N.Y. MRE Law § 257

§ 257. Public stairs. 1. Every stair and fire-stair shall, except as\notherwise provided in subdivisions three and four of this section and in\nsection two hundred fifty-nine, be constructed as provided for\nfire-stairs in sections two hundred two and two hundred five for\nfireproof dwellings.\n 2. Every stair and fire-stair shall be at least three feet in clear\nwidth throughout, and at all floor levels shall have landings at least\nthree feet eight inches in clear width.\n 3. Every stair and fire-stair shall be completely separated from every\nother stair and fire-stair and from every public hall and shaft by\nfireproof walls, with fireproof doors and assemblies, with the doors\nself-closing and without transoms, at all openings, except that in\ndwellings two stories or less in height such walls may be fire-retarded.\nThe doors giving access to such stairs shall not be held open by any\ndevice whatever.\n 4. Except in the case of an interior enclosed stair separated from and\ndirectly accessible to the public hall by a self-closing fireproof door\nand except as provided in subdivision five, there shall be provided to\nlight and ventilate every stair at every story a window or windows\nopening on a street, court or yard.\n 5. In a dwelling occupied by two families or less on every story:\n a. If such dwelling is three stories or less in height, there may be\nprovided for any stair, in lieu of windows, a stairwell sixteen inches\nor more in clear width extending from the entrance story to the roof.\n b. If such dwelling is a permanently occupied dwelling and is two\nstories or less in height, there may be provided for any stair, in lieu\nof windows, a stairwell six inches or more in clear width. For the\npurposes of this paragraph, a section of a permanently occupied dwelling\nmay be deemed a separate multiple dwelling.\n c. If such dwelling is two stories in height and has no public hall on\nthe first story, no stairwell or stair windows need be provided.\n