Foundation drainage, dampproofing/waterproofing and under‑floor spaces

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

• CRC § 2.3 High relevance — show source text

  R405.2.3 Drainage system. In other than Group I soils, a sump shall be provided to drain the porous layer and footings. The sump shall be not less than 24 inches (610 mm) in diameter or 20 inches square (0.0129 m [2] ), shall extend not less than 24 inches (610

  4-42 2025 CALIFORNIA RESIDENTIAL CODE

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

  FOUNDATIONS

  mm) below the bottom of the basement floor and shall be capable of positive gravity or mechanical drainage to remove any accumulated water. The drainage system shall discharge into an approved sewer system or to daylight.

  SECTION R406 —FOUNDATION WATERPROOFING AND DAMPPROOFING

  R406.1 Concrete and masonry foundation dampproofing. Except where required by Section R406.2 to be waterproofed, foundation walls that retain earth and enclose interior spaces and floors below grade shall be dampproofed from the finished grade to the

                                                                                      higher of the top of the footing or 6 inches (152 mm) below the top of the basement floor. Masonry walls shall have not less than [3] / 8
  

  inch (9.5 mm) Portland cement parging applied to the exterior of the wall. The parging shall be dampproofed in accordance with one of the following:

  1. Bituminous coating.
  2. Three pounds per square yard (1.63 kg/m [2] ) of acrylic modified cement.
  3. One-eighth-inch (3.2 mm) coat of surface-bonding cement complying with ASTM C887.
  4. Any material permitted for waterproofing in Section R406.2.
  5. Other approved methods or materials.

  Exception: Parging of unit masonry walls is not required where a material is approved for direct application to the masonry.

  Concrete walls shall be dampproofed by applying any one of the listed dampproofing materials or any one of the waterproofing materials listed in Section R406.2 to the exterior of the wall.

  R406.2 Concrete and masonry foundation waterproofing. In areas where a high water table or other severe soil-water conditions are known to exist, exterior foundation walls that retain earth and enclose interior spaces and floors below grade shall be waterproofed from the finished grade to the higher of the top of the footing or 6 inches (152 mm) below the top of the basement floor. Walls shall be waterproofed in accordance with one of the following:

  1. Two-ply hot-mopped felts.
  2. Fifty-five-pound (25 kg) roll roofing.
  3. Forty-mil (1 mm) polymer-modified asphalt.
  4. Sixty-mil (1.5 mm) flexible polymer cement.
  5. One-eighth-inch (3 mm) cement-based, fiber-reinforced, waterproof coating.
  6. Sixty-mil (1.5 mm) solvent-free liquid-applied synthetic rubber.

  All joints in membrane waterproofing shall be lapped and sealed with an adhesive compatible with the membrane.

  Exception: Organic-solvent-based products such as hydrocarbons, chlorinated hydrocarbons, ketones and esters shall not be used for ICF walls with expanded polystyrene form material. Use of plastic roofing cements, acrylic coatings, latex coatings, mortars and pargings to seal ICF walls is permitted. Cold-setting asphalt or hot asphalt shall conform to Type C of ASTM D449. Hot asphalt shall be applied at a temperature of less than 200°F (93°C).

• CRC § 1805.2.2. High relevance — show source text

  Waterproofing shall be applied from the bottom of the wall to not less than 12 inches (305 mm) above the maximum elevation of the ground-water table. The remainder of the wall shall be dampproofed in accordance with Section 1805.2.2. Waterproofing shall consist of two-ply hot-mopped felts, not less than 6-mil (0.006 inch; 0.152 mm) polyvinyl chloride, 40-mil (0.040 inch; 1.02 mm) polymer-modified asphalt, 6-mil (0.006 inch; 0.152 mm) polyethylene or other approved methods or materials capable of bridging nonstructural cracks. Joints in the membrane shall be lapped and sealed in accordance with the manufacturer’s installation instructions.

  1805.3.2.1 Surface preparation of walls. Prior to the application of waterproofing materials on concrete or masonry walls, the walls shall be prepared in accordance with Section 1805.2.2.1.

  1805.3.3 Joints and penetrations. Joints in walls and floors, joints between the wall and floor and penetrations of the wall and floor shall be made watertight utilizing approved methods and materials.

  1805.4 Subsoil drainage system. Where a hydrostatic pressure condition does not exist, dampproofing shall be provided and a base shall be installed under the floor and a drain installed around the foundation perimeter. A subsoil drainage system designed and constructed in accordance with Section 1805.1.3 shall be deemed adequate for lowering the ground-water table.

  18-8 2025 CALIFORNIA BUILDING CODE

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

  SOILS AND FOUNDATIONS

  1805.4.1 Floor base course. Floors of basements, except as provided for in Section 1805.1.1, shall be placed over a floor base course not less than 4 inches (102 mm) in thickness that consists of gravel or crushed stone containing not more than 10 percent of material that passes through a No. 4 (4.75 mm) sieve.

  Exception s:

  1. Where a site is located in well-drained gravel or sand/gravel mixture soils, a floor base course is not required. 2. [HCD 1] When a capillary break is installed in accordance with the California Green Building Standards Code (CALGreen), Chapter 4, Division 4.5.

  1805.4.2 Foundation drain. A drain shall be placed around the perimeter of a foundation that consists of gravel or crushed stone containing not more than 10-percent material that passes through a No. 4 (4.75 mm) sieve. The drain shall extend not less than 12 inches (305 mm) beyond the outside edge of the footing. The thickness shall be such that the bottom of the drain is not higher than the bottom of the base under the floor, and that the top of the drain is not less than 6 inches (152 mm) above the top of the footing. The top of the drain shall be covered with an approved filter membrane material. Where a drain tile or perforated pipe is used, the invert of the pipe or tile shall not be higher than the floor elevation. The top of joints or the top of perforations shall be protected with an approved filter membrane material.

• CRC § 3.2 High relevance — show source text

  1805 A .3.2 Walls. Walls required to be waterproofed shall be of concrete or masonry and shall be designed and constructed to withstand the hydrostatic pressures and other lateral loads to which the walls will be subjected.

  Waterproofing shall be applied from the bottom of the wall to not less than 12 inches (305 mm) above the maximum elevation of the ground-water table. The remainder of the wall shall be dampproofed in accordance with Section 1805 A .2.2. Waterproofing shall consist of two-ply hot-mopped felts, not less than 6-mil (0.006 inch; 0.152 mm) polyvinyl chloride, 40-mil (0.040 inch; 1.02 mm) polymer-modified asphalt, 6-mil (0.006 inch; 0.152 mm) polyethylene or other approved methods or materials capable of bridging nonstructural cracks. Joints in the membrane shall be lapped and sealed in accordance with the manufacturer’s installation instructions.

  1805 A .3.2.1 Surface preparation of walls. Prior to the application of waterproofing materials on concrete or masonry walls, the walls shall be prepared in accordance with Section 1805 A .2.2.1.

  1805 A .3.3 Joints and penetrations. Joints in walls and floors, joints between the wall and floor and penetrations of the wall and floor shall be made watertight utilizing approved methods and materials.

  1805 A .4 Subsoil drainage system. Where a hydrostatic pressure condition does not exist, dampproofing shall be provided and a base shall be installed under the floor and a drain installed around the foundation perimeter. A subsoil drainage system designed and constructed in accordance with Section 1805 A .1.3 shall be deemed adequate for lowering the ground-water table.

  1805 A .4.1 Floor base course. Floors of basements, except as provided for in Section 1805 A .1.1, shall be placed over a floor base course not less than 4 inches (102 mm) in thickness that consists of gravel or crushed stone containing not more than 10 percent of material that passes through a No. 4 (4.75 mm) sieve.

  Exception: Where a site is located in well-drained gravel or sand/gravel mixture soils, a floor base course is not required.

  18A-8 2025 CALIFORNIA BUILDING CODE

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

  SOILS AND FOUNDATIONS

  1805 A .4.2 Foundation drain. A drain shall be placed around the perimeter of a foundation that consists of gravel or crushed stone containing not more than 10-percent material that passes through a No. 4 (4.75 mm) sieve. The drain shall extend not less than 12 inches (305 mm) beyond the outside edge of the footing. The thickness shall be such that the bottom of the drain is not higher than the bottom of the base under the floor, and that the top of the drain is not less than 6 inches (152 mm) above the top of the footing. The top of the drain shall be covered with an approved filter membrane material. Where a drain tile or perforated pipe is used, the invert of the pipe or tile shall not be higher than the floor elevation.

• CRC § 4.1 High relevance — show source text

  Drainage tiles or perforated pipe shall be placed on not less than 2 inches (51 mm) of washed gravel or crushed rock not less than one sieve size larger than the tile joint opening or perforation and covered with not less than 6 inches (152 mm) of the same material.

  Exception: A drainage system is not required where the foundation is installed on well-drained ground or sand-gravel mixture soils according to the Unified Soil Classification System, Group I soils, as detailed in Table R401.4.1(2).

  R405.1.1 Precast concrete foundation. Precast concrete walls that retain earth and enclose habitable or useable space located below-grade that rest on crushed stone footings shall have a perforated drainage pipe installed below the base of the wall on either the interior or exterior side of the wall, not less than 1 foot (305 mm) beyond the edge of the wall. If the exterior drainage pipe is used, an approved filter membrane material shall cover the pipe. The drainage system shall discharge into an approved sewer system or to daylight.

  R405.2 Wood foundations. Wood foundations enclosing habitable or usable spaces located below grade shall be adequately drained in accordance with Sections R405.2.1 through R405.2.3.

  R405.2.1 Base. A porous layer of gravel, crushed stone or coarse sand shall be placed to a minimum thickness of 4 inches (102 mm) under the basement floor. Provision shall be made for automatic draining of this layer and the gravel or crushed stone wall footings.

  R405.2.2 Vapor retarder. A 6-mil-thick (0.15 mm) polyethylene vapor retarder shall be applied over the porous layer with the basement floor constructed over the polyethylene.

  R405.2.3 Drainage system. In other than Group I soils, a sump shall be provided to drain the porous layer and footings. The sump shall be not less than 24 inches (610 mm) in diameter or 20 inches square (0.0129 m [2] ), shall extend not less than 24 inches (610

  4-42 2025 CALIFORNIA RESIDENTIAL CODE

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

  FOUNDATIONS

  mm) below the bottom of the basement floor and shall be capable of positive gravity or mechanical drainage to remove any accumulated water. The drainage system shall discharge into an approved sewer system or to daylight.

  SECTION R406 —FOUNDATION WATERPROOFING AND DAMPPROOFING

  R406.1 Concrete and masonry foundation dampproofing. Except where required by Section R406.2 to be waterproofed, foundation walls that retain earth and enclose interior spaces and floors below grade shall be dampproofed from the finished grade to the

                                                                                      higher of the top of the footing or 6 inches (152 mm) below the top of the basement floor. Masonry walls shall have not less than [3] / 8
  

  inch (9.5 mm) Portland cement parging applied to the exterior of the wall. The parging shall be dampproofed in accordance with one of the following:

  1. Bituminous coating.
  2. Three pounds per square yard (1.63 kg/m [2] ) of acrylic modified cement.
  3. One-eighth-inch (3.2 mm) coat of surface-bonding cement complying with ASTM C887.
  4. Any material permitted for waterproofing in Section R406.2.
  5. Other approved methods or materials.
• CRC § 4-6 High relevance — show source text

  R403 Footings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

  R404 Foundation and Retaining Walls . . . . . . . . . . . . . . . . 4-24

  R405 Foundation Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . 4-42

  R406 Foundation Waterproofing and Dampproofing . . . 4-43

  R407 Columns. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-44

  R408 Under-Floor Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-44

  CHAPTER 5 FLOORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3

  R501 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3

  R502 Wood Floor Framing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3

  R503 Floor Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12

  R504 Pressure Preservative-Treated Wood

  Floors (On Ground) . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14

  R505 Cold-Formed Steel Floor Framing . . . . . . . . . . . . . . . 5-14

  R506 Concrete Floors (On Ground) . . . . . . . . . . . . . . . . . . . 5-26

  R507 Exterior Decks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26

  CHAPTER 6 WALL CONSTRUCTION. . . . . . . . . . . . . . . . . . . 6-3

  R601 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

  R602 Wood Wall Framing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

  R603 Cold-Formed Steel Wall Framing. . . . . . . . . . . . . . . . 6-53

  R604 Wood Structural Panels . . . . . . . . . . . . . . . . . . . . . . . . 6-93

  R605 Particleboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-93

  R606 General Masonry Construction. . . . . . . . . . . . . . . . . . 6-93

• CRC § 1202.4. High relevance — show source text

  1804 A .7 Controlled low-strength material (CLSM). Where shallow foundations will bear on controlled low-strength material (CLSM), the CLSM shall comply with the provisions of an approved geotechnical report, as set forth in Section 1803 A .

  SECTION 1805 A —DAMPPROOFING AND WATERPROOFING

  1805 A .1 General. Walls or portions thereof that retain earth and enclose interior spaces and floors below grade shall be waterproofed and dampproofed in accordance with this section, with the exception of those spaces containing groups other than residential and institutional where such omission is not detrimental to the building or occupancy.

  Ventilation for crawl spaces shall comply with Section 1202.4.

  1805 A .1.1 Story above grade plane. Where a basement is considered a story above grade plane and the finished ground level adjacent to the basement wall is below the basement floor elevation for 25 percent or more of the perimeter, the floor and walls shall be dampproofed in accordance with Section 1805 A .2 and a foundation drain shall be installed in accordance with Section 1805 A .4.2. The foundation drain shall be installed around the portion of the perimeter where the basement floor is below ground level. The provisions of Sections 1803 A .5.4, 1805 A .3 and 1805 A .4.1 shall not apply in this case.

  1805 A .1.2 Under-floor space. The finished ground level of an under-floor space such as a crawl space shall not be located below the bottom of the footings. Where there is evidence that the ground-water table rises to within 6 inches (152 mm) of the ground

  2025 CALIFORNIA BUILDING CODE 18A-7

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

  SOILS AND FOUNDATIONS

  level at the outside building perimeter, or that the surface water does not readily drain from the building site, the ground level of the under-floor space shall be as high as the outside finished ground level, unless an approved drainage system is provided. The provisions of Sections 1803 A .5.4, 1805 A .2, 1805 A .3 and 1805 A .4 shall not apply in this case.

  1805 A .1.2.1 Flood hazard areas. For buildings and structures in flood hazard areas as established in Section 1612 A .3, the finished ground level of an under-floor space such as a crawl space shall be equal to or higher than the outside finished ground level on one side or more.

  Exception: Under-floor spaces of Group R-3 buildings that meet the requirements of FEMA TB 11.

• CRC § 2.4 High relevance — show source text

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

  FOUNDATIONS

  R404.2.4 Backfilling. Wood foundation walls shall not be backfilled until the basement floor and first floor have been constructed or the walls have been braced. For crawl space construction, backfill or bracing shall be installed on the interior of the walls prior to placing backfill on the exterior.

  R404.2.5 Drainage and dampproofing. Wood foundation basements shall be drained and dampproofed in accordance with Sections R405 and R406, respectively.

  R404.2.6 Fastening. Wood structural panel foundation wall sheathing shall be attached to framing in accordance with Table R602.3(1) and Section R402.1.1.

  R404.3 Wood sill plates. Wood sill plates shall be not less than 2-inch by 4-inch (51 mm by 102 mm) nominal lumber. Sill plate anchorage shall be in accordance with Sections R403.1.6 and R602.11.

  R404.4 Retaining walls. Retaining walls that are not laterally supported at the top and that retain in excess of 48 inches (1219 mm) of unbalanced fill, or retaining walls exceeding 24 inches (610 mm) in height that resist lateral loads in addition to soil, shall be designed in accordance with accepted engineering practice to ensure stability against overturning, sliding, excessive foundation pressure and water uplift. Retaining walls shall be designed for a safety factor of 1.5 against lateral sliding and overturning. This section shall not apply to foundation walls supporting buildings.

  R404.5 Precast concrete foundation walls.

  R404.5.1 Design. Precast concrete foundation walls shall be designed in accordance with accepted engineering practice. The design and manufacture of precast concrete foundation wall panels shall comply with the materials requirements of Section R402.3 or ACI 318. The panel design drawings shall be prepared by a registered design professional where required by the statutes of the jurisdiction in which the project is to be constructed in accordance with Section R106.1.

  R404.5.2 Precast concrete foundation design drawings. Precast concrete foundation wall design drawings shall be submitted to the building official and approved prior to installation. Drawings shall include, at a minimum, the following information:

  1. Design loading as applicable.

  2. Footing design and material.

  3. Concentrated loads and their points of application.

  4. Soil bearing capacity.

  5. Maximum allowable total uniform load.

  6. Seismic design category.

  7. Basic wind speed.

  R404.5.3 Identification. Precast concrete foundation wall panels shall be identified by a certificate of inspection label issued by an approved third-party inspection agency.

  SECTION R405 —FOUNDATION DRAINAGE

  R405.1 Concrete or masonry foundations. Drains shall be provided around concrete or masonry foundations that retain earth and enclose habitable or usable spaces located below grade. Drainage tiles, gravel or crushed stone drains, perforated pipe or other approved systems or materials shall be installed at or below the top of the footing or below the bottom of the slab and shall discharge by gravity or mechanical means into an approved drainage system. Gravel or crushed stone drains shall extend not less than 1 foot (305 mm) beyond the outside edge of the footing and 6 inches (152 mm) above the top of the footing and be covered with an approved filter membrane material. The top of open joints of drain tiles shall be protected with strips of building paper.

• CRC § 1804.6 High relevance — show source text

  3. In coastal high hazard areas, unless such fill is conducted or placed to avoid diversion of water and waves toward any building or structure.
  4. Where design flood elevations are specified but floodways have not been designated, unless it has been demonstrated that the cumulative effect of the proposed flood hazard area encroachment, when combined with all other existing and anticipated flood hazard area encroachment, will not increase the design flood elevation more than 1 foot (305 mm) at any point.

  1804.6 Compacted fill material. Where shallow foundations will bear on compacted fill material, the compacted fill shall comply with the provisions of an approved geotechnical report, as set forth in Section 1803.

  Exception: Compacted fill material 12 inches (305 mm) in depth or less need not comply with an approved report, provided that the in-place dry density is not less than 90 percent of the maximum dry density at optimum moisture content determined in accordance with ASTM D1557. The compaction shall be verified by special inspection in accordance with Section 1705.6.

  1804.7 Controlled low-strength material (CLSM). Where shallow foundations will bear on controlled low-strength material (CLSM), the CLSM shall comply with the provisions of an approved geotechnical report, as set forth in Section 1803.

  SECTION 1805—DAMPPROOFING AND WATERPROOFING

  1805.1 General. Walls or portions thereof that retain earth and enclose interior spaces and floors below grade shall be waterproofed and dampproofed in accordance with this section, with the exception of those spaces containing groups other than residential and institutional where such omission is not detrimental to the building or occupancy.

  Ventilation for crawl spaces shall comply with Section 1202.4.

  1805.1.1 Story above grade plane. Where a basement is considered a story above grade plane and the finished ground level adjacent to the basement wall is below the basement floor elevation for 25 percent or more of the perimeter, the floor and walls shall be dampproofed in accordance with Section 1805.2 and a foundation drain shall be installed in accordance with Section 1805.4.2. The foundation drain shall be installed around the portion of the perimeter where the basement floor is below ground level. The provisions of Sections 1803.5.4, 1805.3 and 1805.4.1 shall not apply in this case.

  2025 CALIFORNIA BUILDING CODE 18-7

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

  SOILS AND FOUNDATIONS

  1805.1.2 Under-floor space. The finished ground level of an under-floor space such as a crawl space shall not be located below the bottom of the footings. Where there is evidence that the ground-water table rises to within 6 inches (152 mm) of the ground level at the outside building perimeter, or that the surface water does not readily drain from the building site, the ground level of the under-floor space shall be as high as the outside finished ground level, unless an approved drainage system is provided. The provisions of Sections 1803.5.4, 1805.2, 1805.3 and 1805.4 shall not apply in this case.

• CRC § 1.3 High relevance — show source text

  1805 A .1.3 Ground-water control. Where the ground-water table is lowered and maintained at an elevation not less than 6 inches (152 mm) below the bottom of the lowest floor, the floor and walls shall be dampproofed in accordance with Section 1805 A .2. The design of the system to lower the ground-water table shall be based on accepted principles of engineering that shall consider, but not necessarily be limited to, permeability of the soil, rate at which water enters the drainage system, rated capacity of pumps, head against which pumps are to operate and the rated capacity of the disposal area of the system.

  1805 A .2 Dampproofing. Where hydrostatic pressure will not occur as determined by Section 1803 A .5.4, floors and walls shall be dampproofed in accordance with this section.

  1805 A .2.1 Floors. Dampproofing materials for floors shall be installed between the floor and the base course required by Section 1805 A .4.1, except where a separate floor is provided above a concrete slab.

  Where installed beneath the slab, dampproofing shall consist of not less than 6-mil (0.006 inch; 0.152 mm) polyethylene with joints lapped not less than 6 inches (152 mm), or other approved methods or materials. Where permitted to be installed on top of the slab, dampproofing shall consist of mopped-on bitumen, not less than 4-mil (0.004 inch; 0.102 mm) polyethylene, or other approved methods or materials. Joints in the membrane shall be lapped and sealed in accordance with the manufacturer’s installation instructions.

  1805 A .2.2 Walls. Dampproofing materials for walls shall be installed on the exterior surface of the wall, and shall extend from the top of the footing to above ground level. Dampproofing shall consist of a bituminous material, 3 pounds per square yard (16 N/m [2] ) of acrylic modified cement, [1] / 8 inch (3.2 mm) coat of surface-bonding mortar complying with ASTM C887, any of the materials permitted for waterproofing by Section 1805.3.2 or other approved methods or materials.

  1805 A .2.2.1 Surface preparation of walls. Prior to application of dampproofing materials on concrete walls, holes and recesses resulting from the removal of form ties shall be sealed with a bituminous material or other approved methods or materials. Unit masonry walls shall be parged on the exterior surface below ground level with not less than [3] / 8 inch (9.5 mm) of Portland cement mortar. The parging shall be coved at the footing.

  Exception: Parging of unit masonry walls is not required where a material is approved for direct application to the masonry.

  1805 A .3 Waterproofing. Where the ground-water investigation required by Section 1803 A .5.4 indicates that a hydrostatic pressure condition exists, and the design does not include a ground-water control system as described in Section 1805 A .1.3, walls and floors shall be waterproofed in accordance with this section.

  1805 A .3.1 Floors. Floors required to be waterproofed shall be of concrete and designed and constructed to withstand the hydrostatic pressures to which the floors will be subjected.

• CRC § 1.5 High relevance — show source text

  Exception: Parging of unit masonry walls is not required where a material is approved for direct application to the masonry.

  Concrete walls shall be dampproofed by applying any one of the listed dampproofing materials or any one of the waterproofing materials listed in Section R406.2 to the exterior of the wall.

  R406.2 Concrete and masonry foundation waterproofing. In areas where a high water table or other severe soil-water conditions are known to exist, exterior foundation walls that retain earth and enclose interior spaces and floors below grade shall be waterproofed from the finished grade to the higher of the top of the footing or 6 inches (152 mm) below the top of the basement floor. Walls shall be waterproofed in accordance with one of the following:

  1. Two-ply hot-mopped felts.
  2. Fifty-five-pound (25 kg) roll roofing.
  3. Forty-mil (1 mm) polymer-modified asphalt.
  4. Sixty-mil (1.5 mm) flexible polymer cement.
  5. One-eighth-inch (3 mm) cement-based, fiber-reinforced, waterproof coating.
  6. Sixty-mil (1.5 mm) solvent-free liquid-applied synthetic rubber.

  All joints in membrane waterproofing shall be lapped and sealed with an adhesive compatible with the membrane.

  Exception: Organic-solvent-based products such as hydrocarbons, chlorinated hydrocarbons, ketones and esters shall not be used for ICF walls with expanded polystyrene form material. Use of plastic roofing cements, acrylic coatings, latex coatings, mortars and pargings to seal ICF walls is permitted. Cold-setting asphalt or hot asphalt shall conform to Type C of ASTM D449. Hot asphalt shall be applied at a temperature of less than 200°F (93°C).

  R406.3 Dampproofing for wood foundations. Wood foundations enclosing habitable or usable spaces located below grade shall be dampproofed in accordance with Sections R406.3.1 through R406.3.4.

  R406.3.1 Panel joint sealed. Plywood panel joints in the foundation walls shall be sealed full length with a caulking compound capable of producing a moistureproof seal under the conditions of temperature and moisture content at which it will be applied and used.

  R406.3.2 Below-grade moisture barrier. A 6-mil-thick (0.15 mm) polyethylene film shall be applied over the below-grade portion of exterior foundation walls prior to backfilling. Joints in the polyethylene film shall be lapped 6 inches (152 mm) and sealed with adhesive. The top edge of the polyethylene film shall be bonded to the sheathing to form a seal. Film areas at grade level shall be protected from mechanical damage and exposure by a pressure-preservative treated lumber or plywood strip attached to the wall several inches above finished grade level and extending approximately 9 inches (229 mm) below grade. The joint between the strip and the wall shall be caulked full length prior to fastening the strip to the wall. Where approved, other coverings appropriate to the architectural treatment shall be permitted to be used. The polyethylene film shall extend down to the bottom of the wood footing plate but shall not overlap or extend into the gravel or crushed stone footing.

• CRC § 3-82 High relevance — show source text

  R336 Large Family Day-Care Homes . . . . . . . . . . . . . . . . . . . 3-82

  R337 Materials and Construction Methods for Exterior

  Wildfire Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-83

  R338 Electric Vehicle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-83

  2025 CALIFORNIA RESIDENTIAL CODE xxi

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

  CONTENTS

  R339 Reserved . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-84

  R340 Pollutant Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-84

  CHAPTER 4 FOUNDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

  R401 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

  R402 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

  R403 Footings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6

  R404 Foundation and Retaining Walls . . . . . . . . . . . . . . . . 4-24

  R405 Foundation Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . 4-42

  R406 Foundation Waterproofing and Dampproofing . . . 4-43

  R407 Columns. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-44

  R408 Under-Floor Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-44

  CHAPTER 5 FLOORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3

  R501 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3

  R502 Wood Floor Framing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3

  R503 Floor Sheathing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12

  R504 Pressure Preservative-Treated Wood

• CRC § 1202.4. High relevance — show source text

  Ventilation for crawl spaces shall comply with Section 1202.4.

  1805.1.1 Story above grade plane. Where a basement is considered a story above grade plane and the finished ground level adjacent to the basement wall is below the basement floor elevation for 25 percent or more of the perimeter, the floor and walls shall be dampproofed in accordance with Section 1805.2 and a foundation drain shall be installed in accordance with Section 1805.4.2. The foundation drain shall be installed around the portion of the perimeter where the basement floor is below ground level. The provisions of Sections 1803.5.4, 1805.3 and 1805.4.1 shall not apply in this case.

  2025 CALIFORNIA BUILDING CODE 18-7

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

  SOILS AND FOUNDATIONS

  1805.1.2 Under-floor space. The finished ground level of an under-floor space such as a crawl space shall not be located below the bottom of the footings. Where there is evidence that the ground-water table rises to within 6 inches (152 mm) of the ground level at the outside building perimeter, or that the surface water does not readily drain from the building site, the ground level of the under-floor space shall be as high as the outside finished ground level, unless an approved drainage system is provided. The provisions of Sections 1803.5.4, 1805.2, 1805.3 and 1805.4 shall not apply in this case.

  1805.1.2.1 Flood hazard areas. For buildings and structures in flood hazard areas as established in Section 1612.3, the finished ground level of an under-floor space such as a crawl space shall be equal to or higher than the outside finished ground level on one side or more.

  Exception: Under-floor spaces of Group R-3 buildings that meet the requirements of FEMA TB 11.

  1805.1.3 Ground-water control. Where the ground-water table is lowered and maintained at an elevation not less than 6 inches (152 mm) below the bottom of the lowest floor, the floor and walls shall be dampproofed in accordance with Section 1805.2. The design of the system to lower the ground-water table shall be based on accepted principles of engineering that shall consider, but not necessarily be limited to, permeability of the soil, rate at which water enters the drainage system, rated capacity of pumps, head against which pumps are to operate and the rated capacity of the disposal area of the system.

  1805.2 Dampproofing. Where hydrostatic pressure will not occur as determined by Section 1803.5.4, floors and walls for other than wood foundation systems shall be dampproofed in accordance with this section. [OSHPD 1R, 2 & 5] Wood foundation systems are not permitted by OSHPD. Wood foundation systems shall be constructed in accordance with AWC PWF.

  1805.2.1 Floors. Dampproofing materials for floors shall be installed between the floor and the base course required by Section 1805.4.1, except where a separate floor is provided above a concrete slab.