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Stair treads and risers shall comply with Sections 1011.5.1 through 1011.5.5.3.
1011.5.1 Dimension Reference Surfaces
For the purpose of this section, all dimensions are exclusive of carpets, rugs or runners.
1011.5.2 Riser Height and Tread Depth
Stair riser heights shall be 7 inches (178 mm) maximum and 4 inches (102 mm) minimum. The riser height shall be measured vertically between the nosings of adjacent treads or between the stairway landing and the adjacent tread. Rectangular tread depths shall be 11 inches (279 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. Winder treads shall have a minimum tread depth of 11 inches (279 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 1030.14.2.
  3. In Group R-3 occupancies; within dwelling units in Group R-2 occupancies; and in Group U occupancies that are accessory to a Group R-3 occupancy or accessory to individual dwelling units in Group R-2 occupancies; the maximum riser height shall be 73/4 inches (197 mm); the minimum tread depth shall be 10 inches (254 mm); the minimum winder tread depth at the walkline shall be 10 inches (254 mm); and the minimum winder tread depth shall be 6 inches (152 mm). A nosing projection not less than 3/4 inch (19.1 mm) but not more than 11/4 inches (32 mm) shall be provided on stairways with solid risers where the tread depth is less than 11 inches (279 mm).
  4. See Section 503.1 of the International Existing Building Code for the replacement of existing stairways.
  5. In Group I-3 facilities, stairways providing access to guard towers, observation stations and control rooms, not more than 250 square feet (23 m2) in area, shall be permitted to have a maximum riser height of 8 inches (203 mm) and a minimum tread depth of 9 inches (229 mm).
1011.5.3 Winder Treads
Winder treads are not permitted in means of egress stairways except within a dwelling unit.
Exceptions:
  1. Curved stairways in accordance with Section 1011.9.
  2. Spiral stairways in accordance with Section 1011.10.
1011.5.4 Dimensional Uniformity
Stair treads and risers shall be of uniform size and shape. 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. The greatest winder tread depth at the walkline within any flight of stairs shall not exceed the smallest by more than 3/8 inch (9.5 mm).
Exceptions:
  1. Stairways connecting stepped aisles to cross aisles or concourses shall be permitted to comply with the dimensional nonuniformity in Section 1030.14.2.
  2. Consistently shaped winders, complying with Section 1011.5, differing from rectangular treads in the same flight of stairs.
  3. Nonuniform riser dimension complying with Section 1011.5.4.1.
1011.5.4.1 Nonuniform Height Risers
Where the bottom or top riser adjoins a sloping public way, walkway or driveway having an established grade and serving as a landing, the bottom or top riser is permitted to be reduced along the slope to less than 4 inches (102 mm) in height, with the variation in height of the bottom or top riser not to exceed one unit vertical in 12 units horizontal (8-percent slope) of stair width. The nosings or leading edges of treads at such nonuniform height risers shall have a distinctive marking stripe, different from any other nosing marking provided on the stair flight. The distinctive marking stripe shall be visible in descent of the stair and shall have a slip-resistant surface. Marking stripes shall have a width of not less than 1 inch (25 mm) but not more than 2 inches (51 mm).
1011.5.5 Nosing and Riser Profile
Nosings shall have a curvature or bevel of not less than 1/16 inch (1.6 mm) but not more than 9/16 inch (14.3 mm) from the foremost projection of the tread. Risers shall be solid and vertical or sloped under the tread above from the underside of the nosing above at an angle not more than 30 degrees (0.52 rad) from the vertical.
1011.5.5.1 Nosing Projection Size
The leading edge (nosings) of treads shall project not more than 11/4 inches (32 mm) beyond the tread below.
1011.5.5.2 Nosing Projection Uniformity
Nosing projections of the leading edges shall be of uniform size, including the projections of the nosing's leading edge of the floor at the top of a flight.
1011.5.5.3 Solid Risers
Risers shall be solid.
Exceptions:
  1. Solid risers are not required for stairways that are not required to comply with Section 1009.3, provided that the opening between treads does not permit the passage of a sphere with a diameter of 4 inches (102 mm).
  2. Solid risers are not required for occupancies in Group I-3 or in Group F, H and S occupancies other than areas accessible to the public. The size of the opening in the riser is not restricted.
  3. Solid risers are not required for spiral stairways constructed in accordance with Section 1011.10.

Related Code Sections

1011.5.2 Means of Egress, Riser Height and Tread Depth
with Section 1011.10. Stairways connecting stepped aisles to cross aisles or concourses shall be permitted to use the riser/tread dimension in Section ...
1011.5.4 Means of Egress, Dimensional Uniformity
Stair treads and risers shall be of uniform size and shape. The tolerance between the largest and smallest riser height or between the largest ...
1011.5.4 Means of Egress, Dimensional Uniformity
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