504.2 Treads and Risers.
All steps on a flight of stairs shall have uniform riser heights and uniform tread depths. Risers shall be 100 mm (4″) high minimum and 180 mm (7″) high maximum. Treads shall be 280 mm (11″) deep minimum.
504.3 Open Risers.
Open risers are not permitted.
504.4 Tread Surface.
Stair treads shall comply with 302. Changes in level are not permitted.
The radius of curvature at the leading edge of the tread shall be 13 mm (1/2″) maximum. Nosings that project beyond risers shall have the underside of the leading edge curved or beveled. Risers shall be permitted to slope under the tread at an angle of 30 degrees maximum from vertical. The permitted projection of the nosing shall extend 38 mm (1 1/2″) maximum over the tread below.
Stairs shall have handrails complying with 505.
504.7 Wet Conditions.
Stair treads and landings subject to wet conditions shall be designed to prevent the accumulation of water.