§ 31. Size of rooms. 1. The provisions of this section, except subdivision six, shall apply only to multiple dwellings erected after April eighteenth, nineteen hundred twenty-nine, and shall apply to all such dwellings unless otherwise expressly limited.

2. Except as in this section and in section thirty-three otherwise expressly provided, rooms, except kitchens, water-closet compartments and bathrooms, shall meet the following minimum requirements as to size:

a. In each apartment in a class A multiple dwelling there shall be at least one living room containing at least one hundred thirty-two square feet of floor area.

b. Every living room, except as provided in paragraph e, shall contain at least eighty square feet of floor space.

c. Every room shall be at least eight feet high, the measurements to be taken from the finished floor to the finished underside of the ceiling beams except that as many as four beams crossing the ceiling of any basement room may be disregarded if none of them exceeds twelve inches in width or extends below the ceiling more than six inches.

d. Every living room shall be at least eight feet in its least horizontal dimension, except as provided in paragraph e and except that any number of bedrooms up to one-half of the total number in any apartment containing three or more bedrooms may have a least horizontal dimension of seven feet or more.

e. A one-room apartment in a class B multiple dwelling may be as small as sixty square feet in its floor area and six feet in its least dimension.

3. The requirements of this section with respect to the least horizontal dimension and the minimum area of rooms shall not be applicable to any room in a fireproof class B multiple dwelling occupied as a lodging house in which every apartment, other than one apartment occupied exclusively by a person or persons engaged in the maintenance or supervision of such multiple dwelling, consists of one room and in which every such room opens directly upon a public hall.

4. Dining bays with a floor area of fifty-five square feet or less shall not be considered as rooms or alcoves and shall not be required to comply with the provisions of section thirty-two. Every such dining bay shall be equipped with such appropriate permanent fittings as may be required by the department and shall be provided with at least one window opening directly upon a street or upon a lawful yard, court or space above a setback. Such window shall have an area of at least one-eighth of the floor area of such dining bay.

5. A portion of any apartment used as an entrance hall to such apartment may be designated as a foyer. Such a foyer shall not be considered a room if the department shall so permit and if either

a. Its floor area does not exceed ten per centum of the total floor area of such apartment, or

b. Every room in such apartment exceeds in area the minimum required area of such room by more than twenty per centum and the floor area of such foyer does not exceed twenty per centum of the floor area of such apartment.

6. a. Exept in class B dwellings and dormitories, no room shall be occupied for sleeping purposes by more than two adults, considering children of twelve years of age or more as adults and two children between the ages of two and eleven years inclusive as the equivalent of one adult. Children under two years of age need not be considered as occupants. No room shall have sleeping accomodations for more persons than can be accommodated in conformity with the provisions of this subdivision.

b. Every room in every dwelling, whenever erected, shall have at least four hundred cubic feet of air for each adult, and two hundred cubic feet of air for each child occupying such room. Except in class B dwellings, dormitories and except as otherwise provided in subdivision two of section thirty-one or in section thirty-four for dwellings erected after April eighteenth, nineteen hundred twenty-nine, and in sections one hundred seventy-four, two hundred fourteen and two hundred sixteen, every living room shall (1) contain sixty square feet or more of floor space, (2) be at least six feet wide at its narrowest part, (3) if a sleeping room, contain seventy-five square feet or more of floor space and (4) if less than seventy-five square feet in floor area, shall not be occupied by more than one adult.