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Technical Specifications

The Iron Shop’s Code spiral staircase kits will address and meet compliancy with each of the requirements that are listed below. This information will apply to the BOCA Code, UBC Code, IRC 2009, IRC 2012, IBC 2009, and IBC 2012 codes.

IRC 2012 Stair Building Code

1009.12 Spiral Stairs. Spiral stairways are permitted, provided the minimum width shall be 26 inches (660 mm) with each tread having a 7 1⁄2 inch (190 mm) minimum tread depth a 12 inches from the narrower edge. All treads shall be identical, and the rise shall be no more than 9 1⁄2 inches (241 mm).

A minimum headroom of 6 feet, 6 inches (1982 mm) shall be provided (See diagram below).

  1. Minimum clear walking path of 26 inches. A 5-foot diameter or larger stair will provide this width.
  2. Each tread will have a minimum tread depth of 7 1/2 inch at 12 inches from the narrow edge.
  3. All treads will be identical.
  4. The tread rise shall not be more than 9 1/2 inches high.
  5. Landing width shall not be less than the required width of the stairway. Minimum spiral stair tread width is 26 inches.
  6. Minimum headroom of 6 foot 6 inches shall be provided, measuring plumb from the edge of the landing down to the tread below.
  7. Stair balusters shall be spaced so a 4-inch object cannot pass between. The IRC 2009 & 2012 permits a 4 3/8 inch space.
  8. Balcony/Well Enclosure guardrail balusters shall be spaced so a 4-inch object cannot pass between.
  9. Balcony/Well Enclosure guardrail height shall not be less than 36 inches. (If your state or municipality requires 42-inch tall guardrails, the sales order must reflect this detail.)
  10. The stairway shall be equipped with one handrail on the wide edge of the tread.
  11. Handrail height, measured vertically from the tread nosing, shall be not less than 34 inches and not more than 38 inches.
  12. Handrail grip size. Handrails with a circular cross section shall have an outside diameter of at least 1 1/4 inches and not greater than 2 inches. If the handrail is not circular, it shall have a perimeter dimension not greater than 6 1/4 inches. Handrails with a perimeter greater than 6 1/4 inches, shall provide a graspable finger recess area on both sides of the profile.
  13. A 300 lb. concentrated load is required

The Iron Shop’s standard spiral package does not address the open space between each tread (open rise stair). *If your code, IRC 2009, IRC 2012 or IBC 2009 requires not more than a 4” space in this area, you will need to order our riser bars, Lip-up design treads, or riser plates.

IRC 2012 Stair Building Code

The clear width at and below the handrails at spiral stairways shall not be less than 26 inches (660 mm) and the walkline radius shall not be greater than 24 ½ inches (622 mm). Each tread shall have a depth of not less than 6 ¾ inches (171 mm) at the walkline. Treads shall be identical, and the rise shall be not more than 9 ½ inches (241 mm). Headroom shall not be less than 6 feet 6 inches (1982 mm).

IRC 2021 R311.7.10.1 Spiral Stairways

The clear width at and below the handrails at spiral stairways shall not be less than 26 inches (660 mm) and the walkline radius shall not be greater than 24 ½ inches (622 mm). Each tread shall have a depth of not less than 6 ¾ inches (171 mm) at the walkline. Treads shall be identical, and the rise shall be not more than 9 ½ inches (241 mm). Headroom shall not be less than 6 feet 6 inches (1982 mm).

Engineered Drawings

Stair Kit Dimensions

Spiral Stair Specifications

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