IRC 2015 spiral stairs for egress

[Antonio B]

IRC 2015 - Am I correct in understanding that spiral stairs now qualify as a primary means of egress from an upper level?
They fall within Section R311.7 as mentioned below in R311.4.
Some stairs within 311.7 are specifically excluded such as Alternating Tread Devices (R311.7.11).
However there is no specific exclusion mentioned for spiral stairs. Does that mean they are now included?

R311.4 Vertical Egress
Egress from habitable levels including habitable attics and basements not provided with an egress door in accordance with Section R311.2 shall be by a ramp in accordance with Section R311.8 or a stairway in accordance with Section R311.7.

R311.7.10 Special Stairways
Spiral stairways and bulkhead enclosure stairways shall comply with the requirements of Section R311.7 except as specified in Sections R311.7.10.1 and R311.7.10.2.

R311.7.11 Alternating Tread Devices
Alternating tread devices shall not be used as an element of a means of egress.

 

[cda]

Welcome

 

[cda]

Appears yes

http://www.minnehahacounty.org/dept/pl/buildingInfo/building_handbook.pdf

 

[cda]

Appears same wording in 09?

Why the question???

 

[Antonio B]

Appears same wording in 09?

Why the question???

Thanks for the PDF link.
Why? As I recall, through 2012, spiral stairs were not allowed as a primary egress, which ruled them out of a lot of applications. This change opens up more design options.

 

[Francis Vineyard]

"In the previous editions of the code, spiral stairways were not restricted in size. 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. Stairs beyond the limit stated would be considered curved stairs. This change correlates with the new IRC definition of spiral stairway, which omits any reference to a supporting column as found in the IBC.

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 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. 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.

In summary the code adds a definition of spiral stairway that omits any requirement for a center post to allow for design flexibility. The code now limits the size of spiral stairways by restricting the radius at the walkline to a dimension not greater the 24½ inches. 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."

Source Significant Changes to The 2015 IRC

 

[steveray]

We didn't have a requirement for vertical egress before, so no stairs were required, so spiral should have been allowed....

 

[PJC89]

Agreed - permitted.

Section R311.7 except as specified in Sections R311.7.10.1 andR311.7.10.2.
R311.7.10.1 Spiral Stairways

Spiral stairways are permitted, provided that the clear width at and below the handrail is not less than 26 inches (660 mm) and the walkline radius is not greater than 241/2 inches (622 mm). Each tread shall have a depth of not less than 63/4 inches (171 mm) at the walkline. All treads shall be identical, and the rise shall be not more than 91/2 inches (241 mm). Headroom shall be not less than 6 feet 6 inches (1982 mm).

https://up.codes/viewer/general/int_residential_code_2015/chapter/3/building-planning#R311