StacksVerified U.S. regulatory reference

29 CFR §1917.121

Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov ↗
  1. (a)Definition. “Spiral stairway” means one with closed circular form, uniform sector-shaped treads and a supporting column.
  2. (b)Requirements. Spiral stairways shall meet the following requirements:
    1. (1)Stairways shall conform to the minimum dimensions of Figure F-1;
    2. (2)Stairway risers shall be uniform and shall range from 6 1/2 to 10 1/2 inches (16.5 to 26.67 cm) in height;
    3. (3)Minimum loading capability shall be 100 pounds per square foot (4.79kN), and minimum tread center concentrated loading shall be 300 pounds (1334 N);
    4. (4)Railings shall conform to the requirements of § 1917.112(c)(1). If balusters are used, there shall be a minimum of one per tread. Handrails shall be a minimum of 1 1/4 inches (3.18 cm) in outside diameter; and
    5. (5)Vertical clearance shall be at least 6 feet, 6 inches (1.98 m) above the top step.
  3. (c)Maintenance. Spiral stairways shall be maintained in safe condition.