The International Residential Code for One-and Two-Family Dwellings (IRC) and the International Building Code (IBC) address staircase railings. 1)The clear height over stairs shall be measured vertically, over the clear width of the stair, from a straight line. The tolerance between the largest and smallest riser height or between the largest  and smallest tread depth shall not exceed 3/8 inch (9.5 mm) in any flight of stairs. Guards shall comply with the provisions of section 1013.2 through 1013.7. //