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Got a CA WUI Code Ch. 5 correction?

WUI fire-resistant construction

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

The 2025 California Wildland-Urban Interface Code (Title 24, Part 7) Chapter 5 holds the wildfire construction rules that used to sit in CRC R337; the 2025 CRC R337 is now only a pointer to Part 7. It applies to new buildings in State Responsibility Areas, in High and Very High Fire Hazard Severity Zones, and in locally designated WUI areas. Section 504 requires a Class A roof, protected eaves, noncombustible gutters, compliant exterior walls and wall coverings, enclosed or protected underfloors, compliant deck walking surfaces, tempered multipane or rated glazing, compliant exterior doors and listed ember-resistant vents.

How to fix it

  1. Confirm the parcel is in a WUI area

    Before you revise anything, verify the parcel is in a State Responsibility Area, a High or Very High Fire Hazard Severity Zone, or a locally designated Wildland-Urban Interface Area. Use the CAL FIRE FHSZ viewer at osfm.fire.ca.gov to confirm. In a Local Responsibility Area, a High or Very High zone triggers the 2025 California Wildland-Urban Interface Code (Title 24, Part 7), which replaced CRC R337. Note the designation on your cover sheet so the plan-checker doesn't have to look it up.

  2. Specify a Class A roof assembly on the plans

    The roof must be a Class A assembly tested to ASTM E108 or UL 790. On your roof plan and specifications, note the manufacturer, product name, and Class A listing. Clay or concrete tile, metal and slate count as Class A without testing only on noncombustible decks; over a wood deck, cite the tested Class A assembly. Where tile or another profile leaves an airspace over a combustible deck, show a 72-lb mineral-surfaced cap sheet or a Class A-tested underlayment, bird stops at the eaves and mudded hip and ridge caps. The listing must appear on the plans, not just in a cut sheet addendum.

  3. Call out ignition-resistant exterior wall cladding with listing numbers

    Exterior wall coverings must be noncombustible, ignition-resistant material (IRM) labeled for exterior use, or exterior fire-retardant-treated wood, unless they are part of an approved wall assembly. Fiber-cement, stucco, brick, and stone qualify. If you're using fiber-cement, cite the specific product's noncombustible (ASTM E136) or ignition-resistant (30-minute extended ASTM E84 or ASTM E2768) test listing on the exterior elevation sheets and in the material schedule. A note saying "fiber-cement" without the listing number will be flagged. If using wood-based siding, it must be fire-retardant-treated wood labeled for exterior use or part of an approved wall assembly (for example over 5/8-inch Type X gypsum sheathing), not just fire-retardant paint.

  4. Show listed ember-resistant vents

    All attic, crawlspace, foundation, and under-floor vents must be ember-resistant: fully covered with State Fire Marshal-listed Wildfire Flame and Ember Resistant vents or WUI vents tested to ASTM E2886. Specify the listed vent product by name and model number. Mesh alone (1/16- to 1/8-inch, noncombustible and corrosion-resistant) is the rule only for vents on a sloped roof. Standard 1/4-inch foundation screen fails. Check the product against the State Fire Marshal listing before you specify it. Keep gable-end and dormer vents at least 10 feet from lot lines. Note the vent product on the floor plan or foundation plan.

  5. Detail enclosed or noncombustible eave and soffit construction

    Open rafter-tail eaves are allowed only if the exposed roof deck underside is noncombustible, ignition-resistant, exterior fire-retardant-treated wood or another listed option. Otherwise show enclosed soffits protected with noncombustible or ignition-resistant material: fiber-cement soffit panels, stucco on wire lath, or metal panels. On the exterior elevation and building sections, detail the soffit material and note its listing. Fascias are required at enclosed eaves and must be ignition-resistant, exterior fire-retardant-treated wood, 1-hour rated material or 2-inch nominal lumber. Don't leave eave construction to a generic note on the cover sheet.

  6. Update the window schedule with WUI-compliant glazing specs

    Windows in a WUI area must be multi-pane with at least one tempered pane, glass block, 20-minute fire-protection-rated glazing, or glazing meeting SFM Standard 12-7A-2. Add a column to your window schedule for "WUI compliance" and note the glazing spec for each opening. Skylights must also meet this requirement, and operable skylights need a noncombustible mesh screen with openings no larger than 1/8 inch. Single-pane windows and dual-pane units with no tempered pane will be flagged. If you're using a manufacturer's WUI-listed window assembly, note the listing number in the schedule.

  7. Note door ratings for all exterior and garage door openings

    Exterior doors must be noncombustible, solid-core wood at least 1-3/4 inches thick, rated for at least 20 minutes, or have an exterior surface tested to ASTM E2707 or SFM Standard 12-7A-1. Garage doors must limit gaps at the bottom, sides and top to 1/8 inch. Add a rating note or listing number to your door schedule for every exterior door opening. Glazed doors, including sliding glass doors, and windows within doors follow the glazing rules, so list their glazing spec in the schedule. Automatic garage door openers need battery backup.

  8. Address deck, balcony, and underfloor assembly materials

    The walking surface of decks, balconies, porches and stairs must be ignition-resistant, noncombustible, exterior fire-retardant-treated wood, or a material that passes the listed ASTM E2632/E2726 or SFM 12-7A-4 tests. Composite decking products may be acceptable if they carry a WUI listing. Note the deck material, thickness, and any treatment or listing on the plans. Show 6-inch metal flashing at deck-to-wall intersections. Underfloor areas of the building must be enclosed to grade with compliant exterior walls, or the exposed floor underside and supports must be 1-hour rated, heavy timber or exterior fire-retardant-treated wood.

  9. Add a WUI compliance summary block to the cover sheet

    Many plan-checkers want to see a dedicated compliance note block on the cover sheet listing the WUI measures for the project: zone designation, roof class and listing, wall cladding product and listing, vent type, eave detail reference, and door and window ratings. This is not required by code, but it speeds review because it gives the plan-checker one place to verify all WUI Code requirements instead of hunting across sheets. A one-page WUI checklist appended to the set also works well.

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Why you got flagged

Plan-checkers flag WUI construction when the construction documents for a parcel in a WUI area don’t call out compliant assemblies. The most common miss: the plan set shows fiber-cement or stucco cladding without saying how it complies. Reviewers need to see the product and its basis, noncombustible or ignition-resistant with the test listing. A generic note like "fiber-cement siding per manufacturer" does not pass.

Eave and soffit detailing is another consistent trigger. CWUIC 504.3 protects the underside of enclosed eaves and soffits, and 504.3.1 protects the exposed roof deck under open eaves, with noncombustible, ignition-resistant, exterior fire-retardant-treated or other listed materials. Sets that show open rafter tails over ordinary plywood or a wood soffit with no listing draw a correction.

Vent specifications get flagged when the plans show standard attic, crawlspace or foundation vents. CWUIC 504.10.1 requires vents listed by the State Fire Marshal as Wildfire Flame and Ember Resistant, or WUI vents tested to ASTM E2886. Standard louvers and 1/4-inch screen fail, and the listed product has to appear on the plans.

Window and door specs are often missing from the schedules. Windows and glazed doors need multipane glazing with at least one tempered pane or another listed option, and exterior doors must be noncombustible, solid-core wood at least 1-3/4 inches thick, 20-minute rated, or tested to ASTM E2707 or SFM 12-7A-1. When the schedule lists only size and manufacturer, the plan-checker has no basis to approve those assemblies.

Finally, notes that cite CRC R337 as the source of these rules send the reviewer to a 2025 section that only redirects to Part 7. Cite the CWUIC sections instead.

The official code

2025 California Wildland-Urban Interface Code (Title 24, Part 7), Chapter 5 (replaces CRC R337)

Read the source →

Common questions

What happened to CRC R337 in the 2025 code?
It became a pointer. The 2025 CRC R337 user note says the provisions for materials and construction methods for exterior wildfire exposure are now located in Part 7, the California Wildland-Urban Interface Code, which applies to buildings and structures in the WUI. The construction rules are in CWUIC Chapter 5, mainly Section 504. Cite those sections on your plans for permits under the 2025 code.
Does the WUI Code apply to ADUs?
Yes. CWUIC 101.3.1 applies to new buildings with residential occupancy and to new accessory buildings in a WUI area, so a new ADU must meet Chapter 5: Class A roofing, compliant walls and cladding, listed vents, and compliant windows, doors and decks. There is no ADU exemption. The existing main house doesn’t have to be upgraded, but additions and alterations must meet the rules for new construction (101.5).
What roof materials qualify as Class A in a WUI area?
Any roof assembly that achieves a Class A classification tested to ASTM E108 or UL 790. Brick, masonry or an exposed concrete deck, and metal, tile or slate on noncombustible decks, are treated as Class A without testing. Over a wood deck, use a tested Class A assembly and cite its listing. Fire-retardant-treated wood shakes are allowed only as part of a Class A assembly and must be listed by the State Fire Marshal.
Can I use any fiber-cement siding to meet the WUI wall covering requirement?
Only with documentation. Wall coverings must be noncombustible, ignition-resistant material labeled for exterior use, or exterior fire-retardant-treated wood. Noncombustible means passing ASTM E136; ignition-resistant means passing the 30-minute extended ASTM E84 or ASTM E2768 test, with a label showing the results. Pull the product’s data sheet and cite which basis it meets in your material schedule. Paints and coatings are not an approved method of protection.
Is 1/8-inch mesh enough for my vents?
Usually not anymore. CWUIC 504.10.1 requires ventilation openings to be fully covered with vents listed by the State Fire Marshal as Wildfire Flame and Ember Resistant, or WUI vents tested to ASTM E2886. Mesh between 1/16 and 1/8 inch, noncombustible and corrosion-resistant, is the rule for vents on a sloped roof, such as dormer vents. Name the listed vent product and model on the plans.
Does an existing home in a WUI area need to be upgraded?
Not as a whole. CWUIC 101.5 lets you add to or alter an existing building without bringing the whole building up to the code, as long as the addition or alteration meets the rules for new construction. For roofs, 507.1 requires a roof covering for new construction when the roof is replaced or 50 percent or more is replaced in a 12-month period, and any roof covering applied during an addition, alteration or repair must be at least Class A. Check local amendments, which can be stricter.
Are open rafter-tail eaves allowed in a WUI area?
Yes, if the exposed roof deck on the underside of the open eave is protected. CWUIC 504.3.1 accepts noncombustible material, ignition-resistant material, exterior fire-retardant-treated wood, 1-hour rated material, 5/8-inch Type X gypsum sheathing behind an exterior covering, or a listed exterior 1-hour assembly. Enclosed eaves have their own list in 504.3, including 2-inch nominal lumber. Show a section through the eave with the material called out.
Which parcels does the WUI Code cover?
CWUIC 101.3.1 covers all State Responsibility Area lands, Local Responsibility Area lands the State Fire Marshal identifies as High or Very High Fire Hazard Severity Zones, High and Very High zones designated by cities and other local agencies, and land locally designated as a Wildland-Urban Interface Area. Check the parcel against the state fire hazard maps and your local designation before you start, and note it on the cover sheet.

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