Stair Rise and Run Code Requirements
Stairs are the most code-sensitive part of a house and the most common reason a finished project fails inspection. Here is what the code actually requires.
The residential numbers
| Item | IRC requirement |
|---|---|
| Riser height | 7" minimum, 7¾" maximum (7¼" max when total rise > 151") |
| Tread depth | 10" minimum, nosing to nosing |
| Consistency | No two consecutive risers differ by more than 3/8" |
| Width | 36" minimum; 44" if serving more than one occupant |
| Headroom | 6'-8" minimum along the entire walking line |
| Landing | At least as wide as the stair, 36" deep minimum |
| Total rise between landings | 12'-6" maximum without an intermediate landing |
| Handrail | 30–34" above the nosing line; required above 12 risers |
How inspectors measure
- Riser: from the top of one tread nosing to the top of the next. Measured on the open side of the stair.
- Tread: nosing to nosing, not including the nosing overhang.
- Total rise: the sum of all risers, not floor-to-floor. The finish floor and the tread thickness occupy part of that gap.
Getting the tread depth right usually means the riser comes out wrong. If you have fixed rise and run from the floor plan, the step count is forced. Many people discover at this point that the planned run is too short for the required code stair.
Comfortable vs compliant
The Blondel formula — riser + tread between 17 and 18 inches — produces stairs most adults find natural. A 7" riser with an 11" tread sums to 18. A 7¾ riser with a 10" tread sums to 17.75, legal but steep. A 7" riser with a 10" tread sums to 17 and feels shallow.
If you have flexibility in the run, aim for a sum of 17.5. If you do not, compliance still matters more than comfort — a code failure blocks the sale.
Permits and stair builds
Stairs are permitted work in most US jurisdictions, including simple interior ones. The reason is liability: a code failure can block a sale and creates an insurance question. Build stairs with a permit.
One exception worth knowing: many codes do not require a handrail on interior stairs with fewer than three risers, though it is strongly recommended regardless.
Common failures
- Using the floor-to-floor dimension as total rise, forgetting to subtract the finished floor and tread thickness.
- Riser inconsistency at the top or bottom, where the last measurement is a fraction.
- Headroom measured only at the middle, not along the entire walking line including landings.
- Landing depth measured from the last riser rather than from the nosing.
- Notch-cutting the stringer too deeply on the first and last steps to make the stair fit.
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