er 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. 1. No part of such dwelling shall be used for business purposes.
2. 2. No part of such dwelling shall be arranged, designed for or occupied by roomers, boarders or lodgers.
3. 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. 4. The required stairs shall comply with the provisions of subdivision three of section fifty-two of this chapter.
5. 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. 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.