IRC Stair Building Code Requirements
| Dimension | IRC Minimum | Recommended |
|---|---|---|
| Riser height | 4" min, 7¾" max | 7–7½" |
| Tread (run) depth | 10" min | 11" |
| Stair width | 36" min | 42–48" (comfort) |
| Headroom clearance | 6'8" min | 7'0" recommended |
| Handrail height | 34–38" above tread | 36" typical |
| Riser variation | 3⁄8" max between adjacent risers | 0 (consistent) |
Frequently Asked Questions
What is the standard riser height for stairs?+
The IRC building code requires risers between 4 and 7¾ inches. The most comfortable riser height is 7 to 7½ inches. Crucially, all risers in a single staircase must be within ⅜ inch of each other — inconsistent risers are a trip hazard and a code violation.
How do I calculate the number of stairs I need?+
Divide your total rise (floor-to-floor height in inches) by your target riser height, then round to the nearest whole number. For 108 inches ÷ 7 = 15.4, round up to 16 steps. The actual riser becomes 108 ÷ 16 = 6.75 inches — verify this is within the 4–7¾ inch range.
What is the standard tread depth for stairs?+
IRC requires a minimum of 10 inches of run (tread depth, not including nosing). Most comfortable stairs use 11 inches. Add a 1–1¼ inch nosing overhang for comfort and code compliance, bringing the total tread to 11–12¼ inches.
How long should my stair stringers be?+
Stringer length = √(total rise² + total run²). For a 9-foot rise with an 11-inch run per step, the diagonal is about 13.5 feet. Purchase 2×12 lumber at least 2 feet longer than the calculated diagonal to allow for cutting.