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Building Code Reference

Got a CBC 1011.5.2 correction?

Stair tread and riser

For builders in California, Greater Seattle, the Las Vegas area, the Denver area and Kansas City · CrossBeam Permits

What this code requires, how to fix it, and how cities and counties review it

What this code requires

CBC 1011.5.2 is the California Building Code section that sets the maximum riser height and minimum tread depth for commercial stair flights. Risers cannot exceed 7 inches tall, and treads must be at least 11 inches deep, measured horizontally from nosing to nosing. Its companion, CBC 1011.5.4, limits how much individual risers and treads can vary within a single flight, which prevents the uneven stepping surfaces that cause trips. Any occupancy served by a commercial means-of-egress stair is covered, including offices, retail buildings, apartment buildings outside the dwelling units, and mixed-use.

How to fix it

  1. Calculate riser height from actual floor-to-floor dimensions

    Start with the confirmed floor-to-floor height (structural slab to structural slab, or finish floor to finish floor once slab thickness and topping are accounted for). Divide by the number of risers you plan to use. The result must be 7 inches or less. If the math gives you 7.1 inches, you need one more riser. Do the calculation before drawing the stair section, not after, because redesigning a stair on a corrections resubmit costs you 60 days. Show the calculation in a stair schedule or notes on the plan.

  2. Set tread depth at 11 inches minimum nosing-to-nosing

    The 11-inch minimum tread depth under CBC 1011.5.2 is measured horizontally from the front face of one tread nosing to the front face of the next. This is a nosing-to-nosing measurement. With uniform nosings it equals the riser-face to riser-face run, so a 1.25-inch nosing does not let you shorten the run below 11 inches. Labeling the overall tread board width as the tread depth is a common drawing error that triggers a correction.

  3. Verify uniformity: no more than 3/8 inch variation within a flight

    Check that every riser in the flight is within 3/8 inch of every other riser in the same flight, and that every tread is within 3/8 inch of every other tread. This is especially important at landings where the slab transitions. Show the riser and tread dimensions for each step in a stair section or schedule, not just a single typical callout. If you have a non-typical riser at the top or bottom because of a landing thickness adjustment, call it out explicitly and verify it falls within the 3/8 inch tolerance.

  4. Add a dimensioned stair section to the drawings

    Include a full stair section at 1/4 inch = 1 foot or larger that shows: riser height (dimension each riser if they vary), tread depth nosing-to-nosing, nosing projection (1-1/4 inches maximum), headroom clearance (minimum 80 inches along the stair path), and floor-to-floor height with the math. A plan-checker who can read the geometry directly from the section rarely writes a correction. One who has to infer it usually does.

  5. Confirm nosing projection and profile meet CBC 1011.5.5

    CBC 1011.5.5 governs nosing shape and projection. Nosings may project no more than 1-1/4 inches beyond the tread below, and projections must be uniform. The leading edge needs a curvature or bevel of 1/16 to 9/16 inch, and a riser that slopes under the tread above may lean no more than 30 degrees from vertical. Check the nosing detail in your specs against what is drawn. A stair that meets 1011.5.2 dimensions but has a code-violating nosing gets flagged on 1011.5.5, and you will need another resubmit.

  6. Do not use residential riser heights on commercial egress stairs

    CRC R318.7.5 allows residential stairs up to 7-3/4 inch risers. CBC 1011.5.2 caps commercial stairs at 7 inches. If your project has any commercial occupancy in the egress path (Group B office, Group M retail, Group R-2 apartment stairs outside the dwelling units), the commercial cap applies to those stairs. On a mixed-use project, confirm with your plan-checker which stairways are in the commercial egress path and apply CBC 1011.5.2 to those. Do not assume that because one stair serves residential units only, it gets the residential allowance.

  7. Cross-check stair guards and handrails while revising the section

    While you are revising the stair section to address 1011.5.2, check CBC 1014 (handrails) and CBC 1015 (guards) at the same time. Plan-checkers reviewing a stair correction often look at the full stair and mark up related items. Handrail height is 34 to 38 inches above the stair nosings. Guard height is 42 inches minimum on commercial egress stairs. Catching those in the same resubmit is faster than getting a second corrections letter.

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Why you got flagged

The most common reason plan-checkers flag CBC 1011.5.2 is that the stair geometry on the drawings does not match the code minimums. A contractor submits plans with risers dimensioned at 7.5 or even 7.75 inches because that is what fits the floor-to-floor height cleanly, and the reviewer marks it up because commercial code caps risers at 7 inches. The residential allowance of 7-3/4 inches under the CRC does not carry over here.

Another common flag comes from uniformity violations. CBC 1011.5.4 limits the variation between any two risers in the same flight and between any two treads in the same flight. Designers sometimes dimension a stair that averages out correctly but allows individual steps to drift. A plan-checker who measures adjacent risers and finds more than 3/8 inch variation will mark it up, even if the average is compliant.

Mixed-use projects hit this code when the architect uses residential stair tables for stairways inside a commercial occupancy. A four-story mixed-use building with retail on the ground floor has commercial stair requirements throughout the egress path, not just on the retail floor. Using CRC R318.7.5 dimensions on a commercial egress stair will get flagged every time.

The fourth scenario is missing geometry notes. Some plan sets draw the stair correctly but do not call out the riser height, tread depth, or the nosing projection in a stair section or detail. Without those callouts, a plan-checker cannot verify compliance and will write a correction asking for dimensions.

The official code

California Building Code Chapter 10 — Means of Egress, Stair Dimensions

Read the source →

Common questions

What is the maximum riser height for commercial stairs in California?
Under CBC 1011.5.2, the maximum riser height for commercial stairs is 7 inches. This is stricter than the residential code, which allows up to 7-3/4 inches under CRC R318.7.5. The 7-inch cap applies to stairs in the means of egress for Group B, Group M, Group R-2 (apartment stairs outside the dwelling units), and other commercial occupancies. If your floor-to-floor height does not divide evenly into risers at 7 inches or less, you need to add a riser rather than exceed the cap. For example, a 10-foot floor-to-floor height (120 inches) divided by 7 inches gives you 17.1 risers, so you would use 18 risers at 6.67 inches each.
Does CBC 1011.5.2 apply to ADUs?
Generally no. Accessory dwelling units are regulated under the California Residential Code, which uses CRC R318.7.5 for stair dimensions. ADU stairs follow the residential standard of 7-3/4 inch maximum risers and 10-inch minimum tread depth. CBC 1011.5.2 applies when the stair is part of a commercial egress path, which is unusual for a single-family ADU. The exception would be an ADU that is part of a larger commercial project where the egress stair serves commercial occupancies, or a building with more than two dwelling units classified Group R-2, where stairs outside the dwelling units take the 7-inch and 11-inch limits. When in doubt, check the occupancy classification with your plan department before finalizing the stair design.
How much can risers vary within a single flight?
CBC 1011.5.4 limits riser variation to 3/8 inch between the largest and smallest riser in the same flight. The same 3/8-inch limit applies to tread depth variation within a flight. This matters most at the top and bottom of a flight where landing transitions or slab conditions can push one step out of the typical geometry. If you have a non-typical riser at either end of a flight, dimension it explicitly in your stair section so the plan-checker can verify compliance without guessing. The variation limit exists because uneven steps are a trip hazard. A person descending a stair develops a rhythm based on the first few steps, and if the last step is even a half-inch taller, it breaks that rhythm at the worst possible moment.
Can I use the residential stair table for a 4-story mixed-use building?
No. On a four-story mixed-use project, the egress stairways serving commercial occupancies must meet CBC 1011.5.2, not the residential CRC dimensions. The commercial cap of 7 inches per riser and 11-inch minimum tread applies throughout the commercial portion of the egress path. Only a stair entirely within a dwelling unit gets the 7-3/4-inch riser and 10-inch tread allowance (CBC 1011.5.2 exception for R-3 and R-2 dwelling units); a common stair serving several units still takes the commercial limits, so get any exception confirmed in writing before you build it. Many plan-checkers apply the commercial standard to all stairs in a mixed-use building to keep the egress path consistent.
What is the difference between tread depth and run in CBC 1011.5.2?
Tread depth is measured nosing-to-nosing: from the front face of one tread to the front face of the next, measured horizontally. Run is measured riser-face to riser-face. With uniform nosings the two are equal, because each nosing shifts both ends of the measurement by the same amount. CBC 1011.5.2 sets the 11-inch minimum as the nosing-to-nosing measurement. A common drawing error is labeling the overall tread board width (say, 12.25 inches including a 1.25-inch nosing) as the tread depth. Label both dimensions explicitly in your stair section and avoid any ambiguity about which measurement is which.
Does the 3/8 inch uniformity rule apply across all flights or just one flight?
The 3/8-inch uniformity tolerance applies within a single flight, defined as the portion of stair between two landings. Across different flights separated by landings, risers can differ from each other without directly violating 1011.5.4. That said, large riser-height changes from one flight to the next can still draw scrutiny from a thorough plan-checker and may raise accessibility questions under CBC Chapter 11B for buildings subject to those requirements. Keep all flights in the same stairway close to the same geometry. If you have two flights and you are tempted to make one with 6.5-inch risers and another with 7-inch risers, consider whether a uniform riser across both flights is possible given the floor heights.

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