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Got a CRC R302.11 correction?

Fireblocking concealed spaces

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 R302.11 requires fireblocking in combustible construction to stop fire from traveling through hidden cavities inside walls, floors, and ceilings. Fireblocking must be installed at floor and ceiling levels, at the top and bottom of stair stringers, in soffits and cove ceilings, at every 10 feet horizontally in concealed wall cavities, and at any pipe or duct penetration through a floor or ceiling. Most framing inspections on single-family and ADU projects flag R302.11 when the plans don't show fireblocking locations or the field installation skips the duct and pipe penetrations.

How to fix it

  1. Add a fireblocking general note to the framing plan

    On the framing plan sheet, add a general note that states fireblocking is provided per CRC R302.11 at all floor and ceiling levels, at the top and bottom of stair stringers, in soffits and cove ceilings, and at 10-foot horizontal intervals in any concealed wall cavity exceeding 10 feet. This single note tells the plan-checker the subject has been addressed. Without it, they assume you missed it.

  2. Show fireblocking at floor-ceiling platform transitions

    At each floor level, the wall framing section must show where the rim joist, blocking, or top plate seals off the stud cavity from the floor cavity above. In platform framing, the double top plate and rim joist typically do this automatically, but you still need to call it out on the section detail. A wall section at 1/4-inch scale showing the platform framing with a leader note 'fireblocking per R302.11' is usually enough to get the check.

  3. Detail pipe and duct penetrations through floor-ceiling assemblies

    For each location where a pipe, duct, or conduit passes through a floor or ceiling, add a penetration detail showing how the annular space around the element is filled. Common solutions: 2-inch nominal lumber blocking cut to fit around the pipe, approved intumescent firestop caulk, or listed firestop collars. The detail should call out the specific material and note that it is listed for the application. One generic penetration detail with a plan note covering all similar penetrations usually satisfies the plan-checker.

  4. Call out soffit and cove ceiling fireblocking locations

    On the interior elevation or reflected ceiling plan, mark each kitchen soffit, tray ceiling, and dropped cabinet overhang. Add a note that fireblocking is installed at the intersection of each soffit with the exterior wall. The interior elevation sheet is a good place for this because it shows the soffit geometry; add a section cut or leader note pointing to the intersection location. The framing plan should cross-reference back to this detail.

  5. Check stair stringer fireblocking at top and bottom

    At the top and bottom of each stair stringer, fireblocking must close off the concealed space beneath the stairs. Show this on the stair section detail. If the underside of the stairs is enclosed with drywall per CRC R302.7 (under-stair protection), that assembly often satisfies the fireblocking requirement at the same time. Call it out specifically so the plan-checker can see that both R302.7 and R302.11 are addressed in the same detail.

  6. Verify 10-foot horizontal intervals in tall wall cavities

    Measure the height of any combustible wall cavity from the lowest horizontal obstruction (sole plate, fire block, or floor) to the next one above. If that dimension exceeds 10 feet, you need an intermediate fireblocking row. This shows up in two-story great rooms, open stairwell walls, and cathedral walls. Add a horizontal blocking note on the wall framing plan at the 10-foot interval, specifying 2x blocking or equivalent material tight to the studs with gaps filled.

  7. Confirm fireblocking material meets R302.11.1

    CRC R302.11.1 lists accepted materials: 2-inch nominal lumber, 2 layers of 1-inch nominal lumber with joints broken, 23/32-inch wood structural panels, 3/4-inch particleboard, 1/2-inch gypsum board, 1/4-inch cement-based millboard, batts or blankets of mineral wool or glass fiber, or cellulose insulation installed as tested per ASTM E119 or UL 263 for the application. Penetrations at ceiling and floor level can instead use an approved material under R302.11, Item 4. Your plans don't need to call out all of these, but if you are using an unconventional material like spray foam or intumescent caulk at penetrations, note that it is listed for that application.

  8. Cross-check with R302.12 for draftstopping if applicable

    If your project has a floor-ceiling assembly with usable space above and below, a concealed space over 1,000 square feet, and a suspended ceiling or open-web or perforated floor framing, CRC R302.12 adds draftstopping requirements on top of fireblocking. The plan-checker may flag both R302.11 and R302.12 together. Confirm whether your project triggers draftstopping, and if so, add those callouts in the same revision. Fixing both codes in one resubmit saves another 60-day correction cycle.

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Why you got flagged

Here is why plan-checkers flag R302.11 more often than contractors expect: the code covers a lot of ground, and most framing plans only show structural members, not the fireblocking that has to fill the gaps between them.

The most common flag is missing fireblocking callouts on the framing plan altogether. A plan-checker reviewing the floor framing or wall framing sheets looks for a general note or detail showing where fireblocking goes at each floor and ceiling platform. If that note isn't there, it gets flagged even if the contractor knows exactly how to do it in the field.

The second scenario is penetrations. Any pipe, duct, or conduit that passes through a floor or ceiling assembly has to be fireblocked at the opening. HVAC chases are a repeat offender: a plumber cores a 4-inch hole for a drain stack and nobody calls out the annular space around the pipe. The plan-checker sees no detail, writes up R302.11.

Soffits and dropped ceilings are the third common miss. Kitchen soffits, tray ceilings, and built-in cabinet overhangs create concealed horizontal spaces. Those spaces need fireblocking at their intersections with exterior walls. It is easy to draw the soffit on a finish plan and forget the fireblocking note on the framing plan.

The fourth scenario is tall wall cavities. Any combustible wall cavity that runs more than 10 feet without a horizontal obstruction needs fireblocking at that interval. In two-story open stairwell walls or vaulted ceiling framing, this catches people off guard when the stud cavity runs 14 feet uninterrupted from sole plate to rafter.

The official code

California Residential Code (2025 ed.) — Chapter 3, Section R302.11 Fireblocking

Read the source →

Common questions

Does CRC R302.11 apply to ADUs?
Yes. ADUs are governed by the same California Residential Code as single-family homes. Fireblocking requirements under R302.11 apply to any combustible wood-frame construction, which is most ADUs. Attached ADUs that share a wall with the main dwelling have additional fire separation requirements under R302.3 (two-family dwellings), but the base fireblocking obligation under R302.11 applies regardless.
What materials count as fireblocking under CRC R302.11.1?
The accepted materials list under R302.11.1 includes 2-inch nominal lumber, two layers of 1-inch nominal lumber with offset joints, 23/32-inch wood structural panels, 3/4-inch particleboard, 1/2-inch gypsum board, 1/4-inch cement-based millboard, mineral wool or glass fiber batts or blankets, and cellulose insulation installed under specific tested conditions. For pipe and duct penetrations, listed intumescent firestop caulk and collars are also accepted. The material just has to be tight to the framing with no gaps larger than the tolerances in the listing.
How do I fireblock a pipe penetration through the floor?
Cut 2-inch nominal lumber blocking to fit around the pipe in the joist bay, fitting it tight against the subfloor and the pipe. For round pipes where tight-fitting lumber is impractical, use an approved intumescent firestop caulk or listed firestop collar sized to the pipe diameter. The caulk or collar has to be listed for that specific application and pipe material. Show the detail on your plans with the product name or a note that a listed firestop product is used.
Can I use spray foam to fireblock wall cavities?
Not as a standalone solution. Standard two-component spray polyurethane foam is not listed as a fireblocking material under R302.11.1 unless it has a specific fire-resistance listing for that application. Intumescent firestop products, which are different from general-purpose spray foam, can be listed for penetration sealing. For open wall cavities at floor and ceiling levels, the standard approach is 2-inch nominal lumber blocking or gypsum board. Check the product's listing documentation before specifying it.
What is the 10-foot rule for wall cavity fireblocking?
CRC R302.11 requires a horizontal fireblocking row anywhere a combustible wall cavity exceeds 10 feet in height without an obstruction. The measurement is the continuous unobstructed vertical space inside the wall. In standard 8 or 9-foot ceilings, the double top plate closes off the cavity before 10 feet, so no intermediate block is needed. In tall first-floor walls, two-story open walls, or cathedral knee walls, measure the stud cavity height. If it goes past 10 feet, add blocking.
Do I need fireblocking if I already have fire sprinklers?
Yes, generally. CRC R302.11 applies to combustible construction and is not waived by the presence of a residential sprinkler system under R309 or NFPA 13D. The two systems address different failure modes: sprinklers control active fires in occupied spaces, fireblocking slows spread through hidden cavities that sprinklers can't reach. A few jurisdictions allow minor fireblocking exceptions in fully sprinklered buildings, but that is jurisdiction-specific and requires a code analysis to confirm.
Will the framing inspector check fireblocking in the field?
Yes. Framing inspections in California include a check that fireblocking is installed at the locations required by R302.11. The inspector will look at floor-ceiling transitions, stair stringer ends, and any visible penetration locations. If the fireblocking is covered by drywall before inspection, the inspection has to happen while the framing is still exposed. Getting the framing rough-in inspection signed off before drywall is the standard sequence. Don't close up walls with unfilled penetrations.

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