IBC Chapter Ten - Means of Egress
1009.3.1 Dimensional uniformity
Code Excerpt:
1009.3.1 Dimensional uniformity
Stair treads and risers shall be of uniform size and shape. The tolerance between the largest and smallest riser or between the largest and smallest tread shall not exceed 0.375 inch (9.5 mm) in any flight of stairs.
Exceptions:
1. No uniform riser dimensions of aisle stairs complying with Section
1024.11.2.2. Consistently shaped winder, complying with Section 1009.8, differing
from rectangular treads in the same stairway flight.
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 stairway width. The nosings or leading edges of treads at such non-uniform 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 width of at least 1 inch (25 mm) but not more than 2 inches (51 mm).
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