SECTION R311  MEANS OF EGRESS
Pursuant to the UCC, delete Section R311.7.5 and replace as follows:
   R-R311.7.5 Stair treads and risers. Stair treads and risers shall meet the requirements of this Section. For the purposes of this Section, dimensions and dimensioned surfaces shall be exclusive of carpets, rugs or runners.
      R-R311.7.5.1 Risers. The riser height shall be not more than 8-1/4 inches (210 mm). The riser shall be measured vertically between leading edges of the adjacent treads. The greatest riser height within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm). Risers shall be vertical or sloped from the underside of the nosing of the tread above at an angle not more than 30 degrees (0.51 rad) from the vertical. Open risers are permitted provided that the openings located more than 30 inches (762 mm), as measured vertically, to the floor or grade below do not permit the passage of a 4-inch-diameter (102 mm) sphere.
      Exceptions:
         1.   The opening between adjacent treads is not limited on spiral stairways.
         2.   The riser height of spiral stairways shall be in accordance with Section R311.7.10.1.
      R-R311.7.5.2 Treads. The tread depth shall be not less than 9 inches (229 mm). The tread depth shall be measured from tread nosing to tread nosing. The greatest tread depth within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm). Treads may have a uniform projection of not more than 1-1/2 inches (38 mm) when solid risers are used.