CWUIC · California Wildland-Urban Interface Code

Ignition‑Resistant Building Materials and Testing

This hub summarizes CWUIC performance and test requirements for ignition‑resistant exterior materials, the primary tests referenced, and the key code sections (§503–§504).

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Last reviewed: July 6, 2026

Overview

This portion of the California Wildland‑Urban Interface Code (CWUIC) sets performance, testing and labeling requirements for exterior materials and assemblies used in Wildland‑Urban Interface areas to reduce the risk of ignition from wildfire exposures. The rules live in Chapter 5 (Special Building Construction) and are intended to supplement the California Building Code by specifying when materials must be noncombustible, fire‑retardant treated, or meet ignition‑resistant test criteria; see the chapter objective at §501.2 and the scope of ignition‑resistant construction in §503 and §504.

Key material requirements are in §503.2: materials must be noncombustible (ASTM E136), identified fire‑retardant‑treated wood, or “other ignition‑resistant” materials proven by testing (extended ASTM E84 / UL 723 for 30 minutes or ASTM E2768) with specified limits on flame spread and flame front. Weathering and post‑exposure performance (e.g., ASTM D2898, ASTM E1354 protocols for wood‑plastic composites) are expressly required so field exposure does not degrade performance.

Construction‑specific applications and test paths are addressed in §504 (roofs, eaves, gutters, exterior walls, decks and accessory structures). Where performance tests are specified, the code references the appropriate ASTM/UL methods and conditions of acceptance (for example, decking performance under ASTM E2632/E2726 and boxed‑in soffit acceptance under ASTM E2957), and requires labeling and qualification by approved agencies per the standards‑of‑quality provisions.

In this section

Code references

Grounded in the retrieved California Wildland-Urban Interface Code — click a citation to read the verbatim passage:

  • CWUIC § 504.3 High relevance — show source text

    504.3 Protection of enclosed eaves. The exposed underside of enclosed roof eaves and soffits shall be protected on the exposed underside by one or more of the following:

    1. Noncombustible materials.

    2. Ignition-resistant building materials. 3. Materials approved for not less than 1-hour fire-resistance-rated construction on the exterior side, as tested in accordance with ASTM E119 or UL 263.

    4. 2-inch (51 mm) nominal dimension lumber . 5. 1-inch (25 mm) nominal fire-retardant-treated lumber or [3] / 4 -inch (19.1 mm) nominal fire-retardant-treated plywood, identified for exterior use and complying with Section 2303.2 of the California Building Code . 6. Boxed-in roof eave soffit assemblies with an underside that meets the performance criteria in Section 504.7.2 when tested in accordance with the test procedures set forth in ASTM E2957. 7. Boxed-in roof eave soffit assemblies with an underside that meets the performance criteria in accordance with the test proce- dures set forth in SFM Standard 12-7A-3.

    Facias are required and shall be ignition-resistant building materials , fire-retardant-treated wood labeled for exterior use and complying with Section 2303.2 of the California Building Code, materials approved for not less than 1-hour fire-resistance-rated construction or 2-inch (51 mm) nominal dimension lumber.

    504.3.1 Protection of open eaves. The exposed roof deck on the underside of unenclosed roof eaves shall consist of one or more of the following:

    1. Noncombustible material.

    2. Ignition-resistant building material. 3. Fire-retardant-treated wood labeled for exterior use and complying with Section 2303.2 of the California Building Code. 4. Materials approved for not less than 1-hour fire-resistance-rated construction on the exterior side, as tested in accordance with ASTM E119 or UL 263.

    5. 2-inch (51 mm) nominal dimension lumber. 6. One layer of [5] / 8 -inch (16 mm) Type X gypsum sheathing applied behind an exterior covering on the underside of the roof deck.

    7. The exterior portion of a 1-hour fire-resistance-rated exterior assembly, as tested in accordance with ASTM E119 or UL 263, applied to the underside of the roof deck designed for exterior fire exposure, including assemblies using the gypsum panel and sheathing products listed in the Gypsum Association Fire Resistance Design Manual.

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    Facias, if provided, shall be of fire-retardant-treated wood labeled for exterior use and complying with Section 2303.2 of the Cali- fornia Building Code, ignition-resistant building materials, materials approved for not less than 1-hour fire-resistance-rated construction or 2-inch (51 mm) nominal dimension lumber.

  • CWUIC § 504.11.3 High relevance — show source text

    504.11.3 Accessory buildings greater than 120 square feet, located 3 feet or more but less than 50 feet. Accessory buildings that are greater than 120 square feet (11.15 m2) in size and separated from an applicable building on the same lot by a distance of 3 feet (914 mm) or more but less than 50 feet (15 240 mm) shall be constructed of noncombustible materials or of ignition-resistant building materials as described in Section 503.2.4.

    504.11.4 Accessory buildings 120 square feet or less, located 3 feet or more but less than 50 feet. Where required by the code offi- cial, accessory buildings 120 square feet (11.15 m2) or less and separated from an applicable building on the same lot by a distance of 3 feet (914 mm) or more but less than 50 feet (15 240 mm) shall be constructed of noncombustible materials or of ignition-resistant building materials as described in Section 503.2.4.

    504.11.5 Miscellaneous structures located 3 feet or more but less than 50 feet. Where required by the code official, miscellaneous structures that require a permit and are separated from an applicable building on the same lot by a distance of 3 feet (914 mm) or more but less than 50 feet (15 240 mm) shall be constructed of noncombustible materials or of ignition-resistant building materials as described in Section 503.2.4.

    504.11.6 Roof construction. Roof assemblies and roof coverings of accessory buildings required to be constructed entirely of noncombustible materials or of ignition-resistant building materials shall comply with Sections 504.2 and 504.2.1. Roofs shall have a roofing assembly installed in accordance with its listing and the manufacturer’s installation instructions. Roof assemblies in Fire Hazard Severity Zones shall comply with a Class A fire classification when tested in accordance with ASTM E108 or UL 790.

    SECTION 505— RESERVED

    SECTION 506— RESERVED

    SECTION 507—REPLACEMENT OR REPAIR OF ROOF COVERINGS

    507.1 General. The roof covering on buildings or structures in existence prior to the adoption of this code that are replaced or have 50 percent or more replaced in a 12-month period shall be replaced with a roof covering required for new construction in accordance with Sections 504.2 and 504.2.1. All portions of a roof covering applied during an addition, alteration or repair to an existing structure shall meet at least a Class A fire classification.

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    5-10 2025 CALIFORNIA WILDLAND-URBAN INTERFACE CODE

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    CALIFORNIA WILDLAND-URBAN INTERFACE CODE – MATRIX ADOPTION TABLE

    CHAPTER 6 – FIRE PROTECTION REQUIREMENTS

    (Matrix Adoption Tables are nonregulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)

  • CWUIC § 0.125 High relevance — show source text

    Exception: Materials having a structural base of noncombustible material as determined in accordance with ASTM E136, or with ASTM E2652 using the acceptance criteria prescribed by ASTM E136, and a surfacing of not more than 0.125 inch (3.18 mm) in thick- ness having a flame spread index not greater than 50 when tested in accordance with ASTM E84 or UL 723 shall be acceptable as noncombustible.

    SECTION 502— RESERVED

    SECTION 503—IGNITION-RESISTANT CONSTRUCTION AND MATERIAL

    503.1 General. Buildings and structures hereafter constructed, modified or relocated into or within wildland-urban interface areas shall meet the construction requirements in accordance with Chapter 5 . Materials required to be ignition-resistant building materials shall comply with the requirements of Section 503.2.

    Exceptions:

    1. New accessory buildings and miscellaneous structures complying with Section 504.11. 2. Additions to and remodels of buildings originally constructed prior to July 1, 2008. 3. Group C occupancy special buildings conforming to the limitations specified in Section 450.4.1 of the California Building Code.

    503.2 Ignition-resistant building material. Ignition-resistant building materials shall be designed for exterior use and weather expo- sure and shall comply with any one of the requirements in Section 503.2.1 through 503.2.4.3.3 .

    503.2.1 Noncombustible material. Noncombustible material shall comply with the requirements in Section 501.4 .

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    503.2.2 Fire-retardant-treated wood. Fire-retardant-treated wood shall be identified for exterior use and shall meet the requirements of Section 2303.2 of the California Building Code .

    503.2.3 Fire-retardant-treated wood roof coverings. Roof assemblies containing fire-retardant-treated wood shingles and shakes shall comply with the requirements of Section 1505.6 of the California Building Code and shall be classified as Class A roof assemblies as required in Section 1505.2 of the California Building Code .

    503.2.4 Other ignition-resistant building material. Material shall be tested on the front and back faces in accordance with the extended ASTM E84 or UL 723 test, for a total test period of 30 minutes, or with the ASTM E2768 test. The materials shall bear identification showing the fire test results. Panel products shall be tested with a ripped or cut longitudinal gap of [1] / 8 inch (3.2 mm). The materials, when tested in accordance with the test procedures set forth in ASTM E84 or UL 723 for a test period of 30 minutes, or with ASTM E2768, shall comply with Sections 503.2.4.1 through 503.2.4.3.

    Exception: Materials composed of a combustible core and a noncombustible exterior covering made from either aluminum at a minimum 0.019 inch (0.48 mm) thickness or corrosion-resistant steel at a minimum 0.0149 inch (0.38 mm) thickness shall not be required to be tested with a ripped or cut longitudinal gap.

  • CWUIC § 2303.2 High relevance — show source text

    1. Noncombustible material.

    2. Ignition-resistant building material. 3. Fire-retardant-treated wood labeled for exterior use and complying with Section 2303.2 of the California Building Code. 4. Materials approved for not less than 1-hour fire-resistance-rated construction on the exterior side, as tested in accordance with ASTM E119 or UL 263.

    5. 2-inch (51 mm) nominal dimension lumber. 6. One layer of [5] / 8 -inch (16 mm) Type X gypsum sheathing applied behind an exterior covering on the underside of the roof deck.

    7. The exterior portion of a 1-hour fire-resistance-rated exterior assembly, as tested in accordance with ASTM E119 or UL 263, applied to the underside of the roof deck designed for exterior fire exposure, including assemblies using the gypsum panel and sheathing products listed in the Gypsum Association Fire Resistance Design Manual.

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    Facias, if provided, shall be of fire-retardant-treated wood labeled for exterior use and complying with Section 2303.2 of the Cali- fornia Building Code, ignition-resistant building materials, materials approved for not less than 1-hour fire-resistance-rated construction or 2-inch (51 mm) nominal dimension lumber.

    504.4 Gutters and downspouts. Gutters and downspouts shall be constructed of noncombustible material. Gutters shall be provided with an approved means to prevent the accumulation of leaves and debris in the gutter.

    504.5 Exterior walls. Exterior walls of buildings or structures shall be constructed with one or more of the following methods, unless they are covered with an exterior wall covering complying with Sections 504.5.2 and 504.5.2.1:

    1. 1-hour fire-resistance-rated construction on the exterior side.

    2. Noncombustible materials.

    3. Heavy timber. Assembly of sawn lumber or glue-laminated wood with the smallest minimum nominal dimension of 4 inches (102 mm). Sawn or glue-laminated planks splined, tongue-and-grove or set close together and well spiked. 4. Log wall construction. 5. Wall assemblies that have been tested in accordance with the test procedures for a 10-minute direct flame contact exposure test set forth in ASTM E2707 with the conditions of acceptance shown in Section 504.9.3. 6. Wall assemblies that meet the performance criteria in accordance with the test procedures for a 10-minute direct flame contact exposure test set forth in SFM Standard 12-7A-1. 7. Wall assemblies suitable for exterior fire exposure containing one layer of [5] / 8 -inch (15.9 mm) Type X gypsum sheathing applied behind the exterior wall covering or cladding on the exterior side of the framing. 8. Wall assemblies suitable for exterior fire exposure with a 1-hour fire-resistance rating, rated from the exterior side, as tested in accordance with ASTM E119 or UL 263.

    9. Fire-retardant-treated wood labeled for exterior use and complying with Section 2303.2 of the California Building Code .

  • CWUIC § 504.7.3.2 High relevance — show source text

    504.7.3.2 Decking surfaces. The walking surface material of decks, porches, balconies and stairs shall be constructed with any of the following materials: 1. Material that complies with the performance requirements of Section 504.7.3.3 when tested in accordance with ASTM E2632 and ASTM E2726.

    2. Ignition-resistant building material that complies with the performance requirements of Section 503.2.4. 3. Material that complies with the performance requirements of both SFM Standard 12-7A-4 and Section 503.2.4. 4. Fire-retardant-treated wood labeled for exterior use and complying with Section 2303.2 of the California Building Code.

    5. Noncombustible material.

    6. Any material that complies with the performance requirements of SFM Standard 12-7A-4A and any attached exterior wall covering that is noncombustible or ignition-resistant building materials. Exception: Wall material shall be permitted to be of any material that otherwise complies with this chapter when the decking surface material complies with the performance requirements of ASTM E84 or UL 723 with a Class B flame spread index.

    7. Any material that complies with the performance requirements of Section 504.7.3.4 when tested in accordance with ASTM E2632 and any attached exterior wall covering that is noncombustible or ignition-resistant building materials. Exception: Wall material shall be permitted to be of any material that otherwise complies with this chapter when the decking surface material complies with the performance requirements of ASTM E84 or UL 723 with a Class B flame spread index.

    504.7.3.3 Performance requirements for Section 504.7.3.2, Item 1. Materials shall be tested in accordance with both ASTM E2632 and ASTM E2726 and comply with the conditions of acceptance in Sections 504.7.3.3.1 and 504.7.3.3.2. The material shall also be tested in accordance with ASTM E84 or UL 723 and comply with the performance requirements of Section 503.2.4.

    504.7.3.3.1 Conditions of acceptance for ASTM E2632. The ASTM E2632 test shall be conducted on a minimum of three test specimens and meet the conditions of acceptance in Items 1 through 3. If any one of the three tests does not meet the conditions of acceptance, three additional tests shall be performed. All three additional tests must meet the conditions of acceptance. 1. Peak heat release rate of less than or equal to 25 kW/ft2 (269 kW/m2).

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    SPECIAL BUILDING CONSTRUCTION REGULATIONS

    2. Absence of sustained flaming or glowing combustion of any kind at the conclusion of the 40-minute observation period. 3. Absence of falling particles that are still burning when reaching the burner or floor.

  • CWUIC § 503.1 High relevance — show source text

    1||||||| |502|RESERVED|N||||||||| |503|Ignition-resistant
    construction and
    material|Y||704A||||||| |503.1|General|Y||701A.3||||||| |503.2|Ignition-resistant
    building material|Y||707A.3 #2||||||| |503.2.1|Noncombustible
    material|Y||704A.4 #1||||||| |503.2.2|Fire-retardant-
    treated wood|Y||704A.4 #2||||||| |503.2.3|Fire-retardant-
    treated wood roof
    coverings|Y||705A.1||||||| |503.2.4|Other ignition-
    resistant building
    material|Y||704A.3||||||| |503.2.4.1|Flame spread|Y||704A.3 #1||||||| |503.2.4.2|Flame front|Y||704A.3 #2||||||| |503.2.4.3|Weathering|Y||703A.5.1||||||| |503.2.4.3.1|Evaluation require-
    ments for weathering|Y||703A.5.2
    703A.5.2.1||||||| |503.2.4.3.2|Wood-plastic
    composite materials|Y||703A.6|||||||

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    APPENDIX H—REFERENCED CALIFORNIA DOCUMENTS

    2025 CWUIC—continued Col2 Adopted
    Yes/No    		 IWUIC
    Section    		 CBC
    Section    		 CFC
    Section    		 Title 14,
    Division 1.5
    Section    		 Title 19,
    Division 1
    Section    		 Gov Code
    Section    		 PRC
    Section    		 HSC
    Section
    Section Title Title Title Title Title Title Title Title Title Title
    Chapter 5 Special building construction regulations Special building construction regulations Special building construction regulations Special building construction regulations Special building construction regulations Special building construction regulations Special building construction regulations Special building construction regulations Special building construction regulations Special building construction regulations
    503.2.4.3.3 Plastic lumber
    materials    		 Y 703A.6
    503.2.5 Surface treatment
    protection    		 Y 703A.5.3
    503.3 Standards of quality Y 703A.1
    503.3.1 Qualification by
    testing    		 Y 703A.2
    503.3.2 Approved agency Y 703A.3
    503.3.3 Labeling Y 703A.4
    _503.3.
  • CWUIC § 503.2.2 Medium relevance — show source text

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    SPECIAL BUILDING CONSTRUCTION REGULATIONS

    503.2.2 Fire-retardant-treated wood. Fire-retardant-treated wood shall be identified for exterior use and shall meet the requirements of Section 2303.2 of the California Building Code .

    503.2.3 Fire-retardant-treated wood roof coverings. Roof assemblies containing fire-retardant-treated wood shingles and shakes shall comply with the requirements of Section 1505.6 of the California Building Code and shall be classified as Class A roof assemblies as required in Section 1505.2 of the California Building Code .

    503.2.4 Other ignition-resistant building material. Material shall be tested on the front and back faces in accordance with the extended ASTM E84 or UL 723 test, for a total test period of 30 minutes, or with the ASTM E2768 test. The materials shall bear identification showing the fire test results. Panel products shall be tested with a ripped or cut longitudinal gap of [1] / 8 inch (3.2 mm). The materials, when tested in accordance with the test procedures set forth in ASTM E84 or UL 723 for a test period of 30 minutes, or with ASTM E2768, shall comply with Sections 503.2.4.1 through 503.2.4.3.

    Exception: Materials composed of a combustible core and a noncombustible exterior covering made from either aluminum at a minimum 0.019 inch (0.48 mm) thickness or corrosion-resistant steel at a minimum 0.0149 inch (0.38 mm) thickness shall not be required to be tested with a ripped or cut longitudinal gap.

    503.2.4.1 Flame spread. The material shall exhibit a flame spread index not exceeding 25.

    503.2.4.2 Flame front. The material shall exhibit a flame front that does not progress more than 10 feet 6 inches (3200 mm) beyond the centerline of the burner at any time during the test.

    503.2.4.3 Weathering. Ignition-resistant building materials shall maintain their performance in accordance with this section under conditions of use. The materials shall meet the performance requirements for weathering (including exposure to temperature, moisture and ultraviolet radiation) contained in Sections 503.2.4.3.1 through 503.2.4.3.3, as applicable to the materials and conditions of use.

    503.2.4.3.1 Evaluation requirements for weathering. Fire-retardant-treated wood, wood-plastic composite materials and plastic lumber materials shall be evaluated after weathering in accordance with Method A “Test Method for Accelerated Weathering of Fire-Retardant-Treated Wood for Fire Testing” in ASTM D2898.

    503.2.4.3.2 Wood-plastic composite materials. Wood-plastic composite materials shall also demonstrate acceptable fire performance after weathering by the following procedure: first testing in accordance with ASTM E1354 at an incident heat flux of 50 kW/m [2] in the horizontal orientation, then weathering in accordance with ASTM D7032 and then retesting in accordance with ASTM E1354 and exhibiting an increase of no more than 10 percent in peak rate of heat release when compared to the peak heat release rate of the nonweathered material.

  • CWUIC § 1.5 Medium relevance — show source text
    2025 CWUIC—continued Col2 Adopted
    Yes/No    		 IWUIC
    Section    		 CBC
    Section    		 CFC
    Section    		 Title 14,
    Division 1.5
    Section    		 Title 19,
    Division 1
    Section    		 Gov Code
    Section    		 PRC
    Section    		 HSC
    Section
    Section Title Title Title Title Title Title Title Title Title Title
    Chapter 5 Special building construction regulations Special building construction regulations Special building construction regulations Special building construction regulations Special building construction regulations Special building construction regulations Special building construction regulations Special building construction regulations Special building construction regulations Special building construction regulations
    503.2.4.3.3 Plastic lumber
    materials    		 Y 703A.6
    503.2.5 Surface treatment
    protection    		 Y 703A.5.3
    503.3 Standards of quality Y 703A.1
    503.3.1 Qualification by
    testing    		 Y 703A.2
    503.3.2 Approved agency Y 703A.3
    503.3.3 Labeling Y 703A.4
    503.3.4 Fire-retardant-
    treated wood shin-
    gles and shakes    		 Y 703A.5.2.2
    504 Ignition-resistant
    construction    		 Y 704A
    504.1 General Y 705A.1
    504.2 Roof assembly Y 705A.2
    1505.2
    504.2.1 Roof covering voids Y 705A.2
    504.2.1.1 Airspace under roof
    covering    		 Y 705A.2.1
    504.2.1.2 Roof underlayment Y 705A.2.2
    504.2.2 Roof valleys Y 705A.3
    504.3 Protection of
    enclosed eaves    		 Y 707A.6
    504.3.1 Protection of open
    eaves    		 Y 707A.5
    504.4 Gutters and
    downspouts    		 Y 705A.4
    504.5 Exterior walls Y 707A.4
    504.5.1 Flashing Y 504.5.1
    504.5.2 Exterior wall covering Y 707A.3
    704A.4 #3
    504.5.2.1 Extent of exterior wall
    covering    		 Y 707A.3.1
    504.6 Underfloor enclosure Y 707A.9
    504.
  • CWUIC § 504.7 Medium 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 § 501.2 Medium relevance — show source text

    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:

    1. The fire-resistance rating of building elements, components or assemblies based on the prescriptive designs prescribed in Section 721 of the California Building Code .
    2. 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.

    Exception: Materials having a structural base of noncombustible material as determined in accordance with ASTM E136, or with ASTM E2652 using the acceptance criteria prescribed by ASTM E136, and a surfacing of not more than 0.125 inch (3.18 mm) in thick- ness having a flame spread index not greater than 50 when tested in accordance with ASTM E84 or UL 723 shall be acceptable as noncombustible.

    SECTION 502— RESERVED

    SECTION 503—IGNITION-RESISTANT CONSTRUCTION AND MATERIAL

    503.1 General. Buildings and structures hereafter constructed, modified or relocated into or within wildland-urban interface areas shall meet the construction requirements in accordance with Chapter 5 . Materials required to be ignition-resistant building materials shall comply with the requirements of Section 503.2.

    Exceptions:

    1. New accessory buildings and miscellaneous structures complying with Section 504.11. 2. Additions to and remodels of buildings originally constructed prior to July 1, 2008. 3. Group C occupancy special buildings conforming to the limitations specified in Section 450.4.1 of the California Building Code.

    503.2 Ignition-resistant building material. Ignition-resistant building materials shall be designed for exterior use and weather expo- sure and shall comply with any one of the requirements in Section 503.2.1 through 503.2.4.3.3 .

    503.2.1 Noncombustible material. Noncombustible material shall comply with the requirements in Section 501.4 .

    2025 CALIFORNIA WILDLAND-URBAN INTERFACE CODE 5-3

  • CWUIC § 5.2.2 Medium relevance — show source text

    5.2.2_||||||| |504|Ignition-resistant
    construction|Y||704A||||||| |504.1|General|Y||705A.1||||||| |504.2|Roof assembly|Y||705A.2
    1505.2||||||| |504.2.1|Roof covering voids|Y||705A.2||||||| |504.2.1.1|Airspace under roof
    covering|Y||705A.2.1||||||| |504.2.1.2|Roof underlayment|Y||705A.2.2||||||| |504.2.2|Roof valleys|Y||705A.3||||||| |504.3|Protection of
    enclosed eaves|Y||707A.6||||||| |504.3.1|Protection of open
    eaves|Y||707A.5||||||| |504.4|Gutters and
    downspouts|Y||705A.4||||||| |504.5|Exterior walls|Y||707A.4||||||| |504.5.1|Flashing|Y|504.5.1|||||||| |504.5.2|Exterior wall covering|Y||707A.3
    704A.4 #3||||||| |504.5.2.1|Extent of exterior wall
    covering|Y||707A.3.1||||||| |504.6|Underfloor enclosure|Y||707A.9||||||| |504.7|Projections|Y||707A.8||||||| |504.7.1|Underside of
    projections|Y||707A.9,
    707A.10||||||| |504.7.2|Conditions of accep-
    tance for ASTM E2957|Y||707A.11||||||| |504.7.3|Decks|Y||709A.1||||||| |504.7.3.1|Flashing|Y||709A.1.1||||||| |504.7.3.2|Decking surfaces|Y||709A.3||||||| |504.7.3.3|Performance require-
    ments for Section
    504.7.3.2, Item 1|Y||709A.4.2||||||| |504.7.3.3.1|Conditions of accep-
    tance for ASTM E2632|Y||709A.4.1||||||| |504.7.3.3.2|Conditions of accep-
    tance for ASTM E2726|Y||709A.4.2||||||| |504.7.3.4|Performance require-
    ments for Section
    504.7.3.2, Item 7|Y||709A.5||||||| |504.8|Exterior glazing|Y||708A.2.1||||||| |504.8.1|Structural glass
    veneer|Y||708A.2.2||||||| |504.8.2|Operable skylights|Y||708A.2.3||||||| |504.9|Exterior doors|Y||708A.3|||||||

  • CWUIC § 3.2 Medium relevance — show source text

    3.2|||||||| |404.4|Hydrants|Y|||507.5|||||| |404.5|Adequate water
    supply|Y|||507.3|1275.02(b)||||| |404.6|Reserved|N||||||||| |404.7|Obstructions|Y|||507.5.4|||||| |404.8|Identification|Y||||1275.04(a)||||| |404.9|Testing and
    maintenance|Y|||507.5.2|||||| |404.10|Reliability|Y|||507.5.2|||||| |404.10.1|Objective|Y|404.10.1|||||||| |404.10.2|Clearance of fuel|Y|||4907.1|||||| |404.10.3|Standby power|Y|||507.5.2|||||| |Chapter 5|Special building construction regulations|Special building construction regulations|Special building construction regulations|Special building construction regulations|Special building construction regulations|Special building construction regulations|Special building construction regulations|Special building construction regulations|Special building construction regulations|Special building construction regulations| |501|General|Y||701A||||||| |501.1|Scope|Y||701A.3||||||| |501.2|Objective|Y||701A.2||||||| |501.3|Fire-resistance-rated
    construction|Y||703.2.1.5||||||| |501.4|Noncombustibility
    tests|Y||703.3||||||| |501.4.1|Noncombustible
    materials|Y||703.3.1||||||| |502|RESERVED|N||||||||| |503|Ignition-resistant
    construction and
    material|Y||704A||||||| |503.1|General|Y||701A.3||||||| |503.2|Ignition-resistant
    building material|Y||707A.3 #2||||||| |503.2.1|Noncombustible
    material|Y||704A.4 #1||||||| |503.2.2|Fire-retardant-
    treated wood|Y||704A.4 #2||||||| |503.2.3|Fire-retardant-
    treated wood roof
    coverings|Y||705A.1||||||| |503.2.4|Other ignition-
    resistant building
    material|Y||704A.3||||||| |503.2.4.1|Flame spread|Y||704A.3 #1||||||| |503.2.4.2|Flame front|Y||704A.3 #2||||||| |503.2.4.3|Weathering|Y||703A.5.1||||||| |503.2.4.3.1|Evaluation require-
    ments for weathering|Y||703A.5.2
    703A.5.2.1||||||| |503.2.4.3.2|Wood-plastic
    composite materials|Y||703A.6|||||||

    APPENDIX H-28 2025 CALIFORNIA WILDLAND-URBAN INTERFACE CODE

    on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

    APPENDIX H—REFERENCED CALIFORNIA DOCUMENTS

Frequently asked questions

How are materials qualified as “ignition‑resistant” under the CWUIC?

Materials qualify by meeting one of the §503.2 paths: noncombustible per ASTM E136, fire‑retardant‑treated wood identified for exterior use, or “other ignition‑resistant” materials shown by the prescribed tests (extended ASTM E84/UL 723 for 30 minutes or ASTM E2768) and the code’s flame‑spread/flame‑front limits. See §503.2.

Which test standards does the code reference for decking, projections and soffits?

Decking performance references ASTM E2632 and ASTM E2726 (with acceptance criteria) and also requires ASTM E84/UL 723 performance where noted; boxed‑in soffit/soffit assemblies reference ASTM E2957 for acceptance. See §504.7 and §504.7.3.3 for decking and §504.3/504.7.2 for soffits.

Must materials demonstrate retained performance after weathering?

Yes. §503.2.4.3 requires that ignition‑resistant materials maintain performance after exposure; specific weathering evaluation methods (e.g., ASTM D2898 for fire‑retardant‑treated wood, ASTM D7032 + ASTM E1354 retest for wood‑plastic composites) are called out.

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Related in the CWUIC

Roof Assembly, Coverings and Replacement Rules

Windows, Doors, Garage Doors and Accessory Structure Requirements

Eaves, Soffits, Gutters, Underfloor Protection and Vents

Special Building Construction Regulations (ignition‑resistant construction, roof/vent/assembly requirements)

California Wildland-Urban Interface Code