The headroom in stairways shall be not less than 6 feet 8 inches (2032 mm) measured vertically from the sloped line adjoining the tread nosing or from the floor surface of the landing or platform on that portion of the stairway.Įxceptions: 1. Handrails shall not project more than 41/2 inches (114 mm) on either side of the stairway and the clear width of the stairway at and below the handrail height, including treads and landings, shall be not less than 311/2 inches (787 mm) where a handrail is installed on one side and 27 inches (698 mm) where handrails are provided on both sides.Įxception: The width of spiral stairways shall be in accordance with Section R311.7.10.1.
Stairways shall be not less than 36 inches (914 mm) in clear width at all points above the permitted handrail height and below the required headroom height. The method of measurement for tread depth now matches the winder provisions and measures at the intersection of the walkline and the tread nosings rather than prependicular ot the leading edge of the tread.R311.7.1 Width. The code now limits the size of spiral stairways by restricting the radius at the walkline to a dimension not greater the 24½ inches. In summary the code adds a definition of spiral stairway that omits any requirement for a center post to allow for design flexibility. The intent of the change in measuring methods, which occurred in the 2009 edition of the IRC, was to provide for consistent tread depth measurements conforming with stair design methodology, not to change or increase tread depth.
This editorial change simply adjusts the spiral stair tread depth in conformance with the method of measuring for winder tread depth at the intersections of the walkline with the nosings instead of the prior method, which was square to the leading edge.The effective tread depth remains unchanged. Treads within spiral stairways meet the definition of winder treads and are sometimes interpreted to be measured for tread depth in the same fashion. This change correlates with the new IRC definition of spiral stairway, which omits any reference to a supporting column as found in the IBC.
Stairs beyond the limit stated would be considered curved stairs. The revised provisions define a reasonable limit of the radius at the walkline for the design of spiral stairways, while still maintaining the exceptions for headroom, riser height, and tread depth when compared to conventional stairs. "In the previous editions of the code, spiral stairways were not restricted in size.
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