This type of staircase begins with a wider flight at the bottom, which splits into two narrower flights, one turning left and one turning right, at a landing partway up.
Bifurcated stairs, also known as split stairs, are a grand architectural feature where a single stairway splits into two smaller flights going in opposite directions. They are often seen in large and luxurious residential or commercial buildings. The Americans with Disabilities Act (ADA) and the International Building Code (IBC) both provide guidelines to ensure these stairways are safe, functional, and accessible. Here are some guidelines for ADA and IBC-compliant bifurcated stairs:
- Width: The IBC typically requires stairways to have a minimum width of 44 inches, though this can be reduced to 36 inches in certain residential situations. ADA does not explicitly mention stair width, but it should be sufficient to allow for the easy passage of individuals, including those using assistive devices.
- Rise and Run: IBC states that the maximum riser height should be 7.75 inches, and the minimum tread depth should be 10 inches. ADA does not explicitly define riser height and tread depth, but it focuses on ensuring stairs are accessible and safe for all individuals.
- Handrails: Both ADA and IBC require handrails on both sides of the stairs. They should be between 34 and 38 inches high, according to both ADA and IBC. Handrails should extend beyond the top and bottom of the stair flight and be returned smoothly to the floor, wall, or post.
- Stair Landings: Landings are required at the top and bottom of the stairs, and where the stairs change direction (i.e., at the bifurcation point), according to both ADA and IBC. ADA requires that landings be at least as wide as the stairway and at least 60 inches long, measured in the direction of travel. IBC requires that landing length be not less than the width of the stairway.
- Stair Nosing: The IBC recommends that the stair nosing should not be more than 1.25 inches and not less than 0.75 inches. ADA suggests that nosings should be visually contrasted from the rest of the tread to avoid tripping hazards and be beveled or rounded.
- Guards and Balusters: IBC requires guards to be at least 42 inches high, and openings in balusters should not allow the passage of a 4-inch diameter sphere.
- Accessible Routes: The ADA requires an accessible route to be provided where stairs are present. This might involve installing ramps, lifts, or elevators alongside the stairs.
Remember, these are general guidelines, and the specific rules can vary depending on local building codes and the exact requirements of the ADA and IBC. Always consult with a professional or local building authority when designing or evaluating bifurcated stairs for compliance.