This information will apply to the BOCA Code, UBC Code, IRC 2006, and IFC 2006 codes.

This document is a learning tool to aid builders and homeowners to accurately and consistently interpret the building code related to Spiral Stairways.

spiral stair top


•  Spiral stairways are permitted, provided the minimum width shall be 26 inches with each tread having a 7-1/2 inch minimum tread depth at 12 inches from the narrower edge. Landing width shall not be less than the required width of the stairway.





•  All treads shall be identical, and the rise shall be no more than 9-1/2 inches.






overhead clearance


•  A minimum headroom of 6-1/2 feet
(78 inches) shall be provided.







•  Stair balusters shall be spaced so a 4-inch object cannot pass between. The IRC 2003 & 2006 permits a 4-3/8 inches space. Handrail height, measured vertically from the tread nosing, shall be not less than 34 inches and not more than 38 inches.


•  Handrail grip size: Type I-Handrails with a circular cross section shall have an outside diameter of at least 1-1/4 inches and not greater than 2 inches ( UBC minimum cross section of 1-1/2 inch diameter). If the handrail is not circular, it shall have a perimeter dimension not greater than 6-1/4 inches. Type II-Handrails, with a perimeter greater than 6-1/4 inches, shall provide a graspable finger recess area on both sides of the profile.


•  A 300 lb. concentrated load is required.