R311.7.10.1

Section R311.7.10.1 is titled 'Spiral stairways' and covers the requirements for stairways that ascend in a tight circular arrangement as defined in chapter 2. This section overrides some requirements covered in previous subsections of R311.7. Clear width at and below the handrail, maximum walkline radius, tread depth at the walkline, tread shape uniformity, riser height, and headroom are established. The purpose of this section is to reduce trip and fall hazards. It is worth noting that spiral stairways are allowed as an element in a means of egress system.

The model shows a spiral stairway with each of the alternate dimensions depicted. The walkline, which follows the curve of the steps, is displayed as the maximum allowed by the section, but the dimension is not denoted in the model for clarity. The walkline measurement is made in a straight line from end to end of the walkline on each tread. Note that spiral stairways are not allowed a variance in tread or riser dimensions as allowed for standard stairways.