Stair Building Code: IRC Rise and Run Requirements

Stair building codes exist to prevent falls — the leading cause of residential injuries. For houses, townhomes, and their decks, the governing code is the International Residential Code (IRC), which most US jurisdictions adopt with local amendments. Commercial buildings fall under the stricter International Building Code (IBC) — see the comparison below. Here's what you need to know.

IRC rise and run requirements

These are the core dimensional requirements from IRC Section R311.7 for residential stairs:

• Maximum rise per step: 7.75 inches (7¾") per IRC R311.7.5.1. This is the vertical distance from the top of one tread to the top of the next.
• Minimum tread depth: 10 inches, measured horizontally from nosing to nosing (IRC R311.7.5.2).
• Nosing projection: 0.75 to 1.25 inches beyond the face of the riser. Required when treads are less than 11 inches deep (IRC R311.7.5.3).
• Maximum variation between steps: 3/8 inch (IRC R311.7.5.1 and R311.7.5.2). The tallest riser and the shortest riser cannot differ by more than 3/8 inch. This is one of the most commonly failed inspection items.

The comfort rule: Rise plus run should equal 17 to 18 inches. This isn't in the IRC, but it's a widely accepted industry standard. A 7.5-inch rise with a 10.5-inch run gives you 18 inches — right in the sweet spot. Stairs that follow this rule feel natural to walk on.

Handrail and guard requirements

• Handrail height: 34 to 38 inches, measured vertically from the stair nosing to the top of the handrail (IRC R311.7.8.1).
• When required: Handrails are required on at least one side when there are 4 or more risers (IRC R311.7.8).
• Guards (railings): Required when the walking surface is more than 30 inches above grade (IRC R312.1.1). Guards must be at least 36 inches high (IRC R312.1.2); commercial projects under the IBC require 42 inches.
• Graspable profile: The handrail must have a graspable cross-section — circular with a diameter of 1.25 to 2 inches, or a non-circular profile with a perimeter of 4 to 6.25 inches (IRC R311.7.8, grip size). A flat 2×4 on edge does not meet this requirement.
• Guard openings: The 4-inch sphere test applies — no opening in the guard can allow a 4-inch sphere to pass through (IRC R312.1.3). On the open sides of stairs, exceptions allow a 4⅜-inch sphere, and a 6-inch sphere for the triangle at the tread and riser. See our baluster spacing guide for calculations.

Headroom and width

• Minimum headroom: 6 feet 8 inches (80 inches), measured vertically from the stair nosing to any overhead obstruction (IRC R311.7.2).
• Minimum stair width: 36 inches clear, measured between finished walls or between the guard and the wall (IRC R311.7.1).
• Enclosed vs. open stairs: Width is measured differently. For enclosed stairs, measure between finished wall surfaces. For open stairs, measure from the guard to the opposite edge.

Common code violations

These are the issues that most frequently cause inspection failures:

• Inconsistent riser heights. The 3/8-inch maximum variation rule catches many DIY builders. If your total rise doesn't divide evenly, you cannot just make one step shorter or taller. Every step must be within 3/8 inch of every other step.
• Treads too shallow. Using 2×10 lumber for treads gives you only 9.25 inches of actual depth — less than the 10-inch minimum. You need 2×12 stock or purpose-made stair treads.
• Missing handrail. Even outdoor deck stairs with 4 or more risers require a handrail. A guard rail (the railing with balusters) is not a handrail unless it has a graspable top rail at the correct height.
• Guard openings too large. The 4-inch sphere test applies to guard openings along decks, landings, and balconies (IRC R312.1.3). The stair-specific allowances — 4⅜ inches on the open sides of stairs, 6 inches for the tread-riser triangle — are exceptions, not the rule, and some jurisdictions delete them. Use our baluster spacing calculator to get this right.

Residential (IRC) vs. commercial (IBC)

A common point of confusion: the IRC and the IBC are different codes with different stair limits. Everything above is residential (IRC) — it applies to one- and two-family dwellings, townhouses, and their decks. Anything else — a shop open to the public, a multi-family building, an office — falls under the IBC, which is stricter:

• Maximum rise: IRC 7¾" vs. IBC 7" (IBC 1011.5.2).
• Minimum tread depth: IRC 10" vs. IBC 11" (IBC 1011.5.2).
• Guard height: IRC 36" vs. IBC 42" (IBC 1015.3).

Stairs sized to the IRC limits will fail inspection on a commercial project. If you're unsure which code applies, ask your building department when you pull the permit.

Local code amendments

The IRC is the baseline. States and municipalities can — and do — amend it. Notable differences:

• California (CBC/CRC): Additional seismic and structural requirements for stair framing. Some jurisdictions require 42-inch guards on residential decks.
• New York: NYC has its own building code with stricter requirements in several areas.
• Florida (FBC): Enhanced wind resistance requirements that can affect railing and guard construction, especially in coastal areas.

Always check with your local building department before starting. A quick phone call or visit to the permit counter can save you from tearing out completed work. Ask specifically about stair rise, run, handrail, and guard requirements — those are the areas where local amendments are most common.

Sources

• 2021 International Residential Code (IRC), Sections R311.7 (stairways) and R312.1 (guards) — ICC Digital Codes.
• 2021 International Building Code (IBC), Sections 1011 (stairways) and 1015 (guards) — cited above for the commercial comparison.

Section numbers on this page refer to the 2021 editions. Your jurisdiction may adopt an earlier or later edition, with amendments — confirm requirements with your local building department before you build.