CBC · California Building Code

How are wood veneers and fire-retardant-treated wood treated for exterior-cladding limits?

In plain terms: plain wood cladding is limited by area and height under §1405 and wood veneers must meet thickness/backing rules in §1404.6. If the wood is properly fire‑retardant‑treated, labeled for exterior use and meets the testing and manufacturing requirements in §2303.2, the code allows much more exterior use (no small‑distance area cap and up to 60 ft height). Make sure you have the FRTW labels and manufacturer data showing compliance, and follow the veneer thickness, backing and projection rules.

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Last reviewed: July 5, 2026

What the code requires — 2-4 sentences

Wood veneers and fire‑retardant‑treated wood (FRTW) are treated differently from ordinary combustible exterior wall coverings in the CBC. Wood veneers must meet the minimum thickness, backing and projection rules in §1404.6. Combustible exterior wall coverings are limited by area and height in §1405, but FRTW that complies with §2303.2 is permitted broader use (no area limit at ≤5 ft fire separation and permitted up to 60 ft high) and must meet the FRTW testing, labeling and material‑spec requirements in §2303.2 .

Requirements in detail

Which sections control

  • Wood veneers: §1404.6 (thickness, height, backing, projection) .
  • Combustible exterior wall covering limits and ignition‑resistance testing: §1405 (area limits, height limits, NFPA 268 testing, exceptions) .
  • Fire‑retardant‑treated wood: §2303.2 (definition, testing protocols, labeling, “Exterior” designation and design‑value adjustments) .

Key decision‑relevant dimensions and values

Item Value / Limit Code Reference
Maximum height for most combustible exterior wall coverings 40 ft above grade plane §1405.1.1.2
Height allowance for FRTW exterior wall coverings Up to 60 ft above grade plane (regardless of fire separation) §1405.1.1.3
Area limit for combustible coverings on walls with fire separation ≤5 ft ≤10% of an exterior wall surface (Types I, II, III, IV‑HT) — wood/FRTW exception applies §1405.1.1.1 (and §1405.1.1)
Fire separation distance triggering sustained‑flame restriction 5 ft or less — special NFPA 268 sustained‑flame criterion applies §1405.1.1.1.1 and §1405.1.1.1
Wood veneer minimum thickness / acceptable panel types 1" nominal solid veneer, or 0.438" exterior hardboard siding, or 0.375" exterior‑type wood structural panels or particleboard §1404.6(see 1st paragraph)
Maximum projection for open/spaced wood veneers (no concealed spaces) 24 in. maximum projection from the building wall §1404.6(3)
Veneer backing requirement Attached to or furred from a noncombustible backing meeting other code provisions §1404.6(2)
FRTW definition (flame spread performance) Flame spread index ≤25 per ASTM E84/UL 723 (with additional time/progression criteria) or alternate ASTM E2768 criteria §2303.2 and §2303.2.1
FRTW labeling requirement for exterior use FRTW exposed to weather must be identified “Exterior” and labeled; label must include treatment, flame spread, treating manufacturer, etc. §2303.2.5 and §2303.2.7
Design values & manufacturer obligations for FRTW Manufacturer must publish adjusted design values/treatment adjustment factors (ASTM test methods specified) §2303.2.6 / §2303.2.6.1‑.3

How these provisions interact — plain explanation

  • If you intend to use wood veneer on the exterior of a Type I/II/III/IV building, you must meet the thickness/panel type, limit the veneer to the permitted height, attach it to a noncombustible backing, and keep projections ≤24 in. (§1404.6) .
  • Combustible exterior wall coverings are otherwise tightly limited by area and height (10% area when fire separation ≤5 ft; 40 ft height generally) (§1405) .
  • If the exterior combustible cladding is fire‑retardant‑treated wood that meets §2303.2 test, labeling and drying/design‑value requirements, the CBC relaxes the area limit at close separations and increases the allowable height to 60 ft; but the FRTW must be properly produced, labeled and for exterior exposure be identified as “Exterior” per §2303.2 and supporting subsections .

Exceptions & special cases

  • Wood and wood‑based products are excepted from the NFPA 268 ignition‑resistance test requirement in §1405.1.1.1 (the test requirement has specific exceptions including wood) — but other NFPA 268 sustained‑flame provisions still apply where explicitly stated (for example fire separation ≤5 ft requires no sustained flaming per NFPA 268) .
  • FRTW installed in exterior, damp or wet locations must be identified/labeled for “Exterior” use; that marking signals that the treatment resists increased flame spread after ASTM D2898 rain testing (§2303.2.7 and §2303.2.5) .
  • Wood veneers that are fire‑retardant‑treated follow both §1404.6 (thickness, backing, projection, height) and the FRTW provisions in §2303.2 (testing/labeling/design values) — note §1404.6 explicitly references FRTW height allowance when used .

Common mistakes

  • Treating untreated exterior wood as if it has the FRTW height/area privileges — only wood that meets §2303.2 tests and labeling is eligible for the expanded allowances in §1405.1.1.3 .
  • Overlooking the veneer thickness/backing rules: specifying thin decorative veneers or loose sidings that do not meet the §1404.6 thickness/panel types or that are not backed by noncombustible backing can make the installation noncompliant .
  • Forgetting projection and concealed‑space limitations for open or spaced veneers (24 in max; concealed spaces change the performance requirements) §1404.6(3) .
  • Using FRTW labeled only for interior use or not dried to required moisture contents: exterior exposure requires the “Exterior” designation and the moisture/drying and labeling criteria in §2303.2 .
  • Assuming NFPA 268 testing never applies to wood: §1405 requires NFPA 268 ignition‑resistance where combustible coverings are otherwise permitted, and it contains sustained‑flame criteria for separations ≤5 ft — even though wood is an exception for some test paths, the sustained‑flame provisions still affect installation near property lines or openings .

Worked example — concrete scenario

Scenario: A Type III office building has an exterior wall where the nearest property line or adjacent building face is 4.5 ft away (fire separation distance 4.5 ft). The architect proposes using 3,000 ft² of exterior wall cladding made of laminated wood veneer panels attached to a sheathing system.

Apply the code:

  • Because the fire separation distance is ≤5 ft, the general rule in §1405.1.1 requires combustible exterior coverings to be limited to 10% of the exterior wall surface area for Types I–IV‑HT, unless an exception applies .
  • If the proposed veneer is plain (untreated) wood, it would be subject to that 10% area cap and the NFPA 268 sustained‑flame limitation for ≤5 ft separations (§1405.1.1.1.1) .
  • If instead the veneer panels are factory fire‑retardant‑treated and properly labeled for “Exterior” use and meet §2303.2 testing and labeling requirements, then the special allowance applies: FRTW that complies with §2303.2 is not limited in wall surface area where fire separation distance is 5 ft or less and is permitted up to 60 ft in height (§1405.1.1.3 and §2303.2) — so the 3,000 ft² could be acceptable from the area‑limit standpoint, provided the FRTW documentation, labels and installation meet §2303.2 and the veneer also satisfies the §1404.6 thickness/backing/projection requirements .
  • Practically, the design team must: (1) obtain FRTW producer data showing ASTM E84/UL723 or ASTM E2768 compliance and that the product is labeled and identified “Exterior” per §2303.2; (2) ensure veneer thickness and backing match §1404.6; and (3) follow fastening and durability requirements for exterior FRTW (manufacturer instructions and applicable fastener requirements) before plan approval .

Related provisions

  • §1405.1.1.1 (NFPA 268 ignition/resistance and sustained‑flame criteria)
  • §1404.6 (Wood veneers — thickness, backing, projection, height)
  • §2303.2 (Fire‑retardant‑treated wood — definition, testing, labeling, design values)
  • §2303.2.6 (Design‑value adjustments and manufacturer publication requirements for FRTW)
  • §1405 Table 1405.1.1.1.2 (minimum fire separation distances and tolerable incident radiant heat flux)

Code references

Grounded in the retrieved California Building Code — click a citation to read the verbatim passage:

  • CBC § 2303.2 High relevance — show source text
    1. Combustible exterior wall coverings shall be limited to 40 feet (12 192 mm) in height above grade plane. Exceptions:
    2. Metal composite material (MCM) systems complying with Section 1406.
    3. Exterior insulation and finish systems (EIFS) complying with Section 1407.
    4. High-pressure decorative exterior-grade compact laminate (HPL) systems complying with Section 1408.
    5. Exterior wall coverings containing foam plastic insulation complying with Section 2603.
    6. Combustible exterior wall coverings constructed of fire-retardant-treated wood complying with Section 2303.2 for exterior installation shall not be limited in wall surface area where the fire separation distance is 5 feet (1524 mm) or less and shall be permitted up to 60 feet (18 288 mm) in height above grade plane regardless of the fire separation distance.
    7. Wood veneers shall comply with Section 1404.6.

    1405.1.1.1 Ignition resistance. Where permitted by Section 1405.1.1, combustible exterior wall coverings shall be tested in accordance with NFPA 268.

    Exceptions:

    1. Wood or wood-based products.
    2. Other combustible materials covered with an exterior weather covering, other than vinyl sidings, included in and complying with the thickness requirements of Table 1404.2.
    3. Aluminum having a minimum thickness of 0.019 inch (0.48 mm).

    1405.1.1.1.1 Fire separation 5 feet or less. Where installed on exterior walls having a fire separation distance of 5 feet (1524 mm) or less, combustible exterior wall coverings shall not exhibit sustained flaming as defined in NFPA 268.

    1405.1.1.1.2 Fire separation greater than 5 feet. For fire separation distances greater than 5 feet (1524 mm), any exterior wall covering shall be permitted that has been exposed to a reduced level of incident radiant heat flux in accordance with the NFPA 268 test method without exhibiting sustained flaming. The minimum fire separation distance required for the exterior wall covering shall be determined from Table 1405.1.1.1.2 based on the maximum tolerable level of incident radiant heat flux that does not cause sustained flaming of the exterior wall covering.

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    EXTERIOR WALLS

  • CBC § 504.5.1 High relevance — show source text

    Such material shall extend from the top of the foundation to the underside of the roof sheathing.

    504.5.1 Flashing. A minimum of 6 inches (152 mm) of metal flashing or noncombustible material applied vertically on the exterior of the wall shall be installed at the ground, decking and roof intersections.

    504.5.2 Exterior wall coverings. Exterior wall coverings shall comply with one or more of the following requirements:

    1. Noncombustible material.

    2. Ignition-resistant building material labeled for exterior use. 3. Fire-retardant-treated wood labeled for exterior use and complying with the requirements of Section 2303.2 of the Califor- nia Building Code. 4. Fire-retardant-treated wood shingles and shakes which have been qualified in accordance with Section 1505.6 of the Cali- fornia Building Code for use as “Class B” roof covering shall be an acceptable alternative wall covering material where installed over solid sheathing.

    Exception: Exterior wall coverings which are a component of an approved wall assembly complying with Section 504.5.

    504.5.2.1 Extent of exterior wall covering. Where provided, exterior wall coverings shall extend from the top of the foundation to the roof, and terminate at 2-inch (50.8 mm) nominal solid wood blocking between rafters at all roof overhangs, or in the case of enclosed eaves, terminate at the enclosure.

    504.6 Underfloor enclosure. Buildings or structures shall have underfloor areas enclosed to the ground with exterior walls in accordance with Section 504.5.

    Exception: Complete enclosure shall not be required where the underside of exposed floors and exposed structural columns, beams and supporting walls are protected as required for exterior 1-hour fire-resistance-rated construction or heavy timber construction or fire-retardant-treated wood. The fire-retardant-treated wood shall be labeled for exterior use and meet the requirements of Section 2303.2 of the California Building Code .

    504.7 Projections . Unenclosed accessory structures attached to buildings with habitable spaces and projections, other than decks, shall be heavy timber construction or constructed of one of the following:

    1. Noncombustible materials.

    2. Fire-retardant-treated wood identified for exterior use and meeting the requirements of Section 2303.2 of the California Building Code .

    3. Ignition-resistant building materials in accordance with Section 503.2. 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. One layer of [5] / 8 -inch (15.9 mm) Type X gypsum sheathing applied behind the exterior covering on the underside of the ceiling. 6. 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 ceiling assembly, including assemblies using the gypsum panel and sheathing products listed in the Gypsum Association Fire Resistance Design Manual. 7. The underside of a floor projection assembly that meets the performance criteria in Section 504.7.2 when tested in accordance with the test procedures set forth in ASTM E2957.

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  • CBC § 1404.19 High relevance — show source text

    [BS] 1404.19 Fiber-mat reinforced cementitious backer units. Fiber-mat reinforced cementitious backer units shall be permitted on exterior walls and shall meet the requirements of Section 1404.19.1.

    [BS] 1404.19.1 Installation. Installation of fiber-mat reinforced cementitious backer units used as an exterior substrate for the application of exterior finish materials shall be in accordance with backer unit manufacturer’s installation instructions. Panels shall be installed using corrosion-resistant fasteners. Finish materials shall be installed in accordance with approved finish material manufacturer’s instructions.

    SECTION 1405—COMBUSTIBLE MATERIALS ON THE EXTERIOR SIDE OF EXTERIOR WALLS

    1405.1 Combustible exterior wall coverings. Combustible exterior wall coverings shall comply with this section.

    Exception: Plastics complying with Chapter 26.

    1405.1.1 Types I, II, III and IV-HT construction. On buildings of Types I, II, III and IV-HT construction, exterior wall coverings shall be permitted to be constructed of combustible materials, complying with the following limitations:

    1. Combustible exterior wall coverings shall not exceed 10 percent of an exterior wall surface area where the fire separation distance is 5 feet (1524 mm) or less.
    2. Combustible exterior wall coverings shall be limited to 40 feet (12 192 mm) in height above grade plane. Exceptions:
    3. Metal composite material (MCM) systems complying with Section 1406.
    4. Exterior insulation and finish systems (EIFS) complying with Section 1407.
    5. High-pressure decorative exterior-grade compact laminate (HPL) systems complying with Section 1408.
    6. Exterior wall coverings containing foam plastic insulation complying with Section 2603.
    7. Combustible exterior wall coverings constructed of fire-retardant-treated wood complying with Section 2303.2 for exterior installation shall not be limited in wall surface area where the fire separation distance is 5 feet (1524 mm) or less and shall be permitted up to 60 feet (18 288 mm) in height above grade plane regardless of the fire separation distance.
    8. Wood veneers shall comply with Section 1404.6.

    1405.1.1.1 Ignition resistance. Where permitted by Section 1405.1.1, combustible exterior wall coverings shall be tested in accordance with NFPA 268.

    Exceptions:

    1. Wood or wood-based products.
    2. Other combustible materials covered with an exterior weather covering, other than vinyl sidings, included in and complying with the thickness requirements of Table 1404.2.
    3. Aluminum having a minimum thickness of 0.019 inch (0.48 mm).

    1405.1.1.1.1 Fire separation 5 feet or less. Where installed on exterior walls having a fire separation distance of 5 feet (1524 mm) or less, combustible exterior wall coverings shall not exhibit sustained flaming as defined in NFPA 268.

  • CBC § 2303.2.6.2. High relevance — show source text

    Adjustments to flexural, tension, compression and shear design values for fire-retardant-treated lumber shall be determined in accordance with Section 2303.2.6.2. Design values and treatment adjustment factors for fire-retardant-treated laminated veneer lumber shall be determined in accordance with Section 2303.2.6.3.

    2303.2.6.1 Fire-retardant-treated plywood. The effect of treatment and redrying after treatment, and any treatment-based effects due to exposure to high temperatures and high humidities on the flexure properties of fire-retardant-treated softwood plywood shall be determined in accordance with ASTM D5516. The test data developed in accordance with ASTM D5516 shall be used to develop treatment adjustment factors in accordance with ASTM D6305. Each manufacturer shall publish the allowable maximum loads and spans for service as floor and roof sheathing for its treatment based on the adjusted design values and taking into account the climatological location.

    2303.2.6.2 Fire-retardant-treated lumber. For each species of wood that is treated, the effect of treatment and redrying after treatment and any treatment-based effects due to exposure to high temperatures and high humidities on the allowable design properties of fire-retardant-treated lumber shall be determined in accordance with ASTM D5664. The test data developed in accordance with ASTM D5664 shall be used to develop treatment adjustment factors for use at or near room temperature and at elevated temperatures and humidity in accordance with ASTM D6841. Each manufacturer shall publish the treatment adjustment factors for service at maximum temperatures of not less than 80°F (27°C) and for roof framing. The roof framing modification factors shall take into consideration the climatological location.

    2303.2.6.3 Fire-retardant-treated laminated veneer lumber. The effect of treatment and redrying after treatment and any treatment-based effects due to exposure to high temperatures and high humidities on the allowable design properties of fireretardant-treated laminated veneer lumber shall be determined in accordance with ASTM D8223. Each manufacturer shall publish reference design values and treatment-based design value adjustment factors in accordance with ASTM D8223, taking into account the climatological location.

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    WOOD

    [BF] 2303.2.7 Exposure to weather, damp or wet locations. Where fire-retardant-treated wood is exposed to weather, or damp or wet locations, it shall be identified as “Exterior” to indicate there is no increase in the listed flame spread index as defined in Section 2303.2 when subjected to ASTM D2898.

    2303.2.8 Interior applications. Interior fire-retardant-treated wood shall have moisture content of not over 28 percent when tested in accordance with ASTM D3201 procedures at 92-percent relative humidity. Interior fire-retardant-treated wood shall be tested in accordance with Section 2303.2.6.1 or 2303.2.6.2. Interior fire-retardant-treated wood designated as Type A shall be tested in accordance with the provisions of this section.

  • CBC § 50.8 High relevance — show source text
    1. Wood floor assemblies using dimension lumber or structural composite lumber equal to or greater than 2-inch by 10-inch (50.8 mm by 254 mm) nominal dimension, or other approved floor assemblies demonstrating equivalent fire performance.
    2. Wood floor assemblies less than 600 square feet (55.7 m [2] ) within detached accessory structures with no habitable space above them.

    R302.14 Combustible insulation clearance. Combustible insulation shall be separated not less than 3 inches (76 mm) from recessed luminaires, fan motors and other heat-producing devices.

    Exception: Where heat-producing devices are listed for lesser clearances, combustible insulation complying with the listing requirements shall be separated in accordance with the conditions stipulated in the listing.

    Recessed luminaires installed in the building thermal envelope shall meet the requirements of the California Energy Code .

    R302.15 Fire-retardant-treated wood. Fire-retardant-treated wood (FRTW) is any wood product that, when impregnated with chemicals by a pressure process or other means during manufacture, shall have, when tested in accordance with ASTM E84 or UL 723, a listed flame spread index of 25 or less. In addition, the ASTM E84 or UL 723 test shall be continued for an additional 20-minute period and the flame front shall not progress more than 10.5 feet (3200 mm) beyond the center line of the burners at any time during the test.

    R302.15.1 Pressure process. For wood products impregnated with chemicals by a pressure process, the process shall be performed in closed vessels under pressures not less than 50 pounds per square inch gauge (psig) (344.7 kPa).

    R302.15.2 Other means during manufacture. For wood products impregnated with chemicals by other means during manufacture, the treatment shall be an integral part of the manufacturing process of the wood product. The treatment shall provide permanent protection to all surfaces of the wood product. The use of paints, coating, stains or other surface treatments is not an approved method of protection as required by this section.

    R302.15.3 Testing. For fire-retardant-treated wood products, the front and back faces of the wood product shall be tested in accordance with and produce the results required in Section R302.15.

    R302.15.3.1 Fire testing of fire-retardant-treated wood structural panels. Fire-retardant-treated wood structural panels shall be tested with a ripped or cut longitudinal gap of [1] / 8 inch (3.2 mm).

    302.15.4 Labeling. In addition to the labels required by Section R802.1.1 for sawn lumber and Section R803.2.1 for wood structural panels, each piece of fire-retardant-treated lumber and fire-retardant-treated wood structural panel shall be labeled. The label shall contain:

    1. The identification mark of an approved agency in accordance with Section 1703.5 of the California Building Code.

    2. Identification of the treating manufacturer.

    3. The name of the fire-retardant treatment.

    4. The species of wood treated.

    5. Flame spread index and smoke-developed index.

    6. Method of drying after treatment.

    7. Conformance to applicable standards in accordance with Sections R302.15.5 through R302.15.10.

    8. For FRTW exposed to weather, or a damp or wet location, the words “No increase in the listed classification when subjected to the Standard Rain Test” (ASTM D2898).

  • CBC § 25.4 High relevance — show source text

    In a horizontal orientation, the indicated 8-inch and 12-inch fastener spacing in furring shall be achieved by use of two fasteners into studs at 16 inches
    and 24 inches on center, respectively.|For SI: 1 inch = 25.4 mm, 1 pound per square foot (psf) = 0.0479 kPa, 1 pound per square inch = 0.00689 MPa.
    DR = Design Required, o.c. = on center.
    a. Wood framing and furring shall be spruce-pine-fir or any wood species with a specific gravity of 0.42 or greater in accordance with ANSI/AWC NDS.
    b. Nail fasteners shall comply with ASTM F1667, except nail length shall be permitted to exceed ASTM F1667 standard lengths.
    c. The thickness of wood structural panels complying with the specific gravity requirements of Note a shall be permitted to be included in satisfying the minimum required
    penetration into framing.
    d. Where the required cladding fastener penetration into wood material exceeds3/4 inch and is not more than 11/2 inches, a minimum 2-inch nominal wood furring or an
    approved design shall be used.
    e. Foam sheathing shall have a minimum compressive strength of 15 psi in accordance with ASTM C578 or ASTM C1289.
    f. Furring shall be spaced not greater than 24 inches on center in a vertical or horizontal orientation. In a vertical orientation, furring shall be located over wall studs and attached with
    the required fastener spacing. In a horizontal orientation, the indicated 8-inch and 12-inch fastener spacing in furring shall be achieved by use of two fasteners into studs at 16 inches
    and 24 inches on center, respectively.|

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    EXTERIOR WALLS

    1404.6 Wood veneers. Wood veneers on exterior walls of buildings of Types I, II, III and IV construction shall be not less than 1 inch (25 mm) nominal thickness, 0.438-inch (11.1 mm) exterior hardboard siding or 0.375-inch (9.5 mm) exterior-type wood structural panels or particleboard and shall conform to the following:

    1. The veneer shall not exceed 40 feet (12 190 mm) in height above grade. Where fire-retardant-treated wood is used, the height shall not exceed 60 feet (18 290 mm) in height above grade.

    2. The veneer is attached to or furred from a noncombustible backing that is fire-resistance rated as required by other provisions of this code.

    3. Where open or spaced wood veneers (without concealed spaces) are used, they shall not project more than 24 inches (610 mm) from the building wall.

    [BS] 1404.7 Anchored masonry veneer. Anchored masonry veneer shall comply with the provisions of Sections 1404.7 through 1404.10 and Sections 13.1 and 13.2 of TMS 402.

    [BS] 1404.7.1 Tolerances. Anchored masonry veneers in accordance with Chapter 14 are not required to meet the tolerances in Article 3.3 G.1 of TMS 602.

    **[BS] 1404.8 Stone veneer.

  • CBC § 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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    SPECIAL BUILDING CONSTRUCTION REGULATIONS

    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 .

  • CBC § 603.1.1 High relevance — show source text

    ** Combustible materials shall be permitted in buildings of Type I or II construction in the following applications and in accordance with Sections 603.1.1 through 603.1.3:

    1. Fire-retardant-treated wood complying with Section 2303.2 shall be permitted in: 1.1. Nonbearing partitions where the required fire-resistance rating is 2 hours or less except in shaft enclosures within Group I-2 occupancies and ambulatory care facilities. 1.2. Nonbearing exterior walls where fire-resistance-rated construction is not required. 1.3. Roof construction, including girders, trusses, framing and decking. Exceptions:

    2. In buildings of Type IA construction exceeding two stories above grade plane, fire-retardant-treated wood is not permitted in roof construction where the vertical distance from the upper floor to the roof is less than 20 feet (6096 mm).

    3. Group I-2, roof construction containing fire-retardant-treated wood shall be covered by not less than a Class A roof covering or roof assembly, and the roof assembly shall have a fire-resistance rating where required by the construction type. 1.4. Balconies, porches, decks and exterior stairways not used as required exits on buildings three stories or less above grade plane.

    4. Thermal and acoustical insulation, other than foam plastics, having a flame spread index of not more than 25. Exceptions:

    5. Insulation placed between two layers of noncombustible materials without an intervening airspace shall be allowed to have a flame spread index of not more than 100.

    6. Insulation installed between a finished floor and solid decking without intervening airspace shall be allowed to have a flame spread index of not more than 200.

    7. Foam plastics in accordance with Chapter 26.

    8. Roof coverings that have an A, B or C classification.

    9. Interior floor finish and floor covering materials installed in accordance with Section 804.

    10. Millwork such as doors, door frames, window sashes and frames.

    11. Interior wall and ceiling finishes installed in accordance with Section 803.

    12. Trim installed in accordance with Section 806.6.

    13. Where not installed greater than 15 feet (4572 mm) above grade, show windows, nailing or furring strips and wooden bulkheads below show windows, including their frames, aprons and show cases.

    14. Finish flooring installed in accordance with Section 805.

    15. Partitions dividing portions of stores, offices or similar places occupied by one tenant only and that do not establish a corridor serving an occupant load of 30 or more shall be permitted to be constructed of fire-retardant-treated wood complying with Section 2303.2, 1-hour fire-resistance-rated construction or of wood panels or similar light construction up to 6 feet (1829 mm) in height.

    16. Stages and platforms constructed in accordance with Sections 410.2 and 410.3, respectively.

    17. Combustible exterior wall coverings, balconies and similar projections and bay or oriel windows in accordance with Chapter 14 and Section 705.2.3.1.

    18. Blocking such as for handrails, millwork, cabinets and window and door frames.

    19. Light-transmitting plastics as permitted by Chapter 26.

    20. Mastics and caulking materials applied to provide flexible seals between components of exterior wall construction.

    21. Exterior plastic veneer installed in accordance with Section 2605.2.

    22. Nailing or furring strips as permitted by Section 803.15.

  • CBC § 2303.2.6.3 High relevance — show source text

    Each manufacturer shall publish the treatment adjustment factors for service at maximum temperatures of not less than 80°F (27°C) and for roof framing. The roof framing modification factors shall take into consideration the climatological location.

    2303.2.6.3 Fire-retardant-treated laminated veneer lumber. The effect of treatment and redrying after treatment and any treatment-based effects due to exposure to high temperatures and high humidities on the allowable design properties of fireretardant-treated laminated veneer lumber shall be determined in accordance with ASTM D8223. Each manufacturer shall publish reference design values and treatment-based design value adjustment factors in accordance with ASTM D8223, taking into account the climatological location.

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    WOOD

    [BF] 2303.2.7 Exposure to weather, damp or wet locations. Where fire-retardant-treated wood is exposed to weather, or damp or wet locations, it shall be identified as “Exterior” to indicate there is no increase in the listed flame spread index as defined in Section 2303.2 when subjected to ASTM D2898.

    2303.2.8 Interior applications. Interior fire-retardant-treated wood shall have moisture content of not over 28 percent when tested in accordance with ASTM D3201 procedures at 92-percent relative humidity. Interior fire-retardant-treated wood shall be tested in accordance with Section 2303.2.6.1 or 2303.2.6.2. Interior fire-retardant-treated wood designated as Type A shall be tested in accordance with the provisions of this section.

    2303.2.9 Moisture content. Fire-retardant-treated wood shall be dried to a moisture content of 19 percent or less for lumber and 15 percent or less for wood structural panels before use. For wood kiln-dried after treatment (KDAT), the kiln temperatures shall not exceed those used in kiln drying the lumber and plywood submitted for the tests described in Section 2303.2.6.1 for plywood and 2303.2.6.2 for lumber.

    2303.2.10 Types I and II construction applications. See Section 603.1 for limitations on the use of fire-retardant-treated wood in buildings of Type I or II construction.

    2303.3 Hardwood and plywood. Hardwood and decorative plywood shall be manufactured and identified as required in HPVA HP-1.

    2303.4 Trusses. Wood trusses shall comply with Sections 2303.4.1 through 2303.4.7.

    2303.4.1 Design. Wood trusses shall be designed in accordance with the provisions of this code and accepted engineering practice. Members are permitted to be joined by nails, glue, bolts, timber connectors, metal connector plates or other approved framing devices.

  • CBC § 602.4.3.2 High relevance — show source text

    The ASTM E1354 test shall be conducted on specimens at the thickness intended for use, in the horizontal orientation and at an incident radiant heat flux of 50 kW/m [2] .

    602.4.3.2 Interior protection. Mass timber elements are permitted to be unprotected.

    602.4.3.3 Floors. Floor finishes in accordance with Section 804 shall be permitted on top of the floor construction.

    602.4.3.4 Roof coverings. Roof coverings in accordance with Chapter 15 shall be permitted on the outside surface of the roof assembly.

    602.4.3.5 Concealed spaces. Concealed spaces shall not contain combustibles other than electrical, mechanical, fire protection, or plumbing materials and equipment permitted in plenums in accordance with the California Mechanical Code, and shall comply with all applicable provisions of Section 718. Combustible construction forming concealed spaces shall be protected with noncombustible protection with a minimum assigned time of 40 minutes, as specified in Table 722.7.1(1).

    602.4.3.6 Shafts. Shafts shall be permitted in accordance with Sections 713 and 718. Shafts and elevator hoistway and interior exit stairway enclosures shall be protected with noncombustible protection with a minimum assigned time of 40 minutes, as specified in Table 722.7.1(1), on both the inside of the shaft and the outside of the shaft.

    602.4.4 Type IV-HT. Type IV-HT (Heavy Timber) construction is that type of construction in which the exterior walls are of noncombustible materials and the interior building elements are of solid wood, laminated heavy timber or structural composite lumber (SCL), without concealed spaces or with concealed spaces complying with Section 602.4.4.3. The minimum dimensions for permitted materials including solid timber, glued-laminated timber, SCL and cross-laminated timber (CLT) and the details of Type IV construction shall comply with the provisions of this section and Section 2304.11. Exterior walls complying with Section 602.4.4.1 or 602.4.4.2 shall be permitted. Interior walls and partitions not less than 1-hour fire-resistance rated or heavy timber conforming with Section 2304.11.2.2 shall be permitted.

    602.4.4.1 Fire-retardant-treated wood in exterior walls. Fire-retardant-treated wood framing and sheathing complying with Section 2303.2 shall be permitted within exterior wall assemblies with a 2-hour rating or less.

    602.4.4.2 Cross-laminated timber in exterior walls. Cross-laminated timber (CLT) not less than 4 inches (102 mm) in thickness complying with Section 2303.1.4 shall be permitted within exterior wall assemblies with a 2-hour rating or less. Heavy timber structural members appurtenant to the CLT exterior wall shall meet the requirements of Table 2304.11 and be fire-resistance rated as required for the exterior wall. The exterior surface of the cross-laminated timber and heavy timber elements shall be protected by one of the following:

    1. Fire-retardant-treated wood sheathing complying with Section 2303.2 and not less than [15] / 32 inch (12 mm) thick.

    2. Gypsum board not less than [1] / 2 inch (12.7 mm) thick.

    3. A noncombustible material.

  • CBC § 504.5 High relevance — show source text

    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 .

    Such material shall extend from the top of the foundation to the underside of the roof sheathing.

    504.5.1 Flashing. A minimum of 6 inches (152 mm) of metal flashing or noncombustible material applied vertically on the exterior of the wall shall be installed at the ground, decking and roof intersections.

    504.5.2 Exterior wall coverings. Exterior wall coverings shall comply with one or more of the following requirements:

    1. Noncombustible material.

    2. Ignition-resistant building material labeled for exterior use. 3. Fire-retardant-treated wood labeled for exterior use and complying with the requirements of Section 2303.2 of the Califor- nia Building Code. 4. Fire-retardant-treated wood shingles and shakes which have been qualified in accordance with Section 1505.6 of the Cali- fornia Building Code for use as “Class B” roof covering shall be an acceptable alternative wall covering material where installed over solid sheathing.

    Exception: Exterior wall coverings which are a component of an approved wall assembly complying with Section 504.5.

    504.5.2.1 Extent of exterior wall covering. Where provided, exterior wall coverings shall extend from the top of the foundation to the roof, and terminate at 2-inch (50.8 mm) nominal solid wood blocking between rafters at all roof overhangs, or in the case of enclosed eaves, terminate at the enclosure.

    504.6 Underfloor enclosure. Buildings or structures shall have underfloor areas enclosed to the ground with exterior walls in accordance with Section 504.5.

  • CBC § 15.6 High relevance — show source text

    R302.15.6 Fire-retardant-treated wood structural panels. The effect of treatment and the method of redrying after treatment, and exposure to high temperatures and high humidities on the flexure properties of fire-retardant-treated softwood plywood shall be determined in accordance with ASTM D5516. The test data developed by ASTM D5516 shall be used to develop adjustment factors, maximum loads and spans, or both for untreated plywood design values in accordance with ASTM D6305. Each manufacturer shall publish the allowable maximum loads and spans for service as floor and roof sheathing for their treatment.

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    BUILDING PLANNING

    R302.15.7 Fire-retardant-treated lumber. For each species of wood treated, the effect of the treatment and the method of redrying after treatment and exposure to high temperatures and high humidities on the allowable design properties of fire-retardant-treated lumber shall be determined in accordance with ASTM D5664. The test data developed by ASTM D5664 shall be used to develop modification factors for use at or near room temperature and at elevated temperatures and humidity in accordance with ASTM D6841. Each manufacturer shall publish the modification factors for service at temperatures of not less than 80°F (27°C) and for roof framing. The roof framing modification factors shall take into consideration the climatological location.

    R302.15.8 Exposure to weather. Where fire-retardant-treated wood is exposed to weather or damp or wet locations, it shall be identified as “Exterior” to indicate there is not an increase in the listed flame spread index as defined in Section R302.15 when subjected to ASTM D2898.

    R302.15.9 Interior applications. Interior fire-retardant-treated wood shall have a moisture content of not over 28 percent when tested in accordance with ASTM D3201 procedures at 92-percent relative humidity. Interior fire-retardant-treated wood shall be tested in accordance with Section R302.15.6 or R302.15.7. Interior fire-retardant-treated wood designated as Type A shall be tested in accordance with the provisions of this section.

    R302.15.10 Moisture content. Fire-retardant-treated wood shall be dried to a moisture content of 19 percent or less for fireretardant-treated lumber and 15 percent or less for fire-retardant-treated wood structural panels before use. For wood kiln dried after treatment (KDAT), the kiln temperatures shall not exceed those used in kiln drying the fire-retardant-treated wood structural panels and fire-retardant-treated lumber submitted for the tests described in Section R302.15.6 for fire-retardant-treated wood structural panels and Section R302.15.7 for fire-retardant-treated lumber.

    SECTION R303—FOAM PLASTIC

    R303.1 General. The provisions of this section shall govern the materials, design, application, construction and installation of foam plastic materials.

    R303.1.1 Spray-applied foam plastic. Single- and multiple-component spray-applied foam plastic insulation shall comply with the provisions of Section R303 and ICC 1100.

    R303.1.2 Insulating sheathing. Foam plastic materials used as insulating sheathing shall comply with the provisions of Section R303 and the material standards in Table R303.1.2.

Frequently asked questions

Do all wood veneers get the same height privileges as fire‑retardant‑treated wood?

No. Standard (untreated) wood veneers are subject to the general combustible covering limits (40 ft height and area limits where applicable). Only wood that meets §2303.2 FRTW requirements is allowed the expanded 60 ft height and relaxed area limits in §1405.1.1.3 .

What documentation do I need on file for FRTW used as exterior cladding?

Provide manufacturer test reports or listings showing compliance with the referenced ASTM/UL test(s), and the FRTW pieces must be labeled (including the “Exterior” designation for weather exposure) per §2303.2.5 and §2303.2.7 .

If my veneer is mounted over a noncombustible backup, does that change the rules?

Veneers must be attached to or furred from a noncombustible backing per §1404.6(2). That backing is a requirement for veneered cladding; it does not by itself negate the combustible‑cladding area or height rules unless the cladding is otherwise compliant (for example FRTW in §2303.2) .

Are wood products exempt from NFPA 268 testing for exterior wall coverings?

Wood/wood‑based products are listed as exceptions in §1405.1.1.1’s test requirement language, but the code still imposes NFPA 268 sustained‑flame and reduced‑flux criteria in specific situations (for instance ≤5 ft fire separation or when a reduced incident radiant flux exposure is required), so you cannot ignore NFPA 268 consequences near close separations or for permitted combustible coverings .

Do veneer projections create a different classification?

Open or spaced wood veneers without concealed spaces are limited to a 24‑inch projection from the wall per §1404.6(3). If the veneer forms concealed spaces, additional restrictions or tested assemblies may be required under other sections .

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