§ 9. Buildings converted or altered. 1. On or after July first, nineteen hundred fifty-two, no multiple dwelling shall be enlarged or its lot diminished so that the yard or other unoccupied areas shall be diminished in size or area below the minimum requirements of this chapter.

2. A building not a dwelling, if converted on or after July first, nineteen hundred fifty-two, to a multiple dwelling, shall thereupon become subject to all the provisions of this chapter applicable to new multiple dwellings of like class and kind. "Class" shall mean the use of a multiple dwelling for either permanent or transient occupancy or both. "Kind" shall mean the type of construction of a building, either fireproof or non-fireproof.

3. No dwelling shall be altered or converted so as to be in violation of any provision of this chapter relating to dwellings of like class and kind, and, except as provided in subdivision four, a dwelling, altered or converted to be occupied primarily for permanent-residence use, shall comply with article three; and a dwelling converted or altered to be occupied primarily for transient use shall comply with article four.

4. If any multiple dwelling three or more stories in height is altered after July first, nineteen hundred fifty-three so as to increase its height or bulk for living purposes or so as to increase the number of living rooms by more than twenty per centum, such dwelling shall be made to conform to the requirements of this chapter with respect to new dwellings of like class and kind erected after such date.

5. It shall be unlawful to convert a frame dwelling to a multiple residence, except that a frame dwelling not more than two stories and attic in height and erected before July first, nineteen hundred fifty-two, as a one-family or two-family residence may be converted to a multiple dwelling for permanent occupancy by complying with article three; and if such residence is converted to be occupied, as a rule, for transient use, it shall comply with article four.