N.Y. Multiple Residence Law § 132

§ 132. Stairs. Every interior and exterior stair and fire-stair shall\nbe provided with proper balustrades and handrails. Every such stair and\nfire-stair three feet eight inches or more in width shall be provided\nwith a handrail on each side. Each tread, exclusive of nosing, shall be\nnot less than nine and one-half inches wide; each riser shall not exceed\nseven and three-quarter inches in height; and the product of the number\nof inches in the width of the tread and the number of inches in the\nheight of the riser shall be at least seventy and at the most\nseventy-five. Winding stairs shall be unlawful in any public part of the\ndwelling.\n