Page 97 - 2018_IRC

BUILDING PLANNING

R311.7.2 Headroom. The headroom in stairways shall be foremost projection of adjacent treads at the intersec-
not less than 6 feet 8 inches (2032 mm) measured verti- tions with the walkline. Winder treads shall have a
cally from the sloped line adjoining the tread nosing or tread depth of not less than 6 inches (152 mm) at any
from the floor surface of the landing or platform on that point within the clear width of the stair. Within any
portion of the stairway. flight of stairs, the largest winder tread depth at the
Exceptions: walkline shall not exceed the smallest winder tread
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by more than / inch (9.5 mm). Consistently shaped
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1. Where the nosings of treads at the side of a flight winders at the walkline shall be allowed within the
extend under the edge of a floor opening through same flight of stairs as rectangular treads and shall
which the stair passes, the floor opening shall not not be required to be within / inch (9.5 mm) of the
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project horizontally into the required headroom rectangular tread depth. 8
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more than 4 / inches (121 mm). Exception: The tread depth at spiral stairways
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2. The headroom for spiral stairways shall be in shall be in accordance with Section R311.7.10.1.
accordance with Section R311.7.10.1. R311.7.5.3 Nosings. Nosings at treads, landings and
R311.7.3 Vertical rise. A flight of stairs shall not have a floors of stairways shall have a radius of curvature at
vertical rise larger than 151 inches (3835 mm) between the nosing not greater than / inch (14 mm) or a bevel
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floor levels or landings. not greater than / inch (12.7 mm). A nosing projection
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R311.7.4 Walkline. The walkline across winder treads not less than / inch (19 mm) and not more than 1 / 4
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and landings shall be concentric to the turn and parallel to inches (32 mm) shall be provided on stairways. The
the direction of travel entering and exiting the turn. The greatest nosing projection shall not exceed the smallest
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walkline shall be located 12 inches (305 mm) from the nosing projection by more than / inch (9.5 mm) within
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inside of the turn. The 12-inch (305 mm) dimension shall a stairway.
be measured from the widest point of the clear stair width Exception: A nosing projection is not required where
at the walking surface. Where winders are adjacent within the tread depth is not less than 11 inches (279 mm).
a flight, the point of the widest clear stair width of the R311.7.5.4 Exterior plastic composite stair treads.
adjacent winders shall be used. Plastic composite exterior stair treads shall comply
R311.7.5 Stair treads and risers. Stair treads and risers with the provisions of this section and Section
shall meet the requirements of this section. For the pur- R507.2.2.
poses of this section, dimensions and dimensioned sur- R311.7.6 Landings for stairways. There shall be a floor
faces shall be exclusive of carpets, rugs or runners. or landing at the top and bottom of each stairway. The
R311.7.5.1 Risers. The riser height shall be not more width perpendicular to the direction of travel shall be not
than 7 / inches (196 mm). The riser shall be measured less than the width of the flight served. For landings of
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vertically between leading edges of the adjacent treads. shapes other than square or rectangular, the depth at the
The greatest riser height within any flight of stairs shall walk line and the total area shall be not less than that of a
not exceed the smallest by more than / inch (9.5 mm). quarter circle with a radius equal to the required landing
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Risers shall be vertical or sloped from the underside of width. Where the stairway has a straight run, the depth in
the nosing of the tread above at an angle not more than 30 the direction of travel shall be not less than 36 inches (914
degrees (0.51 rad) from the vertical. At open risers, open- mm).
ings located more than 30 inches (762 mm), as measured Exception: A floor or landing is not required at the top
vertically, to the floor or grade below shall not permit the of an interior flight of stairs, including stairs in an
passage of a 4-inch-diameter (102 mm) sphere. enclosed garage, provided that a door does not swing
Exceptions: over the stairs.
1. The opening between adjacent treads is not R311.7.7 Stairway walking surface. The walking surface
limited on spiral stairways. of treads and landings of stairways shall be sloped not
steeper than one unit vertical in 48 inches horizontal (2-per-
2. The riser height of spiral stairways shall be in cent slope).
accordance with Section R311.7.10.1.
R311.7.8 Handrails. Handrails shall be provided on not
R311.7.5.2 Treads. The tread depth shall be not less less than one side of each flight of stairs with four or more
than 10 inches (254 mm). The tread depth shall be mea- risers.
sured horizontally between the vertical planes of the
foremost projection of adjacent treads and at a right R311.7.8.1 Height. Handrail height, measured verti-
angle to the tread’s leading edge. The greatest tread cally from the sloped plane adjoining the tread nosing, or
depth within any flight of stairs shall not exceed the finish surface of ramp slope, shall be not less than 34
smallest by more than / inch (9.5 mm). inches (864 mm) and not more than 38 inches (965 mm).
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R311.7.5.2.1 Winder treads. Winder treads shall Exceptions:
have a tread depth of not less than 10 inches (254 1. The use of a volute, turnout or starting easing
mm) measured between the vertical planes of the shall be allowed over the lowest tread.

72 2018 INTERNATIONAL RESIDENTIAL CODE ®
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