IRC Stair Code Requirements
The International Residential Code (IRC) sets minimum safety standards for residential stairs in Section R311. The values below reflect the 2021 IRC — the most recent edition adopted by most US jurisdictions as of 2026. Always verify with your local building department, since some jurisdictions amend the IRC with stricter or looser requirements.
Riser and Tread Requirements
| Requirement | Code Value | IRC Section |
|---|---|---|
| Maximum riser height | 7-3/4" (196 mm) | R311.7.5.1 |
| Minimum riser height | 4" (102 mm) | R311.7.5.1 |
| Minimum tread depth | 10" (254 mm) | R311.7.5.2 |
| Maximum riser variation | 3/8" between largest and smallest | R311.7.5.1 |
| Maximum tread variation | 3/8" between largest and smallest | R311.7.5.2 |
| Nosing projection | 3/4" min, 1-1/4" max | R311.7.5.3 |
| Nosing radius | 9/16" maximum | R311.7.5.3 |
Width, Headroom, Landing & Handrail Requirements
| Requirement | Code Value | IRC Section |
|---|---|---|
| Minimum headroom | 6'-8" (80") measured vertically | R311.7.2 |
| Minimum stair width | 36" clear above handrail | R311.7.1 |
| Minimum width below handrail | 31.5" (one rail) or 27" (two rails) | R311.7.1 |
| Minimum landing depth | 36" in direction of travel | R311.7.6 |
| Handrail height | 34" to 38" above tread nosing | R311.7.8.1 |
| Handrail grip (circular) | 1-1/4" to 2" diameter | R311.7.8.3 |
| Handrail grip (non-circular) | 4" to 6-1/4" perimeter | R311.7.8.3 |
| Handrail clearance to wall | 1-1/2" minimum | R311.7.8 |
| Handrail required when | 4 or more risers | R311.7.8 |
| Guard height (open side) | 34" min from tread nosing | R312.1.1 |
| Guard opening (sphere test) | 4" sphere shall not pass | R312.1.3 |
| Stairway illumination | Required for all interior stairs | R303.7 |
Headroom Requirements
Minimum headroom above any point on a stair tread, measured vertically from the tread nosing line, is 6'-8" (80 inches). This applies to the entire length of the stair, including the landing at top and bottom. Insufficient headroom is one of the most common stair code failures, especially when remodeling existing homes.
Stair Width
Minimum clear stair width above the handrail is 36 inches. Below the handrail (measured between the wall and the handrail itself), minimum clear width is 31.5 inchesif there's a handrail on one side, or 27 inchesif there are handrails on both sides. The handrail itself can project up to 4.5" into the required clear width on each side.
Landing Requirements
A landing is required at the top and bottom of every stair. Landing dimensions must be at least as wide as the stair, and the depth must be at least 36 inches in the direction of travel. Landings must be level (no slope greater than 1/48, or about 2% for drainage).
Exception: A landing is NOT required at the top of an interior flight of stairs if a door at the top doesn't swing over the stairs. If a door swings toward the stairs, a landing is required.
Handrail Requirements
Handrails must be continuous for the full length of the stair between the top riser and the bottom riser. They can return to the wall, terminate in a newel post, or turn into a safety terminal at each end. Handrails are required on at least one side of any stair with four or more risers.
Handrails must be graspable — either a circular cross-section with diameter between 1.25" and 2", or a non-circular section with a perimeter between 4" and 6.25" with a maximum cross-section of 2.25". Minimum clear space between handrail and wall is 1.5".
Guardrail Requirements
When a stair has open sides (like an open stringer against a stairwell), guards are required when the floor surface is more than 30" above the adjacent surface. Guards must be at least 34" high from the tread nosing. Along landings, guards must be at least 36" high.
No opening in the guard may allow the passage of a 4-inch diameter sphere. Exception: the triangular opening formed by the riser, tread, and bottom rail of a guard may allow up to a 6-inch sphere.
Winders and Curved Stairs
Winder treads (treads that are narrower on one side, used at stair corners) must have a minimum tread depth of 6 inches at any point and a minimum depth of 10 inches at a point 12 inches from the narrower edge. Spiral stairs have their own separate requirements under IRC R311.7.10.
Common Code Failures
- Inconsistent risers.The first or last riser is often different from the interior risers because the finish floor thickness wasn't accounted for. When framing stairs, the bottom riser is the subfloor-to-tread-top dimension at the base (usually shorter because the bottom of the stringer sits on concrete or a bare floor), and the top riser is from the top of the last tread to the finish floor of the upper level. Both need to match the interior riser height within 3/8".
- Nosing projection on closed stringers. When stairs are enclosed on both sides by walls, contractors sometimes omit the nosing projection because it's not visually prominent. The IRC still requires nosing for any tread less than 11" deep.
- Handrail grip.Decorative handrails made from flat molding (like a 2x4 cap rail) fail because they're not graspable per the IRC perimeter and cross-section requirements. The handrail must fit the hand.
- Stairs over basement landings. Basement stairs often fail headroom above the landing because the ceiling framing above wasn't planned around stair geometry.
Calculate Your Specific Stairs
- Stair Calculator — design code-compliant stairs from any total rise and run
- How to Calculate Stairs Guide — walkthrough of the full stair design process