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Building Code Reference

Got a CRC R302.2 correction?

Townhouse wall fire separation

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 R302.2 is the California Residential Code section that governs fire separation between townhouse units. Every pair of adjacent townhouses must be separated by two 1-hour fire-resistance-rated wall assemblies, or by a common wall rated 1 hour where an R309 sprinkler system is provided and 2 hours where it is not. The separation must run continuously from the foundation to the underside of the roof sheathing with no gaps. A common wall cannot contain plumbing, ducts or vents, and electrical box penetrations must be protected per R302.4. Most townhouse projects and attached multi-unit conversions receive R302.2 corrections when the separation wall detail is missing from the plans or penetration protection is left unspecified.

How to fix it

  1. Identify which assembly option applies to your project

    CRC R302.2 gives you two paths. Option 1 (R302.2.1): two separate 1-hour fire-resistance-rated wall assemblies, one for each unit. Option 2 (R302.2.2): a single common wall rated for exposure from both sides, 1-hour where the building has an R309 sprinkler system and 2-hour where it does not. The rating is set by sprinkler protection, not by the property line. Confirm the sprinkler status and the lot layout before choosing your assembly type. Write the chosen option into the general notes on the title sheet so the reviewer can see the rationale without hunting through the structural sheets.

  2. Add a rated-wall assembly detail to the plan set

    Create a dedicated wall section detail at 1"=1' or 1/2"=1' scale. The detail must show: (a) the specific UL Design number or equivalent listing for the assembly, (b) the stud size and spacing, (c) the number of drywall layers on each face and their type, and (d) the extent from foundation to roof sheathing. Make sure the listed design carries the rating you need: UL Design U305, for example, is a 1-hour wood-stud assembly with 5/8" Type X gypsum board on each side, so it does not meet a 2-hour requirement. Reference the detail on the floor plan with a keynote so the reviewer can trace it directly. A note saying 'fire wall per R302.2' without a drawn detail does not satisfy the requirement.

  3. Show the wall extending continuously to the roof deck

    Add a building section that shows the separation wall running from the slab or floor framing up through any attic space to the underside of the roof sheathing. A shared open attic between two townhouse units is a code violation. The separation wall must partition the attic. Show blocking or cripple framing in the attic space on the framing plan. Any roof line change or stepped plate height needs to be addressed in the building section so the reviewer can confirm continuity without guessing at the framing geometry.

  4. Specify a listed firestop system for every penetration

    List all items crossing the separation wall. A common wall under R302.2.2 cannot contain openings, plumbing, mechanical equipment, ducts or vents (water-filled sprinkler piping excepted), so re-route those items; electrical outlet boxes in its membrane must follow R302.4. For double walls and any permitted penetration, specify a listed firestop system that maintains the wall's fire rating, such as listed electrical outlet box covers for back-to-back box installations. Reference the manufacturer's UL listing or ESR number for each penetration detail. Generic descriptions like 'firestop per code' will not pass review.

  5. Confirm no plumbing runs inside the separation wall cavity

    R302.2.2 prohibits concealing plumbing inside the common wall assembly. If the original design routes a DWV stack or supply line through the wall cavity between units, re-route it to run within one unit's framing bay or in an external chase. Mark the revision on the plumbing plan with a revision cloud and delta. This correction requires a design change, not just a detail fix, so it affects rough-in layout. Catch it before construction starts.

  6. Protect structural elements that penetrate or bear on the separation wall

    Steel moment frames, parallam beams, and LVL headers that frame into or through the separation wall must be protected to maintain the rated assembly. A bare steel post set into the common wall cavity is a rating breach. Detail the protection method for each structural element at the wall: encasement in Type X gypsum board per the thickness required for the rating, or an alternative listed system. Show this on the structural detail sheet and cross-reference it on the wall assembly detail. The plan checker will verify every element shown in the wall section against the listed assembly requirements.

  7. Mark all changed sheets with revision clouds on resubmittal

    On resubmittal, mark every sheet you changed with a revision delta and cloud. The plan checker should be able to find all R302.2 fixes quickly without re-reading the entire set. Sheets that typically need revision clouds: title sheet (general notes updated), floor plan (separation wall keynoted), wall section or detail sheet (rated assembly detail added), building section (continuous separation to roof deck shown), and plumbing plan (re-route or firestop annotated). Include a written response letter that maps each comment number to the specific sheet and detail where you addressed it. Plan checkers appreciate this and it shortens the re-review cycle.

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Why you got flagged

Plan-checkers flag R302.2 most often when the structural drawings show the townhouse footprint and unit layout but don't include a rated-wall assembly detail. The plan set needs a dedicated detail sheet or a clear call-out on the wall section naming the specific assembly, the fire rating, and the UL design number or equivalent. Submitting plans that say 'fire wall per code' without a drawn detail is not enough — the reviewer needs to know exactly what assembly you're building.

A second common trigger is penetrations left unspecified. When a gas line, DWV stack, or HVAC duct is shown in or through a common wall, R302.2.2 does not allow it at all, and penetrations that are permitted must keep the wall's fire rating. Plans that show a pipe or duct in the common wall, or a permitted penetration without a listed firestop detail, get flagged, even if the wall assembly itself is correctly specified.

The third scenario is incomplete vertical extent. R302.2 requires the separation to run from the foundation slab or floor framing all the way to the underside of the roof sheathing without interruption. Projects that spec the rated wall only between floor levels, or that show an attic framed continuously across both units, receive a correction noting that the separation does not extend to the roof deck.

Finally, projects sometimes get flagged when the designer specified a 1-hour common wall but the building has no R309 sprinkler system. Without sprinklers, the common wall rating steps up to 2 hours, and the structural drawing must reflect that.

The official code

California Residential Code R302.2, Townhouse Fire Separation — California Building Standards Commission, Department of General Services

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Common questions

Does CRC R302.2 require a 1-hour or 2-hour fire wall between townhouses?
It depends on the assembly and on sprinklers. Two separate 1-hour rated walls, one per unit, satisfy R302.2.1. A single common wall under R302.2.2 must be 1-hour rated where the building has an R309 automatic sprinkler system and 2-hour rated where it does not. California requires sprinklers in new townhouses under R309.1, so most new projects can use a 1-hour common wall. Confirm the sprinkler status of the building, then choose the assembly accordingly before you detail the wall section.
Can plumbing run inside a townhouse fire separation wall?
No. R302.2.2 prohibits plumbing inside the common wall assembly. This catches a lot of projects where a bathroom DWV stack or kitchen sink drain was routed through the shared wall for layout convenience. If your plans show any pipe in the separation wall cavity, it needs to be re-routed within one unit's framing bay or through an external chase. This is one of the harder corrections to fix after rough-in is complete, so if you're reviewing a plan set before submission, check the plumbing plan against the separation wall location specifically. Catching it at plan check is much less painful than catching it during framing inspection.
Does the fire separation wall between townhouses need to go all the way to the roof?
Yes. R302.2 requires the separation to extend from the foundation to the underside of the roof sheathing without interruption. A shared open attic between two townhouse units violates this requirement. The separation wall must continue through the attic space to the roof deck, or the attic must be partitioned with rated framing. The building section in your plan set should show this continuity. Plan checkers look for this specifically. A wall section that stops at the top plate level will be flagged on first review.
Does adding a sprinkler system remove the R302.2 separation wall requirement?
No, a sprinkler system does not eliminate the separation wall requirement between townhouse units. CRC R302.2 establishes a fundamental fire separation between dwelling units regardless of sprinkler coverage. Sprinklers do change the rating: R302.2.2 lets a common wall drop from 2 hours to 1 hour where an R309 system is provided, but the townhouse separation requirement is not waived. If you are considering a rating trade-off based on sprinklers, review the specific exception language in the current adopted edition and confirm the approach with your plan checker before drawing the detail. Do not reduce the rated assembly and assume it will pass without that confirmation.
What UL design number works for a 2-hour townhouse common wall?
Note that UL Design U305 is a 1-hour assembly with one layer of 5/8" Type X gypsum board on each face, so it does not meet a 2-hour requirement. UL Design U301 and U349 are also referenced for wood-framed walls. The specific assembly you choose must match what you are actually building: stud spacing, drywall type, and number of layers all must align with the listed design. Don't just name a UL design number in the general notes. Show the assembly in the wall section detail so the plan checker can verify the match. If you're using a proprietary assembly, include the manufacturer's ESR number.
How do I protect an HVAC duct that crosses a townhouse fire separation wall?
If the separation is a common wall, it cannot carry ducts or vents at all under R302.2.2, so the duct has to be re-routed. A plain sheet metal duct sleeve through the wall does not fix that. Where a double-wall separation is used, any penetration must keep the rating of each wall, so show the listed protection method on the mechanical plan at the penetration point. Some projects avoid the penetration entirely by running separate HVAC systems for each unit, which is the cleanest solution from a plan-check standpoint and worth considering if the mechanical layout allows it.
Does CRC R302.2 apply to an ADU that shares a wall with the main house?
R302.2 covers townhouses specifically: buildings with three or more attached townhouse units, each extending from foundation to roof with a yard or public way on at least two sides. A detached ADU does not trigger R302.2. An attached ADU that creates two dwelling units in one building is a two-family dwelling, separated under R302.3 rather than R302.2. If the conversion results in two separate dwelling units in one building, the assemblies between them need to meet R302.3. Confirm the occupancy classification and required separation with your building department during pre-application, before you finalize the design.

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