Section 171 - Alterations1. A building, other than a frame building, originally occupied as a one-family or two-family dwelling may be altered to a converted dwelling if its bulk and volume has not been increased since April eighteenth, nineteen hundred twenty-nine, and if it is converted in conformity with the other provisions of this article.2. Except as permitted in subdivision nine of section nine and subdivision six of section one hundred seventy-two, it shall be unlawful:a. To increase the height or number of stories of any converted dwelling or to increase the height or number of stories of any building in converting it to a multiple dwelling.b. To reduce the room or window area of any converted dwelling or make any other alteration therein if such alteration decreases the light, ventilation, fire protection or sanitation thereof.c. To convert to a multiple dwelling any dwelling which exceeds six stories in height unless it was occupied as a multiple dwelling on April fifteenth, nineteen hundred thirty;d. To convert any dwelling to a class A multiple dwelling occupied by five families or more upon any story unless such dwelling is fireproof or is converted in conformity with the requirements of subdivision three or was occupied as a class A multiple dwelling on April fifteenth, nineteen hundred thirty.e. To combine any converted dwelling with another building which exceeds six stories in height.f. To enlarge or extend any converted dwelling so as to exceed by more than twenty-five per centum the area which such dwelling had on any floor at the time of its conversion, except as provided in paragraph h.g. To convert to a multiple dwelling any dwelling not so converted before April fifteenth, nineteen hundred thirty, if after such date it has been increased in number of stories or combined with another building more than six stories in height or enlarged or extended so as to exceed by more than twenty-five per centum the area of such dwelling or its area on any floor as shown by the plan approved by the department before its erection, except as provided in paragraph h.h. Paragraphs f and g shall not apply to, or be deemed to prohibit, any rear extension of the first story of any converted dwelling permitted under the provisions of section one hundred seventy-two.3. Converted dwellings six stories or less in height may be combined if such dwellings when combined conform to the requirements of this subdivision. a. No frame building shall be a part of any such combination.b. Every entrance hall, stair hall, public hall, stair and stair enclosures shall be constructed of fireproof materials throughout and every door opening therefrom and door assembly shall be fireproof with the door self-closing and without transoms. Every public hall shall be at least three feet six inches in clear width and enclosed with masonry walls not less than eight inches in thickness. Every stair and stair hall shall be constructed and arranged throughout as provided in sections thirty-five, thirty-six, fifty and fifty-two, and as provided in sections one hundred two, one hundred five and one hundred six for fireproof dwellings erected after April eighteenth, nineteen hundred twenty-nine, and shall be at least three feet in clear width with all landings at floor levels at least three feet six inches in clear width. In every combination of three or more such dwellings, fire-stairs shall be located so that there shall be horizontal access in the public hall from every apartment to two or more fire-stairs, one or more of which shall be within fifty feet horizontally in the line of travel of one or more required means of egress from such apartment. Every stair, fire-stair and fire-tower shall extend to the roof through a fireproof bulkhead constructed in compliance with the provisions of section one hundred four for fireproof multiple dwellings.c. The ceiling of the cellar, or of the lowest story, if there be no cellar, shall be fire-retarded.d. There shall be at least two means of egress from every apartment or suite of rooms containing three or more living rooms. Such means shall be remote from each other, with the first means opening to a public hall which is connected with a stair not more than fifty feet distant from such means of egress. The second means of egress shall be directly accessible to a fire-tower or fire-stair, or to an outside fire-escape.e. No window to the outer air shall be required opening from any public hall, vestibule, stair, or stair hall artificially lighted and ventilated mechanically as provided in section one hundred seven for fireproof multiple dwellings. If any windows are provided, they and their assemblies shall be fireproof and glazed with wire glass, and if such windows are used in lieu of mechanical ventilation and artificial lighting, they shall also be arranged as provided for stairs and public halls in non-fireproof multiple dwellings erected after April eighteenth, nineteen hundred twenty-nine.f. No elevator shall be required, but should one be installed it shall conform to the provisions of section fifty-one relating to elevators and section one hundred five for fireproof dwellings.g. None of the combined dwellings shall be required to comply with sections one hundred seventy-eight, one hundred eighty-five, one hundred eighty-seven, one hundred eighty-eight and one hundred ninety or with subdivisions one, two and three of section one hundred eighty-nine.h. When any business is conducted in any portion of dwellings so combined, the ceilings and walls of such portion shall be fire-retarded and every door and door assembly shall be fireproof with the door self-closing.4. Nothing in this article shall be deemed to prohibit a combination of class A and B occupancy in any converted dwelling. If more than fifty per centum of the rooms therein are used for class A occupancy, the dwelling shall be deemed a class A dwelling, otherwise a class B dwelling.N.Y. Mult. Dwell. Law § 171