Open-riser stair
A stair with no riser boards, leaving a gap between treads; gap rejects a 4 in sphere.
An open-riser (or open-tread) stair omits the riser boards, leaving an open gap between one tread and the next for a lighter, more transparent look — common on modern and floating staircases. Because the gap is open, code controls it the same way it controls baluster spacing: the IRC requires that a 4 in (102 mm) sphere cannot pass through, so any open riser taller than 4 in needs a partial riser or backer. Example: a 7½ in (191 mm) riser height on an open stair exceeds 4 in, so each gap must be partly closed. Open risers also leave the stringers doing all the stiffening, since there are no riser boards to brace against racking. The trade-off for the airy look is a stricter sphere check.
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Written by the Stairs Calc editorial team. Methodology and code references: see our methodology.
Built and maintained by builders, drafters and engineers who plan stairs for a living — every code limit is transcribed from the published standard and cited to its exact section.
Last reviewed 2026-06-20 against IRC 2021/2024
Stairs Calc gives accurate geometry and checks it against published building-code limits, but results are estimates for planning. Codes are adopted and amended locally and change over time. Always confirm dimensions against your local adopted code and a licensed professional before you build.