CWUIC · California Wildland-Urban Interface Code
How are underfloor enclosures and crawlspace vents required to resist ember intrusion?
Homes in the WUI must either enclose crawlspaces to the ground or protect exposed floor undersides (§ 504.6), and any crawlspace or underfloor vents must prevent ember and flame intrusion by using State Fire Marshal‑listed WUI vents tested to ASTM E2886 or by covering openings with noncombustible, corrosion‑resistant mesh sized between 1/16" and 1/8" (§§ 504.10.1–504.10.2).
Last reviewed: July 6, 2026
What the code requires — 2–4 sentences
Buildings must enclose underfloor areas to the ground or protect the underside of floor structures as allowed by exception, and any underfloor/crawlspace ventilation openings must be protected to resist ember and flame intrusion either by a tested/approved WUI vent or by a noncombustible mesh with tightly‑sized openings. The underfloor enclosure requirement is found at § 504.6 and the vent performance and prescriptive mesh options are at § 504.10.1 and § 504.10.2.
The single most important rule: cover crawlspace and underfloor ventilation openings either with an OSFM‑listed WUI (ember‑resistant) vent tested to ASTM E2886, or with noncombustible, corrosion‑resistant mesh having openings between 1/16" and 1/8" — and enclose underfloor areas to the ground unless the specific exception applies.
Requirements in detail
Underfloor enclosure (what § 504.6 requires)
- Enclose underfloor areas to the ground with exterior walls constructed in accordance with § 504.5. § 504.6 requires the enclosure to the ground unless the exception applies.
- Exception: a complete enclosure is not required where the underside of exposed floors and exposed structural members are protected as required for exterior 1‑hour fire‑resistance‑rated construction, heavy timber construction, or where fire‑retardant‑treated wood labeled for exterior use meeting CBC § 2303.2 is used.
Note: because § 504.6 ties the enclosure material to § 504.5, selecting enclosure materials means meeting the exterior wall material choices described in § 504.5 (noncombustible, ignition‑resistant, or approved fire‑retardant‑treated wood).
Crawlspace/underfloor ventilation (what § 504.10 requires)
- Vent openings for underfloor areas, foundations and crawl spaces must comply with either:
- the performance route using a Wildfire Flame and Ember Resistant (WUI) vent that is approved/listed by the California State Fire Marshal and tested to ASTM E2886 (§ 504.10.1); or
- the prescriptive mesh route (for off‑ridge/ridge/dormer style openings) where vent openings are covered with noncombustible, corrosion‑resistant mesh with openings no smaller than 1/16" (1.6 mm) and no larger than 1/8" (3.2 mm) (§ 504.10.2).
- Performance acceptance criteria (for ASTM E2886 / WUI vents) under § 504.10.1 are (paraphrased from the code):
- No flaming ignition of the cotton material during the Ember Intrusion Test.
- No flaming ignition during the Integrity Test portion of the Flame Intrusion Test.
- Maximum unexposed‑side temperature ≤ 662°F (350°C) during the test.
- Materials used for the mesh/prescriptive option must be noncombustible and corrosion‑resistant (for example, stainless or hot‑dip galvanized steel) per § 504.10.2.
- Locations: gable‑end and dormer vents have a minimum distance to lot lines; underfloor ventilation openings should be located “as close to grade as practical” per § 504.10.3.
Decision‑relevant numbers and values (quick table)
| Decision / value | Key dimension / threshold | Notes | Code Reference |
|---|---|---|---|
| WUI vent performance criteria | No flaming ignition (Ember Intrusion & Integrity tests); max unexposed temp ≤ 662°F (350°C) | Vents must be approved/listed by CA State Fire Marshal and tested to ASTM E2886 | § 504.10.1 |
| Mesh prescriptive option | Mesh opening min 1/16" (1.6 mm) — max 1/8" (3.2 mm) | Mesh and vent material must be noncombustible and corrosion‑resistant | § 504.10.2 |
| Underfloor enclosure | Enclose to grade with exterior walls per § 504.5 | Exception for properly protected underside or approved FRTW/heavy timber | § 504.6 (links to § 504.5) |
| Vent location | Underfloor vents located as close to grade as practical; gable/dormer vents ≥ 10 ft from lot lines | Placement can affect ember accumulation and accessibility for inspection/maintenance | § 504.10.3 |
Exceptions & special cases
- The underfloor enclosure exception permits leaving the underside exposed when the underside and structural members are protected by exterior 1‑hour fire‑resistance‑rated construction, heavy timber, or labeled fire‑retardant‑treated wood for exterior use (see § 504.6). That is the only exception in § 504.6.
- Vent compliance may be achieved either by the performance path (listed WUI vents tested to ASTM E2886) or the prescriptive mesh path — choose one; the code does not allow mixing performance certs with oversized mesh. See § 504.10.1 and § 504.10.2.
- The ASTM standard referenced for WUI vent testing is ASTM E2886; the CWUIC incorporates the ASTM test conditions and states the performance conditions (no flaming cotton, no flaming during integrity test, temperature limit). Jurisdictions and product labels will reference this test.
Common mistakes
- Installing a plastic or combustible screen (e.g., plastic insect screen) and assuming it meets the requirement — mesh must be noncombustible for the prescriptive route per § 504.10.2.
- Using mesh with openings larger than 1/8" (3.2 mm) or smaller than 1/16" (1.6 mm) when relying on the prescriptive mesh option. That makes the installation non‑compliant with § 504.10.2.
- Assuming any vent labeled “spark arrestor” or “bug screen” is acceptable — for the performance route you need a WUI vent listed/approved by the CA State Fire Marshal and tested to ASTM E2886 as required by § 504.10.1. Check the OSFM product listing.
- Forgetting the underfloor enclosure requirement: enclosing vented underfloor areas to the ground is required by § 504.6 unless the specific exception applies. Don’t treat vents as an alternative to enclosing underfloor areas.
Worked example — concrete scenario
Scenario: A homeowner has a 24" high crawlspace with four existing rectangular vents, each nominally 12" × 8" (net opening). The homeowner wants to upgrade to meet CWUIC requirements.
Option A — Performance path:
- Replace each existing vent with an OSFM‑listed WUI vent that is tested to ASTM E2886 and labeled as an approved WUI product. That satisfies § 504.10.1 (no further prescriptive mesh sizing needed). Confirm the product appears on the California State Fire Marshal WUI product list before installation.
Option B — Prescriptive mesh path:
- Leave the opening size (12"×8") but fully cover each opening with a noncombustible, corrosion‑resistant mesh whose openings are between 1/16" and 1/8". Example: install stainless‑steel hardware cloth with a mesh specification within that range and fasten it so it fully covers the vent opening and is secured against wind/impact. This complies with § 504.10.2 provided the mesh and fastenings are noncombustible and corrosion resistant.
Underfloor enclosure check:
- If the homeowner’s underfloor area is not already enclosed to the ground with exterior walls compliant with § 504.5, the structure must be enclosed per § 504.6 or the underside must be upgraded to one of the exception methods (e.g., exterior 1‑hour construction or labeled FRTW/heavy timber). If choosing the enclosure path, the wall materials must meet § 504.5 material requirements.
Related provisions (CWUIC)
- § 504.6 — Underfloor enclosure (primary enclosure requirement and exception).
- § 504.5 — Exterior wall material choices that § 504.6 references for enclosures.
- § 504.10.1 — Performance requirements for WUI (ember‑resistant) vents (ASTM E2886 criteria).
- § 504.10.2 — Prescriptive mesh requirements (mesh size, noncombustible, corrosion‑resistant).
- § 504.10.3 — Vent location notes (underfloor vent location / gable‑end/dormer distances).
- Referenced test standard: ASTM E2886 — test method for exterior vents (incorporated by reference for § 504.10.1).
Code references
Grounded in the retrieved California Wildland-Urban Interface Code — click a citation to read the verbatim passage:
CWUIC § 504.10.1 High relevance — show source text
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
SPECIAL BUILDING CONSTRUCTION REGULATIONS
lation, foundations and crawl spaces, or any other opening intended to permit ventilation, either in a horizontal or vertical surface, shall be in accordance with Section 504.10.1 or Section 504.10.2 to resist building ignition from the intrusion of burning embers and flame through the ventilation openings.
504.10.1 Performance requirements. Ventilation openings shall be fully covered with Wildfire Flame and Ember Resistant vents approved and listed by the California State Fire Marshal, or WUI vents, tested in accordance with ASTM E2886, to demonstrate compliance with all the following requirements:
- There shall be no flaming ignition of the cotton material during the Ember Intrusion Test.
- There shall be no flaming ignition during the Integrity Test portion of the Flame Intrusion Test.
- The maximum temperature of the unexposed side of the vent shall not exceed 662°F (350°C).
504.10.2 Off ridge and ridge vents. Vents that are installed on a sloped roof, such as dormer vents, shall comply with all of the following: 1. Vents shall be covered with a mesh where the dimensions of the mesh therein shall be a minimum of [1] / 16 inch (1.6 mm) and shall not exceed [1] / 8 inch (3.2 mm) in diameter.
2. The vent and mesh material shall be noncombustible.
3. The vent and mesh material shall be corrosion resistant.
504.10.3 Vent locations. Gable-end and dormer vents shall be located not less than 10 feet (3048 mm) from lot lines. Underfloor ventilation openings shall be located as close to grade as practical.
504.11 Accessory buildings and miscellaneous structures. Accessory buildings and miscellaneous structures that have the potential to pose a significant exterior fire exposure hazard during wildfires shall be constructed to conform to the ignition-resistance require- ments of this section.
504.11.1 Applicability . Sections 504.11.2 through 504.11.6 apply to buildings accessory to an applicable building on the same lot, and attached or detached miscellaneous structures that require a building permit, including but not limited to trellises, arbors, patio covers, gazebos and similar structures.
Exceptions: 1. Decks shall comply with the requirements of Section 504.7.3. 2. Awnings and canopies shall comply with the requirements of Section 3105 of the California Building Code.
504.11.2 Miscellaneous structures and accessory buildings within 3 feet. Miscellaneous structures that require a permit, and accessory buildings of any size, when separated from an applicable building on the same lot by a distance of less than 3 feet (914 mm), shall be constructed of noncombustible materials or ignition-resistant building materials as described in Section 503.2.4.
CWUIC § 504.9.3 High relevance — show source text
Gaps between doors and door openings_ shall be controlled by one or more of the following methods: 1. Weather-stripping products constructed of materials that which comply with both of the following: 1.1. The tensile strength of the material shall be tested in accordance with ASTM D638 before and after exposure to ASTM G155 for a period of 2,000 hours, and the maximum allowable difference in tensile strength values between exposed and nonexposed samples shall not exceed 10 percent. 1.2. When tested to UL 94, the materials shall have a flammability rating of V-2 or better. 2. Door overlaps onto jambs and headers. 3. Garage door jambs and headers covered with metal flashing.
504.9.3 Conditions of acceptance for ASTM E2707. The ASTM E2707 test shall be conducted on a minimum of three test specimens and meet the conditions of acceptance in Items 1 and 2. If any one of the three tests do not meet the conditions of acceptance, three additional tests shall be performed. All three additional tests must meet the conditions of acceptance. 1. Absence of flame penetration through the wall assembly at any time. 2. Absence of evidence of glowing combustion on the interior surface of the assembly at the end of the 70-minute test.
504.10 Vents. Where provided, ventilation openings for enclosed attics, gable ends, ridge ends, under eaves and cornices, enclosed eave soffit spaces, enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters, underfloor venti
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SPECIAL BUILDING CONSTRUCTION REGULATIONS
lation, foundations and crawl spaces, or any other opening intended to permit ventilation, either in a horizontal or vertical surface, shall be in accordance with Section 504.10.1 or Section 504.10.2 to resist building ignition from the intrusion of burning embers and flame through the ventilation openings.
504.10.1 Performance requirements. Ventilation openings shall be fully covered with Wildfire Flame and Ember Resistant vents approved and listed by the California State Fire Marshal, or WUI vents, tested in accordance with ASTM E2886, to demonstrate compliance with all the following requirements:
- There shall be no flaming ignition of the cotton material during the Ember Intrusion Test.
- There shall be no flaming ignition during the Integrity Test portion of the Flame Intrusion Test.
- The maximum temperature of the unexposed side of the vent shall not exceed 662°F (350°C).
504.10.2 Off ridge and ridge vents. Vents that are installed on a sloped roof, such as dormer vents, shall comply with all of the following: 1. Vents shall be covered with a mesh where the dimensions of the mesh therein shall be a minimum of [1] / 16 inch (1.6 mm) and shall not exceed [1] / 8 inch (3.2 mm) in diameter.
2. The vent and mesh material shall be noncombustible.
3. The vent and mesh material shall be corrosion resistant.
CWUIC § 1.1 High relevance — show source text
Openings in roof framing members shall conform to the requirements of Section R802.7. Required ventilation openings shall open directly to the outside air and shall be protected to prevent the entry of birds, rodents, snakes and other similar creatures.
R806.1.1 Vents in the Wildland Urban Interface (WUI). Where provided, ventilation openings for enclosed attics, gable ends, ridge ends, under eaves and cornices, enclosed eave soffit spaces, enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters, underfloor ventilation, foundations and crawl spaces, or any other opening intended to permit ventilation, either in a horizontal or vertical plane, shall be in accordance with Part 7, California Wildland-Urban Interface Code to resist building ignition from the intrusion of burning embers and flame through the ventilation openings. R806.2 Minimum vent area. The minimum net free ventilating area shall be [1] / 150 of the area of the vented space. Exception: The minimum net free ventilation area shall be [1] / 300 of the vented space provided both of the following conditions are met:
- In Climate Zones 6, 7 and 8, a Class I or II vapor retarder is installed on the warm-in-winter side of the ceiling.
- Not less than 40 percent and not more than 50 percent of the required ventilating area is provided by ventilators located in the upper portion of the attic or rafter space. Upper ventilators shall be located not more than 3 feet (914 mm) below the ridge or highest point of the space, measured vertically. The balance of the required ventilation provided shall be located in the bottom one-third of the attic space. Where the location of wall or roof framing members conflicts with the installation of upper ventilators, installation more than 3 feet (914 mm) below the ridge or highest point of the space shall be permitted.
R806.3 Vent and insulation clearance. Where eave or cornice vents are installed, blocking, bridging and insulation shall not block the free flow of air. Not less than a 1-inch (25 mm) space shall be provided between the insulation and the roof sheathing and at the location of the vent.
R806.4 Installation and weather protection. Ventilators shall be installed in accordance with manufacturer’s instructions. Installation of ventilators in roof systems shall be in accordance with the requirements of Section R903. Installation of ventilators in wall systems shall be in accordance with the requirements of Section R703.1.
R806.5 Unvented attic and unvented enclosed rafter assemblies. Unvented attics and unvented enclosed roof framing assemblies created by ceilings that are applied directly to the underside of the roof framing members and structural roof sheathing applied directly to the top of the roof framing members/rafters, shall be permitted where all the following conditions are met:
- The unvented attic space is completely within the building thermal envelope.
- Interior Class I vapor retarders are not installed on the ceiling side (attic floor) of the unvented attic assembly or on the ceiling side of the unvented enclosed roof framing assembly.
- Where wood shingles or shakes are used, a minimum [1] / 4 -inch (6.4 mm) vented airspace separates the shingles or shakes and the roofing underlayment above the structural sheathing.
CWUIC § 5-1 High relevance — show source text
2025 CALIFORNIA WILDLAND-URBAN INTERFACE CODE 5-1
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5 SPECIAL BUILDING CONSTRUCTION REGULATIONS
User notes:
About this chapter: Chapter 5 provides regulations that establish minimum standards for the location, design and construction of buildings and structures based on construction within a Fire Hazard Severity Zone or a Wildland-Urban Interface (WUI) Area.
The construction provisions of Chapter 5 are intended to supplement the requirements of the California Building Code and California Residential Code and address mitigation of the unique hazards posed to buildings by wildfire and to reduce the hazards of building fires spreading to wildland fuels. This is accomplished by requiring ignition-resistant construction materials. Construction features regulated include underfloor areas; roof coverings; eaves and soffits; gutters and downspouts; exterior walls, doors and windows; ventilation openings and accessory structures.
SECTION 501—GENERAL
501.1 Scope. Buildings and structures in a wildland-urban interface area shall be constructed in accordance with the California Build- ing Code and this code.
Exceptions:
- Group U accessory structures not exceeding 120 square feet (11 m [2] ) in floor area where located not less than 50 feet (15 240 mm) from applicable buildings.
- Group U agricultural buildings not less than 50 feet (15 240 mm) from applicable buildings.
501.2 Objective. The objective of this chapter is to establish minimum standards to locate, design and construct buildings and structures or portions thereof for the protection of life and property, to resist damage from wildfires, and to mitigate building and structure fires from spreading to wildland fuels.
501.3 Fire-resistance-rated construction. Where this code requires 1-hour fire-resistance-rated construction, the fire-resistance rating of building elements, components or assemblies shall be determined in accordance with the test procedures set forth in ASTM E119 or UL 263.
Exceptions:
- The fire-resistance rating of building elements, components or assemblies based on the prescriptive designs prescribed in Section 721 of the California Building Code .
- The fire-resistance rating of building elements, components or assemblies based on the calculation procedures in accordance with Section 722 of the California Building Code .
501.4 Noncombustibility tests. The tests indicated in Section 501.4.1 shall serve as criteria for acceptance of noncombustible building materials. The term “noncombustible” does not apply to the flame spread characteristics of interior finish or trim materials. A material shall not be classified as a noncombustible building construction material if it is subject to an increase in combustibility or flame spread beyond the limitations herein established through the effects of age, moisture or other atmospheric conditions.
501.4.1 Noncombustible materials. Materials required to be noncombustible shall be tested in accordance with ASTM E136 and pass the test. Alternately, materials required to be noncombustible shall be tested in accordance with ASTM E2652 using the accep- tance criteria prescribed by ASTM E136.
CWUIC § 504.7 High relevance — show source text
Ignition Source Control Appendix A, A104 Ignition-Resistant Building Material 202, 503 Ignition-Resistant Construction 504 Appendages 504.7 Detached accessory structures 504.11 Eaves 504.3
Exterior doors 504.9
Exterior walls 504.5
Gutters and downspouts 504.4 Protection of eaves 504.3 Roof covering 504.2 Underfloor protection 504.6 Vents 504.10
Windows 504.8 Ignition-Resistant Construction and Material 503 Inspection and Enforcement 109 Abatement 109.3.8 Authority to inspect 109.1.2 Citations 109.3.4
Enforcement 109.2 Placarding 109.3.5.3 Prosecution 109.3.6
Reinspections 109.1.3 Right of entry 104.4 Testing 109.1.4 Unsafe conditions 109.3.5
Key Box 403.1
Land Use Limitations Appendix A, A108 Legal Defense of the Code Official 104.8.1 Liability of the Code Official 104.8
Log Wall Construction 202 LP-Gas Installations 606
Maintenance 101.6 Maintenance of Defensible Space 604 Modified area 604.2 Responsibility 604.3 Trees 604.4 Mapping of Wildland-Urban Interface Area 302.2 Multilayered Glazed Panels 202
Noncombustible Roof Covering 202
Outbuilding 202
Peer Review 104.2.2.7, 202 Permits
Application 105.4 Approval 105.5 Expiration 105.8 Issuance 105.6 Preliminary inspection 105.4.1 Refusal to issue 105.6.1
Required 105.2 Retention 105.9
Revocation 105.10 Validity 105.7 Work exempt from permit 105.3 Placarding as Unsafe 109.3.5.3 Powers and Duties of the Code
Official 104.1
Practical Difficulties 104.2.3 Protection of Pumps and Water Storage Facilities Appendix A, A107
Rafter Tail 202 Referenced Standards 102.4, Chapter 7 Registered Design Professional 104.2.1.2, 104.2.2.6.2, 106.1, 202 Residential Unit 202 Retroactivity 101.4 Ridgelline 202 Road 202 Roof Covering 202 Roof Covering System 202 Roof Coverings, Replacement or Repair of 507
Roof Deck 202
Scope 101 Self-Defense Mechanism Appendix G Service Utilities 111
Slope 202 Spark Arrestors 605 Stop Work Order 113 Storage of Firewood and Combustible Materials 607 Strategic Ridgeline 202 Structure 202
Subdivision 202
CWUIC § 504.9 High relevance — show source text
504.9 Exterior doors. Exterior doors shall be constructed in accordance with any of the following:
1. Noncombustible construction .
2. Solid-core wood not less than 1 [3] / 4 inches thick (44 mm) . 3. The exterior door shall be constructed of solid core wood that complies with the following requirements: 3.1. Stiles and rails shall not be less than 1 3/8 inches (35 mm) thick. 3.2. Raised panels shall not be less than 11/4 inches (32 mm) thick, except for the exterior perimeter of the raised panel that shall be permitted to taper to a tongue not less than 3/8 inch (10 mm) thick. 4. Have a fire protection rating of not less than 20 minutes when tested according to NFPA 252, UL 10B or UL 10C . 5. The exterior surface or cladding meeting the performance requirements of Section 504.9.3 when tested in accordance with ASTM E2707.
6. The exterior surface or cladding shall be tested to meet the performance requirements of SFM Standard 12-7A-1.
Windows within doors and glazed doors shall be in accordance with Section 504.8.
504.9.1 Garage doors. Automatic garage door openers for vehicle doors serving a residential building shall be equipped with a battery backup function.
504.9.2 Garage door perimeter gap. Exterior garage doors shall resist the intrusion of embers by preventing gaps between doors and door openings, at the bottom, sides and tops of doors, from exceeding [1] / 8 inch (3.2 mm). Gaps between doors and door openings shall be controlled by one or more of the following methods: 1. Weather-stripping products constructed of materials that which comply with both of the following: 1.1. The tensile strength of the material shall be tested in accordance with ASTM D638 before and after exposure to ASTM G155 for a period of 2,000 hours, and the maximum allowable difference in tensile strength values between exposed and nonexposed samples shall not exceed 10 percent. 1.2. When tested to UL 94, the materials shall have a flammability rating of V-2 or better. 2. Door overlaps onto jambs and headers. 3. Garage door jambs and headers covered with metal flashing.
504.9.3 Conditions of acceptance for ASTM E2707. The ASTM E2707 test shall be conducted on a minimum of three test specimens and meet the conditions of acceptance in Items 1 and 2. If any one of the three tests do not meet the conditions of acceptance, three additional tests shall be performed. All three additional tests must meet the conditions of acceptance. 1. Absence of flame penetration through the wall assembly at any time. 2. Absence of evidence of glowing combustion on the interior surface of the assembly at the end of the 70-minute test.
504.10 Vents. Where provided, ventilation openings for enclosed attics, gable ends, ridge ends, under eaves and cornices, enclosed eave soffit spaces, enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters, underfloor venti
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CWUIC § 3.8 High relevance — show source text
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ROOF-CEILING CONSTRUCTION
R804.3.8 Roof tie-down. Roof assemblies shall be connected to walls below in accordance with Table R804.3. A continuous load path shall be provided to transfer uplift loads to the foundation.
SECTION R805—CEILING FINISHES
R805.1 Ceiling installation. Ceilings shall be installed in accordance with the requirements for interior wall finishes as provided in Sections R702.1 through R702.6.
SECTION R806—ROOF VENTILATION
Note: The IECC climate zones used by this section differ from those used by the California Energy Code to determine applicability of energy efficiency measures. Comparison of IECC and California Energy Code climate zones is shown in Table R702.7.3.
R806.1 Ventilation required. Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters shall have cross ventilation for each separate space by ventilating openings protected against the entrance of rain or snow. Ventilation openings shall have a least dimension of [1] / 16 inch (1.6 mm) minimum and [1] / 4 inch (6.4 mm) maximum. Ventilation openings having a least dimension larger than [1] / 4 inch (6.4 mm) shall be provided with corrosion-resistant wire cloth screening, hardware cloth, perforated vinyl or similar material with openings having a least dimension of [1] / 16 inch (1.6 mm) minimum and [1] / 4 inch (6.4 mm) maximum. Openings in roof framing members shall conform to the requirements of Section R802.7. Required ventilation openings shall open directly to the outside air and shall be protected to prevent the entry of birds, rodents, snakes and other similar creatures.
R806.1.1 Vents in the Wildland Urban Interface (WUI). Where provided, ventilation openings for enclosed attics, gable ends, ridge ends, under eaves and cornices, enclosed eave soffit spaces, enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters, underfloor ventilation, foundations and crawl spaces, or any other opening intended to permit ventilation, either in a horizontal or vertical plane, shall be in accordance with Part 7, California Wildland-Urban Interface Code to resist building ignition from the intrusion of burning embers and flame through the ventilation openings. R806.2 Minimum vent area. The minimum net free ventilating area shall be [1] / 150 of the area of the vented space. Exception: The minimum net free ventilation area shall be [1] / 300 of the vented space provided both of the following conditions are met:
- In Climate Zones 6, 7 and 8, a Class I or II vapor retarder is installed on the warm-in-winter side of the ceiling.
- Not less than 40 percent and not more than 50 percent of the required ventilating area is provided by ventilators located in the upper portion of the attic or rafter space. Upper ventilators shall be located not more than 3 feet (914 mm) below the ridge or highest point of the space, measured vertically. The balance of the required ventilation provided shall be located in the bottom one-third of the attic space.
CWUIC § 601.3 Medium relevance — show source text
Dead-end Road 202 Defensible Space 403, 601.3 Vegetation Plan 603 Definitions 202 Designation of Wildland-Urban Interface Area 302.1
Director 202 Driveway 202 Dumping Appendix A, A106 Dwelling 202
Exterior Covering 202
INDEX
Fees 109 Findings of Fact Appendix E Fire Chief 202 Fire Danger Rating System Appendix D Fire Flow Calculation Area Application 404.5 Defined 202 Fire Hazard Severity Zones 1.1.2, 202, 302.1, 302.2, Appendix D, Appendix H Fire Protection Plans 602
Fire Weather 202
Fire-Resistance-Rated Construction 501.3 Fire-Resistive Vegetation Appendix F Fire-Retardant-Treated Lumber or
Wood 503.2, 504.5, 504.7, 504.11 Flame Spread Index 202 Flashing 504.2.1, 504.5.1 Fuel Break 202, 609 Fuel Models Appendix D Fuel Modification 202
Fuel Modification Distance 603.2
Fuel Mosaic 202 Fuel-Loading 202
General Requirements Appendix A Green Belt 202
Greenways 202
Hammerhead/T 202 Hazardous Land Use 202
Hazardous Materials 202 Heavy Timber Construction 202
Ignition Source Control Appendix A, A104 Ignition-Resistant Building Material 202, 503 Ignition-Resistant Construction 504 Appendages 504.7 Detached accessory structures 504.11 Eaves 504.3
Exterior doors 504.9
Exterior walls 504.5
Gutters and downspouts 504.4 Protection of eaves 504.3 Roof covering 504.2 Underfloor protection 504.6 Vents 504.10
Windows 504.8 Ignition-Resistant Construction and Material 503 Inspection and Enforcement 109 Abatement 109.3.8 Authority to inspect 109.1.2 Citations 109.3.4
Enforcement 109.2 Placarding 109.3.5.3 Prosecution 109.3.6
Reinspections 109.1.3 Right of entry 104.4 Testing 109.1.4 Unsafe conditions 109.3.5
Key Box 403.1
Land Use Limitations Appendix A, A108 Legal Defense of the Code Official 104.8.1 Liability of the Code Official 104.8
Log Wall Construction 202 LP-Gas Installations 606
Maintenance 101.6 Maintenance of Defensible Space 604 Modified area 604.2 Responsibility 604.3 Trees 604.4 Mapping of Wildland-Urban Interface Area 302.2 Multilayered Glazed Panels 202
Noncombustible Roof Covering 202
Outbuilding 202
CWUIC § 0.060 Medium relevance — show source text
Class CC1: Plastic materials that have a burning extent of 1 inch (25 mm) or less where tested at a nominal thickness of 0.060 inch (1.5 mm), or in the thickness intended for use, in accordance with ASTM D635. Class CC2: Plastic materials that have a burning rate of 2 [1] / 2 inches per minute (1.06 mm/s) or less where tested at a nominal thickness of 0.060 inch (1.5 mm), or in the thickness intended for use, in accordance with ASTM D635.
[BS] 2606.5 Structural requirements. Light-transmitting plastic materials in their assembly shall be of adequate strength and durability to withstand the loads indicated in Chapter 16. Technical data shall be submitted to establish stresses, maximum unsupported spans and such other information for the various thicknesses and forms used as deemed necessary by the building official.
[BS] 2606.6 Fastening. Fastening shall be adequate to withstand the loads in Chapter 16. Proper allowance shall be made for expansion and contraction of light-transmitting plastic materials in accordance with accepted data on the coefficient of expansion of the material and other material in conjunction with which it is employed.
2606.7 Light-diffusing systems. Unless the building is equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1, light-diffusing systems shall not be installed in the following occupancies and locations:
Group A with an occupant load of 1,000 or more.
Theaters with a stage and proscenium opening and an occupant load of 700 or more.
Group I-2.
Group I-3.
Interior exit stairways and ramps and exit passageways.
2606.7.1 Support. Light-transmitting plastic diffusers shall be supported directly or indirectly from ceiling or roof construction by use of noncombustible hangers. Hangers shall be not less than No. 12 steel-wire gage (0.106 inch) galvanized wire or equivalent.
2606.7.2 Installation. Light-transmitting plastic diffusers shall comply with Chapter 8 unless the light-transmitting plastic diffusers will fall from the mountings before igniting, at an ambient temperature of not less than 200°F (111°C) below the ignition temperature of the panels. The panels shall remain in place at an ambient room temperature of 175°F (79°C) for a period of not less than 15 minutes. 2606.7.3 Size limitations. Individual panels or units shall not exceed 10 feet (3048 mm) in length nor 30 square feet (2.79 m [2] ) in area.
2606.7.4 Automatic sprinkler system. In buildings that are equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1, plastic light-diffusing systems shall be protected both above and below unless the sprinkler system has been specifically approved for installation only above the light-diffusing system, or the light-diffusing system is listed and labeled in accordance with UL 723S. Areas of light-diffusing systems that are protected in accordance with this section shall not be limited.
California Wildland-Urban Interface Code Medium relevance — show source text
12
gage nails with1/2″ heads, 6″ o.c., and
finished with casein paint.|See
Note 13|25 min||1||1,
12–14|1/3| |F/C-W-32|1/2″|Gypsum wallboard:1/2″ with 11/2″ No. 12
gage nails with1/2″ heads, 18″ o.c., with
asbestos paper applied with paperhang-
ers’ paste and secured with 11/2″ No. 15
gage nails with3/16″ heads and finished
with casein paint; combined nail spacing
6″ o.c.|See
Note 13|30 min||1||1,
12–14|1/2| |F/C-W-33|3/8″|Gypsum wallboard: two layers3/8″ secured
with 11/2″ No. 15 gage nails with3/8″ heads,
6″ o.c.|See
Note 13|30 min||1||1,
12–14|1/2| |F/C-W-34|1/2″|Perforated gypsum lath:3/8″, plastered
with 11/8″ No. 13 gage nails with5/16″ heads,
4″ o.c.;1/2″ sanded gypsum plaster.|See
Note 13|30 min||1||1,
12–14|1/2| |F/C-W-35|1/2″|Same as F/C-W-34, except with 11/8″ No. 13
gage nails with3/8″ heads, 4″ o.c.|See
Note 13|45 min||1||1,
12–14|3/4| |F/C-W-36|1/2″|Perforated gypsum lath:3/8″, nailed with
11/8″ No. 13 gage nails with3/8″ heads, 4″
o.c.; joints covered with 3″ strips of metal
lath with 13/4″ No. 12 gage nails with1/2″
heads, 5″ o.c.;1/2″ sanded gypsum plaster.|See
Note 13|1 hr||1||1,
12–14|1| |F/C-W-37|1/2″|Gypsum lath:3/8″ and lower layer of3/8″
perforated gypsum lath nailed with 13/4″
No. 13 gage nails with5/16″ heads, 4″ o.c.;
1/2″ sanded gypsum plaster or1/2″ Portland
cement plaster.|See
Note 13|45 min||1||1,
12–14|3/4| |F/C-W-38|3/4″|Metal lath: nailed with 11/4″ No. 11 gage
nails with3/8″ heads or 6d common nails
driven 1″ and bent over, 6″ o.c.;3/4″ sanded
gypsum plaster.|See
Note 13|45 min||1||1,
12–14|3/4| |F/C-W-39|3/4″|Same as F/C-W-38, except nailed with
11/2″ No.CWUIC § 3-3 Medium relevance — show source text
301 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-3
302 Wildland-Urban Interface Area Designations . . . . . .3-3
CHAPTER 4 WILDLAND-URBAN INTERFACE AREA
REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . 4-3
401 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-3
402 Applicability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-3
403 Access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-3
404 Water Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-7
CHAPTER 5 SPECIAL BUILDING CONSTRUCTION
REGULATIONS . . . . . . . . . . . . . . . . . . . . . . . . 5-3
501 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-3
502 Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-3
503 Ignition-Resistant Construction and Material. . . . . .5-3
504 Ignition-Resistant Construction. . . . . . . . . . . . . . . . . .5-4
505 Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-9
506 Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-9
507 Replacement or Repair of Roof Coverings. . . . . . . . .5-9
CHAPTER 6 FIRE PROTECTION REQUIREMENTS. . . . . . .6-3
601 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3
602 Fire Protection Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3
603 Vegetation Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4
604 Maintenance of Defensible Space . . . . . . . . . . . . . . . 6-5
CWUIC § 25.4 Medium relevance — show source text
@ 16″|—|32″
(287)|25″
(356)|36″
(263)|29″
(345)|21″
(428)|29″
(367)|20″
(484)|—|23″
(471)|—|—| |2 × 12 @ 12″|—|42″
(209)|31″
(263)|—|37″
(253)|27″
(317)|36″
(271)|27″
(358)|17″
(447)|31″
(348)|19″
(462)|—| |2 × 12 @ 8″|—|48″
(136)|45″
(169)|—|48″
(164)|38″
(206)|—|40″
(233)|26″
(294)|36″
(230)|29″
(304)|18″
(379)| |For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa.
a. Tabulated values are for clear-span roof supported solely by exterior bearing walls.
b. Spans are based on No. 2 Grade lumber of Douglas fir-larch, Southern pine, hem-fir and spruce-pine-fir for repetitive (three or more) members.
c. Ratio of backspan to cantilever span shall be not less than 3:1.
d. Connections capable of resisting the indicated uplift force shall be provided at the backspan support.
e. Uplift force is for a backspan to cantilever span ratio of 3:1. Tabulated uplift values are permitted to be reduced by multiplying by a factor equal to 3 divided by the actual
backspan ratio provided (3/backspan ratio).
f. See Section R301.2.2.6, Item 1, for additional limitations on cantilevered floor joists for detached one- and two-family dwellings in Seismic Design Category D0, D1 or D2 and
townhouses in Seismic Design Category C, D0, D1 or D2.
g. Linear interpolation shall be permitted for building widths and ground snow loads other than shown.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa.
a. Tabulated values are for clear-span roof supported solely by exterior bearing walls.
b. Spans are based on No. 2 Grade lumber of Douglas fir-larch, Southern pine, hem-fir and spruce-pine-fir for repetitive (three or more) members.
c. Ratio of backspan to cantilever span shall be not less than 3:1.
d. Connections capable of resisting the indicated uplift force shall be provided at the backspan support.
e. Uplift force is for a backspan to cantilever span ratio of 3:1. Tabulated uplift values are permitted to be reduced by multiplying by a factor equal to 3 divided by the actual
backspan ratio provided (3/backspan ratio).
f.CWUIC § 2.1 High relevance — show source text
This appendix is for informational purposes and is not intended for adoption.
User notes:
About this appendix: Appendix G is an information appendix that provides discussion of some elements of the proposed self-defense mechanisms and their role in enhancing the protection of exposed structures in the wildland-urban interface. The items provided in this appendix provide owners with suggestions for increasing the survivability of their structure. These items are not mandatory but can be considered by owners to increase the safety of structures.
SECTION G101—GENERAL
G101.1 Identification of the problem. The California Wildland-Urban Interface Code establishes a set of minimum standards to reduce the loss of property from wildfire. The purpose of these standards is to prevent wildfire spreading from vegetation to a building. Many homes were built in the wildland-urban interface areas prior to the implementation of provisions found in this code. As a result, many homes are lacking in their ability to survive an approaching wildfire. Many of the features discussed in this appendix are designed as low- cost features to retrofit existing homes. Additionally, recommendations are provided beyond the minimum code requirements for those homeowners who desire to increase the survivability of their home. This appendix chapter provides a discussion of some possible self- defense features to enhance survivability and harden the structure against an approaching wildfire.
G101.2 Structural survivability. The home-hardening features listed in Section G101.2.1 were developed as a best practices guide to assist homeowners in increasing the ignition resistance of their homes from wildfires. Some of these items are based on upgrading to more stringent building materials when that building component is due for replacement as part of its normal maintenance or lifespan, such as the roof covering.
G101.2.1 Home-hardening features. If homes are not already provided with the suggested protection, the following items should be considered in hardening a home against wildfire. 1. When it is time to replace your roof, replace it with roof assembly classified as Class A when tested in accordance with ASTM E108 or UL 790.
2. Block any spaces at the eaves between your roof covering and sheathing with noncombustible materials (bird stops). 3. Install a noncombustible rain gutter and downspouts. Install rain gutter covers to prevent the accumulation of leaves and debris in the gutters. 4. Cover your chimney and stovepipe outlets with a noncombustible, corrosion-resistant metal mesh screen (spark arrestor), with [3] / 8 -inch (9.5 mm) to [1] / 2 -inch (12.7 mm) openings. 5. Install ember- and flame-resistant vents. Choose products that have been approved and labeled as OSFM Wildland-Urban Interface (WUI) Products. A temporary solution is to cover the vent openings with a noncombustible and corrosion-resistant mesh with [1] / 16 -inch (1.6 mm) to [1] / 8 -inch (3.2 mm) openings. 6. Caulk and plug gaps greater than [1] / 8 inch (3.2 mm) around exposed rafters and blocking to prevent ember intrusion into the attic or other enclosed spaces. 7. _Inspect exterior siding for dry rot, gaps, cracks and warping.
CWUIC § 2.1 Medium relevance — show source text
G101.2.1 Home-hardening features. If homes are not already provided with the suggested protection, the following items should be considered in hardening a home against wildfire. 1. When it is time to replace your roof, replace it with roof assembly classified as Class A when tested in accordance with ASTM E108 or UL 790.
2. Block any spaces at the eaves between your roof covering and sheathing with noncombustible materials (bird stops). 3. Install a noncombustible rain gutter and downspouts. Install rain gutter covers to prevent the accumulation of leaves and debris in the gutters. 4. Cover your chimney and stovepipe outlets with a noncombustible, corrosion-resistant metal mesh screen (spark arrestor), with [3] / 8 -inch (9.5 mm) to [1] / 2 -inch (12.7 mm) openings. 5. Install ember- and flame-resistant vents. Choose products that have been approved and labeled as OSFM Wildland-Urban Interface (WUI) Products. A temporary solution is to cover the vent openings with a noncombustible and corrosion-resistant mesh with [1] / 16 -inch (1.6 mm) to [1] / 8 -inch (3.2 mm) openings. 6. Caulk and plug gaps greater than [1] / 8 inch (3.2 mm) around exposed rafters and blocking to prevent ember intrusion into the attic or other enclosed spaces. 7. Inspect exterior siding for dry rot, gaps, cracks and warping. Caulk or plug gaps greater than [1] / 8 inch (3.2 mm) in siding and replace any damaged boards, including those with dry rot. 8. Install weather stripping to fill gaps greater than [1] / 8 inch (3.2 mm) between garage doors and door frames to prevent ember intrusion. The weather stripping must be compliant with UL Standard 10C. 9. When it’s time to replace your windows, replace them with multipaned windows that have at least one pane of tempered glass. Choose products that have been approved and labeled as OSFM Wildland-Urban Interface (WUI) Products. 10. When it’s time to replace your siding or deck, use noncombustible, ignition-resistant, or other OSFM-approved Wildland- Urban Interface (WUI) Products. 11. Cover openings to operable skylights with noncombustible metal mesh screen with openings in the screen not to exceed [1] / 8 inch (3.2 mm). 12. Install a minimum 6-inch metal flashing, applied vertically on the exterior of the wall at the deck-to-wall intersection to protect the combustible siding material. 13. _Enclose openings beneath decks or cantilevered construction with one of the materials required in Section 504.5.
Frequently asked questions
Do crawlspace vents have to be covered?
Yes. Under CWUIC any ventilation openings for underfloor/crawlspace areas must comply with § 504.10 — either an OSFM‑listed WUI vent tested to ASTM E2886 (performance route) or a noncombustible corrosion‑resistant mesh with openings 1/16"–1/8" (prescriptive route).
Can I use plastic insect screening over crawlspace vents?
No. The prescriptive mesh option in § 504.10.2 requires noncombustible material; plastic/insect screening is combustible and does not meet the code.
If I install listed WUI vents, do I still need to enclose the underfloor area?
Possibly — § 504.6 requires underfloor areas to be enclosed to the ground with exterior walls per § 504.5, unless the underside is protected by the exception methods. Vents address ember entry at openings but do not by themselves eliminate the underfloor enclosure requirement in § 504.6.
How do I confirm a vent product complies with the performance route?
Use only products approved/listed by the California State Fire Marshal as WUI vents that were tested to ASTM E2886 and meet the acceptance criteria in § 504.10.1 (no flaming ignition in the Ember Intrusion Test and Integrity Test; max unexposed temp ≤ 662°F). Check the OSFM product listing and the manufacturer test documentation.
Are there maintenance requirements?
The code text emphasizes construction and materials; routine homeowner practice should include inspecting vents/mesh for corrosion, holes, or detached fasteners and replacing/repairing with compliant materials as needed so the vent protection remains effective (the CWUIC prescriptive mesh must remain noncombustible and intact). See § 504.10 for the compliance paths.
More in California Wildland-Urban Interface Code
- Administration and Definitions
- Board of Appeals, Administration & Enforcement (permits, code official duties, appeals process)
- Wildland‑Urban Interface Area Designation & Mapping
- Fire Service Access & Water Supply (fire apparatus roads, driveways, hydrants, draft sites, standby power)
- Wildland‑Urban Interface Area Requirements (access, water, premises identification, key boxes)
- Referenced Standards & Test Methods
- Special Building Construction Regulations (ignition‑resistant construction, roof/vent/assembly requirements)
- Appendices and Model Ordinances (vegetation plans, severity‑zone adoption, home‑hardening guidance)
- Fire Protection Requirements (fire protection plans, systems, safety element provisions)
- Referenced California Documents & Matrix (CCR/Title 14 & 19 cross‑references, statutory references)
- Vegetation Management & Defensible Space (vegetation plans, maintenance, fire‑smart characteristics)
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California Wildland-Urban Interface Code