Stairway Tread, Riser, and Handrail Requirements — IRC 2018 R311.7

Quick Answer

IRC 2018 Section R311.7 requires stairways to have treads at least 10 inches deep (measured nose-to-nose), risers no more than 7-3/4 inches high, no riser variation greater than 3/8 inch within a stair flight, a minimum 36-inch stairway width, and a graspable handrail on at least one side for any stair with four or more risers. These dimensional controls prevent the most common causes of stair-related falls.

What R311.7 Actually Requires

IRC 2018 Section R311.7 covers the full geometry of a residential stairway. The key requirements are:

Width: Stairways shall not be less than 36 inches clear of handrails. Where handrails project more than 4.5 inches into the stairway width, the projection reduces the clear width measurement (R311.7.1).

Headroom: Stairways shall have a minimum headroom of 6 feet 8 inches measured vertically from the tread nosing to the nearest overhead obstruction (R311.7.2).

Risers: Maximum riser height is 7-3/4 inches (R311.7.5.1). Risers shall be vertical or sloped under the nosing no more than 30 degrees from vertical. Open risers are permitted only where a 4-inch sphere cannot pass through the opening between treads.

Treads: Minimum tread depth is 10 inches, measured horizontally between the tread nosings (R311.7.5.2). The nosing must project 3/4 inch to 1-1/4 inches beyond the face of the riser below. Where treads are solid (no open riser), the nosing projection is required; where the riser is open, the nosing projection may be omitted.

Consistency: The greatest riser height within any stair flight shall not exceed the smallest riser height by more than 3/8 inch. The greatest tread depth within any flight shall not exceed the smallest tread depth by more than 3/8 inch (R311.7.5.3). This uniformity requirement prevents the stumble caused by an unexpected step variation.

Handrails: Handrails shall be provided on at least one side of each stair with four or more risers (R311.7.8). Handrail height shall be not less than 34 inches and not more than 38 inches, measured vertically from the tread nosings to the top of the handrail. Handrails shall be continuous from a point directly above the top riser to a point directly above the lowest riser. A graspable handrail must be Type I (circular cross-section 1.25 to 2 inches in diameter) or Type II (non-circular with a 4- to 6.25-inch perimeter and a maximum cross-section dimension of 2.25 inches).

Why This Rule Exists

Stair falls are among the most common causes of residential injury. The tread and riser dimensional requirements — particularly the uniformity rule — address the biomechanics of stair negotiation. Humans walk stairs semi-automatically, relying on consistent step geometry; a single unexpected riser variation is enough to cause a misstep. The handrail requirements address recovery: when a person begins to lose balance on a stair, a graspable handrail that they can actually grip (as opposed to a decorative 2x4 flat rail) is the difference between catching themselves and falling. The headroom requirement prevents head injuries in low-ceiling stair configurations.

What the Inspector Checks at Rough and Final

At framing inspection the inspector checks stair carriage layout: riser height consistency, tread depth from stringer cut dimensions, headroom clearance, and handrail backing location. At final inspection the inspector measures: (1) each riser height and calculates maximum variation; (2) each tread depth and variation; (3) nosing projection dimensions; (4) stairway clear width; (5) headroom at the tightest point; and (6) handrail height, continuity from top to bottom riser, and graspability. The inspector will grasp the handrail to test structural adequacy — handrails must resist a 200-pound concentrated load applied at any point and in any direction.

What Contractors Need to Know

Calculate total rise carefully before cutting stringers. Divide the total rise by the number of risers to get the individual riser height, and verify that the result is no greater than 7-3/4 inches. Confirm the tread run dimension provides at least 10 inches nose-to-nose. If the layout does not work with standard riser and tread dimensions, adjust the floor-to-floor height if possible, or consult with the designer about adding or removing a step.

Cut all stringer risers and treads from a consistent reference before assembly. Variations introduced by inconsistent lumber thickness, humped subfloor, or out-of-level finish floor will produce riser variation exceeding the 3/8-inch tolerance. Measure every riser and tread before the inspector arrives — catching a violation during self-inspection allows correction before the official visit.

The first and last risers in a stair flight are the most common sources of variation violations. The bottom riser is affected by the finished floor thickness at the base of the stair, and the top riser is affected by the finished floor thickness at the top landing. Measure both risers after finish flooring is installed, not just after the stringer is cut, to verify the 3/8-inch tolerance is maintained through completion.

What Homeowners Get Wrong

Homeowners replacing deck stairs frequently use an easy-calculation approach that results in non-uniform risers. When the deck height does not divide evenly into whole-number riser counts, they sometimes leave the top or bottom riser at a different height than the others. Even a single riser that is more than 3/8 inch different from the others fails R311.7.5.3.

Another common error is installing a flat 2x4 top rail as the handrail on a stair. A 2x4 installed flat on edge (1.5 inches wide) is not a graspable handrail by any definition — it cannot be gripped during a fall. IRC 2018 R311.7.8.3 specifies graspable handrail profiles, and a flat 2x4 does not comply. A round pipe or cylindrical handrail meets Type I requirements and costs no more to install.

Homeowners building basement stairs also frequently skip the handrail on one side because the stair is only 36 inches wide and bordered by walls on both sides. The code requires a handrail on at least one side for any stair with four or more risers regardless of width.

Homeowners also sometimes confuse the guard (guardrail) requirement with the handrail requirement. A guard prevents people from falling off an open side of a stair or landing and is covered under R312. A handrail is a graspable rail intended to be held while ascending or descending. The two serve different safety functions and are often both required simultaneously — a stair with an open side needs both a guard at the open edge and a graspable handrail within reach. Installing a decorative wood top rail that satisfies the guard height requirement does not automatically satisfy the graspable handrail requirement. Verify both R311.7.8 (handrail) and R312 (guard) compliance independently for any open-sided stairway.

Homeowners remodeling a home with interior stairs — particularly when replacing hardwood treads or adding a carpet runner — should also re-verify riser uniformity after the finish materials are installed. Adding a carpet runner with a thick pad to an existing wood stair can change the effective tread depth at each step, and the bottom step's effective height changes if the finish floor at the base of the stair is altered. A stair that was within the 3/8-inch uniformity tolerance before a renovation may fall outside it after new flooring is installed. Measure riser heights and tread depths with all finish floor materials in place before calling for final inspection.

State and Local Amendments

IRC 2018 R311.7 stairway requirements are adopted in Texas, Georgia, Virginia, North Carolina, South Carolina, Tennessee, Alabama, Mississippi, Kentucky, and Missouri. Most of these states adopt R311.7 without amendment. Some local jurisdictions require handrails on both sides for stairs wider than 44 inches, which is a provision more common in commercial codes that has been locally adopted for residential use in some areas.

IRC 2021 did not change the riser height, tread depth, nosing projection, or handrail height requirements. The 7-3/4-inch maximum riser and 10-inch minimum tread remain the same in the 2021 edition. IRC 2021 added clarifying language about nosing projections for open riser stairs and updated the handrail graspability requirements to clarify Type I and Type II profiles, but the dimensional limits are unchanged.

When to Hire a Licensed Contractor

Stair construction and modification requires a building permit in virtually all jurisdictions. The riser uniformity requirement is particularly difficult to achieve without careful layout, and mistakes require cutting new stringers — a significant repair. A licensed carpenter or general contractor experienced in stair framing will calculate layout correctly before cutting, verify dimensions against the code, and coordinate the framing inspection. For basement stairs that will be enclosed by drywall, the stair inspection must occur before the walls are closed.

Common Violations Found at Inspection

• Single riser more than 3/8 inch different from the others — typically the bottom or top step where the layout did not divide evenly
• Tread depth less than 10 inches — particularly on deck stairs where a 2x10 tread is used without accounting for the nosing projection from the tread above
• Nosing projection outside the 3/4-inch to 1-1/4-inch range — either too short (no nosing) or too long (exceeds 1-1/4 inches)
• Handrail height outside the 34-to-38-inch range — measured to the top of the rail from the nosing line
• Flat 2x4 or 2x6 top rail installed as handrail — not a graspable profile per R311.7.8.3
• Handrail not continuous from top riser to bottom riser — handrail ends before reaching the last step
• Headroom less than 6 feet 8 inches — particularly at basement stair opening in a tight floor joist situation
• Open riser spacing allows a 4-inch sphere to pass — applicable to open-tread stairs