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