CBC · California Building Code

Preservative-treated wood, moisture limits and where treatment is required

If wood is within the clearances the CBC lists (for example joists <18" from crawlspace ground, girders <12", framing <8" from exterior earth), it must be naturally durable or treated to AWPA standards; treated wood that will be enclosed and can’t dry must be dried to 19% moisture or less before being covered, and each treated piece must carry the required quality mark showing preservative, retention and end use.

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Last reviewed: July 5, 2026

What the code requires — 2-4 sentences

The CBC requires that lumber, timber, plywood, piles and poles required by the decay/termite-protection rules be preservative-treated to AWPA standards and bear an inspection/quality mark; where those same treated members are to be enclosed and cannot dry in service they must be dried to a maximum moisture content of 19% before being covered. The locations that require naturally durable or preservative-treated wood (and in some cases waterborne preservatives) and the numeric clearances that trigger treatment are specified in § 2304.12 and § 2304.12.1; the material/labeling and moisture rules are in § 2303.1.9.

Requirements in detail

Standards, identification and treatment scope

  • Preservative-treated lumber, timber, plywood, piles and poles required by § 2304.12 must conform to the American Wood Protection Association commodity and handling standards (AWPA U1 and M4). The code requires an inspection-agency quality mark that identifies treating plant, preservative type, minimum retention, end use, AWPA standard and the accredited inspection agency. § 2303.1.9 and § 2303.1.9.1 are the controlling sections for these requirements.

  • Field-cut ends, notches and drilled holes of treated wood are to be field-treated in accordance with AWPA M4 (see referenced handling/field-treatment requirements called out in the CBC and the related residential provisions).

Moisture limit and drying before concealment

  • If preservative-treated wood is used in enclosed locations where drying in service cannot readily occur, that preservative-treated wood shall be at a moisture content of 19 percent or less before being covered with insulation, interior wall finish, floor covering or other materials. This is stated in § 2303.1.9.2.

  • Some treated products required for interior use must be dried per manufacturer’s recommendations before finishing; and preservative-treated wood used in interior locations is required to be protected with two coats of a listed finish unless a waterborne preservative has been used (see § 2304.12.2 and cross-references).

Where treatment (or naturally durable wood) is required — key clearances and locations

The primary “decision rules” are numeric clearances and specific locations. Use the table below for quick reference.

Location / condition Numeric trigger or requirement Required material Code Reference
Wood joists or wood structural floors in crawl/unexcavated areas Closer than 18 in. (457 mm) from exposed ground Naturally durable or preservative-treated (AWPA U1) § 2304.12.1.1
Wood girders in crawl/unexcavated areas Closer than 12 in. (305 mm) from exposed ground Naturally durable or preservative-treated (AWPA U1) § 2304.12.1.1
Wood framing members in contact with exterior foundation walls Less than 8 in. (203 mm) from exposed earth Naturally durable or preservative-treated (AWPA U1) § 2304.12.1.2 § 2304.12.1.3
Sleepers and sills on slab in direct contact with earth Any slab in direct contact with earth Naturally durable or preservative-treated § 2304.12.1.4
Wood siding, sheathing and wall framing Clearance < 6 in. (152 mm) from earth or < 2 in. (51 mm) above certain horizontal concrete surfaces Naturally durable or preservative-treated § 2304.12.1.5
Posts/columns supported by slab/footing in direct earth contact Posts or columns supported by a concrete or masonry slab/footing in direct contact with earth Naturally durable or preservative-treated; with listed exceptions (see code) § 2304.12.2.2 § 2304.12.2.6
Wood in contact with exposed earth or fresh water Contact with exposed earth Naturally durable for decay/termite resistance or preservative-treated in accordance with AWPA U1 for soil/freshwater use § 2304.12.2.6
Enclosed locations that cannot dry (moisture before covering) Before being covered with insulation/finish Treated wood moisture content ≤ 19% § 2303.1.9.2

Notes:

  • The CBC specifically calls for AWPA U1 for end-use categories (above-ground, ground-contact, soil/freshwater, etc.) and AWPA M4 for handling/field-treatment procedures where field treatment is required. § 2303.1.9 references these standards.
  • Some interior uses of preservative-treated wood require additional finishing (two coats) unless waterborne preservatives are used; see § 2304.12.2.

Exceptions & special cases

  • Posts or columns meeting all three exception conditions (not exposed to weather or protected, supported by piers/metal pedestals projecting ≥1 in. above slab and separated by an impervious moisture barrier, and located ≥8 in. above exposed earth) are exempt from the requirement to be preservative-treated in § 2304.12.2.2 (Exception).

  • Untreated wood is permitted when it is continuously and entirely below groundwater level or continuously submerged in fresh water (exception in § 2304.12.2.6).

  • The code allows local exceptions where historical climatic experience shows that naturally durable or preservative-treated wood is not required for exposed members in certain geographic regions (exception noted in § 2304.12.2.3).

  • For some uses the CBC specifically requires waterborne preservatives for above-ground uses called out in § 2304.12.1 (see title and cross-reference). Always read the individual location clauses (2304.12.1.1–.1.5).

Common mistakes

  • Assuming "pressure-treated" is enough without verifying the AWPA use category and minimum retention and the inspection quality mark required by § 2303.1.9.1. Check the stamp/label for end-use (soil contact, above-ground, etc.).

  • Forgetting the 19% moisture-content limit for treated wood that will be enclosed and cannot dry in service — covering treated members that are wetter than 19% violates § 2303.1.9.2.

  • Not field‑treating cuts and holes per AWPA M4 after cutting installed treated members; the code requires field treatment per the referenced AWPA handling standard.

  • Using incompatible fasteners or connectors with certain preservatives (this is covered in the residential code cross-references); failure to use the corrosion-resistant fasteners recommended in the code can cause premature failures — check the fastener/connectors requirements in the related provisions (see Related provisions).

  • Applying surface finishes over wet-treated wood: preservative-treated wood that must be finished or enclosed is to be dried per manufacturer’s instructions before finishing (see § 2304.12.2).

Worked example — concrete scenario with numbers

Scenario: A single-story house has a crawlspace where the underside of the floor joists are 12 inches above the finished ground surface inside the crawlspace. The homeowner will cover the underside of the joists with insulation and install finished subfloor and interior finishes.

Code application:

  • Because the joists are closer than 18 in. to exposed ground in the crawlspace, they fall under the requirement that wood joists or wood structural floors closer than 18 in. to exposed ground must be naturally durable or preservative-treated (AWPA U1) — § 2304.12.1.1 applies.
  • Any preservative-treated wood used here that will be enclosed (insulation/finish covering that prevents drying) must be at a moisture content of 19% or less before being covered — § 2303.1.9.2 applies. The builder must verify the treated lumber bears the required quality mark (treatment type, retention, end use, etc.) per § 2303.1.9.1.
  • If the joists are treated with a non-waterborne preservative and will be used in an interior, enclosed location, the code expects the product to be dried and finish-protected as required by § 2304.12.2; otherwise, consider a waterborne-preservative product that avoids the additional finishing requirement.

So: because clearance = 12 in (<18 in), treated wood is required; confirm AWPA use category and label; ensure treated lumber is dry ≤19% before insulation/finish is installed.

Related provisions (select CBC / CRC sections)

  • § 2303.1.9 — Preservative-treated wood (standards and moisture content rule is § 2303.1.9.2).
  • § 2303.1.9.1 — Identification / quality mark requirements for treated wood.
  • § 2303.1.9.2 — Moisture content limit (19% for enclosed locations).
  • § 2304.12 — Protection against decay and termites (general requirement and scope).
  • § 2304.12.1 — Locations requiring waterborne preservatives or naturally durable wood (above-ground specific rules).
  • § 2304.12.1.1 — Joists, girders, subfloor clearances (18 in. / 12 in.).
  • § 2304.12.1.2 / § 2304.12.1.3 / § 2304.12.1.4 — Wood supported by exterior foundation walls; exterior walls below grade; sleepers and sills.
  • § 2304.12.2 — Other locations and special finishing/drying requirements; includes interior finishing requirements and soil/freshwater contact rules.
  • § 2306.1.3 — Allowable stresses for preservative-treated wood (treatment need not alter allowable stresses, with limitations).
  • Residential code cross-references (R304 / R305) for parallel requirements and field-treatment/fastener guidance (see R304.1 / R304.2 / R304.3).

If you want, I can produce a one‑page compliance checklist for inspectors or contractors listing the exact label language to look for, the common preservative names and AWPA use categories, and a sample sign-off form that documents the lumber label, measured moisture content (method), and field re-treatment steps.

Code references

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

  • CBC § 2303.1.6.3 High relevance — show source text

    2303.1.6.3 Wall insulation. Where installed and fireblocked to comply with Chapter 7, fiberboards are permitted as wall insulation in all types of construction. In fire walls and fire barriers, unless treated to comply with Section 803.1 for Class A materials, the boards shall be cemented directly to the concrete, masonry or other noncombustible base and shall be protected with an approved noncombustible veneer anchored to the base without intervening airspaces.

    2303.1.6.3.1 Protection. Fiberboard wall insulation applied on the exterior of foundation walls shall be protected below ground level with a bituminous coating.

    2303.1.7 Hardboard. Hardboard siding shall conform to the requirements of ANSI A135.6 and, where used structurally, shall be identified by the label of an approved agency. Hardboard underlayment shall meet the strength requirements of [7] / 32 -inch (5.6 mm) or [1] / 4 -inch (6.4 mm) service class hardboard planed or sanded on one side to a uniform thickness of not less than 0.200 inch (5.1 mm). Prefinished hardboard paneling shall meet the requirements of ANSI A135.5. Other basic hardboard products shall meet the requirements of ANSI A135.4. Hardboard products shall be installed in accordance with manufacture’s recommendations.

    2303.1.8 Particleboard. Particleboard shall conform to ANSI A208.1. Particleboard shall be identified by the grade mark or certificate of inspection issued by an approved agency. Particleboard shall not be utilized for applications other than indicated in this section unless the particleboard complies with the provisions of Section 2306.3.

    2303.1.8.1 Floor underlayment. Particleboard floor underlayment shall conform to Type PBU of ANSI A208.1. Type PBU underlayment shall be not less than [1] / 4 -inch (6.4 mm) thick and shall be installed in accordance with the instructions of the Composite Panel Association.

    2303.1.9 Preservative-treated wood. Lumber, timber, plywood, piles and poles supporting permanent structures required by Section 2304.12 to be preservative treated shall conform to AWPA U1 and M4. Lumber and plywood used in permanent wood foundation systems shall conform to Chapter 18.

    2303.1.9.1 Identification. Wood required by Section 2304.12 to be preservative treated shall bear the quality mark of an inspection agency that maintains continuing supervision, testing and inspection over the quality of the preservative-treated wood. Inspection agencies for preservative-treated wood shall be listed by an accreditation body that complies with the requirements of the American Lumber Standards Treated Wood Program, or equivalent. The quality mark shall be on a stamp or label affixed to the preservative-treated wood, and shall include the following information:

    1. Identification of treating manufacturer.
    2. Type of preservative used.
    3. Minimum preservative retention (pcf).
    4. End use for which the product is treated.
    5. AWPA standard to which the product was treated.
    6. Identity of the accredited inspection agency.

    2303.1.9.2 Moisture content. Where preservative-treated wood is used in enclosed locations where drying in service cannot readily occur, such wood shall be at a moisture content of 19 percent or less before being covered with insulation, interior wall finish, floor covering or other materials.

  • CBC § 2303.1.9.2 High relevance — show source text
    1. AWPA standard to which the product was treated.
    2. Identity of the accredited inspection agency.

    2303.1.9.2 Moisture content. Where preservative-treated wood is used in enclosed locations where drying in service cannot readily occur, such wood shall be at a moisture content of 19 percent or less before being covered with insulation, interior wall finish, floor covering or other materials.

    2303.1.10 Structural composite lumber. Structural capacities for structural composite lumber shall be established and monitored in accordance with ASTM D5456.

    2303.1.11 Structural log members. Stress grading of structural log members of nonrectangular shape, as typically used in log buildings, shall be in accordance with ASTM D3957. Such structural log members shall be identified by the grade mark of an approved lumber grading or inspection agency. In lieu of a grade mark on the material, a certificate of inspection as to species and grade issued by a lumber grading or inspection agency meeting the requirements of this section shall be permitted.

    2303.1.12 Round timber poles and piles. Round timber poles and piles shall comply with ASTM D3200 and ASTM D25, respectively.

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    2303.1.13 Engineered wood rim board. Engineered wood rim boards shall conform to ANSI/APA PRR 410 or shall be evaluated in accordance with ASTM D7672. Structural capacities shall be in accordance with ANSI/APA PRR 410 or established in accordance with ASTM D7672. Rim boards conforming to ANSI/APA PRR 410 shall be marked in accordance with that standard.

    [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.

  • CBC § 2303.1.8.1 High relevance — show source text

    2303.1.8.1 Floor underlayment. Particleboard floor underlayment shall conform to Type PBU of ANSI A208.1. Type PBU underlayment shall be not less than [1] / 4 -inch (6.4 mm) thick and shall be installed in accordance with the instructions of the Composite Panel Association.

    2303.1.9 Preservative-treated wood. Lumber, timber, plywood, piles and poles supporting permanent structures required by Section 2304.12 to be preservative treated shall conform to AWPA U1 and M4. Lumber and plywood used in permanent wood foundation systems shall conform to Chapter 18.

    2303.1.9.1 Identification. Wood required by Section 2304.12 to be preservative treated shall bear the quality mark of an inspection agency that maintains continuing supervision, testing and inspection over the quality of the preservative-treated wood. Inspection agencies for preservative-treated wood shall be listed by an accreditation body that complies with the requirements of the American Lumber Standards Treated Wood Program, or equivalent. The quality mark shall be on a stamp or label affixed to the preservative-treated wood, and shall include the following information:

    1. Identification of treating manufacturer.
    2. Type of preservative used.
    3. Minimum preservative retention (pcf).
    4. End use for which the product is treated.
    5. AWPA standard to which the product was treated.
    6. Identity of the accredited inspection agency.

    2303.1.9.2 Moisture content. Where preservative-treated wood is used in enclosed locations where drying in service cannot readily occur, such wood shall be at a moisture content of 19 percent or less before being covered with insulation, interior wall finish, floor covering or other materials.

    2303.1.10 Structural composite lumber. Structural capacities for structural composite lumber shall be established and monitored in accordance with ASTM D5456.

    2303.1.11 Structural log members. Stress grading of structural log members of nonrectangular shape, as typically used in log buildings, shall be in accordance with ASTM D3957. Such structural log members shall be identified by the grade mark of an approved lumber grading or inspection agency. In lieu of a grade mark on the material, a certificate of inspection as to species and grade issued by a lumber grading or inspection agency meeting the requirements of this section shall be permitted.

    2303.1.12 Round timber poles and piles. Round timber poles and piles shall comply with ASTM D3200 and ASTM D25, respectively.

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    2303.1.13 Engineered wood rim board. Engineered wood rim boards shall conform to ANSI/APA PRR 410 or shall be evaluated in accordance with ASTM D7672. Structural capacities shall be in accordance with ANSI/APA PRR 410 or established in accordance with ASTM D7672. Rim boards conforming to ANSI/APA PRR 410 shall be marked in accordance with that standard.

  • CBC § 2304.12.2 High relevance — show source text

    2304.12.2 Other locations. Wood used in the locations specified in Sections 2304.12.2.1 through 2304.12.2.8 shall be naturally durable wood or preservative-treated wood in accordance with AWPA U1. Preservative-treated wood used in interior locations shall be protected with two coats of urethane, shellac, latex epoxy or varnish unless waterborne preservatives are used. Prior to application of the protective finish, the wood shall be dried in accordance with the manufacturer’s recommendations. 2304.12.2.1 Girder ends. The ends of wood girders entering exterior masonry or concrete walls shall be provided with a [1] / 2 inch (12.7 mm) airspace on top, sides and end, unless naturally durable or preservative-treated wood is used.

    2304.12.2.2 Posts or columns. Posts or columns supporting permanent structures and supported by a concrete or masonry slab or footing that is in direct contact with the earth shall be of naturally durable or preservative-treated wood.

    Exception: Posts or columns that meet all of the following:

    1. Are not exposed to the weather, or are protected by a roof, eave, overhang, or other covering if exposed to the weather.

    2. Are supported by concrete piers or metal pedestals projected not less than 1 inch (25 mm) above the slab or deck and are separated from the concrete pier by an impervious moisture barrier.

    3. Are located not less than 8 inches (203 mm) above exposed earth.

    2304.12.2.3 Supporting member for permanent appurtenances. Naturally durable or preservative-treated wood shall be utilized for those portions of wood members that form the structural supports of buildings, balconies, porches or similar permanent building appurtenances where such members are exposed to the weather without adequate protection from a roof, eave, overhang or other covering to prevent moisture or water accumulation on the surface or at joints between members.

    Exception: Sawn lumber in buildings located in a geographical region where experience has demonstrated that climatic conditions preclude the need to use durable materials where the structure is exposed to the weather.

    2304.12.2.4 Supporting members for permeable floors and roofs. Wood structural members that support moisture-permeable floors or roofs that are exposed to the weather, such as concrete or masonry slabs, shall be of naturally durable or preservative-treated wood unless separated from such floors or roofs by an impervious moisture barrier. The impervious moisture barrier system protecting the structure supporting floors shall provide positive drainage of water that infiltrates the moisture-permeable floor topping.

    2304.12.2.5 Ventilation beneath balcony or elevated walking surfaces. Enclosed framing in exterior balconies and elevated walking surfaces that have weather-exposed surfaces shall be provided with openings that provide a net free cross-ventilation area not less than [1] / 150 of the area of each separate space.

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    2304.12.2.6 Wood in contact with the ground or fresh water. Wood used in contact with exposed earth shall be naturally durable for both decay and termite resistance or preservative treated in accordance with AWPA U1 for soil or freshwater use.

    Exception: Untreated wood is permitted where such wood is continuously and entirely below the ground-water level or submerged in fresh water.

  • CBC § 1609.1.1 High relevance — show source text

    ANSI/AWC WFCM—2024: Wood Frame Construction Manual for One- and Two-Family Dwellings

    1609.1.1, 1609.1.1.1, 2302.1, 2308.2.4, 2308.10.7.2, 2309.1

    AWC STJR—2024: Span Tables for Joists and Rafters

    2306.1.1, 2308.8.2.1, 2308.11.1, 2308.11.2

    AWC WCD No. 4—2003: Wood Construction Data—Plank and Beam Framing for Residential Buildings

    2306.1.2

    AWCI Association of the Wall and Ceiling Industry, 513 West Broad Street, Suite 210, Falls Church, VA 22046

    12-B—14: Technical Manual 12B, Third Edition; Standard Practice for the Testing and Inspection of Field Applied Thin Film Intumescent Fire-resistive Materials; an Annotated Guide

    1705.16

    AWPA American Wood Protection Association, P.O. Box 361784, Birmingham, AL 35236-1784

    C1—03: All Timber Products—Preservative Treatment by Pressure Processes

    1505.6

    M4—21: Standard for the Handling, Storage, Field Fabrication and Field Treatment of Preservative-treated Wood Products

    1810.3.2.4.1, 2303.1.9

    U1—23: USE CATEGORY SYSTEM: User Specification for Treated Wood Except Commodity Specification H Table 1507.9.6, 1807.1.4, 1807.3.1, 1809.12, 1810.3.2.4.1, 1812.2, 1812A.2, 2303.1.9, 2304.12.1, 2304.12.2, 2304.12.2.6, 2304.12.2.7, 2304.12.2.8, 2306.1.3

    AWS American Welding Society, 8669 NW 36 Street, #130, Miami, FL 33166-6672

    B5.1—2013-AMD1: Specification for the Qualification of Welding Inspectors

    1705.2.7, 1705A.2.7

    D1.1/D1.1M—20: Structural Welding Code—Steel 1705.2.7, Table 1705A.2.1, 1705A.2.7, 2003.1, 2201.4.1, 2202.4.2, 2202.4.3, 2202.4.4, 2202.4.5, 2215.6.2, 2216.2, 2201A.4.1, 2202A.4.2, 2202A.4.3, 2202A.4.4, 2202A.4.5, 2216A.2

    D1.2/D1.2M—14: Structural Welding Code—Aluminum

    2003.1

    D1.3/D1.3M—2018: Structural Welding Code—Sheet Steel Table 1705A.2.1, 1705.2.7, 1705A.2.7

  • CBC § 2304.12.2.4 Medium relevance — show source text

    Exception: Sawn lumber in buildings located in a geographical region where experience has demonstrated that climatic conditions preclude the need to use durable materials where the structure is exposed to the weather.

    2304.12.2.4 Supporting members for permeable floors and roofs. Wood structural members that support moisture-permeable floors or roofs that are exposed to the weather, such as concrete or masonry slabs, shall be of naturally durable or preservative-treated wood unless separated from such floors or roofs by an impervious moisture barrier. The impervious moisture barrier system protecting the structure supporting floors shall provide positive drainage of water that infiltrates the moisture-permeable floor topping.

    2304.12.2.5 Ventilation beneath balcony or elevated walking surfaces. Enclosed framing in exterior balconies and elevated walking surfaces that have weather-exposed surfaces shall be provided with openings that provide a net free cross-ventilation area not less than [1] / 150 of the area of each separate space.

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    2304.12.2.6 Wood in contact with the ground or fresh water. Wood used in contact with exposed earth shall be naturally durable for both decay and termite resistance or preservative treated in accordance with AWPA U1 for soil or freshwater use.

    Exception: Untreated wood is permitted where such wood is continuously and entirely below the ground-water level or submerged in fresh water.

    2304.12.2.6.1 Posts or columns. Posts and columns that are supporting permanent structures and embedded in concrete that is exposed to the weather or in direct contact with the earth shall be of preservative-treated wood.

    2304.12.2.7 Termite protection. In geographical areas where hazard of termite damage is known to be very heavy, wood floor framing in the locations specified in Section 2304.12.1.1 and exposed framing of exterior decks or balconies shall be of naturally durable species (termite resistant) or preservative treated in accordance with AWPA U1 for the species, product preservative and end use or provided with approved methods of termite protection.

    2304.12.2.8 Wood used in retaining walls and cribs. Wood installed in retaining or crib walls shall be preservative treated in accordance with AWPA U1 for soil and freshwater use.

    2304.12.3 Attic ventilation. For attic ventilation, see Section 1202.2.2.

    2304.12.4 Under-floor ventilation (crawl space). For under-floor ventilation (crawl space), see Section 1202.4.

    2304.12.8 Separate wood framing. [SPCB] Correct the conditions in frame and stucco walls and similar appurtenant construction so that the wood framing is separate from the main structure by a complete concrete or masonry plug with no voids that will allow infestations to enter the structure from the wall. If there is no plug, the foundation shall be 2 inches (51 mm) or more above the grade levels and at least as high as the adjoining slabs or 4-inch (102 mm) concrete barrier seat off installed.

  • CBC § 2304.12.1.3 Medium relevance — show source text

    Exception: [DSA-SS and OSHPD 1, 1R, 2, 4 & 5] At exterior walls where the earth is paved with an asphalt or concrete slab at least 18 inches (457 mm) wide and draining away from the building, the bottom of sills are permitted to be 6 inches (152 mm) above the top of such slab. Other equivalent means of termite and decay protection may be accepted by the enforcement agency.

    2304.12.1.3 Exterior walls below grade. Wood framing members and furring strips in direct contact with the interior of exterior masonry or concrete walls below grade shall be of naturally durable or preservative-treated wood.

    2304.12.1.4 Sleepers and sills. Sleepers and sills on a concrete or masonry slab that is in direct contact with earth shall be of naturally durable or preservative-treated wood.

    2304.12.1.4.1 Additional requirements. [DSA-SS and OSHPD 1, 1R, 2, 4 & 5] Stud walls or partitions at shower or toilet rooms with more than two plumbing fixtures, excluding floor drains, and stud walls adjacent to unroofed paved areas shall rest on a concrete curb extending at least 6 inches (152 mm) above finished floor and pavement level.

    2304.12.1.5 Wood siding. Clearance between wood siding and earth on the exterior of a building shall be not less than 6 inches (152 mm) or less than 2 inches (51 mm) vertical from concrete steps, porch slabs, patio slabs and similar horizontal surfaces exposed to the weather except where siding, sheathing and wall framing are of naturally durable or preservativetreated wood.

    2304.12.2 Other locations. Wood used in the locations specified in Sections 2304.12.2.1 through 2304.12.2.8 shall be naturally durable wood or preservative-treated wood in accordance with AWPA U1. Preservative-treated wood used in interior locations shall be protected with two coats of urethane, shellac, latex epoxy or varnish unless waterborne preservatives are used. Prior to application of the protective finish, the wood shall be dried in accordance with the manufacturer’s recommendations. 2304.12.2.1 Girder ends. The ends of wood girders entering exterior masonry or concrete walls shall be provided with a [1] / 2 inch (12.7 mm) airspace on top, sides and end, unless naturally durable or preservative-treated wood is used.

    2304.12.2.2 Posts or columns. Posts or columns supporting permanent structures and supported by a concrete or masonry slab or footing that is in direct contact with the earth shall be of naturally durable or preservative-treated wood.

    Exception: Posts or columns that meet all of the following:

    1. Are not exposed to the weather, or are protected by a roof, eave, overhang, or other covering if exposed to the weather.

    2. Are supported by concrete piers or metal pedestals projected not less than 1 inch (25 mm) above the slab or deck and are separated from the concrete pier by an impervious moisture barrier.

    3. Are located not less than 8 inches (203 mm) above exposed earth.

  • CBC § 2303.1.7 Medium relevance — show source text

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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

    2309 Wood Shingles and Shakes 1507.8, 1507.9 Wood Structural Panels (see Wood) 2303.1.5 Bracing 2308.10 Decorative 2303.3 Diaphragms 2305.2, 2306.2 Fastening 2304.10 Fire-retardant-treated 2303.2 Quality 2303.1.5 Roof sheathing 2304.8, 2308.11.9 Seismic shear panels 2305.1, 2308.10.6.2

    Shear walls 2306.3 Sheathing 2304.6.1 Standards 2306.1

    Subfloors 805.1.1

    Veneer 1404.6

    Yards or Courts 1201.1, 1205 Exit discharge 1027.4, 1029.1 Group I-2 407.10 Group I-3 408.3.6, 408.6.2 Light, natural 1204 Occupant load 1004.7 Parking garage, open 406.5.5 Unlimited area building 507.2, 507.2.1

    2025 CALIFORNIA BUILDING CODE INDEX-23

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

    INDEX-24 2025 CALIFORNIA BUILDING CODE

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

    HISTORY NOTE APPENDIX

    2025 California Building Code California Code of Regulations, Title 24, Part 2 Volume 2

    HISTORY:

  • CBC § 722.1 Medium relevance — show source text

    3102

    AWC American Wood Council, 222 Catoctin Circle SE, Suite 201, Leesburg, VA 20175

    ANSI/AWC NDS—2024: National Design Specification (NDS) for Wood Construction—with 2018 [DSA-SS, DSA-SS/CC, OSHPD 1, 1R, 2, 4 and 5] 2024 NDS Supplement 202, 722.1, Table 1404.5.3.2, Table 1604.3, 1809.12, 1810.3.2.4, Table 1810.3.2.6, 1905.7.2, Table 2304.6.1, Table 2304.10.2, 2304.13, 2305.1.2, 2306.1, Table 2306.2(1), Table 2306.2(2), Table 2306.3(1), Table 2306.3(2), 2307.1

    ANSI/AWC PWF—2021: Permanent Wood Foundation Design Specification

    1805.2, 1807.1.4, 2304.10.6.2

    ANSI/AWC SDPWS—2021: Special Design Provisions for Wind and Seismic 202, 1604.4, 2305.1, 2305.1.2, 2305.2, 2305.3, 2306.1, 2306.2, 2306.3, Table 2306.3(1), Table 2306.3(3), 2307.1

    ANSI/AWC WFCM—2024: Wood Frame Construction Manual for One- and Two-Family Dwellings

    1609.1.1, 1609.1.1.1, 2302.1, 2308.2.4, 2308.10.7.2, 2309.1

    AWC STJR—2024: Span Tables for Joists and Rafters

    2306.1.1, 2308.8.2.1, 2308.11.1, 2308.11.2

    AWC WCD No. 4—2003: Wood Construction Data—Plank and Beam Framing for Residential Buildings

    2306.1.2

    AWCI Association of the Wall and Ceiling Industry, 513 West Broad Street, Suite 210, Falls Church, VA 22046

    12-B—14: Technical Manual 12B, Third Edition; Standard Practice for the Testing and Inspection of Field Applied Thin Film Intumescent Fire-resistive Materials; an Annotated Guide

    1705.16

    AWPA American Wood Protection Association, P.O. Box 361784, Birmingham, AL 35236-1784

    C1—03: All Timber Products—Preservative Treatment by Pressure Processes

    1505.6

    M4—21: Standard for the Handling, Storage, Field Fabrication and Field Treatment of Preservative-treated Wood Products

    1810.3.2.4.1, 2303.1.9

  • CBC § 2304.11.4.1 Medium relevance — show source text

    2304.11.4.1 Cross-laminated timber roofs. Cross-laminated timber roofs shall be not less than 3 inches (76 mm) in thickness and shall be continuous from support to support and mechanically fastened to one another.

    2304.11.4.2 Sawn, wood structural panel, or glued-laminated plank roofs. Sawn, wood structural panel, or glued-laminated plank roofs shall be one of the following:

    1. Sawn or glued laminated, splined or tongue-and-groove plank, not less than 2 inches (51 mm) nominal in thickness.
    2. 1 [1] / 8 -inch-thick (32 mm) wood structural panel (exterior glue).
    3. Planks not less than 3 inches (76 mm) nominal in width, set on edge close together and laid as required for floors.

    2304.12 Protection against decay and termites. Wood shall be protected from decay and termites in accordance with the applicable provisions of Sections 2304.12.1 through 2304.12.4.

    2304.12.1 Locations requiring waterborne preservatives or naturally durable wood. Wood used above ground in the locations specified in Sections 2304.12.1.1 through 2304.12.1.5 shall be naturally durable wood or preservative-treated wood using waterborne preservatives, in accordance with AWPA U1 for above-ground use.

    2025 CALIFORNIA BUILDING CODE 23-23

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

    WOOD

    2304.12.1.1 Joists, girders and subfloor. Wood joists or wood structural floors that are closer than 18 inches (457 mm) or wood girders that are closer than 12 inches (305 mm) to the exposed ground in crawl spaces or unexcavated areas located within the perimeter of the building foundation shall be of naturally durable or preservative-treated wood.

    2304.12.1.1.1 [SPCB] There shall be a clearance of at least 18 inches (457 mm) between the underside of wood floor joists and the finished surface of the ground, and at least 12 inches (305 mm) between the underside of any other wood horizontal framing member and the finished surface of the ground. The ground underneath floor joists shall be leveled or smoothed off so as to maintain a reasonably even surface.

    Exception: For purposes of structural pest control inspection, a minimum of 12 inches (305 mm) of clearance under-floor joists shall be considered adequate except that such clearance shall not be necessary where the subarea soil is of such a nature as to prevent excavation or where excavation would create a hazard from shifting soil or other causes.

    2304.12.1.2 Wood supported by exterior foundation walls. Wood framing members, including wood sheathing, that are in contact with exterior foundation walls and are less than 8 inches (203 mm) from exposed earth shall be of naturally durable or preservative-treated wood.

    Exception: [DSA-SS and OSHPD 1, 1R, 2, 4 & 5] At exterior walls where the earth is paved with an asphalt or concrete slab at least 18 inches (457 mm) wide and draining away from the building, the bottom of sills are permitted to be 6 inches (152 mm) above the top of such slab. Other equivalent means of termite and decay protection may be accepted by the enforcement agency.

  • CBC § 1.1 Medium relevance — show source text

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

    BUILDING PLANNING

    1. Wood siding, sheathing and wall framing on the exterior of a building having a clearance of less than 6 inches (152 mm) from the ground or less than 2 inches (51 mm) measured vertically from concrete steps, porch slabs, patio slabs and similar horizontal surfaces exposed to the weather.

    2. Wood structural members supporting moisture-permeable floors or roofs that are exposed to the weather, such as concrete or masonry slabs, unless separated from such floors or roofs by an impervious moisture barrier. The impervious moisture barrier system protecting the structure supporting floors shall provide positive drainage of water that infiltrates the moisture- permeable floor topping.

    3. Wood furring strips or other wood framing members attached directly to the interior of exterior masonry walls or concrete walls below grade except where an approved vapor retarder is applied between the wall and the furring strips or framing members.

    4. Portions of wood structural members that form the structural supports of buildings, decks, balconies, porches or similar permanent building appurtenances where those members are exposed to the weather without adequate protection from a roof, eave, overhang or other covering that prevents moisture or water accumulation on the surface or at joints between members. Exception: Sawn lumber used in structures located in a geographical region where experience has demonstrated that climatic conditions preclude the need to use naturally durable or preservative-treated wood where the structure is exposed to the weather.

    5. Wood columns in contact with basement floor slabs unless supported by concrete piers or metal pedestals projecting not less than 1 inch (25 mm) above the concrete floor and separated from the concrete pier by an impervious moisture barrier.

    R304.1.1 Field treatment. Field-cut ends, notches and drilled holes of preservative-treated wood shall be treated in the field in accordance with AWPA M4.

    R304.1.2 Ground contact. All wood in contact with the ground, embedded in concrete in direct contact with the ground or embedded in concrete exposed to the weather that supports permanent structures intended for human occupancy shall be approved pressure-preservative-treated wood suitable for ground contact use, except that untreated wood used entirely below groundwater level or continuously submerged in fresh water shall not be required to be pressure-preservative treated.

    R304.1.3 Ventilation required beneath balcony or elevated walking surfaces. Enclosed framing in exterior balconies and elevated walking surfaces that are exposed to rain, snow or drainage from irrigation shall be provided with openings that provide a net-free cross-ventilation area not less than [1] / 150 of the area of each separate space.

    R304.2 Quality mark. Lumber and plywood required to be pressure-preservative treated in accordance with Section R304.1 shall bear the quality mark of an approved inspection agency that maintains continuing supervision, testing and inspection over the quality of the product and that has been approved by an accreditation body that complies with the requirements of the American Lumber Standard Committee treated wood program.

    R304.2.1 Required information. The required quality mark on each piece of pressure-preservative-treated lumber or plywood shall contain the following information:

    1. Identification of the treating plant.
    2. Type of preservative.
    3. The minimum preservative retention.
    4. End use for which the product was treated.
    5. Standard to which the product was treated.
    6. Identity of the approved inspection agency.
    7. The designation “Dry,” if applicable.

Frequently asked questions

Do treated members need to be dried before they are installed?

Yes — when the treated wood will be used in enclosed locations where drying in service cannot readily occur, it must be at 19% moisture content or less before being covered, per § 2303.1.9.2.

What label or stamp do I need to see on treated lumber?

The piece must bear a quality mark from an accredited inspection agency that shows treating manufacturer, preservative type, minimum retention, end use, AWPA standard and inspection agency identity as required by § 2303.1.9.1.

If I cut or drill treated lumber on site, do I need to re-treat the cut?

Yes. Field-cut ends, notches and drilled holes must be treated in accordance with AWPA M4 (field-treatment handling standard) as referenced by the CBC; the code requires appropriate field treatment.

Are there numeric clearances I can memorize for quick decisions?

Yes — common ones are: joists within 18 in. of exposed ground and girders within 12 in. require treated or naturally durable wood; framing contacting exterior foundation walls within 8 in. of exposed ground requires treatment; siding clearance less than 6 in. to exposed earth triggers protection — see § 2304.12.1 clauses.

Can I use a non-waterborne preservative for above‑ground framed members?

For the locations listed in § 2304.12.1 the code requires naturally durable wood or preservative-treated wood using waterborne preservatives in accordance with AWPA U1 for above-ground use (see § 2304.12.1).

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