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Building Code Reference

Got a CRC R602.8 correction?

Fireblocking balloon framing

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 R602.8 is the California Residential Code section that requires fireblocking in balloon-framed wall assemblies. Balloon framing leaves stud cavities open from the bottom plate all the way up through multiple floors — those uninterrupted vertical channels can carry fire from one story to the next in minutes. R602.8 requires physical blocking at every floor level, ceiling level, and any soffited area to cut off those channels. Acceptable materials include nominal 2x lumber, two layers of 1-inch boards with staggered joints, 1/2-inch gypsum board, or mineral wool batts secured so they won’t fall out.

How to fix it

  1. Mark every fireblocking location on the framing plan

    Add a layer or note to the framing plan that explicitly calls out each location where R602.8 blocking is required: at floor and ceiling lines (including where balloon studs pass a floor), horizontally at intervals of 10 feet or less, at soffits and drop ceilings, and around penetrations at ceiling and floor level (R302.11). Use a distinct symbol or hatch and add it to the legend. A note that reads ‘fireblocking per R602.8’ in the general notes is not sufficient — the location callout must appear on the plan.

  2. Specify the blocking material on the plan

    R602.8 points to R302.11.1, which allows several materials, including 2-inch nominal lumber, two thicknesses of 1-inch lumber with broken lap joints, 1/2-inch gypsum board, or mineral wool or glass fiber batts installed so they are securely retained in place. Choose one and call it out explicitly on the framing plan or a keyed detail. If you’re using mineral wool, note the density and that it will be installed tightly against the stud faces so it can’t shift.

  3. Add a section detail at the floor-line transition

    Draw a wall section cut through the balloon-framed area at 1/2"=1’ or larger, showing the floor framing, the continuous balloon studs, and the blocking material installed between the studs at floor-line height. Dimension the blocking thickness. This detail does two things: it satisfies the plan-checker during review and it gives your framing crew a clear target during rough framing inspection. Without this, the inspector has nothing to compare the actual condition against.

  4. Confirm blocking at ceiling and soffit locations

    Beyond the floor-line, R602.8 applies at every ceiling level and at any soffited area where balloon studs continue past the ceiling plane. Check your reflected ceiling plan and any soffit details. If your plans show a dropped soffit in a hallway or kitchen ceiling where balloon framing runs behind it, that junction needs blocking called out the same way the floor-line does. Checkers sometimes pass the floor-line location but flag a missed soffit transition, which means a second round.

  5. Address the old-to-new framing interface on remodels

    If this is an addition or remodel where new balloon framing ties into existing platform framing, add a detail showing the connection at that interface. The stud cavity in the new balloon-framed section can connect to an air channel in the existing framing if the interface isn’t sealed. Show the blocking at that junction point. A note like ‘provide R602.8 blocking at all existing-to-new framing interfaces’ with a detail pointer is the minimum needed to get past the plan-checker.

  6. Cross-reference the fire-blocking schedule in the notes

    In your general structural or architectural notes, add a line that reads: ‘Fireblocking in balloon-framed wall cavities per CRC R602.8. Blocking material: [your chosen material]. Locations shown on framing plan Sheet S-XX.’ That cross-reference creates a direct link between the notes, the plan sheet, and the detail. Plan-checkers reviewing the notes section will hit the reference and can confirm the plans back it up instead of sending a correction for each location.

  7. Verify the detail sheet is indexed in the drawing set

    If you created a new wall section or blocking detail to show R602.8 compliance, make sure it appears in the drawing index on the cover sheet and that the section cut bubble on the framing plan references it with the correct sheet and detail number. Orphaned details that aren’t indexed get overlooked by plan-checkers. The correction sometimes comes back because the plan-checker couldn’t find the detail, not because it wasn’t drawn.

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Why you got flagged

Plan-checkers flag R602.8 most often when framing plans don’t mark fireblocking locations at all. Balloon framing is less common than platform framing in new construction, but it shows up frequently in older homes being remodeled, additions to craftsman bungalows, and two-story ADUs where the builder or designer carried studs continuously past the first floor. If the elevation or framing plan doesn’t explicitly call out blocking at the floor-line transition, the plan-checker has no way to verify it was designed in, so the correction lands on the resubmittal.

The second common flag is when plans do show blocking but don’t specify the material. A note that reads "fireblocking per R602.8" without calling out 2x lumber, gypsum, or mineral wool leaves the inspector without a way to verify at rough framing. The code lists specific acceptable materials and the plans need to match one of them. Calling out "see section R602.8" without a location callout on the framing plan isn’t enough for most plan-checkers.

A third scenario shows up in remodels where the original framing was platform-framed but the addition ties into it with balloon-framing techniques. The plan set may not address the junction between old and new framing at all. The plan-checker flags R602.8 because the detail sheet doesn’t show how fire propagation through that interface is handled. Lack of a connection detail at the existing wall-to-new-wall junction is often the root cause, and no amount of notes in the general section will substitute for an actual detail with dimensions.

The official code

CRC R602.8 — Fireblocking Required (2025 California Residential Code, Title 24, Part 2.5)

Read the source →

Common questions

Does CRC R602.8 apply to platform framing or only balloon framing?
R602.8 specifically covers balloon-framed wall assemblies, where continuous studs run from the foundation past the first floor to the roof. Platform framing has built-in horizontal breaks at each floor level that naturally interrupt stud cavities, so the concern doesn’t apply the same way. Fireblocking requirements for platform-framed concealed spaces fall under CRC R302.11, not R602.8. If your plan-checker cited R602.8 on what looks like a platform-framed project, verify how the studs are detailed at the floor-line — there may be a section of the wall where studs were carried continuously past a floor transition without a plate break.
What materials does CRC R602.8 accept for fireblocking?
R602.8 references the same material list as the general fireblocking section. Acceptable options include: nominal 2x lumber (a single 2x4 or 2x6 cut to fit tight between studs), two layers of 1-inch nominal lumber with broken lap joints, 1/2-inch gypsum board, batts of mineral wool or glass fiber insulation installed snug enough to stay in place, and cement-based millboard. The key thing to get right on plans is calling out which material you’re specifying. Don’t just write ‘fireblocking per R602.8’ — name the material so the inspector knows what to look for at rough framing.
Does R602.8 fireblocking apply to an ADU with balloon-framed walls?
Yes. R602.8 applies to any residential construction using balloon framing, including ADUs. Two-story ADUs where the builder ran continuous studs from the slab to the roof need blocking called out at the floor-line and ceiling line. This is one of the more common R602.8 corrections on ADU projects because designers working from stock drawings sometimes apply platform-framing details to what ends up being balloon framing in the field. If your plans were drawn by someone who mainly does platform-frame work, double-check that the floor-line detail actually shows a plate break. If it doesn’t, you have balloon framing even if that wasn’t the intent.
Where exactly does the blocking have to go in balloon-framed walls?
R602.8 requires fireblocking at every floor level, every ceiling level, and at any soffited area where the balloon-framed stud cavity continues behind the finish. Anywhere the cavity would let smoke or flame travel vertically past a horizontal plane needs blocking. For a standard two-story balloon-framed wall, that means at the first-floor ceiling line and at the second-floor ceiling line. If there’s a dropped soffit in a kitchen or hallway running behind the same stud bay, that soffit transition needs blocking as well.
Can I use spray foam instead of 2x lumber for R602.8 fireblocking?
The current adopted CRC does not list spray foam polyurethane as an approved fireblocking material for filling stud cavities under the general fireblocking provisions. Some code editions allow intumescent-tested sealants for penetration sealing around pipes and conduit, but that’s a different application from filling a balloon-framing stud cavity. If your framer wants to use spray foam, they would need documentation showing the specific product has been tested under the applicable fire standard. The safer path for plan-check purposes is to specify 2x lumber, gypsum board, or mineral wool batts, which are explicitly listed materials in the code.
What happens if the fireblocking isn’t shown on plans at all?
You get the correction letter you’re probably already holding. Plan-checkers can’t approve balloon-framed construction without confirmation that R602.8 compliance is addressed. The correction typically asks for fireblocking locations to be noted on the framing plan and a detail or specification showing the material. Responding means a full resubmittal cycle — typically another 60 days or more at most California building departments. The fix on the drawing side is straightforward; the expensive part is the wait for a second review cycle.

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