Skip to content
CrossBeamStart a pre-check

Building Code Reference

Got a CRC R318.7 correction?

Stairway requirements

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

CRC R318.7 is the California Residential Code section governing stairway construction for residential buildings. It sets the minimum stair width at 36 inches clear, limits riser height to a maximum of 7-3/4 inches, requires a minimum tread depth of 10 inches, and mandates a minimum headroom clearance of 6 feet 8 inches measured vertically above the stair nosing. Landings are required at the top and bottom of every stairway, with minimum dimensions equal to the stair width up to 36 inches. These requirements apply to stairs serving habitable space in single-family homes, ADUs, and multi-unit residential projects under the CRC.

How to fix it

  1. Locate every stairway and add a cross-section detail

    Go through the floor plan and mark every stairway. For each one, confirm a dedicated cross-section detail exists on your A-series sheets, drawn at 1/4 inch equals 1 foot minimum scale. The detail must show the following labeled dimensions: total rise (floor-to-floor), individual riser height, tread depth (nosing to nosing), headroom clearance (vertical plumb from lowest nosing to nearest overhead obstruction), and landing depth at top and bottom. A floor plan hatch with a note reading "stairway per code" will not pass. The plan-checker needs real numbers to verify.

  2. Calculate and confirm riser height

    Measure your floor-to-floor height in inches. Divide by the number of risers you plan to use. The result must be 7-3/4 inches or less per riser. Example: if floor-to-floor is 110 inches and you plan 14 risers, each riser works out to 7.86 inches, which exceeds the maximum. With 15 risers the individual height drops to 7.33 inches. Also check riser consistency within the flight: the tallest riser cannot exceed the shortest by more than 3/8 inch. If your floor system has variations, you may need to adjust the top or bottom riser to stay within tolerance.

  3. Verify tread depth on every step

    Tread depth is measured horizontally from nosing to nosing. The minimum is 10 inches. For straight-run stairs this is straightforward: confirm each tread on the detail is 10 inches or more. Winder treads follow a different rule covered under R318.7.5.2.1: minimum 10 inches at the walkline, 12 inches from the inside of the turn, and not less than 6 inches at any point within the clear width. If your plans include winders, label both measurements on the detail. Tread nosing projections must be between 3/4 inch and 1-1/4 inches (none is required where treads are at least 11 inches deep), which also needs to appear on the detail.

  4. Check headroom at every point along the stair path

    Do not just check headroom at the landing. Stand the 6-foot-8-inch measurement at the nosing of every tread and project it vertically. The most common failure point is the second or third tread from the top of the run, where the floor structure or a beam passes overhead. On the cross-section detail, draw a vertical dimension arrow from the lowest nosing to the nearest overhead obstruction and label it. If anything is below 6 feet 8 inches, you need to either restructure the overhead framing or adjust the stair layout before resubmitting.

  5. Confirm landing dimensions top and bottom

    Measure the landing at the top of the stair and the landing at the bottom. The landing must be at least as wide as the stair and, on a straight run, at least 36 inches in the direction of travel. If a door is at the top of an interior stair, the top landing may be on the other side of the door only if the door does not swing over the stairs (R318.7.6). Label landing dimensions on the cross-section or a separate landing plan detail.

  6. Verify minimum stair width

    The clear width of the stair must be at least 36 inches above the permitted handrail height and below the required headroom height. Handrails are allowed to project into the required width, but each handrail cannot project more than 4.5 inches. At and below handrail height, the clear width can drop to 31-1/2 inches with a handrail on one side and 27 inches with handrails on both sides. Check your detail and confirm the width dimension shown is the clear width, not the wall-to-wall dimension.

  7. Add handrail reference on the same sheet

    Stair corrections under R318.7 typically come paired with a handrail note from R320. If you are revising the stair section, save yourself a second correction round by adding handrail information on the same submittal. The handrail must be graspable, between 34 and 38 inches above the stair nosing, continuous for the full run, and returned or terminated to prevent catching clothing at each end. A single sentence on the detail sheet calling out handrail height and type is enough to satisfy the plan-checker.

  8. Run a consistency check across all stair references on the plans

    Plan-checkers compare numbers between sheets. If your floor plan labels 14 risers but the section shows 15, or the elevation shows a stair height that does not match the floor-to-floor dimension on the foundation plan, the correction comes back regardless of whether each individual number passes. Before resubmitting, pull up every sheet that references stairs and verify all dimensions are internally consistent.

Take the CRC R318.7 fix steps with you

All 8 steps in one email, so you have them on site instead of on this page.

Why you got flagged

Got flagged on your stairway plan? Here is why plan-checkers keep coming back on CRC R318.7.

The most common correction is a missing stair section on the drawings. When a plan-checker opens a set of residential plans and the stairway only shows up on the floor plan as a hatched rectangle, there is no way to verify riser height, tread depth, or headroom. They write it up every time. A separate stair cross-section detail at 1/4 inch equals 1 foot or larger is what resolves this.

The second most common scenario involves rise-run math that does not add up. A contractor will note 8 risers at 7-3/4 inches and 7 treads at 10 inches on the cover sheet, but the actual floor-to-floor height shown in the section dimensions works out to 64 inches, not 62 inches. Plan-checkers run the arithmetic. If the riser count times the riser height does not match the floor-to-floor dimension, the set comes back.

Headroom is a frequent miss on ADU stairways and basement conversions. When a low beam, dropped soffit, or floor joist band cuts the vertical clearance below 6 feet 8 inches anywhere along the stair path, R318.7 is cited. The measurement runs from the nosing of each tread plumb to the nearest obstruction above, not just at the landing. A lot of plans show the headroom at the top landing and miss the tight spot two treads down.

Landing dimensions are the fourth common hit. R318.7 requires a landing at the top and bottom of every stair run, with a minimum length equal to the stair width (up to 36 inches). Plans that show a door opening directly into the stair without a landing, or a landing that is only 24 inches deep, will get a correction.

The official code

2025 California Residential Code R318.7 — Stairways (UpCodes viewer)

Read the source →

Common questions

Does CRC R318.7 apply to ADU stairways?
Yes. Any stairway serving habitable space in an ADU must meet R318.7 requirements. That means minimum 36-inch clear width, maximum 7-3/4 inch risers, minimum 10-inch treads, and 6-foot-8-inch headroom. ADU corrections letters cite R318.7 often because attached ADU conversions frequently involve low garage or basement ceilings. The headroom clearance requirement is the most common specific miss in ADU stair plans. Check the full path from the bottom landing up through the top riser before submitting.
What is the maximum riser height under CRC R318.7?
7-3/4 inches. That is the hard maximum for any individual riser. Within a single stair run, all risers must also be consistent: no two adjacent risers can differ by more than 3/8 inch. If your floor-to-floor height does not divide cleanly into risers at or below 7-3/4 inches, add a riser rather than going over the limit. Example: floor-to-floor of 96 inches. 12 risers at 8.0 inches fails. 13 risers at 7.38 inches passes.
What happens if my stairway headroom is only 6 feet 6 inches?
It fails R318.7. The minimum is 6 feet 8 inches measured vertically from the nosing of each tread to the nearest obstruction above. You cannot average it across the run. If any single point along the stair path falls below 6 feet 8 inches, the correction stands. Your options are to lower the stair structure (raise floor height at top, lower landing at bottom), reframe or re-route the overhead obstruction, or redesign the stair run to avoid the conflict. Confirm the corrected clearance on a revised cross-section with a dimension arrow.
Do I need a landing at the top of every interior stair?
Yes. R318.7 requires a landing at both the top and bottom of every stairway. The landing must be at least as wide as the stair and at least 36 inches in the direction of travel for stairs up to 36 inches wide. A common miss is a door at the top of the stair that swings inward over the landing. The door is allowed, but even with it open the remaining landing depth cannot be less than 36 inches. Show the door swing and landing depth on the same detail.
How do I dimension a stairway section to pass plan check?
Show these items on the cross-section, all labeled with actual dimensions: number of risers, height of each riser, tread depth nosing-to-nosing, total floor-to-floor rise (and confirm it matches the riser count times the riser height), minimum headroom with a vertical dimension arrow from the lowest nosing to the nearest overhead obstruction, stair clear width measured at handrail height, and landing depths top and bottom. Tread nosing projection should also be noted (between 3/4 inch and 1-1/4 inches). A plan that shows all of these items rarely gets a second R318.7 correction.
Can I use winder stairs in a residential project under CRC R318.7?
Yes, with additional requirements. Winder treads must have a minimum depth of 10 inches at a point 12 inches from the narrow end. The narrow end itself cannot be less than 6 inches. These two measurements must both appear on the plans. Winders complicate headroom verification because the tread geometry changes at each step, so show headroom at the tightest point in the winder section. The R318.7.5 subsection governs winder treads specifically. If the plan-checker has questions about the geometry, a 3D or axonometric sketch on the plans sometimes resolves it faster than a note.

Related corrections

Check my plans for this →