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Chapter 3 — BUILDING PLANNING

Section R304 — PROTECTION OF WOOD AND WOOD-BASED PRODUCTS AGAINST DECAY

2025 California Residential Code (Title 24, Part 2.5) · 2025 edition · updated 2026-07-29 · California

Italicized text is a California amendment to the model code, as printed in the official publication.

R304.1 Location required.

Protection of wood and wood-based products from decay shall be provided in the following locations by the use of naturally durable wood or wood that is preservative-treated in accordance with AWPA U1.

  1. In crawl spaces or unexcavated areas located within the periphery of the building foundation, wood joists or the bottom of a wood structural floor where closer than 18 inches (457 mm) to exposed ground, wood girders where closer than 12 inches (305 mm) to exposed ground, and wood columns where closer than 8 inches (204 mm) to exposed ground.
  2. Wood framing members, including columns, that rest directly on concrete or masonry exterior foundation walls and are less than 8 inches (203 mm) from the exposed ground.
  3. Sills and sleepers on a concrete or masonry slab that is in direct contact with the ground unless separated from such slab by an impervious moisture barrier.
  4. The ends of wood girders entering exterior masonry or concrete walls having clearances of less than [1] / 2 inch (12.7 mm) on tops, sides and ends.

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.

Exception: Quality marks on lumber less than 1 inch (25 mm) nominal thickness, or lumber less than nominal 1 inch by 5 inches (25 mm by 127 mm) or 2 inches by 4 inches (51 mm by 102 mm) or lumber 36 inches (914 mm) or less in length shall be applied by stamping the faces of exterior pieces or by end labeling not less than 25 percent of the pieces of a bundled unit.

R304.3 Fasteners and connectors in contact with preservative-treated and fire-retardant-treated wood.

Fasteners, including nuts and washers, and connectors in contact with preservative-treated wood and fire-retardant-treated wood shall be in accordance with this section. The coating weights for zinc-coated fasteners shall be in accordance with ASTM A153. The coating weight for zinccoated nails shall be in accordance with ASTM A153 Class D or ASTM A641 Class 3S. Stainless steel driven fasteners shall be in accordance with the material requirements of ASTM F1667.

R304.3.1 Fasteners for preservative-treated wood. Fasteners, including nuts and washers, for preservative-treated wood shall be of hot-dipped, zinc-coated galvanized steel, stainless steel, silicon bronze or copper. Staples shall be of stainless steel. Coating types and weights for connectors in contact with preservative-treated wood shall be in accordance with the connector manufacturer’s recommendations. In the absence of manufacturer’s recommendations, not less than ASTM A653 type G185 zinc-coated galvanized steel, or equivalent, shall be used.

Exceptions:

  1. One-half-inch diameter (12.7 mm) or greater steel bolts.
  2. Fasteners other than nails, staples and timber rivets shall be permitted to be of mechanically deposited zinc-coated steel with coating weights in accordance with ASTM B695, Class 55 minimum.
  3. Plain carbon steel fasteners in SBX/DOT and zinc borate preservative-treated wood in an interior, dry environment shall be permitted.

3-34 2025 CALIFORNIA RESIDENTIAL CODE

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

BUILDING PLANNING

R304.3.2 Fastenings for wood foundations. Fastenings, including nuts and washers, for wood foundations shall be as required in AWC PWF.

R304.3.3 Fasteners for fire-retardant-treated wood used in exterior applications or wet or damp locations. Fasteners, including nuts and washers, for fire-retardant-treated wood used in exterior applications or wet or damp locations shall be of hot-dipped, zinc-coated galvanized steel, stainless steel, silicon bronze or copper. Fasteners other than nails, staples and timber rivets shall be permitted to be of mechanically deposited zinc-coated steel with coating weights in accordance with ASTM B695, Class 55 minimum.

R304.3.4 Fasteners for fire-retardant-treated wood used in interior applications. Fasteners, including nuts and washers, for fire-retardant-treated wood used in interior locations shall be in accordance with the manufacturer’s recommendations. In the absence of the manufacturer’s recommendations, Section R304.3.3 shall apply.

R304.4 Plastic composites.

Plastic composite exterior deck boards, stair treads, guards and handrails containing wood, cellulosic or other biodegradable materials shall comply with the requirements of Section R507.2.2.

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▸ Contents — 2025 California Residential Code (Title 24, Part 2.5)
2025 California Residential Code (Title 24, Part 2.5)
  1. Chapter 1 — ADMINISTRATION
  2. Chapter 2 — DEFINITIONS
  3. ▸ Chapter 3 — BUILDING PLANNING
    Overview
    1. Section R300 — SITE DRAINAGE
    2. Section R301 — DESIGN CRITERIA
    3. Section R302 — FIRE-RESISTANT CONSTRUCTION
    4. Section R303 — FOAM PLASTIC
    5. Section R304 — PROTECTION OF WOOD AND WOOD-BASED PRODUCTS AGAI…
    6. Section R305 — PROTECTION AGAINST SUBTERRANEAN TERMITES
    7. Section R306 — FLOOD-RESISTANT CONSTRUCTION
    8. Section R307 — STORM SHELTERS
    9. Section R308 — SITE ADDRESS
    10. Section R309 — AUTOMATIC SPRINKLER SYSTEMS
    11. Section R310 — SMOKE ALARMS
    12. Section R311 — CARBON MONOXIDE ALARMS
    13. Section R312 — MINIMUM ROOM AREAS
    14. Section R313 — CEILING HEIGHT
    15. Section R314 — MEZZANINES
    16. Section R315 — SLEEPING LOFTS
    17. Section R316 — HABITABLE ATTICS
    18. Section R317 — GARAGES AND CARPORTS
    19. Section R318 — MEANS OF EGRESS
    20. Section R319 — EMERGENCY ESCAPE AND RESCUE OPENINGS
    21. Section R320 — HANDRAILS
    22. Section R321 — GUARDS AND WINDOW FALL PROTECTION
    23. Section R322 — ACCESSIBILITY
    24. Section R323 — ELEVATORS AND PLATFORM LIFTS
    25. Section R324 — GLAZING
    26. Section R325 — LIGHT, VENTILATION AND HEATING
    27. Section R326 — SANITATION
    28. Section R327 — TOILET, BATH AND SHOWER SPACES
    29. Section R328 — AGING-IN-PLACE DESIGN AND FALL PREVENTION
    30. Section R329 — SOLAR ENERGY SYSTEMS
    31. Section R330 — ENERGY STORAGE SYSTEMS
    32. Section R331 — STATIONARY ENGINE GENERATORS
    33. Section R332 — STATIONARY FUEL CELL POWER SYSTEMS
    34. Section R333 — RESERVED
    35. Section R334 — CONSTRUCTION WASTE REDUCTION, DISPOSAL AND RECY…
    36. Section R335 — SPECIAL PROVISIONS FOR LICENSED 24-HOUR CARE FA…
    37. Section R336 — LARGE FAMILY DAY-CARE HOMES
    38. Section R337 — MATERIALS AND CONSTRUCTION METHODS FOR EXTERIOR…
    39. Section R338 — ELECTRIC VEHICLE
    40. Section 339 — RESERVED
    41. Section R340 — POLLUTANT CONTROL
  4. Chapter 4 — FOUNDATIONS
  5. Chapter 5 — FLOORS
  6. Chapter 6 — WALL CONSTRUCTION
  7. Chapter 7 — WALL COVERING
  8. Chapter 8 — ROOF-CEILING CONSTRUCTION
  9. Chapter 9 — ROOF ASSEMBLIES
  10. Chapter 10 — CHIMNEYS AND FIREPLACES
  11. Chapter 44 — REFERENCED STANDARDS
  12. Appendix AA — BOARD OF APPEALS
  13. Appendix AB — PERMIT FEES
  14. Appendix AC — RESERVED
  15. Appendix BA — RESERVED
  16. Appendix BB — TINY HOUSES
  17. Appendix BC — RESERVED
  18. Appendix BD — RESERVED
  19. Appendix BE — RADON CONTROL METHODS
  20. Appendix BF — PATIO COVERS
  21. Appendix BG — SOUND TRANSMISSION
  22. Appendix BH — AUTOMATIC VEHICULAR GATES
  23. Appendix BI — LIGHT STRAW-CLAY CONSTRUCTION
  24. Appendix BJ — STRAWBALE CONSTRUCTION
  25. Appendix BK — COB CONSTRUCTION (MONOLITHIC ADOBE)
  26. Appendix BL — HEMP-LIME (HEMPCRETE) CONSTRUCTION
  27. Appendix BM — 3D-PRINTED BUILDING CONSTRUCTION
  28. Appendix BN — EXTENDED PLATE WALL CONSTRUCTION
  29. Appendix BO — EXISTING BUILDINGS AND STRUCTURES
  30. Appendix CA — RESERVED
  31. Appendix CB — RESERVED
  32. Appendix CC — RESERVED
  33. Appendix CD — RESERVED
  34. Appendix CE — RESERVED
  35. Appendix CF — RESERVED
  36. Appendix CG — NONSEWERED SANITATION SYSTEMS
  37. Appendix CH — PRIVATE SEWAGE DISPOSAL
  38. Appendix CI — SWIMMING POOL SAFETY ACT
  39. Appendix CJ — EMERGENCY HOUSING
  40. Appendix CK — AREAS PROTECTED BY THE FACILITIES OF THE CENTRAL…

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