The riser height shall be not more than 7 3/4 inches (196 mm). The riser shall be measured vertically between leading edges of the adjacent treads PHOTO 13. The greatest riser height within any flight DRAWING 12 (p. 8) of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm) PHOTO 14. 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 PHOTO 15. At open risers, openings located more than 30 inches (762 mm), as measured vertically, to the floor or grade below shall not permit the passage of a 4-inch-diameter (102 mm)
sphere PHOTO 16.
Exceptions:
1. The opening between adjacent treads is not limited on spiral stairways PHOTO 55, Page 19.
2. The riser height of spiral stairways shall be in accordance with Section R311.7.10.1 PHOTO 52, Page 19.