IRC R311.7: Stairways

Stairs cause more household injuries than almost any other built feature, so Section R311.7 of the International Residential Code (IRC) nails down the geometry that makes them safe to climb: how steep the steps, how much headroom, how wide the run, and what a handrail has to feel like in your hand. This page goes deeper on the stair itself than the broader egress page does, covering headroom, handrail graspability, landings, and winders, the details that get a custom stair rejected or approved.

What R311.7 requires

The core geometry comes in pairs. The maximum riser (the vertical face of a step) is 7.75 inches, and the minimum tread (the depth your foot lands on) is 10 inches. Beyond that, R311.7 sets the surrounding dimensions:

• Width: at least 36 inches above the handrail height.
• Headroom: at least 6 feet 8 inches (80 inches) measured vertically from the nosing line to the ceiling or beam above.
• Uniformity: risers within a flight may vary no more than 3/8 inch, and treads the same.
• Nosing: where treads are solid, a nosing of 3/4 inch to 1.25 inches is required on stairs with closed risers.

Here is the geometry clause:

The maximum riser height shall be 7 3/4 inches. The minimum tread depth shall be 10 inches.

Handrails, landings, and winders

A handrail is required on at least one side of any stair with four or more risers. It must sit 34 to 38 inches above the nosings and be continuous the length of the flight. Graspability matters: a round rail must be 1.25 to 2 inches across, and other shapes have a perimeter and finger-recess spec so a falling hand can actually close around it. A decorative rail too fat or flat to grip fails.

Landings at the top and bottom must be at least as deep as the stair is wide, up to 36 inches. Winders, the pie-shaped treads on a turning stair, must give at least 10 inches of tread depth measured 12 inches in from the narrow side, and never less than 6 inches at the narrow point. These are the details that trip up a dramatic curved or spiral stair.

What it means for an Arizona custom home

On a two-story Scottsdale or Cave Creek custom home, the open feature stair is where R311.7 bites hardest. A designer who pushes the rise to look dramatic or wraps a tight curve has to keep every riser at or under 7.75 inches, hold 6 feet 8 inches of headroom under the floor header above, and land the winders at 10 inches of effective tread. For example, a steel-and-wood floating stair still needs a graspable handrail at 34 to 38 inches and infill that meets the guard rules in R312 . Designing it right on paper costs a revision; rebuilding poured or welded treads after the framing inspector measures them costs real money.

Edition note

The 7.75-inch riser, 10-inch tread, 36-inch width, and 6-foot-8 headroom are unchanged across the 2018, 2021, and 2024 IRC. Handrail graspability and winder details get minor wording tweaks between editions, but the headline numbers hold. Confirm the edition your city enforces on the Arizona building code editions by city page.

How it connects

R311.7 is the stair detail under the broader R311 means of egress page, which covers the whole exit path (doors, halls, the egress door). It works hand in glove with R312 guards for the open sides and rails, and R308 safety glazing for any glass at the bottom landing. All get verified before the certificate of occupancy . For the full check sequence, see what inspections are required when building a house in Arizona .

Source

Read the section on the official ICC site: 2021 IRC R311.7 on codes.iccsafe.org . The ICC I-Codes are copyrighted, so only the short geometry clause is excerpted; the explanation is ours.