Stair code quick reference
The 2021 IRC figures a residential stair is measured against, in one place. These are the model code — your inspector is the one who decides.
| What | Limit | Section |
|---|---|---|
| Maximum riser height | 7 3/4" | R311.7.5.1 |
| Minimum tread depth | 10" | R311.7.5.2 |
| Riser variation across the flight | 3/8" | R311.7.5.1 |
| Maximum rise without a landing | 151" (12.6 ft) | R311.7.3 |
| Minimum stair width | 36" | R311.7.1 |
| Minimum headroom | 80" (6 ft 8 in) | R311.7.2 |
| Nosing projection | 3/4" to 1 1/4" | R311.7.5.3 |
| Nosing required when tread is under | 11" | R311.7.5.3 |
| Minimum throat left in a cut stringer | 5" | Convention |
| Handrail height | 34" to 38" | R311.7.8 |
| Minimum guard height | 36" | R312.1.2 |
| Guard sphere — nothing 4" may pass | 4" | R312.1.3 |
Reading it
- Every riser in a flight has to be within 3/8" of every other. That is the rule that catches a stair built to a landing that was not where the drawing said.
- The throat figure is trade convention rather than a code minimum, and it is what stops a cut stringer folding up.
- 2021 IRC. Amendments are local and common — ring the building department before you cut a stringer.
Sources: 2021 International Residential Code, International Code Council.
For the case this table does not cover
- Stair stringers
Divide the rise into even risers, lay out the notches, and check the result against the code.
- Baluster and slat spacing
Even gaps across any span, checked against the 4-inch guard rule, with tape-measure marks that don't drift.