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Stairs Calc

Riser (board)

The vertical board that closes the gap between two treads on a closed-riser stair.

The riser is the vertical board that fills the space between one tread and the next. Closed-riser stairs have them; open-riser (floating) stairs leave the gap empty for a lighter look. Do not confuse the riser board with riser height, which is the dimension. On open-riser stairs the IRC limits the gap so a 4 in (102 mm) sphere cannot pass through, protecting small children — the same sphere rule that governs balusters. Example: a 7 in riser height on an open stair already exceeds 4 in, so a partial riser or backer is required. Riser boards also add rigidity, stiffening the stringers against racking.

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Related terms

Riser height The vertical height of a single step; every riser must be equal within 3⁄8 in. Tread The horizontal board you step on; its depth equals the run plus the nosing. Baluster (spindle) The vertical infill posts of a railing; gaps must reject a 4 in sphere. Stringer The notched board that carries the treads and risers; usually a 2×12. Open-riser stair A stair with no riser boards, leaving a gap between treads; gap rejects a 4 in sphere.

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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.