling an adequate lighting system which may be turned on when needed, instead of full-time lighting.
(1973 Code, § K-3)