1011.5.2 Riser height and tread depth.
BC § 1011.5.2
Stair riser heights shall be 7 inches (177.8 mm) maximum and 4 inches (101.6 mm) minimum. The riser height shall be measured vertically between the nosings of adjacent treads. Rectangular tread depths shall be 11 inches (279.4 mm) minimum measured horizontally between the vertical planes of the foremost projection of adjacent treads and at a right angle to the tread's nosing. The greatest tread depth within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm). Winder treads shall have a minimum tread depth of 11 inches (279.4 mm) between the vertical planes of the foremost projection of adjacent treads at the intersections with the walkline and a minimum tread depth of 10 inches (254 mm) within the clear width of the stair. Exceptions: 1. Spiral stairways in accordance with Section 1011.10.
2.Stairways connecting stepped aisles to cross aisles or concourses shall be permitted to use the riser/tread dimension in Section 1029.13.2.
3.In Group R-2 occupancies: 3.1. Sum of treads and risers. The sum of two risers plus one tread exclusive of nosing shall be not less than 24 inches (609.6 mm) nor more than 25 1/2 inches (647.7 mm). 3.2. Dimensions of treads and risers. The maximum riser height shall be 7 3/4 inches (196.85 mm) and the minimum tread depth shall be 9 1/2 inches (241.3 mm) plus nosing. Treads may be undercut a distance equal to the nosing. A nosing not less than 3/4 inch (19 mm) but not more than 1 1/4 inches (31.8 mm) shall be provided on stairways with solid risers where the tread depth is less than 11 inches (279.4 mm). 3.3. Tolerances. The greatest riser height, tread depth, and nosing projection, within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm).
4.In Group R-3 occupancies; and in Group U occupancies that are accessory to Group R-3 occupancy or accessory to individual dwelling units in Group R-2 occupancies: 4.1. Sum of treads and risers. The sum of two risers plus one tread exclusive of nosing shall be not less than 24 inches (609.6 mm) nor more than 25 1/2 inches (647.7 mm). 4.2. Dimensions of treads and risers. The maximum riser height shall be 8 1/4 inches (209.6 mm) and the minimum tread depth shall be 9 inches (228.6 mm) plus nosing. Treads may be undercut a distance equal to the nosing. A 1 1/4-inch (31.75 mm) nosing shall be provided on stairways with solid risers where the tread depth is less than 11 inches (279.4 mm). 4.3. Tolerances. The greatest riser height, tread depth, and nosing projection, within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm).
5.In Group R-3 occupancies; and within dwelling units in Group R-2 occupancies; winders shall have a minimum tread depth of 10 inches (254 mm) measured horizontally between the vertical planes of the foremost projection of adjacent treads and at a right angle to the tread's leading edge, when measured at a point 12 inches (304.8 mm) from the side where the treads are narrower. Winder treads shall have a minimum tread depth of 6 inches (152.4 mm) at any point. Within any flight of stairs, the greatest winder tread depth at the 12-inch (304.8 mm) walk line shall not exceed the smallest by more than 3/8 inch (9.5 mm).
6.In Group I-3 facilities, stairways providing access to guard towers, observation stations and control rooms, not more than 250 square feet (23.2 m 2 ) in area, shall be permitted to have a maximum riser height of 8 inches (203.2 mm) and a minimum tread depth of 9 inches (228.6 mm).
