Guide
Stair code requirements: IRC rise, run and headroom
By Uri Haramati · Updated November 13, 2026
Under the International Residential Code (IRC), section R311.7, a stair riser can be at most 7 3/4 in tall, a tread must be at least 10 in deep, headroom must be at least 6 ft 8 in, and the stair must be at least 36 in wide. Most US cities and states adopt the IRC, often with local changes, so confirm the numbers with your building department.
IRC stair requirements at a glance
| Rule | IRC limit | Section |
|---|---|---|
| Riser height | 7 3/4 in max | R311.7.5.1 |
| Riser variation | 3/8 in max between tallest and shortest in a flight | R311.7.5.1 |
| Tread depth | 10 in min, nosing to nosing | R311.7.5.2 |
| Tread variation | 3/8 in max between deepest and shallowest in a flight | R311.7.5.2 |
| Nosing | 3/4 to 1 1/4 in with solid risers; not required when treads are 11 in or deeper | R311.7.5.3 |
| Open risers | Gaps must not pass a 4 in sphere where they are more than 30 in above the floor or grade | R311.7.5.1 |
| Width | 36 in min clear above the handrail | R311.7.1 |
| Headroom | 6 ft 8 in min | R311.7.2 |
| Rise per flight | 151 in (12 ft 7 in) max between floors or landings | R311.7.3 |
| Landings | At the top and bottom; 36 in min deep and as wide as the stair | R311.7.6 |
| Handrail | At least one side when there are 4 or more risers; 34 to 38 in high | R311.7.8 |
| Guards | On open sides more than 30 in above the floor or grade below; 34 in min high along the stair | R312.1 |
Riser height
The riser is measured straight up from the leading edge of one tread to the leading edge of the next. The maximum is 7 3/4 in. Within one flight, the tallest riser may be no more than 3/8 in taller than the shortest, which is why the bottom of a stringer is cut short by one tread thickness. See how to lay out a stringer.
Tread depth and nosing
Tread depth is measured horizontally from the leading edge of one tread to the leading edge of the next, so the nosing overhang does not count. The minimum is 10 in. Stairs with solid risers need a nosing of 3/4 to 1 1/4 in, unless the treads are at least 11 in deep. Winder treads need at least 10 in at the walkline and at least 6 in at the narrow end.
Headroom and width
Headroom is measured straight up from the sloped line that connects the tread nosings, and must be at least 6 ft 8 in for the full length of the stair. Width must be at least 36 in above the handrail. Below the handrail, the clear width can drop to 31 1/2 in with a handrail on one side, or 27 in with handrails on both sides.
Rise per flight and landings
One flight may rise no more than 151 in (12 ft 7 in). A taller stair needs a landing partway. Landings are required at the top and bottom of each stair, at least as wide as the stair and at least 36 in deep in the direction of travel. One exception: an interior stair does not need a landing at the top if no door there swings over the stairs.
Handrails and guards
A stair with four or more risers needs a handrail on at least one side, 34 to 38 in above the tread nosings, and continuous for the full flight. A round handrail must be 1 1/4 to 2 in across. An open side of a stair that is more than 30 in above the floor or ground below needs a guard at least 34 in high. Guard openings on a stair must not pass a 4 3/8 in sphere.
Commercial stairs (IBC)
Commercial and public buildings follow the International Building Code, which is stricter: risers from 4 to 7 in and treads at least 11 in deep (IBC 1011.5.2). Stair Once uses the IRC limits by default, with the IBC limits one tap away.
Local codes vary. The numbers above are from recent editions of the IRC. Your city or state may use an older edition or add its own rules, and the inspector has the final word. Ask your building department before you build, especially for deck stairs and anything that needs a permit.
Check a stair against code in one tap
Stair Once checks every stair against IRC R311.7: riser height, tread depth, nosing, width, headroom and rise per flight. If a stair fails, one plain line says what to change, and a button makes the change.
Questions
What is the maximum stair riser height allowed by code?
Under the IRC, the maximum riser height for a house stair is 7 3/4 in, and the tallest riser in a flight can be no more than 3/8 in taller than the shortest. Commercial stairs under the IBC are limited to 7 in.
What is the minimum stair tread depth?
The IRC minimum is 10 in, measured horizontally from nosing to nosing. Commercial stairs under the IBC need at least 11 in.
What is the minimum headroom for stairs?
The IRC requires at least 6 ft 8 in of headroom, measured straight up from the sloped line along the tread nosings.
Do deck stairs have to meet code?
In most places, yes. Deck stairs are usually held to the same IRC stair rules, and many building departments also ask for a permit and an inspection. Check with yours before you build.