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Home / Code Guides / Stairs

Stair Code Requirements — Rise, Run, Width & Headroom

Residential stairs are governed by four numbers most builders can recite: 7-3/4, 10, 36, and 6-8. Miss the uniformity tolerance, though, and a stair that meets all four still fails.

RequirementModel Code StandardSection
Maximum riser height7-3/4 in., measured vertically between nosingsIRC R311.7.5.1
Minimum tread depth10 in., measured nosing to nosingIRC R311.7.5.2
UniformityLargest riser or tread may not exceed the smallest by more than 3/8 in.IRC R311.7.5.1, R311.7.5.2
Minimum width36 in. clear above the handrail height; 31.5 in. at/below one handrail, 27 in. between twoIRC R311.7.1
Headroom6 ft 8 in. minimum, measured vertically from the nosing lineIRC R311.7.2
Nosing3/4 in. to 1-1/4 in. projection required where treads are less than 11 in. (solid risers)IRC R311.7.5.3
LandingsLanding or floor required at top and bottom; minimum 36 in. in the direction of travelIRC R311.7.6
Riser openingsOpen risers may not pass a 4-in. sphere where the stair is more than 30 in. above grade/floorIRC R311.7.5.1

Worth knowing

  • The commercial (IBC) standard is stricter — 7 in. max rise, 11 in. min tread — which is why "code stairs" answers online conflict.
  • Spiral stairs have their own allowances: 26 in. clear width, 6-3/4 in. tread at the 12-in. walkline, 9-1/2 in. max rise (R311.7.10.1).
  • The 3/8-in. uniformity rule is the most common stair failure — check the first and last riser after flooring changes.
  • Winder treads need 10 in. at the 12-in. walkline and 6 in. minimum at any point.
Sections cite the 2021 International Residential Code and 2023 National Electrical Code as model standards. This is BuildSpec’s own summary — not ICC or NFPA text; read the authoritative language at codes.iccsafe.org. Your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.
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