Auditing a stair you've already built or drawn
This checker is different from a rise-and-run planner: it doesn't tell you the ideal riser or tread for a given rise. It takes the numbers you already have — measured on site, or pulled off a plan set — and tells you exactly which of them fail IRC.
Measure the stair as it actually exists
Riser height, tread depth, and clear width should come from the real stair or the stamped drawing, not a target value. Measure at least the shallowest and steepest step to catch variance.
Add headroom and total rise
Headroom is measured perpendicular from the nosing line, not straight up. Total rise drives the flight-length and landing check, so keep it accurate even if you've already measured it elsewhere.
Open the advanced panels that apply
Skip a panel entirely if it doesn't apply to your stair — an enclosed stair with walls on both sides, for instance, has no guard to check. Every panel you leave alone uses a safe default that won't falsely fail.
Read the compliance strip, not just the headline result
A single "FAIL" can hide which specific item is the problem. Scroll the chip strip below the diagram — each chip names the exact provision, and grey chips mean the figure needs local verification rather than a firm pass or fail.
What runs behind every check
Every pass/fail chip below is one of these comparisons, run against the number you entered.
Step Count & Angle
Used to report flight geometry alongside the pass/fail checks — angle isn't itself an IRC limit, but a steep angle usually means a riser or tread is out of range.
Flights & Landings
IRC caps a single flight at 147" (12'-3") of vertical rise before a landing is required. Anything over that automatically fails the flight-length check.
Sphere-Passage Tests
Guard openings, and open-riser gaps, are checked against a maximum sphere diameter rather than a simple linear measurement — the same logic building inspectors use on site with a physical gauge ball.
Range Checks
Handrail height, guard height, and handrail graspable diameter are two-sided checks — too low or too high (or too thin or too thick) both fail, unlike riser and tread which only have one hard limit.
Auditing a pre-sale basement stair
A 1990s basement stair, measured ahead of a home sale inspection. Total rise 102", 15 risers already in place, open stringer on one side with no guard installed yet.
Riser and tread
Measured riser is 7.9" — over the 7.75" IRC maximum, a straight fail. Measured tread is 9.75" — under the 10" minimum, also a fail. Both numbers came off the same worn stair; a 20-year-old build predating the current code is a common way this happens.
Nosing gets triggered by the tread failure
Because the measured tread (9.75") is under 11", solid-riser nosing is required. The stair has a 1/2" nosing projection, under the typical 3/4" minimum — this check only exists because the tread already failed above; on a stair with an 11"+ tread it wouldn't apply at all.
Total rise and flight length
102" total rise ÷ 147" max flight = well under one flight, so no landing is required — this check passes even though two others on the same stair already failed. Flight-length and riser/tread compliance are independent checks.
The open side changes the required check set
With "Open Side Present" set to Yes, guard height and guard opening both become active checks. No guard exists yet, so entering 0" for guard height fails immediately — a reminder that this stair can't pass sale inspection until a guard is actually installed, not just planned.
This is the pattern worth noticing: several failures on this stair trace back to the same root cause (a tread poured too shallow in the 1990s), and one check — nosing — only exists because another check already failed. Fixing tread depth alone would clear two of the four failures here.
IRC residential stair limits, quick reference
Every figure below is what this checker tests against. Figures marked unconfirmed get a grey, non-committal chip in the live audit above instead of a green or red one — verify those against your locally adopted code edition before relying on them.
| Element | IRC Residential Limit | Status |
|---|---|---|
| Max riser height | 7.75" | Confirmed |
| Min tread depth | 10" | Confirmed |
| Riser height variance, within a flight | 3/8" | Confirmed |
| Tread depth variance, within a flight | 3/8" | Confirmed |
| Min headroom | 80" (6'8") | Confirmed |
| Min clear width | 36" | Confirmed |
| Max flight rise before a landing | 147" (12'-3") | Confirmed |
| Min landing depth | 36" (or stair width, if greater) | Confirmed |
| Handrail height | 34"–38" | Confirmed |
| Handrail graspable diameter (circular) | 1-1/4"–2" | Confirmed |
| Guard height (open sides) | 34" minimum | Confirmed |
| Nosing projection (solid riser, tread <11") | 3/4"–1-1/4" | [VERIFY] |
| Guard opening, sphere that must not pass | 4-3/8" (triangular riser/tread/rail opening: 6") | [VERIFY] |
| Open riser gap, sphere that must not pass | 4" (larger exception may apply under 30" total rise) | [VERIFY] |
Reference only — always confirm against your local jurisdiction's adopted code edition and amendments before relying on a result for a permit or inspection.
Guards, handrails & landings — where audits usually go wrong
A stair can have perfect riser and tread numbers and still fail an inspection on one of these four items, because they're easy to skip when a homeowner or contractor only checks the "obvious" stair math.
When a guard is actually required
A guard isn't required on every stair — only where an open side drops 30" or more to the floor or grade below. A stair boxed in by walls on both sides, or with a drop under 30", can legitimately skip this check entirely by setting "Open Side Present" to No.
Guard opening vs. handrail graspability
A guard passing its opening check says nothing about whether the handrail mounted to it is graspable, and vice versa. It's common for a stair to pass one and fail the other — check both independently rather than assuming one implies the other.
Landing depth is a two-sided minimum
A wide stair needs a landing at least as deep as it is wide, not just 36" flat. A 44"-wide stair with a 36" landing still fails, even though 36" alone clears the baseline minimum.
Nosing is conditional, not universal
Widen the tread to 11" or switch to an open riser and the nosing requirement disappears entirely — it isn't an independent design choice, it's a consequence of the other two settings. This checker hides the field automatically when it doesn't apply.
These are compliance-audit estimates for planning purposes, not a stamped inspection report. A local building official has final say, and some jurisdictions layer additional amendments on top of base IRC language.
Common mistakes when self-auditing a stair
Most failed plan reviews and pre-sale inspections trace back to one of these five habits, not to a genuinely non-compliant stair.
Measuring only one step
Riser and tread must be uniform within 3/8" across the whole flight. A single measurement at the top step can miss a settled or out-of-spec step further down.
Assuming an enclosed stair needs a guard
Guards are only required where an open side drops 30" or more. Checking guard height on a fully walled stairwell produces a meaningless fail — set "Open Side Present" to No first.
Confusing guard opening with baluster spacing style
The 4-3/8" sphere rule is a hard code minimum, not a design preference. "It looks fine" isn't a substitute for the sphere test, especially on horizontal-rail guard designs where gaps run larger than they appear.
Measuring headroom straight up instead of perpendicular
Headroom is measured perpendicular from the nosing line to the obstruction above — not a plumb vertical line. On a steep stair those two measurements can differ by several inches.
Skipping the landing depth check on a wide stair
A landing that clears the flat 36" minimum can still fail if the stair itself is wider than 36" — the landing has to match the wider of the two numbers, not just the code floor.
Treating IRC as the only code that applies
Some jurisdictions adopt IRC with local amendments, or additionally require ADA or IBC compliance for parts of a project. This checker tests base IRC residential figures only — see the related tools below for ADA and IBC checks.
When to run a full IRC stair audit
Unlike a design calculator used before a stair is built, this tool is most useful once a stair already exists on paper or in the field.
Pre-Sale Home Inspection
Catching a non-compliant stair before a buyer's inspector does.
Permit & Plan Review Prep
Self-checking a drawn set before submitting to the building department.
Post-Construction Verification
Confirming a framed stair matches the approved plan before drywall closes it in.
Older Home Renovation
Auditing an existing stair inherited from a pre-code build or an unpermitted addition.
Contractor Quality Control
A second check against a subcontractor's finished stringer and railing work.
Real Estate & Insurance Disputes
Documenting exactly which provisions a stair fails, item by item.