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Spiral stairways and bulkhead enclosure stairways shall comply with the requirements of Section R311.7 except as specified in Sections R311.7.10.1 and R311.7.10.2.
R311.7.10.1 Spiral Stairways
The clear width at and below the handrails at spiral stairways shall be not less than 26 inches (660 mm) and the walkline radius shall be not greater than 241/2 inches (622 mm). Each tread shall have a depth of not less than 63/4 inches (171 mm) at the walkline. Treads shall be identical, and the rise shall be not more than 91/2 inches (241 mm). Headroom shall be not less than 6 feet 6 inches (1982 mm).
R311.7.10.2 Bulkhead Enclosure Stairways
Stairways serving bulkhead enclosures, not part of the required building egress, providing access from the outside grade level to the basement shall be exempt from the requirements of Sections R311.3 and R311.7 where the height from the basement finished floor level to grade adjacent to the stairway is not more than 8 feet (2438 mm) and the grade level opening to the stairway is covered by a bulkhead enclosure with hinged doors or other approved means.

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R311.7.10 Building Planning, Special Stairways
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