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Building Code Reference

Got a CRC R302.1 correction?

Exterior wall fire rating near property line

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 R302.1 sets the exterior wall fire-resistance requirements for residential buildings based on distance from the property line. Any exterior wall closer than 5 feet to a property line must carry a 1-hour fire-resistance rating (3 feet where the building is sprinklered and Table R302.1(2) applies). Within 3 feet, openings such as windows and doors are not permitted at all. Projections — eaves, overhangs, and similar features — cannot extend closer than 2 feet to the property line. Single-family, duplex, and ADU projects all trigger R302.1 when the structure sits close to a side or rear property line.

How to fix it

  1. Measure all wall-to-property-line distances on the site plan

    On your site plan, dimension every exterior wall to the nearest property line. Flag any wall face (not the structure centerline) that falls within 5 feet, or within 3 feet if the building is sprinklered throughout and Table R302.1(2) applies. Also note eave tip distances separately, since projections have a 2-foot minimum. This becomes your R302.1 compliance matrix: one line per affected wall with the measured distance and required action.

  2. Specify the rated wall assembly on elevation and section sheets

    For each wall within 5 feet of the property line, call out a specific tested assembly by designation. Common options include 1-inch stucco over 5/8-inch Type X gypsum board on 2x4 studs at 16 inches on center (similar to UL U305), or 5/8-inch Type X on each face of a light-frame assembly. Write the assembly designation on the exterior elevations and on the wall section detail. Noting ‘1-hour fire rated per code’ without an assembly reference is not enough: the checker needs to verify the construction method. If you’re not sure which assembly your framing contractor will build, pick two or three approved options and note ‘contractor to select from the following rated assemblies.’

  3. Remove or relocate openings within 3 feet of the property line

    Identify any window, door, vent opening, or operable penetration in walls within 3 feet of the property line. R302.1 does not allow openings in this zone, regardless of size. Options: move the opening to a wall face farther than 3 feet from the line; eliminate the opening entirely; or if the program requires light in that room, use a skylight or clerestory window on a roof plane that clears the zone. Mechanical vents (dryer exhaust, bathroom fan) that terminate in this zone also count as openings — either relocate the termination point or run the duct to a compliant wall face.

  4. Check and trim eave overhangs in the 2-foot projection zone

    Measure from the exterior wall face to the tip of the eave on any side within the 5-foot zone. If the eave tip lands within 2 feet of the property line, the eave is not allowed there: cut the rafter tails so the eave tip is at least 2 feet from the line, or reconfigure the roof geometry on that side to a flush or parapet condition. Where the tip lands between 2 and 5 feet from the line, detail 1-hour fire-rated construction on the underside (using 5/8-inch Type X gypsum or another tested assembly). Show the corrected eave dimension explicitly on the roof framing plan and exterior elevation.

  5. Add an R302.1 compliance note to the general notes sheet

    Checkers appreciate a dedicated note that ties the drawings together. Something like: ‘Exterior walls within 5 feet of property line: 1-hour fire-resistance rated per [assembly designation]. No openings permitted within 3 feet of property line. Projections limited to not less than 2 feet from property line.’ Cross-reference the note to the specific sheet and detail where the rated assembly is shown. This reduces back-and-forth because the checker can verify compliance in one pass.

  6. Confirm the rated assembly runs full height

    A common mistake is specifying a rated wall assembly on the elevation but stopping it at the floor platform or at the top plate. The 1-hour rating must run the full height of the wall, from the foundation sill to the roof sheathing. On a two-story building, both stories are affected if both are within 5 feet of the line. Show the vertical extent on a full-height wall section, not just a partial detail, and confirm the floor assembly at the second-story level doesn’t break the fire barrier.

  7. Verify detached ADU setbacks independently from the main house

    If you’re building a detached ADU, treat it as a separate structure for R302.1 purposes. Measure from the ADU exterior walls to all four property lines, and also from the ADU to the main house, since two structures on the same lot must each comply independently. The main house may already have a compliant rated wall facing the ADU; the ADU needs its own. Document both structures’ compliance on the same site plan with clear labeling so the checker can read both at once.

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Why you got flagged

The most common reason plan-checkers cite R302.1 is a missing fire-rating callout on the exterior wall elevation or floor plan. If the plans show a wall within the 5-foot setback zone but don’t include a rated assembly detail — 5/8-inch Type X gypsum on the interior face, or equivalent tested assembly — the checker flags it. The rated assembly has to be referenced by number (e.g., UL U305, GA WP-3210) or spelled out in full on the construction documents, not just noted as ‘1-hour rated wall.’

A second common scenario involves windows or doors shown within 3 feet of the property line. Even a small operable window in a bathroom, a dryer vent trim piece treated as an opening, or a door into a side yard can trigger this correction. The 3-foot rule applies to any opening in the wall, full stop. If that window is essential, the design has to move it or the building footprint has to step back.

Eave and soffit overhangs are the third common trigger. A lot of residential designs have 18- to 24-inch eave overhangs on all sides, and on a tight lot those overhangs can cross into the 2-foot projection zone. Plans often show the building footprint correctly set back but omit the eave dimension, so the checker measures it themselves and flags the violation. The fix is cutting the eave back so its tip stays at least 2 feet from the line, and protecting the underside with 1-hour rated construction where the tip falls between 2 and 5 feet.

ADU projects on existing lots frequently run into all three problems at once. The ADU gets positioned near the rear fence line to preserve yard space, the owner wants windows for light, and the standard house eave detail gets copied without checking the property-line distance. The correction letter comes back with all three items checked.

The official code

California Residential Code R302.1 — Exterior Walls (2025 Edition via DGS Building Standards)

Read the source →

Common questions

Does CRC R302.1 apply to ADUs built in the rear yard?
Yes, it applies to detached ADUs the same way it applies to any new structure. If the ADU’s exterior wall is within 5 feet of the property line, you need a 1-hour rated assembly. No openings within 3 feet, and eave projections must stay at least 2 feet from the line. ADUs built tight to the rear fence line are the single most common R302.1 trigger in plan-check corrections. The detached ADU is treated independently from the main house, so even if the main house wall facing the ADU is rated, the ADU itself still needs to comply on its own.
Can I put a window in an exterior wall that’s 4 feet from the property line?
Yes, with limits. Windows and other openings are prohibited in exterior walls within 3 feet of a property line, and they’re restricted between 3 and 5 feet. In the 3-to-5-foot zone, Table R302.1(1) caps unprotected openings at 25% of the wall area; a sprinklered building under Table R302.1(2) allows unlimited openings at 3 feet or more. Check CRC Table R302.1(1) for the specific limits by distance. At 4 feet from the line, the safest path is to relocate the window to a wall that’s farther away, or to use a skylight on the roof over that room instead.
What rated wall assembly satisfies R302.1?
Several tested assemblies work. The most field-common options are: 5/8-inch Type X gypsum board applied to the interior face of the exterior wall framing (with standard stucco or siding on the outside); a double-layer 1/2-inch gypsum approach using tested assemblies from the Gypsum Association fire-resistance design manual (GA-600); or proprietary assemblies from manufacturers like USG or National Gypsum that are listed in the GA or UL fire-resistance directory. The assembly designation (e.g., UL U305, GA WP-3210) must be cited on the construction documents, not just the rating. Your structural engineer or architect of record typically selects the assembly based on the framing type.
What counts as a projection under CRC R302.1?
Projections include eaves, roof overhangs, balconies, bay windows, and similar architectural features that extend beyond the exterior wall face. Projections cannot extend to within 2 feet of the property line. Gutters attached to eaves generally follow the eave measurement. Flush elements (siding, trim boards) that don’t extend the structure outward are not projections. The key measurement is from the property line to the outermost tip of the projection, measured horizontally.
Does R302.1 apply to lot lines between units in a duplex?
For two-unit dwellings on the same lot sharing a common wall, the party wall requirements under CRC R302.3 govern the separation, not R302.1. CRC R302.1 applies to exterior walls relative to the outer property line of the lot. So if you’re adding a duplex on a lot, each unit’s exterior walls that face the street or adjacent parcels need to comply with R302.1 based on their distance from those property lines.
My wall is exactly 5 feet from the property line — do I need a rated assembly?
No. The 1-hour rating requirement applies to walls with a fire-separation distance of less than 5 feet. A wall at exactly 5 feet does not require a rated assembly, though openings and projections in that wall still have restrictions in adjacent zones. Make sure you’re measuring to the wall face (the exterior surface of the framing or sheathing), not the property setback line from the zoning ordinance, which may differ.

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