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Building Code Reference

Got a CRC R302.7 correction?

Under-stair drywall

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 R302.7 requires that any enclosed usable space beneath a stairway be protected on the enclosed side with 1/2-inch gypsum board. The rule covers walls, the underside of the stair framing, and any soffits in spaces accessed by a door or access panel. Most flagged plans involve closets, storage rooms, or mechanical spaces built under stairs without the drywall spec called out on the drawings.

How to fix it

  1. Confirm whether the under-stair space is enclosed

    Check if any part of the under-stair area is accessed by a door, access panel, or fixed opening. If yes, R302.7 applies and you need to show the gypsum board protection on the drawings. Open storage under open-riser stairs or fully open spaces don't trigger this requirement — only enclosed usable spaces do. When in doubt, treat it as enclosed. A space doesn't have to be finished or habitable to count — an unfinished utility closet accessed by a door is still an enclosed usable space under the code.

  2. Add a wall section or detail showing 1/2" gypsum board

    Create a detail at 1/4"=1' or larger that shows the 1/2" (12.7 mm) gypsum board applied to the walls, the underside of the stair framing (the sloped soffit), and any horizontal soffits within the enclosed space. The detail should call out the board thickness and the fastener schedule (per Table R702.3.5 for 1/2" board on 16" framing: nails at 8" o.c. on walls and 7" on ceilings, or screws at 16" and 12"). Note whether Type X or standard gypsum board is specified. Your structural sheets or interior elevation sheets are the right place for this — wherever the plan-checker expects to see wall finish specs. If the space is large enough to show up on an interior elevation, add the call-out there too.

  3. Update the floor plan to cross-reference the new detail

    On the floor plan sheet, add a note on the under-stair space pointing to your new detail (e.g., "See Detail 1/A5 for under-stair drywall per CRC R302.7"). This cross-reference makes it easy for the plan-checker to find the spec without hunting through the drawing set. Missing cross-references are a common reason for a second round of corrections even when the detail itself is correct. Label the door or access panel on the floor plan as well — the plan-checker needs to see that you've identified it as the trigger for the enclosure rule.

  4. Show all three protected surfaces explicitly

    The code covers three surfaces in the enclosed space: (1) the side walls, (2) the underside of the stair framing — the sloped ceiling that runs parallel to the stair slope, and (3) any soffits or horizontal ceilings. A common mistake is showing drywall on the walls but omitting it on the sloped underside of the treads and risers. The plan-checker will look at all three surfaces. If your detail shows only the walls, you'll get a second correction. A cross-section view works well for this because it shows all surfaces in one view without ambiguity.

  5. Check whether CRC R302.6 also applies

    If the under-stair space shares a wall with an attached garage, CRC R302.6 applies in addition to R302.7. R302.6 requires 1/2" gypsum board on the garage side of the separation, and 5/8" Type X where dwelling space is above the garage. The two sections don't conflict — R302.7 sets 1/2" as the minimum for the enclosed under-stair surfaces; R302.6 sets the garage-side separation. The simplest fix is to spec 5/8" Type X on all surfaces, which satisfies both. Call this out clearly in the detail so the plan-checker can verify compliance with both sections in one read.

  6. Address mechanical rooms under stairs the same way

    If the under-stair space houses a water heater, furnace, or electrical panel, the same 1/2" gypsum board rule applies. These spaces get treated as utility areas with unfinished framing, and that's the source of the correction. Show the drywall on the mechanical room drawings, including any return-air chases or plenums that run through the space. If the mechanical room adjoins the garage, also apply the R302.6 garage-side separation (1/2" gypsum board, or 5/8" Type X below dwelling space). If the water heater has a flue, make sure the penetration through the drywall is fire-stopped — that's a separate but related correction.

  7. Resubmit with a written response addressing each correction item

    When you resubmit, include a written response that specifically calls out the sheet and detail number where you've addressed R302.7. Something like: "CRC R302.7: 1/2" gypsum board shown at under-stair storage room on Detail 1/A5, cross-referenced on Floor Plan A1." Plan-checkers review dozens of sets — a clear response letter cuts resubmittal time. In Orange County cities served by Anaheim Public Utilities or SCE, permit resubmittals go through the same building department process regardless of utility provider.

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Why you got flagged

Here's why plan-checkers flag this: the correction almost always traces back to a closet or storage space built beneath the stairs with no fire-protection detail on the plans.

The most common scenario is a coat closet or under-stair storage room that shows up on the floor plan but lacks any finish or framing call-outs on the interior elevation or wall section. The plan-checker sees an enclosed space, looks for the 1/2" gypsum board spec, and doesn't find it. That's a correction. The space could be perfectly built in the field, but if the drawings don't show it, the reviewer has to flag it.

A second common trigger is a mechanical space under the stairs — water heater, FAU, or electrical panel — that the designer treated as utility space rather than an enclosed usable space. Under-stair mechanical rooms are accessed by a door or panel, which makes them enclosed spaces under the code's definition. The 1/2" drywall requirement applies to all three surfaces: the walls, the underside of the stair framing, and any soffits.

A third pattern shows up in remodels where the original permit pre-dates the current code and the contractor is adding a door to an existing under-stair cavity. Converting open storage to an enclosed space by adding a door creates a new enclosed space under R302.7. The correction notes that the new door requires the drywall protection even if the existing structure was previously unpermitted or open.

The official code

California Residential Code R302.7 — Under-Stair Protection (2025 CRC via DGS Building Standards Commission)

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Common questions

Does CRC R302.7 apply if the under-stair space has no door?
No — R302.7 applies to enclosed usable spaces accessed by a door or access panel. If the space under your stairs is fully open with no door and no access hatch, R302.7 doesn't apply. The moment you add a door or panel, it becomes an enclosed space and the 1/2" gypsum board requirement kicks in for all surfaces: walls, the underside of the framing, and any soffits. This catches a lot of remodel projects — someone adds a door to existing open storage under the stairs, and the permit triggers R302.7 for the entire space.
Can I use 5/8" Type X instead of 1/2" standard gypsum board for R302.7?
Yes — 5/8" Type X satisfies R302.7 and then some, since the minimum is 1/2". If the under-stair space is adjacent to a garage, CRC R302.6 requires 1/2" gypsum board on the garage side, or 5/8" Type X below dwelling space above the garage. Using 5/8" Type X throughout is a clean way to satisfy both R302.6 and R302.7 without tracking which wall gets which spec. The plan-checker will accept it; inspectors will accept it. Just make sure your detail calls it out clearly.
Does the under-stair drywall requirement apply to ADUs?
Yes, if the ADU has an interior stairway with enclosed space below it. R302.7 applies to all dwelling units covered by the California Residential Code, which includes ADUs. Orange County ADU permits regularly get flagged on this section because the stairway detail gets borrowed from a template set that doesn't include the under-stair fire-protection spec. If you're working from a template, check it. Add the 1/2" gypsum board detail to every ADU set that includes an interior stair with any form of enclosed space below.
What surfaces does the 1/2" gypsum board need to cover under R302.7?
All enclosed surfaces in the space: the side walls, the underside of the stair framing (the sloped ceiling that follows the stair pitch), and any horizontal soffits. The sloped underside is the surface most often missed in drawings. Show all three in your detail. If you're drawing a cross-section of the stair assembly, the three surfaces are easy to identify and call out in one view. If any framing is left exposed in the enclosed space, the plan-checker will flag it even if the walls are correctly called out.
Does R302.7 apply to the underside of open-riser stairs?
No. Open-riser stairs — where you can see through the treads — don't create an enclosed space. R302.7 only applies when the under-stair area is enclosed. If you later close in the sides of an open-riser stair to create a storage space, that modification triggers R302.7. The correction is triggered by the enclosure, not by the stairway itself. If you're doing a remodel that closes off a previously open stair, include R302.7 compliance in the permit application from the start.
My correction letter cites R302.7 and R302.6 together — do I fix them separately?
Handle them together since they likely apply to the same space. R302.6 covers the garage-to-dwelling fire separation; R302.7 covers enclosed spaces under interior stairs. If your under-stair storage room has one wall shared with the garage, both apply. In your response, show one detail that identifies each surface and its required treatment: 1/2" gypsum board on the garage side of the shared wall (R302.6, or 5/8" Type X where the garage ceiling is below dwelling space), and 1/2" gypsum board on the enclosed walls and underside of framing (R302.7). Using 5/8" Type X on all surfaces satisfies both with a single spec.

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