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I am working with a designer who said he was pretty sure that the tread width on a spiral staircase would have to be 36" wide if it is the sole means of egress from the second story of an R-3, single family home.
Location: Cameron Park, Eldorado County, California
REF: Referencing the 2016 California Building Code which adopts with amendments from the International Building Code 2015 (IBC 2015)
My research has led to me to conclude that it would be permitted.
Here is a summary of what I found. I have also provided a copy of the applicable code with pertinent items bold and/or underlined.
1. This structure is to be an R-3 occupancy which also meets the definition of a dwelling.
2. One means of egress is required per Section 1006.1, Exemption 1.
3. Throughout section 1011, spiral staircases requirements fall under exceptions for construction standards.
4. Staircase Width and Capacity Standards found in 1011.2 normally call for a 36” width, however spiral staircases are exempt from this per exemption 2 and permit a 26” width tread
5. Section 1011.10 pertains exclusively to Spiral stairways.
Spiral stairways are permitted to be used as a component in the means of egress only within dwelling units or from a space not more than 250 square feet (23 m2) in area and serving not more than five occupants, or from technical production areas in accordance with Section 410.6.
A spiral stairway shall have a 71/2-inch (191 mm) minimum clear tread depth at a point 12 inches (305 mm) from the narrow edge. The risers shall be sufficient to provide a headroom of 78 inches (1981 mm) minimum, but riser height shall not be more than 91/2 inches (241 mm). The minimum stairway clear width at and below the handrail shall be 26 inches (660 mm).
Therefore, spiral stairs are permitted as the sole means of egress in an R-3 dwelling as long as the standards specifically for spiral stairs and all other applicable sections of Chapter 10 Means of Egress are met.
Code compliance can be achieved with a 60” diameter spiral stairway.
A 10’ above finished floor height rise can be achieved in 11 Steps / 12 Risers.
30 degree steps per code = 12 steps per 360 degrees = 330 degrees of rotation.
Please let me know if I am not understanding the code correctly.
Thank you,
Glenn
Location: Cameron Park, Eldorado County, California
REF: Referencing the 2016 California Building Code which adopts with amendments from the International Building Code 2015 (IBC 2015)
My research has led to me to conclude that it would be permitted.
Here is a summary of what I found. I have also provided a copy of the applicable code with pertinent items bold and/or underlined.
1. This structure is to be an R-3 occupancy which also meets the definition of a dwelling.
2. One means of egress is required per Section 1006.1, Exemption 1.
3. Throughout section 1011, spiral staircases requirements fall under exceptions for construction standards.
4. Staircase Width and Capacity Standards found in 1011.2 normally call for a 36” width, however spiral staircases are exempt from this per exemption 2 and permit a 26” width tread
5. Section 1011.10 pertains exclusively to Spiral stairways.
Spiral stairways are permitted to be used as a component in the means of egress only within dwelling units or from a space not more than 250 square feet (23 m2) in area and serving not more than five occupants, or from technical production areas in accordance with Section 410.6.
A spiral stairway shall have a 71/2-inch (191 mm) minimum clear tread depth at a point 12 inches (305 mm) from the narrow edge. The risers shall be sufficient to provide a headroom of 78 inches (1981 mm) minimum, but riser height shall not be more than 91/2 inches (241 mm). The minimum stairway clear width at and below the handrail shall be 26 inches (660 mm).
Therefore, spiral stairs are permitted as the sole means of egress in an R-3 dwelling as long as the standards specifically for spiral stairs and all other applicable sections of Chapter 10 Means of Egress are met.
Code compliance can be achieved with a 60” diameter spiral stairway.
A 10’ above finished floor height rise can be achieved in 11 Steps / 12 Risers.
30 degree steps per code = 12 steps per 360 degrees = 330 degrees of rotation.
Please let me know if I am not understanding the code correctly.
Thank you,
Glenn
