CBC · California Building Code

Requirements and design values for fire‑retardant‑treated wood (FRTW)

FRTW must pass specific fire tests and be labeled; designers must reduce untreated wood design values using manufacturer‑published treatment factors based on the ASTM procedures cited in the CBC, and FRT lumber/panels must meet pre‑use moisture limits and “Exterior” identification when exposed to weather.

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Last reviewed: July 5, 2026

What the code requires — 2-4 sentences

The California Building Code treats fire‑retardant‑treated wood (FRTW) as a manufactured wood product that must meet specific fire‑test, labeling, drying and design‑value requirements before it may be used in construction (see § 2303.2) . Design values for FRTW (including connection values) must be adjusted to account for the effects of the treatment, redrying and the service temperature/humidity conditions, and those adjustment factors and allowable loads/spans must be published by the manufacturer in accordance with the ASTM procedures cited in the code (see § 2303.2.6) . FRTW intended for exterior or wet exposure must be identified for “Exterior” use and shown not to increase flame spread after a rain‑test (see § 2303.2.7 and § 2303.2.5) . Lumber and panel moisture limits before use are required (see § 2303.2.9) .

Requirements in detail

What qualifies as FRTW and required fire testing

  • FRTW is a wood product impregnated by pressure or other integral manufacturing means that, when tested per ASTM E84 (or UL 723), must have a listed flame spread index of 25 or less and must meet the extended‑duration flame‑front criterion described in § 2303.2. An alternate test (ASTM E2768) may also be used to demonstrate compliance (§ 2303.2 and § 2303.2.1) .
  • If a pressure process is used, the code requires closed‑vessel pressure operation at not less than 50 psig (§ 2303.2.2) .

Labeling, identification and “Exterior” marking

  • Every piece of FRT lumber and FRT wood structural panel must be labeled with an approved agency mark, the treating manufacturer, treatment name, species, flame spread and smoke index, method of drying after treatment and conformance with §§ 2303.2.6–2303.2.9. For material intended for weather/damp/wet exposure the label must include the phrase “No increase in the listed classification when subjected to the Standard Rain Test (ASTM D2898)” (§ 2303.2.5) .
  • Where exposed to weather, damp or wet locations, FRTW must be identified as “Exterior” to indicate compliance with ASTM D2898 (§ 2303.2.7) .

Design values and how to use them

  • The code requires that design values for FRTW (including connection values) be subject to all the same adjustments that apply to untreated wood in Chapter 23 and then further adjusted for the effects of the fire‑retardant treatment per an approved investigation considering anticipated temperature and humidity, treatment type and redrying (§ 2303.2.6) .
  • The code prescribes specific ASTM test standards and adjustment procedures by product type:
    • Fire‑retardant‑treated plywood flexure effects: ASTM D5516; adjustment factors per ASTM D6305; manufacturers must publish allowable maximum loads and spans for floor/roof sheathing based on adjusted values and climatological location (§ 2303.2.6.1) .
    • Fire‑retardant‑treated lumber properties: ASTM D5664 testing; adjustment factors derived and applied per ASTM D6841 for room and elevated temperature/humidity conditions; manufacturers must publish treatment adjustment factors for service at maximum temperatures of not less than 80°F (27°C) and for roof framing, taking climatological location into account (§ 2303.2.6.2) .
    • Fire‑retardant‑treated laminated veneer lumber (LVL): ASTM D8223 for effects and reference design values; manufacturers publish treatment‑based adjustment factors (§ 2303.2.6.3) .

Moisture content and kiln‑drying after treatment

  • FRT lumber shall be dried to a moisture content of 19% or less and wood structural panels to 15% or less before use (§ 2303.2.9). For wood kiln‑dried after treatment (KDAT), kiln temperatures must not exceed those used in the drying used for the tests referenced in § 2303.2.6.1 and § 2303.2.6.2 (§ 2303.2.9) .
  • Interior FRTW has an additional moisture requirement: interior FRTW shall have moisture content not over 28% when tested per ASTM D3201 procedures at 92% relative humidity; interior FRTW is also subject to the testing provisions in § 2303.2.6.1 or § 2303.2.6.2 (§ 2303.2.8) .

Table — decision‑relevant values and references

Decision item Required value / action Code reference
Flame spread (ASTM E84 / UL 723) Listed flame spread index ≤ 25; extended test criteria (20 min, flame front limit) § 2303.2
Alternate test option ASTM E2768 (alternate method) § 2303.2.1
Pressure treatment Closed vessels at ≥ 50 psig for pressure impregnation § 2303.2.2
Label contents Agency ID; manufacturer; treatment name; species; flame/smoke indexes; drying method; standards conformance; rain‑test wording for exterior § 2303.2.5
Exterior/wet exposure Identify as “Exterior”; no increase in classification after ASTM D2898 § 2303.2.7
Lumber moisture (pre‑use) ≤ 19% moisture content § 2303.2.9
Panel moisture (pre‑use) ≤ 15% moisture content § 2303.2.9
Interior FRTW moisture (high RH test) ≤ 28% when tested by ASTM D3201 at 92% RH § 2303.2.8
Design‑value adjustments (plywood) ASTM D5516; adjustment factors per ASTM D6305; manufacturer to publish loads/spans § 2303.2.6.1
Design‑value adjustments (lumber) ASTM D5664 testing; adjustments per ASTM D6841; manufacturer publishes factors (incl. ≥80°F service and roof framing) § 2303.2.6.2
Design‑value adjustments (LVL) ASTM D8223; manufacturer publishes reference values and adjustment factors § 2303.2.6.3

Exceptions & special cases

  • Surface treatments are not acceptable substitutes for integral fire‑retardant treatment; the code requires the treatment be integral to the product or applied by the approved pressure/closed‑vessel process (§ 2303.2 and § 2303.2.3) .
  • FRTW used in exterior, damp or wet locations must be specifically identified for exterior use and pass the ASTM D2898 rain‑test requirement; otherwise the material is not acceptable for those exposures (§ 2303.2.7 and § 2303.2.5) .
  • Limitations for use of FRTW in Type I and II construction are addressed elsewhere (see § 2303.2.10 referencing § 603.1); check § 603.1 for those specific restrictions (§ 2303.2.10) .
  • Manufacturer‑published factors are required for roof framing and must account for climatological location; treat roof framing applications with special attention to the published roof‑framing modification factors (§ 2303.2.6.2) .

Common mistakes

  • Relying on surface coatings, paints, stains or field sprays and treating them as FRTW — the code explicitly disallows this as an approved method (§ 2303.2.3) .
  • Using FRTW not labeled with the required information (agency mark, manufacturer, treatment name, moisture/drying info, etc.) — unlabeled material is noncompliant (§ 2303.2.5) .
  • Forgetting to apply manufacturer’s treatment adjustment factors (or using untreated‑wood design values without the required reduction) — the code mandates adjusted design values and published factors (§ 2303.2.6) .
  • Installing FRTW intended only for interior use in exterior or wet locations without the “Exterior” identification and ASTM D2898 compliance (§ 2303.2.7 and § 2303.2.5) .
  • Ignoring moisture limits before use (lumber ≤ 19%, panels ≤ 15%) or exceeding KDAT kiln temperatures used in qualifying tests (§ 2303.2.9) .
  • Applying load‑duration factors > 1.6 to FRTW design (the code restricts load duration factors for FRTW) — check Chapter 23 design rules; § 2306.1.4 reiterates that load duration factors >1.6 shall not be used for FRTW members .

Worked example — how to apply the design‑value adjustment (illustrative)

Scenario (illustrative only): a designer must size a roof rafter made from fire‑retardant‑treated Douglas‑fir #2 where the untreated allowable bending stress (Fb) is 1200 psi (unadjusted). The manufacturer publishes a treatment adjustment factor for roof framing of 0.75 for the climatological zone and KDAT they use.

Steps

  1. Confirm manufacturer‑published treatment adjustment factor and the basis (per § 2303.2.6.2 and ASTM references). The code requires these published values; you must use the manufacturer’s published factor — you cannot invent one (§ 2303.2.6.2) .
  2. Apply general adjustments that would apply to untreated wood (size, repetitive member, temperature, load duration, etc.) per Chapter 23 and then apply the treatment factor. For example (illustrative math only):
    • Start with Fb (untreated) = 1200 psi.
    • Apply treatment factor = 0.75 (manufacturer value; example only) → adjusted Fb = 1200 × 0.75 = 900 psi.
    • Apply other code adjustments (e.g., size factor, duration factor). Remember: load duration factors greater than 1.6 are not permitted for FRTW (§ 2306.1.4) — apply the appropriate duration factor ≤ 1.6 as allowed (§ 2306.1.4) .
  3. Check connection design values and published connection adjustments (connections may also be reduced) as required by § 2303.2.6. Use the manufacturer’s published connection design values if provided.
  4. Validate moisture and KDAT compliance before installation (lumber moisture ≤ 19%, panels ≤ 15%) (§ 2303.2.9) .

Note: this worked example uses a hypothetical factor to demonstrate method only. The CBC requires that the actual treatment adjustment factors and allowable loads/spans be those published by the treating manufacturer based on the ASTM tests indicated in § 2303.2.6; you must use manufacturer data for final design and calculations (§ 2303.2.6.1–.3) .

Related provisions (quick reference)

  • § 2303.2 — Fire‑retardant‑treated wood: definition, fire tests and general rules .
  • § 2303.2.1 — Alternate fire testing (ASTM E2768) .
  • § 2303.2.2 — Pressure‑process requirements (closed vessels, ≥ 50 psig) .
  • § 2303.2.5 — Labeling requirements for FRT lumber and panels .
  • § 2303.2.6 (and .6.1–.6.3) — Mandatory design‑value adjustment procedures and referenced ASTM standards (D5516, D6305, D5664, D6841, D8223) .
  • § 2303.2.7 — Identification and ASTM D2898 rain‑test requirement for exterior use .
  • § 2303.2.8 — Interior application moisture test requirement (ASTM D3201) and testing reference to § 2303.2.6 methods .
  • § 2303.2.9 — Required pre‑use moisture contents and KDAT temperature limits .
  • § 2303.2.10 — Limitations on the use of FRTW in Type I and II construction; see § 603.1 for those limits (§ 2303.2.10) .
  • § 2306.1.4 — Statement on load‑duration factors and rule that load duration factors > 1.6 shall not be used for FRTW design values .

Code references

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

  • CBC § 2303.2.4 High relevance — show source text

    [BF] 2303.2.4 Fire testing of wood structural panels. Wood structural panels shall be tested with a ripped or cut longitudinal gap of [1] / 8 inch (3.2 mm).

    [BF] 2303.2.5 Labeling. In addition to the labels required in Section 2303.1.1 for sawn lumber and Section 2303.1.5 for wood structural panels, each piece of fire-retardant-treated lumber and wood structural panels shall be labeled. The label shall contain the following items:

    1. The identification mark of an approved agency in accordance with Section 1703.5.

    2. Identification of the treating manufacturer.

    3. The name of the fire-retardant treatment.

    4. The species of wood treated.

    5. Flame spread and smoke-developed index.

    6. Method of drying after treatment.

    7. Conformance with appropriate standards in accordance with Sections 2303.2.6 through 2303.2.9.

    8. For fire-retardant-treated wood exposed to weather, damp or wet locations, include the words “No increase in the listed classification when subjected to the Standard Rain Test” (ASTM D2898).

    2303.2.6 Design values. Design values for fire-retardant-treated wood, including connection design values, shall be subject to all adjustments applicable to untreated wood as specified in this chapter and shall be further adjusted to account for the effects of the fire-retardant treatment. Adjustments to design values for the effects of the fire-retardant treatment shall be based on an approved method of investigation that takes into consideration the anticipated temperature and humidity to which the fire-retardant-treated wood will be subjected, the type of treatment and redrying procedures. Adjustments to flexural design values for fire-retardant-treated plywood shall be determined in accordance with Section 2303.2.6.1. 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.

  • CBC § 2303.2 High relevance — show source text

    [BF] 2303.2 Fire-retardant-treated wood. Fire-retardant-treated wood 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. 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 centerline of the burners at any time during the test.

    [BF] 2303.2.1 Alternate fire testing. Fire-retardant-treated wood is also 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 E2768, a listed flame spread index of 25 or less and where the flame front does not progress more than 10.5 feet (3200 mm) beyond the centerline of the burners at any time during the test.

    [BF] 2303.2.2 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) (345 kPa).

    [BF] 2303.2.3 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 in this section.

    [BF] 2303.2.4 Fire testing of wood structural panels. Wood structural panels shall be tested with a ripped or cut longitudinal gap of [1] / 8 inch (3.2 mm).

    [BF] 2303.2.5 Labeling. In addition to the labels required in Section 2303.1.1 for sawn lumber and Section 2303.1.5 for wood structural panels, each piece of fire-retardant-treated lumber and wood structural panels shall be labeled. The label shall contain the following items:

    1. The identification mark of an approved agency in accordance with Section 1703.5.

    2. Identification of the treating manufacturer.

    3. The name of the fire-retardant treatment.

    4. The species of wood treated.

    5. Flame spread and smoke-developed index.

    6. Method of drying after treatment.

    7. Conformance with appropriate standards in accordance with Sections 2303.2.6 through 2303.2.9.

    8. For fire-retardant-treated wood exposed to weather, damp or wet locations, include the words “No increase in the listed classification when subjected to the Standard Rain Test” (ASTM D2898).

    2303.2.6 Design values. Design values for fire-retardant-treated wood, including connection design values, shall be subject to all adjustments applicable to untreated wood as specified in this chapter and shall be further adjusted to account for the effects of the fire-retardant treatment. Adjustments to design values for the effects of the fire-retardant treatment shall be based on an approved method of investigation that takes into consideration the anticipated temperature and humidity to which the fire-retardant-treated wood will be subjected, the type of treatment and redrying procedures.

  • 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 § 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 § 2308.10 High relevance — show source text

    walls 2308.10 Calculated fire resistance 722.6 Ceiling framing 2308.11 Connectors and fasteners 2304.10,

    2308.5

    Contacting concrete, masonry or earth 2304.12.1.3, 2304.12.1.4, 2304.12.2.1, 2304.12.2.2, 2304.12.2.6 Cross-laminated timber 2301.2, 2303.1, 2303.1.4, 2304.11.2.1, 2304.11.3.1, 2304.11.4.1 Cutting, notching and boring of dimensional wood framing 2308.6 Decay, protection against 2304.12 Diaphragms 2305.1, 2305.2, 2306.2 Dimensions 2301.2 Draftstopping 718.3, 718.4 End-jointed lumber 2303.1.1.2 Fiberboard 2303.1.6, Table 2306.3(2) Fireblocking 718.2 Fire-retardant treated 2303.2 Floor and roof framing (see Floor Construction, Wood) 2304.4 Floor sheathing 2304.8 Foundation 1807.1.4, 2304.10.6.2, 2304.12.1.2, 2308.10.8.1, 2308.7 Grade, lumber 2303.1.1

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    INDEX

    Hardboard 2303.1.7 Heavy timber construction 602.4, 2304.11

    Hurricane shutters 1609.2

    I-joist 2303.1.2 Inspection, special 1705.12.1, 1705.13.2, 1705.5 Lateral force-resisting systems 2305 Light-frame construction, conventional 2308 Load and resistance factor design 2307

    Moisture content 2303.1.9.2, 2303.2.9, 2303.7, 2304.9.5.1, Table 2305.2(1), Table 2305.2(2) Nails and staples 2303.6 Plywood, hardwood 2303.3 Preservative treated 1402.6, 1402.9,

    2303.1.9 Roof framing (see Roof Construction, Wood)

    2304.4 Roof sheathing 2304.8 Seismic provisions 2305, 2306, 2308.10.10, 2308.10.6, 2308.10.8 Shear walls 2305, 2306.3 Standards and quality, minimum 2303 Structural panels 2303.1.5 Supporting concrete or masonry 2304.13 Termite, protection against 2304.12 Trusses 2303.4

    Veneer Chapter 14 Wall framing (see Wall, Wood Construction)

    2304.3 Wall sheathing, exterior 2304.6 Wood Frame Construction Manual

  • CBC § 15.3 High relevance — show source text

    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).

    R302.15.5 Strength adjustments. Design values for untreated lumber and wood structural panels as specified in Section R802.1 shall be adjusted for fire-retardant-treated wood. Adjustments to design values shall be based on an approved method of investigation that takes into consideration the effects of the anticipated temperature and humidity to which the fire-retardant-treated wood will be subjected, the type of treatment and redrying procedures.

    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.

  • 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.

    5-6 2025 CALIFORNIA WILDLAND-URBAN INTERFACE CODE

  • CBC § 23-27 High relevance — show source text

    **|Truss Plate Institute, Inc.| ||TPI 1|National Design Standard for Metal Plate Connected Wood Truss Construction|

    2025 CALIFORNIA BUILDING CODE 23-27

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

    WOOD

    TABLE 2306.1—STANDARDS FOR DESIGN AND CONSTRUCTION OF
    WOOD ELEMENTS IN STRUCTURES USING ALLOWABLE STRESS DESIGN—continued    		 Col2 Col3
    STANDARDS
    PROMULGATOR    		 STANDARD TITLE
    West Coast Lumber Inspection Bureau West Coast Lumber Inspection Bureau West Coast Lumber Inspection Bureau
    AITC 104 Typical Construction Details
    AITC 110 Standard Appearance Grades for Structural Glued Laminated Timber
    AITC 113 Standard for Dimensions of Structural Glued Laminated Timber
    AITC 119 Standard Specifications for Structural Glued Laminated Timber of Hardwood Species
    AITC 200 Inspection Manual

    2306.1.1 Joists and rafters. The design of rafter spans is permitted to be in accordance with the AWC STJR.

    2306.1.2 Plank and beam flooring. The design of plank and beam flooring is permitted to be in accordance with the AWC Wood Construction Data No. 4.

    2306.1.3 Preservative-treated wood allowable stresses. The allowable unit stresses for preservative-treated wood conforming to AWPA U1 need not be adjusted for treatment, but are subject to other adjustments. Load duration factors greater than 1.6 shall not be used in the structural design of preservative-treated wood members.

    2306.1.4 Fire-retardant-treated wood allowable stresses. The allowable unit stresses for fire-retardant-treated wood, including connection design values, shall be developed in accordance with the provisions of Section 2303.2.6. Load duration factors greater than 1.6 shall not be used in the structural design of fire-retardant-treated wood members.

    2306.1.5 Lumber decking. The capacity of lumber decking arranged according to the patterns described in Section 2304.9.2 shall be the lesser of the capacities determined for moment and deflection according to the formulas in Table 2306.1.5.

    TABLE 2306.1.5—ALLOWABLE LOADS FOR LUMBER DECKING Col2 Col3
    PATTERN ALLOWABLE AREA LOADa ALLOWABLE AREA LOADa
    PATTERN Moment Deflection
    Simple span w_b_
    8_Fb_
    ′_d_2
    _l_26
    --------------
    =    		 wΔ
    384Δ_E_′
    5_l_4
    ----------------- _d_3
    12
    -----
    =
    Two-span continuous w_b_
    8_Fb_
    ′_d_2
    _l_26
    -------------
    =    		 wΔ
    185Δ_E_′
    _l_4
    ----------------- _d_3
    12
    -----
    =
    Combination simple- and two-span continuous w_b_
    8_Fb_
  • CBC § 2109.2.4.9 High relevance — show source text

    Adobe 2109.2.4.9

    Fire resistance 704.10 Masonry, wood support 2304.13 Liquefied Petroleum Gas Table 414.5.1,

    415.9.2 Listed (definition) 202 Listing Agency (definition) 202 Live Load 1607

    Construction Documents 1603.1.1

    Posting of 106.1 Roof 1607

    Live/Work Units 310.3, 508.5 Accessibility Chapters 11A and 11B Separation 508.2 Load and Resistance Factor Design (LRFD) 1602.1

    Factored load 1604.2

    Limit state 1604.2

    Load combinations 1605 Wood design 2302.1, 2307 Load Combinations 1605 Allowable stress design 1605, 1605.2 Alternative allowable stress load

    combinations 1605.2 Load and resistance factor design 1605 Strength design 1605 Loads 106, 202 Atmospheric ice 1614 Combinations 1605

    Dead 1606

    Factored load 402.8.2.1, 1604.2,

    1709.2

    Flood 1603.1.7, 1612 Impact 1607.12 Live 508.5.8, 1603.1.1, 1607 Load effects 1604.4

    Nominal load 1604.2 Partial loading 1607.3.1, 1607.3.2 Rain 1603.1.9, 1611 Seismic 1603.1.5, 1613 Snow 1603.1.3, 1608 Soil lateral 1610

    Tornado 1603.1.4, 1609.5, 1609.6.3.2 Tsunami 1615

    Wind 1603.1.4, 1609 Lobbies Assembly occupancy 1030.4 Elevator 405.4.3, 1009.2.1, 1009.4, 3006, 3007.6, 3008.6 Exit discharge 1028.2 Underground buildings 405.4.3 Lobby 202 Local Enforcing Agency 1.8.3 Locks and Latches 1010.2, 1010.2.8 Delayed egress locks 1010.2.12 Electromagnetically locked 1010.2.10 Fire Exit Hardware 1010.2.10, 1010.2.8 Group I-2 407.4.1.1, 1010.2.13 Group I-3 408.4 High-rise 403.5.3 Sensor release 1010.2.11

    Toilet rooms Chapter 29 Lodging Houses 310.4, 310.4.2 Lowest Floor 1603.1.7, 1612.4 Lumber

    General provisions Chapter 23 Quality standards 2303

  • CBC § 1604.2 High relevance — show source text

    Nominal load 1604.2 Partial loading 1607.3.1, 1607.3.2 Rain 1603.1.9, 1611 Seismic 1603.1.5, 1613 Snow 1603.1.3, 1608 Soil lateral 1610

    Tornado 1603.1.4, 1609.5, 1609.6.3.2 Tsunami 1615

    Wind 1603.1.4, 1609 Lobbies Assembly occupancy 1030.4 Elevator 405.4.3, 1009.2.1, 1009.4, 3006, 3007.6, 3008.6 Exit discharge 1028.2 Underground buildings 405.4.3 Lobby 202 Local Enforcing Agency 1.8.3 Locks and Latches 1010.2, 1010.2.8 Delayed egress locks 1010.2.12 Electromagnetically locked 1010.2.10 Fire Exit Hardware 1010.2.10, 1010.2.8 Group I-2 407.4.1.1, 1010.2.13 Group I-3 408.4 High-rise 403.5.3 Sensor release 1010.2.11

    Toilet rooms Chapter 29 Lodging Houses 310.4, 310.4.2 Lowest Floor 1603.1.7, 1612.4 Lumber

    General provisions Chapter 23 Quality standards 2303

    Mail Receptacles, Locking 420.13.1 Maintenance Means of egress 1002.1, 3310.2 Property 101.4.4 Mall (see Covered Mall and Open Mall Buildings) Manual Fire Alarm Box 907.4.2

    Manufactured Homes

    Flood resistant G109

    2025 CALIFORNIA BUILDING CODE INDEX-13

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

    INDEX

    Veneer 1403.5, 1404.12 Metal Building System 1705.2.8, Table 1705.2.6, 2210 Metal Composite Material (MCM) 1406 Metal Roof Panel 1504.4.2, 1507.1.1, 1507.4,

    1512.3 Metal Roof Shingle 1504.4.3, 1507.1.1, 1507.5, 1507.5.7, 1512.3 Mezzanines 505 Accessibility Chapters 11A and 11B Area limitations 505.2.1, 505.2.1.1,

    505.3.1

  • CBC § 2303.2.8 High relevance — show source text

    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.

    2303.4.1.1 Truss design drawings. The written, graphic and pictorial depiction of each individual truss shall be provided to the building official for approval prior to installation. Truss design drawings shall be provided with the shipment of trusses delivered to the job site. Truss design drawings shall include, at a minimum, the following information:

    1. Slope or depth, span and spacing.
    2. Location of all joints and support locations.
    3. Number of plies if greater than one.
    4. Required bearing widths.
    5. Design loads as applicable, including: 5.1. Top chord live load. 5.2. Top chord dead load.

    5.3. Bottom chord live load.

    5.4. Bottom chord dead load.

    5.5. Additional loads and locations.

    5.6. Environmental design criteria and loads (such as wind, rain, snow, seismic). 6. Other lateral loads, including drag strut loads. 7. Adjustments to wood member and metal connector plate design value for conditions of use. 8. Maximum reaction force and direction, including maximum uplift reaction forces where applicable. 9. Joint connection type and description, such as size and thickness or gage, and the dimensioned location of each joint connector except where symmetrically located relative to the joint interface. 10. Size, species and grade for each wood member. 11. Truss-to-truss connections and truss field assembly requirements. 12. Calculated span-to-deflection ratio and maximum vertical and horizontal deflection for live and total load as applicable. 13. Maximum axial tension and compression forces in the truss members. 14. Required permanent individual truss member restraint location and the method and details of restraint and diagonal bracing to be used in accordance with Section 2303.4.1.2.

Frequently asked questions

How do I know a piece of lumber is approved FRTW for exterior use?

Check the factory label: it must be marked “Exterior” and include the words indicating “No increase in the listed classification when subjected to the Standard Rain Test (ASTM D2898)” per § 2303.2.5 and § 2303.2.7 .

Can I field‑spray wood and call it FRTW?

No. The code requires the treatment be integral to manufacture (pressure process or other integral method). Surface paints/coatings/stains are not accepted methods to meet FRTW requirements (§ 2303.2.2 and § 2303.2.3) .

Who provides the treatment adjustment factors I must use in design?

The treating manufacturer must publish treatment adjustment factors and allowable loads/spans based on the ASTM procedures specified in § 2303.2.6 (see the product literature and label) — the designer must use those published factors (§ 2303.2.6.1–.3) .

What moisture content must FRT lumber have before I install it?

FRT lumber must be dried to a moisture content of 19% or less before use; wood structural panels must be dried to 15% or less (§ 2303.2.9) .

Are FRTW design values the same as preservative‑treated wood?

No. Preservative‑treated wood allowable stresses that conform to AWPA U1 need not be adjusted for treatment (but are subject to other adjustments), whereas fire‑retardant‑treated wood design values must be adjusted per § 2303.2.6 and related ASTM test/adjustment procedures (§ 2306.1.3 and § 2306.1.4) .

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