Section 27-750. Area of ventilating openings

Ventilating openings in all
  habitable rooms or spaces shall have a free openable area  of  at  least
  five percent of the floor area of the room or space ventilated and where
  there  is  an  enclosed  or  partially enclosed balcony or space above a
  setback  complying  with  section  27-733  of  article  three  of   this
  subchapter  the  ventilating openings shall have a free openable area of
  at least five per cent of the combined  floor  area  of  such  room  and
  portion  of the balcony or space directly adjoining and in front of such
  room. Each required ventilating opening shall have  a  minimum  openable
  area  of  six square feet. Where fresh air is furnished in any habitable
  room or space by mechanical means supplying a minimum of forty  cfm  the
  free  openable  area  of  the openings may be reduced to one-half of the
  above requirements but not less than five and one-half  square  feet  in
  aggregate.  In  all  occupiable  rooms or spaces, the free openable area
  shall be used to calculate the index for ventilation (section 27-753  of
  article  seven  of  this  subchapter), which shall determine the minimum
  requirements for supplementary mechanical ventilation.