N.Y. Multiple Dwelling Law § 170-a: Notwithstanding any other provision of this chapter, a dwelling, other than a frame dwelling, three stories or less in height erected aft...

§ 170-a. Notwithstanding any other provision of this chapter, a

dwelling, other than a frame dwelling, three stories or less in height

erected after April eighteenth, nineteen hundred twenty-nine as a one or

two-family dwelling may be converted to a multiple dwelling to be

occupied by not more than three families in all, with a maximum

occupancy of two families on each floor in a two story building and one

family on each floor in a three story building, provided however that

all the provisions of this article are complied with and provided

further that

1. No part of such dwelling shall be used for business purposes.

2. No part of such dwelling shall be arranged, designed for or

occupied by roomers, boarders or lodgers.

3. The public hall or stair partitions and soffit of stairs shall be

fire-retarded and said partitions fire-stopped. The apartment entrance

doors and door assemblies in such hall shall be fire-proof and

self-closing.

4. The required stairs shall comply with the provisions of subdivision

three of section fifty-two of this chapter.

5. No door opening shall be permitted from a garage within the

building to the stair hall or public hall. However, any other opening to

the residential portion shall be provided with a fire-proof self-closing

door, and the door assemblies shall be fire-proof.

6. The cellar shall not be used for any purpose other than household

storage and mechanical equipment or appliances, and the cellar ceiling

shall be fire-retarded.