Interpretation #7131

Original Request

Code Version: 2007
Code: RESIDENT
Code Description: Residential
Chapter: 3
Section: R311.5.8
Topic: Spiral Stairs

Question

Is it the intent of R311.5.8 that spiral stairs

are to comply with the 4" sphere requirement for

open risers contained in R311.5.3.3, based on the 2007 edition?

Answer Published 02/22/2013 at 9:22 AM

Yes. R311.5.8 Requires spiral stairs, bulkhead enclosure
stairways, and circular stairways comply with the
requirements of R311.5. With only 3 exceptions, and the
requirement 4" sphere in open risers is not one of the
exceptions.

Commentary

R311.5.3.3 Profile clearly permits open risers but provides the opening between treads cannot permit the passage of a 4- inch diameter sphere. "R311.5.3.3 Profile. The radius of curvature at the leading edge of the tread shall be no greater than 9/16 inch (14.3 mm). Every tread less than 10 inches (254 mm) wide shall have a nosing or effective projection of approximately 1 inch (25 mm) over the level immediately below that tread. Beveling of nosing shall not exceed 1/2 inch (12.7 mm). Risers shall be vertical or sloped from the underside of the leading edge of the tread above at an angle not more than 30 (0.51 rad) degrees from the vertical. Open risers are permitted, provided that the opening between treads does not permit the passage of a 4- inch diameter (102 mm) sphere."