Principal buildings shall have no less than 350 square feet of overall habitable space in a single-occupant dwelling unit, of which 120 square feet must be available in a designated sleeping room; for a two-occupant dwelling unit, there shall be no less than 600 square feet of overall habitable space, of which no less than 240 square feet must be available in a designated sleeping room; for dwelling units of three or more occupants, there shall be an additional 100 square feet per occupant of overall habitable space, of which no less than 60 square feet per occupant must be provided in a designated sleeping room.