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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.

RESIDENTIAL STAIR — HEADROOM, WIDTH AND GUARDSD23ceiling or floor above4" SPHEREmust not pass6'-8" MIN34–38"7¾" MAX10" MIN36" MINguard> 30" dropguard requiredPLAN — STAIR WIDTH36" MINclear widthNOTES · IRC 2021 §R311.7 / §R312.1Width: 36" MIN above the handrail; 31½" MIN with a handrail on one side;27" MIN with handrails on both sides (§R311.7.1).Guards on open sides of stairs: 34" MIN from the nosing line; openings4⅜" sphere, triangle 6" (§R312.1.2, §R312.1.3).Guard required > 30" drop, within 36" of the edge (§R312.1.1).Dashed line: line of nosings. Stair, headroom and guard heights drawn to scale at the limits.STAIR AND GUARDS · IRC 2021 §R311.7.1 · §R311.7.2 · §R311.7.5 · §R311.7.8.1 · §R312.1
Residential stair geometry — IRC 2021 R311.7.Open full diagram →
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.

Common questions

What does the code say about maximum riser height for Stairs?

7-3/4 in., measured vertically between nosings. (IRC R311.7.5.1)

What does the code say about minimum tread depth for Stairs?

10 in., measured nosing to nosing. (IRC R311.7.5.2)

What does the code say about uniformity for Stairs?

Largest riser or tread may not exceed the smallest by more than 3/8 in.. (IRC R311.7.5.1, R311.7.5.2)

Adopted edition by state

Base-code year from BuildSpec’s adoption records. States often amend the base code, and your city or county may differ, so confirm with your building department.

Related sections and guides

This guide is BuildSpec’s own summary, not code text. It cites the 2021 International Residential Code and the 2023 National Electrical Code as model standards. The IRC 2021 text itself is in the Code Library for signed-in members; BuildSpec publishes no NEC text, which is at nfpa.org.Neither is an adoption record: your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.
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