VISUAL INTERPRETATION OF THE
SPIRAL STAIR BUILDING CODE
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 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.
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.
