Section 15(2)(c) in Tamil Nadu District Municipalities (Hill Stations) Building Rules, 1993
(c)Treads and risers: Treads and risers shall be so proportioned that the sum of two risers and a tread width is not less than 60 centimetres and more than 62.5 centimetres. No riser shall be more than 17.5 centimetres and no tread width less than 25 centimetres. There shall be no variation in the widths of treads or the heights of risers in any one flight of stairs. No stairway should ordinarily be permitted cutting across any window. The surface material of stairs, treads and landings shall be such as not to involve undue danger of slipping.