No room, which has its floor level below grade, shall be occupied as a habitable room unless it shall conform to all of the following standards, in addition to all other requirements of this Housing Code for habitable rooms:
(a) The room shall have been, prior to the original effective date of this Housing Code originally designed and constructed for, or legally converted to, use as a habitable space.
(b) The walls and floor enclosing the room shall be maintained in such condition as to prevent seepage or leakage of water into the habitable space.
(c) All required openings for light and ventilation shall be located entirely above the adjoining grade.
(d) The height of the finished ceiling of such room above any point of the adjoining ground level shall be at least fifty percent (50%) of the clear ceiling height of the room.