IBC Chapter Ten - Means of Egress
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1009.3 Stair treads and risers
Code Excerpt:
1009.3 Stair treads and risers.
Stair riser heights shall be 7 inches (178 mm) maximum and 4 inches (102 mm) minimum. Stair tread depths shall be 11 inches (279 mm) minimum.
The riser height shall be measured vertically between the leading edges of adjacent treads. The greatest riser height within any flight of stairs shall not exceed the smallest by more than 0.375 inch (9.5 mm). The tread depth shall be measured horizontally between the vertical planes of the foremost projection of adjacent tread and at right angle to the tread’s leading edge. The greatest tread depth within any flight of stairs shall not exceed the smallest by more than 0.375 (9.5 mm). Winder treads shall have a minimum tread depth of 11 inches (279 mm) measured at a right angle to the tread’s leading edge at a point 12 inches (305 mm) from the side where the treads are narrower and a minimum tread depth of 10 inches (254 mm). The greatest winder tread depth at the 12-inch (305 mm) walk line within any flight of stairs shall not exceed the smallest by more than 0.375 inch (9.5 mm).
Exceptions:
1. Circular stairways in accordance with Section 1009.8.
2. Winders in accordance with Section 1009.8
3. Spiral stairways in accordance with Section 1009.9.
4. Aisle stairs in assembly seating areas where the stair pitch or slope is set, for sightline reasons, by the slope of the adjacent seating areas in accordance with Section 1024.11.2.
5. In occupancies in Group R-3, as applicable in Section 101.2, within dwelling units in occupancies in Group R-2, as applicable in Section 101.2, and in occupancies in Group U, which are accessory to an occupancy in Group R-3, as applicable in Section 101.2, the maximum riser height shall be 7.75 inches (197 mm) and the minimum tread depth shall be 10 inches (254 mm), the minimum winder tread depth at the walk line shall be 10 inches (254 mm), and the minimum winder tread depth shall be 6 inches (152 mm). A nosing not less than .75 inch (19.1 mm) but not more than 1.25 inches (32 mm) shall be provided on stairways with solid risers where the tread depth is less than 11 inches (279 mm).
6. See the International Existing Building Code for the replacement of existing stairways.
National Partitions:
This code is why steeper
stairs are non-compliant.
Example: Stairs that must reach 108" high require a minimum of 16
steps (108"/7"). A minimum tread depth of 11" requires a stair length
176" (11" x 16 steps). Therefore the stair length is 14' 8" (176"/12").
Add to that a landing that may be required and a straight 9' high
stairway can extend over 18'.
Others:
Others routinely ignore this requirement especially in storage
mezzanine applications because the stairway takes up too much space.
These non-compliant stairs are in clear violation of this code.
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