3.3 Scenario Practice for Building Planning
Key Takeaways
- Stair geometry: max riser 7-3/4 in, min tread 10 in, headroom 6 ft 8 in (80 in), min width 36 in above the handrail (IRC R311.7).
- Riser and tread uniformity: the largest may not exceed the smallest by more than 3/8 in within a flight (IRC R311.7.5.1).
- Handrails are required on stairs with 4 or more risers, mounted 34-38 in above the nosing, continuous, and graspable (IRC R311.7.8).
- A single flight may rise no more than 12 ft 7 in between floor levels or landings; landings must be at least as wide as the stair and 36 in deep (IRC R311.7.3).
- On stairs with solid risers, a nosing of 3/4 in to 1-1/4 in is required where tread depth is less than 11 in (IRC R311.7.5.3).
Stairway Geometry Scenarios
Stairways (R311.7) generate more inspection findings than almost any other Chapter 3 topic, so the exam tests the geometry hard. Commit the core dimensions and the sections that hold them:
| Stair element | IRC value | Section |
|---|---|---|
| Maximum riser height | 7-3/4 in | R311.7.5.1 |
| Minimum tread depth | 10 in | R311.7.5.2 |
| Riser/tread uniformity tolerance | 3/8 in (largest minus smallest) | R311.7.5.1, .5.2 |
| Minimum headroom | 6 ft 8 in (80 in) | R311.7.2 |
| Minimum width above handrail | 36 in | R311.7.1 |
| Maximum vertical rise of a flight | 12 ft 7 in | R311.7.3 |
| Nosing (solid risers, tread < 11 in) | 3/4 in to 1-1/4 in | R311.7.5.3 |
Worked example: A stair has risers measured at 7-1/2, 7-5/8, 7-3/4, and 7-7/8 in. The 7-7/8 in riser exceeds the 7-3/4 in maximum — a violation by itself. Even if all were under 7-3/4 in, the uniformity rule (largest minus smallest ≤ 3/8 in) would be tested: 7-7/8 − 7-1/2 = 3/8 in, exactly at the limit. A spread of 1/2 in would fail. The same 3/8 in tolerance applies to tread depth.
Headroom and width
Headroom is measured vertically from the sloped line adjoining the tread nosings (or the landing surface) to any overhead obstruction and must be at least 6 ft 8 in (80 in) at every point. Stair width must be at least 36 in above the permitted handrail height and below the required headroom; handrails may project no more than 4-1/2 in into that width from each side. A duct or soffit that dips below 80 in over any tread is a finding.
Reading the geometry like a relationship, not isolated numbers
The riser and tread are tested together because they define safe walking rhythm. A useful field check used on the exam: greater riser height with shallower treads makes a stair steep and noncompliant fast. Open risers, where permitted, must reject a 4-inch sphere (R311.7.5.1), preventing a child from slipping through. Winder treads (R311.7.5.2.1) must have a depth of at least 10 in measured at the walkline (12 in from the narrow side) and never less than 6 in at any point.
Spiral stairways (R311.7.10.1) are a narrow exception: a minimum 26 in clear width, tread depth at least 6-3/4 in at the walkline, riser up to 9-1/2 in, and 6 ft 6 in headroom — values that differ sharply from standard stairs, which is exactly why the exam likes them as distractors against the 7-3/4/10/80 baseline.
Handrails, Landings, and the Egress Door
Handrails (R311.7.8) are required on at least one side of each flight with four or more risers. Handrail top height is measured vertically from the sloped plane at the tread nosings and must be not less than 34 in and not more than 38 in. Handrails must be continuous for the full length of the flight (from a point above the top riser to a point above the bottom riser) and must be graspable: Type I (circular 1-1/4 in to 2 in diameter, or equivalent perimeter 4 in to 6-1/4 in with max 2-1/4 in cross-section) or Type II for larger profiles with a finger recess. A handrail at 33 in or 39 in is a violation.
Landings
Under R311.7.6, a floor or landing is required at the top and bottom of each stairway. The landing width must be not less than the width of the stair served, and the minimum depth in the direction of travel is 36 in. The maximum vertical rise of a single flight before an intermediate landing is 12 ft 7 in (R311.7.3).
- Landing width: ≥ stairway width
- Landing depth (travel direction): ≥ 36 in
- Max flight rise: 12 ft 7 in between floors/landings
The egress door
At least one egress door is required per R311.2: side-hinged, providing a minimum clear width of 32 in (measured between the face of the door and the stop with the door open 90°) and a minimum clear height of 78 in. A standard 36 in nominal door yields about 32 in clear. The exterior landing at the egress door may be up to 7-3/4 in below the top of the threshold if the door does not swing over the landing (R311.3.1). The interior landing at the egress door must not be more than 1-1/2 in lower than the top of the threshold (R311.3.1).
Graspability is its own finding
A handrail at the correct 34-38 in height can still fail on graspability. Type I round handrails must be 1-1/4 in to 2 in in diameter; non-circular Type I profiles need a perimeter of 4 in to 6-1/4 in with a cross-section dimension no more than 2-1/4 in. Larger profiles must be Type II with a finger recess. Handrail ends must return to a wall or post or terminate in newel posts or safety terminals (R311.7.8.2) so a sleeve or strap cannot catch. An inspector who finds a continuous, properly mounted rail must still confirm the profile is graspable — a 2x6 laid flat as a 'handrail' is a common real-world violation the exam reproduces.
An inspector measures stair risers of 7-1/2, 7-3/4, and 8-1/8 inches in one flight. What is the primary IRC violation?
On a residential stair flight with seven risers, at what height must the required handrail be mounted above the tread nosings per IRC R311.7.8?
What is the minimum clear width of the required egress door for a dwelling unit under IRC R311.2?