New York Consolidated Laws, Multiple Residence Law - MRE § 260. One and two-story frame dwellings;  area limitation

1. Fire-stopped partitions shall be constructed between apartments in such dwelling so as to prevent the passage of fire, smoke or gases from one apartment to another.

2. No section of such dwelling shall contain more than three thousand square feet.  Each such section shall be separated from all other sections of the dwelling by fire walls of masonry or other materials having a fire resistive rating of at least two hours.  Such wall (1) shall be unpierced except for openings for heat, utility and other service lines and ducts with such openings sealed with incombustible materials (2) shall extend continuously from the floor of the lowest level of the dwelling, to at least two feet above the level of the finished roof and (3) be fire-stopped at floors and roof in such manner as to prevent the passage of fire, smoke or gases between sections.  Where there is a peaked or sloped roof, such wall may terminate at the top of the roof boards.