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Stair Stringer Rise & Run Code Guide
Stair code compliance comes down to a handful of numbers — maximum riser height, minimum tread depth, and how much those numbers are allowed to vary within one flight — plus a separate, less-discussed set of rules for how far apart and how far a stringer itself is allowed to span.
Last updated: September 6, 2026
Stair code compliance is mostly arithmetic — a fixed total rise and total run have to be divided into steps that stay under a maximum riser height, at or over a minimum tread depth, and consistent with each other within a tight tolerance. Get the division wrong and a stringer that looks fine on the shop floor fails inspection.
This guide covers the IRC riser and tread numbers, the separate rules for how far apart and how far a stringer can span, and the rise/run mistakes that most commonly show up on a first stair build.
Cut vs. Solid Stringers at a Glance
| Stringer Type | Max Horizontal Span | Spacing | Thickness |
|---|---|---|---|
| Cut (open) stringer | 6 ft maximum horizontal span | Typically ≤18" O.C. (tighter often used for heavy-use stairs) | 2x12, minimum 5" throat remaining after notching |
| Solid (closed) stringer | Up to ~13'-3" span (2-stringer stairway, ≤36" wide) | Typically 2 stringers total, positioned at tread ends | 2x12, full un-notched depth retained |
A solid stringer's much longer span allowance only applies to a genuinely un-notched board in a 2-stringer, ≤36"-wide configuration — it isn't a substitute rule for a cut stringer of the same lumber size.
Riser, Tread, and Nosing Code Numbers
These are the numbers most stair inspections check first, and the ones most commonly missed on a first layout:
- Maximum riser height: 7-3/4", measured vertically between consecutive tread nosings.
- Minimum tread depth: 10", measured horizontally, nosing to nosing.
- Maximum riser-to-riser (and tread-to-tread) variance within one flight: 3/8".
- Nosing projection, where present: 3/4" to 1-1/4", with a maximum nosing radius of 9/16" to limit trip hazard.
Worked Example — Solving Rise and Run Together
9 ft (108") Total Rise
Illustrative example
| Step | Calculation | Result |
|---|---|---|
| Minimum risers needed | 108" ÷ 7.75" = 13.94 | Round up to 14 risers |
| Actual riser height | 108" ÷ 14 | 7.71" per riser |
| Treads (one fewer than risers) | 14 risers − 1 | 13 treads, 10" each minimum |
Rounding the riser count UP (never down) is what keeps the resulting riser height under the 7-3/4" maximum — rounding down here would produce a 108" ÷ 13 = 8.31" riser, well over the limit.
Common Mistakes
Dividing Total Rise by Too Few Risers
Using fewer, taller risers to reduce step count pushes individual riser height over the 7-3/4" maximum — always divide total rise by enough risers to keep every one at or under the limit, then check the resulting tread depth still clears 10" minimum.
Ignoring the Riser/Tread Uniformity Rule
Every riser (and separately, every tread) in a flight must stay within 3/8" of the others — a flight with mostly-uniform steps and one adjusted riser at the top or bottom to make the numbers work fails this rule even if every individual riser is under the 7-3/4" cap.
Exceeding the Cut Stringer's 6 ft Span Without Adding Support
A cut stringer notched down to its minimum throat has meaningfully less structural depth than an un-notched board of the same size, and is limited to a 6 ft unsupported span as a result — running a longer flight on cut stringers without a mid-span landing or extra support is a common structural oversight.
Applying Solid Stringer Span Rules to a Cut Stringer Layout
The extended ~13'-3" span allowance applies specifically to solid, un-notched stringers in a 2-stringer, ≤36"-wide configuration — it doesn't carry over to a cut (notched) stringer just because the lumber size matches; the two stringer types have separate, non-interchangeable span limits.
Not Verifying Local Code Adoption and Edition
Stair rise, run, and stringer figures are published by code (in the US, the IRC) and states/jurisdictions frequently apply their own amendments to these exact numbers — confirm the specific table and edition in force locally before finalizing a real stringer.
Relevant Standards and References
Riser/tread requirements are code-specific, and stairs are one of the areas most frequently adjusted by state or local amendment — the underlying safety logic (consistent, non-excessive steps) is universal, but the exact numbers vary.
| Region | Relevant Codes / Guidance |
|---|---|
| United States | IRC Section R311.7 covers maximum riser height, minimum tread depth, riser/tread uniformity, and nosing requirements for residential stairs |
| Europe / UK | UK Building Regulations Approved Document K covers private stair pitch, going (tread depth), and rise requirements; equivalent national regulations apply elsewhere in Europe alongside Eurocode 5 for structural timber design |
| India | The National Building Code of India covers general means-of-egress and stair requirements; specific riser/tread numbers are less uniformly codified for single-family residential stairs than in the IRC |
| Australia / New Zealand | The National Construction Code (NCC) Volume Two, Part H1D7 covers residential (Class 1) stair riser and going dimensions, including the 2R + G formula (twice the riser plus the going, generally 550–700 mm) |
| General guidance | Riser/tread numbers and stringer span limits are code- and edition-specific, and states or councils frequently apply their own amendments — always confirm the exact table and edition your local authority has adopted before cutting a real stringer. |
Final Verdict
Stair rise and run compliance comes down to rounding riser count up (never down), checking that every riser and tread stays within the uniformity tolerance, and matching the stringer type to the span it's actually being asked to cover.
- Round the riser count UP when dividing total rise — never down — to keep every riser at or under 7-3/4".
- Confirm every individual tread still clears the 10" minimum after solving for riser count.
- Check riser-to-riser and tread-to-tread variance stays within 3/8" across the whole flight, not just the average.
- Match stringer type to span: 6 ft max for cut stringers, up to ~13'-3" for a 2-stringer solid layout under 36" wide.
- Don't apply solid-stringer span allowances to a cut (notched) stringer of the same lumber size.
- Confirm the exact table and code edition — and any state/local amendments — your jurisdiction has adopted before cutting a real stringer.
Related calculators
Use these calculators when you need to turn this reference information into project quantities:
- Wood Stair Stringer Calculator
Find riser height, tread depth, and stringer length from total rise and run.
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