Habitable rooms shall have a minimum clear width of eight feet in any part; a minimum clear area of eighty square feet and a minimum clear ceiling height of eight feet for the minimum area, except:
(a) A room which complies with the requirements for natural light and ventilation and in addition has an opening of not less than sixty square feet into an immediately adjoining room may have a minimum floor area of seventy square feet and a least horizontal dimension of seven feet;
(b) A dining space which has legally required ventilation, and in which the window has an area of at least one-eighth the floor area of such dining space;
(c) One-half the number of bedrooms in a dwelling unit containing three or more bedrooms may have at least minimum dimension of seven feet;
(d) A room in a class B multiple dwelling as defined in section four of the multiple dwelling law which may have a minimum floor area of sixty square feet and a least horizontal dimension of six feet.