Section 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.