Stair Building Code Requirements (IRC R311.7)
Stairs are one of the most code-intensive elements in residential construction. Every dimension is regulated — riser height, tread depth, width, headroom, handrail height, and landing size. This is a complete reference for IRC R311.7 residential stair requirements.
Quick reference — IRC R311.7
| Requirement | IRC Residential | IBC Commercial |
|---|---|---|
| Max riser height | 7¾" (7.75") | 7" |
| Min tread depth | 10" | 11" |
| Riser uniformity | Max ⅜" variation | Max ⅜" variation |
| Min stair width | 36" clear | 44" (most occupancies) |
| Min headroom | 6'8" (80") | 6'8" (80") |
| Handrail height | 34"–38" | 34"–38" |
| Handrail required | 4+ risers, one side | Both sides if >44" wide |
| Min landing depth | 36" in travel direction | 44" in travel direction |
| Nosing projection | ¾"–1¼" | ¾"–1¼" |
Riser height — IRC R311.7.5.1
Maximum riser height is 7¾ inches. Minimum is 4 inches. The most important rule — and the most commonly failed at inspection — is the uniformity requirement:
This means you cannot simply make the bottom or top step a different height to absorb rounding. Divide total rise evenly across all risers so every step is identical. A stair with 13 risers at 7.25 inches and one riser at 7.75 inches fails this test — inspectors measure every riser.
Tread depth — IRC R311.7.5.2
Minimum tread depth is 10 inches, measured horizontally from nosing to nosing. The comfortable residential range is 10–11 inches. Tread depth and riser height work together — the ergonomic comfort formula is:
A 7-inch rise with 11-inch run (sum = 18) is the most comfortable combination. The IRC-maximum combination of 7¾-inch rise with 10-inch run (sum = 17.75) is legal but feels noticeably steep on the way down.
Stair width — IRC R311.7.1
Minimum clear width is 36 inches, measured above the handrail height. Below the handrail, the minimum is 31.5 inches on one side or 27 inches on both sides where handrails project into the width. Most residential stairs are built at 36–42 inches.
Headroom — IRC R311.7.2
Minimum headroom is 6 feet 8 inches (80 inches), measured vertically from the sloped plane connecting the leading edges of the treads to the ceiling or soffit above. This measurement must be maintained for the full length of the stairway.
Handrails — IRC R311.7.8
A handrail is required on at least one side of any stairway with 4 or more risers. Key requirements:
- Height: 34–38 inches measured vertically above the leading edge of the treads
- Continuity: Must run the full length of the flight, from top riser to bottom riser
- Graspable profile:Round rails 1¼"–2" diameter. Non-circular profiles must have a perimeter of 4"–6¼" with a max cross-section of 2¼"
- Wall clearance: Minimum 1½ inches between the handrail and any wall
- Bracket spacing: Maximum 48 inches apart, rated 200 lb minimum
Landings — IRC R311.7.6
A landing is required at the top and bottom of every stairway. Key rules:
- Minimum 36 inches in the direction of travel
- Width must be at least the stair width
- Maximum vertical rise between landings: 12 feet 3 inches (147 inches)
- Doors at the top of stairs must not swing over the top step — they must swing over the landing
Nosing — IRC R311.7.5.3
Open risers are not permitted for residential stairs (a 4-inch sphere must not pass through any opening). Where a nosing projection exists, it must be ¾ inch to 1¼ inches. The nosing radius must not exceed 9/16 inch to reduce trip hazard. Solid risers are required.
Most common inspection failures
| Failure | Root cause |
|---|---|
| Riser variation > ⅜" | Measured rough-to-rough instead of finished-to-finished |
| Bottom riser too tall | Flooring thickness not factored in at lower level |
| Headroom too low | Beam or duct not accounted for in stair layout |
| Handrail not graspable | Decorative wide-profile rail without a graspable recess |
| Landing too short | Door swings reduce effective landing depth |
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Use the Stair Calculator →FAQ
What is the maximum riser height for residential stairs?
The IRC sets a maximum riser height of 7¾ inches (7.75") for residential stairs. All risers in a single flight must be within ⅜ inch of each other — this uniformity rule is the most commonly failed inspection point.
What is the minimum tread depth per building code?
IRC R311.7.5.2 requires a minimum tread depth of 10 inches, measured nose to nose. For exterior stairs, some jurisdictions require 11 inches. The comfortable range is 10–11 inches.
How wide do stairs need to be?
IRC R311.7.1 requires a minimum clear width of 36 inches for residential stairs, measured above the handrail height. Some jurisdictions require wider stairs for egress purposes — always check local amendments.
When is a handrail required?
IRC R311.7.8 requires a handrail on at least one side of any stairway with 4 or more risers. Handrail height must be 34–38 inches measured vertically above the leading edge of the treads. It must run continuously for the full length of the flight.
What is the minimum headroom for stairs?
IRC R311.7.2 requires a minimum headroom of 6 feet 8 inches (80 inches) measured vertically from the sloped line connecting the leading edges of the treads to the ceiling above.