IRC Stair Code Requirements
Summary of residential stair requirements from the International Residential Code (IRC). These are the baseline national requirements — your local jurisdiction may have stricter rules.
| Requirement | Code Value | IRC Section |
|---|---|---|
| Maximum riser height | 7-3/4" (196 mm) | R311.7.5.1 |
| Minimum riser height | 4" (102 mm) | R311.7.5.1 |
| Minimum tread depth | 10" (254 mm) | R311.7.5.2 |
| Maximum riser variation | 3/8" between largest and smallest | R311.7.5.1 |
| Maximum tread variation | 3/8" between largest and smallest | R311.7.5.2 |
| Minimum headroom | 6'-8" (80") measured vertically | R311.7.2 |
| Minimum stair width | 36" clear above handrail | R311.7.1 |
| Minimum landing length | Not less than 36" in direction of travel | R311.7.6 |
| Handrail height | 34" to 38" above tread nosing | R311.7.8.1 |
| Handrail graspability | 1-1/4" to 2" circular cross-section | R311.7.8.3 |
| Guard height (open side) | 36" minimum | R312.1.1 |
| Guard opening (4" sphere) | A 4" sphere shall not pass through | R312.1.3 |
| Tread nosing | 3/4" min, 1-1/4" max projection | R311.7.5.3 |
| Winder treads | 10" min at 12" from narrow edge | R311.7.5.2.1 |
| Stairway illumination | Required for all interior stairs | R303.7 |
Understanding Stair Code
Riser Height (R311.7.5.1)
The maximum riser height is 7-3/4"(196mm). Most carpenters target 7" to 7-1/2" for comfort. The minimum is 4". Critically, the variation between the tallest and shortest riser cannot exceed 3/8". This means you need to divide the total rise evenly — you can't have one short riser at the top to make the math work.
Tread Depth (R311.7.5.2)
The minimum tread depth is 10"(254mm), measured from nosing to nosing. Deeper treads are more comfortable — 11" matches a standard 2x12 tread board. Like risers, the variation between treads cannot exceed 3/8".
Rise + Run Comfort Rule
While not in the IRC itself, the rise + run = 17 to 18 inchesrule is a widely used comfort guideline. A 7-1/2" riser with a 10" tread gives 17.5" — right in the sweet spot. Stairs outside this range feel either too steep or too shallow.
Headroom (R311.7.2)
Minimum headroom is 6'-8" (80") measured vertically from the tread nosing to the ceiling or floor structure above. This determines how large the stairwell opening needs to be — the stair calculator computes this automatically.
Landings (R311.7.6)
A landing is required at the top and bottom of every stairway. The landing must be at least as wide as the stair and at least 36" deepin the direction of travel. A door at the top of a stair can swing over the top landing but not reduce it to less than 36" when fully open.
Guards and Balusters (R312)
Open sides of stairs more than 30" above the floor below require a guard at least 36" high. The guard must prevent a 4" sphere from passing through any opening — this is the basis for baluster spacing calculations.