CRC · California Residential Code

What perimeter drainage is required for foundations that retain earth?

If your foundation wall holds back earth and there’s living or usable space below grade, the CRC requires a continuous perimeter drain installed at or below the top of the footing (or below the slab). The drain pipe or tile must sit on at least 2 inches of washed gravel, be covered with 6 inches of the same material, extend 1 foot past the outside edge of the footing with the top 6 inches above the footing, be protected by a filter membrane, and discharge by gravity or a sump/pump to an approved outlet (see § R405.1) .

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Last reviewed: July 6, 2026

What the code requires — 2-4 sentences

The California Residential Code requires that drains be provided around concrete or masonry foundations that retain earth and enclose habitable or usable spaces below grade. Those drains (drainage tiles, gravel/crushed-stone drains, perforated pipe or other approved systems) must be installed at or below the top of the footing or below the bottom of the slab, placed on and covered by prescribed aggregate and protected by an approved filter membrane, and must discharge by gravity or mechanical means to an approved drainage system — § R405.1 .

The single most important rule: provide a continuous perimeter drainage system at or below the top of the footing (or below the slab) that collects and discharges subsurface water away from the foundation — § R405.1 .

Requirements in detail

Scope and when required

  • Applies to concrete or masonry foundations that retain earth and enclose habitable/usable below‑grade spaces — § R405.1 .
  • Exception: A dedicated drainage system is not required when the foundation is installed on well‑drained ground or sand‑gravel mixture soils (Group I soils) as listed in Table R401.4.1(2); the CRC text references that table — § R405.1 Exception . (Note: the contents of Table R401.4.1(2) were not retrieved in the files provided.)

Materials, placement and protection

  • Drain systems may be: drainage tiles, gravel or crushed‑stone drains, perforated pipe or other approved systems — § R405.1 .
  • Where perforated pipe or tile is used, the pipe/tile shall be placed on not less than 2 inches (51 mm) of washed gravel or crushed rock (aggregate size 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; top of open joints of tile protected with building paper or an approved filter membrane — § R405.1 .
  • Gravel or crushed‑stone drains (when used as the drain medium) 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 the top must be covered with an approved filter membrane — § R405.1 .
  • Drainage must discharge by gravity or mechanical means into an approved drainage system (approved sewer, daylight, or other approved outlet) — § R405.1 .

Precast foundations (special requirement)

  • Precast concrete foundations that retain earth and enclose habitable/usable below‑grade spaces and that rest on crushed‑stone footings must have a perforated drainage pipe installed below the base of the wall on either the interior or exterior side, and the pipe must extend not less than 1 foot (305 mm) beyond the edge of the wall. If the pipe is exterior, it must be covered with an approved filter membrane. The system must discharge to an approved sewer or to daylight — § R405.1.1 .

Wood foundations (related requirements)

  • Wood foundations enclosing habitable/usable spaces below grade are to be drained per R405.2. A porous layer (gravel, crushed stone or coarse sand) of minimum 4 inches (102 mm) thickness is required under the basement floor and must be provided with automatic drainage of that layer and the gravel/crushed‑stone wall footings — § R405.2.1 .
  • In soils other than Group I, a sump is required for the porous layer and footings: minimum 24 inches (610 mm) diameter or 20 inches square, and it must extend not less than 24 inches (610 mm) below the bottom of the basement floor; must permit positive gravity or mechanical drainage to remove accumulated water — § R405.2.3 .

Decision‑relevant dimensions/values (quick reference)

Item / question Required value (code) Code Reference
How far beyond footing must gravel drain extend? 1 foot (305 mm) beyond outside edge of footing § R405.1
How high above top of footing must gravel drain top reach? 6 inches (152 mm) above top of footing § R405.1
Bedding under perforated pipe / tile 2 inches (51 mm) of washed gravel/crushed rock § R405.1
Cover over pipe / tile (same material) 6 inches (152 mm) § R405.1
Minimum porous base under basement floor (wood foundations) 4 inches (102 mm) § R405.2.1
Required sump size (non‑Group I soils, wood foundations) 24 in. (610 mm) diameter or 20 in. square; extend 24 in. (610 mm) below bottom of floor § R405.2.3
Drain discharge requirement Discharge by gravity or mechanical means to an approved drainage system (sewer or daylight) § R405.1

Exceptions & special cases

  • Well‑drained sites on Group I soils (per Table R401.4.1(2)) are exempt from a dedicated drainage system — § R405.1 Exception . (Table contents were not retrieved here.)
  • Precast foundation walls on crushed‑stone footings have a distinct rule requiring a perforated pipe below the base of the wall and extending 1 foot beyond the wall edge — § R405.1.1 .
  • Wood foundations: the CRC prescribes a porous base and, in most soils (other than Group I), a sump sized and located per § R405.2.3 — .
  • Where gravity discharge is not possible, mechanical (sump pump) discharge is permitted/provided; the plumbing code provides specific sump and pump sizing and discharge guidance (see Related provisions) — Plumbing Code reference .

Common mistakes

  • Installing the drain invert too high (invert must be at or below the top of footing or below slab) — § R405.1 .
  • Failing to extend gravel drains at least 1 foot (305 mm) beyond the outside edge of the footing or failing to build the drain 6 inches (152 mm) above the top of footing — § R405.1 .
  • Omitting the filter membrane over exterior drains or failing to surround perforated drains with an approved filter — § R405.1 .
  • Using insufficient bedding: perforated pipe/tile must sit on at least 2 inches (51 mm) of washed gravel/crushed rock and be covered with 6 inches (152 mm) of the same material — § R405.1 .
  • Assuming the Group I soils exception applies without confirming the soil classification in Table R401.4.1(2) (table not included in retrieved files) — § R405.1 Exception .

Worked example — concrete scenario

Scenario: A new single‑family basement (concrete foundation wall) will be built that retains earth. Footing top elevation = 0.00 ft. You choose an external perforated drainage pipe.

Steps to apply the code:

  1. Install perforated pipe at or below the top of the footing (here, at elevation ≤ 0.00 ft) and place the pipe on not less than 2 inches (51 mm) of washed gravel/crushed rock (aggregate at least one sieve size larger than the perforations) — § R405.1 .
  2. Cover the pipe with at least 6 inches (152 mm) of the same washed gravel/crushed rock, then place the remainder of the gravel or crushed‑stone drain so the drain extends 1 foot (305 mm) beyond the outside edge of the footing and the top of the drain reaches 6 inches (152 mm) above the top of footing — § R405.1 .
  3. Protect the top of drain joints / perforations with building paper or an approved filter membrane; if the drain pipe is exterior, ensure the filter membrane covers the pipe per the precast rule (same principle) — § R405.1 and § R405.1.1 .
  4. Provide a discharge path: gravity run to daylight or to an approved drainage/sewer system. If gravity is not available, provide a sump and pump sized per local plumbing guidance — § R405.1 ; see California Plumbing Code for sump/pump sizing .

Result: The drain invert is at or below the top of footing, pipe bedding and cover meet the 2 in. / 6 in. requirements, the gravel drain extends 1 ft beyond the footing and is capped with filter membrane, and the system discharges to an approved outlet — compliant with § R405.1 .

Related provisions

  • § R405.1 — Foundation drainage requirements for concrete/masonry foundations (main controlling section) .
  • § R405.1.1 — Precast concrete foundation perforated pipe requirement and filter membrane requirement .
  • § R405.2 / R405.2.1 / R405.2.3 — Wood foundation porous base, vapor retarder and sump sizing/location requirements (porous base 4 in., sump 24 in. diameter or 20 in. square, extend 24 in. below basement floor) .
  • § R406.1 / R406.2 — Dampproofing and waterproofing requirements for foundation walls that retain earth (when waterproofing is required) .
  • California Plumbing Code (subsoil drains / sump & pump details) — guidance on drain diameter, sump dimensions and pump capacity for mechanical discharge where required .
  • Table R401.4.1(2) — soil classification (Group I soils) referenced by the R405.1 exception (table contents not retrieved here) — Table R401.4.1(2) .

Code references

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

  • 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

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    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 § 5.2 High relevance — show source text

    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. Except where otherwise recommended by the drain manufacturer, perforated drains shall be surrounded with an approved filter membrane or the filter membrane shall cover the washed gravel or crushed rock covering the drain. 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.

  • CRC § 2.4 High relevance — show source text

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    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 § 1805.4.1 High relevance — show source text

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    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. The pipe or tile shall be placed on not less than 2 inches (51 mm) of gravel or crushed stone complying with Section 1805.4.1, and shall be covered with not less than 6 inches (152 mm) of the same material.

    1805.4.3 Drainage discharge. The floor base and foundation perimeter drain shall discharge by gravity or mechanical means into an approved drainage system that complies with the California Plumbing Code .

    Exception: Where a site is located in well-drained gravel or sand/gravel mixture soils, a dedicated drainage system is not required.

    SECTION 1806—PRESUMPTIVE LOAD-BEARING VALUES OF SOILS

    1806.1 Load combinations. The presumptive load-bearing values provided in Table 1806.2 shall be used with the allowable stress design load combinations specified in ASCE 7, Section 2.4 or the alternative allowable stress design load combinations of Section 1605.2. The values of vertical foundation pressure and lateral bearing pressure given in Table 1806.2 shall be permitted to be increased by one-third where used with the alternative allowable stress design load combinations of Section 1605.2 that include wind or earthquake loads.

    1806.2 Presumptive load-bearing values. The load-bearing values used in design for supporting soils and rock near the surface shall not exceed the values specified in Table 1806.2 unless data to substantiate the use of higher values are submitted and approved. Where the building official has reason to doubt the classification, strength or compressibility of the soil or rock, the requirements of Section 1803.5.2 shall be satisfied.

  • 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.

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    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 § 4.1 High relevance — show source text

    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.

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    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. The top of joints or the top of perforations shall be protected with an approved filter membrane material. The pipe or tile shall be placed on not less than 2 inches (51 mm) of gravel or crushed stone complying with Section 1805.4.1, and shall be covered with not less than 6 inches (152 mm) of the same material.

    1805 A .4.3 Drainage discharge. The floor base and foundation perimeter drain shall discharge by gravity or mechanical means into an approved drainage system that complies with the California Plumbing Code .

    Exception: Where a site is located in well-drained gravel or sand/gravel mixture soils, a dedicated drainage system is not required.

    SECTION 1806 A —PRESUMPTIVE LOAD-BEARING VALUES OF SOILS

    1806 A .1 Load combinations. The presumptive load-bearing values provided in Table 1806 A .2 shall be used with the allowable stress design load combinations specified in ASCE 7, Section 2.4 or the alternative allowable stress design load combinations of Section 1605 A .2. The values of vertical foundation pressure and lateral bearing pressure given in Table 1806 A .2 shall be permitted to be increased by one-third where used with the alternative allowable stress design load combinations of Section 1605 A .2 that include wind or earthquake loads.

    1806 A .2 Presumptive load-bearing values. The load-bearing values used in design for supporting soils and rock near the surface shall not exceed the values specified in Table 1806 A .2 unless data to substantiate the use of higher values are submitted and approved. Where the building official has reason to doubt the classification, strength or compressibility of the soil or rock, the requirements of Section 1803 A .5.2 shall be satisfied.

  • 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.

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    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 § 19.1 High relevance — show source text

    Such subsoil drains shall be permitted to be positioned inside or outside of the footing, shall be of perforated or open-jointed approved drain tile or pipe, not less than 3 inches (80 mm) in diameter, and shall be laid in gravel, slag, crushed rock, approved [3] ⁄ 4 of an inch (19.1 mm) crushed, recycled glass aggregate, or other approved porous material with not less than 4 inches (102 mm) surrounding the pipe. Filter media shall be provided for exterior subsoil piping. Exception: [HCD 1 & HCD 2] Subsoil drains are mandatory only when required by the Authority Having Jurisdiction due to geological conditions.

    TABLE 1101.4.6

    MATERIALS FOR SUBSOIL DRAINPIPE AND FITTINGS

    2025 CALIFORNIA PLUMBING CODE 205

    ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

    STORM DRAINAGE

    1101.6.1 Discharge. Subsoil drains shall be piped to a storm drain, to an approved water course, to the front street curb or gutter, to an alley, or the discharge from the subsoil drains shall be conveyed to the alley by a concrete gutter. Where a continuously flowing spring or groundwater is encountered, subsoil drains shall be piped to a storm drain or an approved water course. 1101.6.2 Sump. Where it is not possible to convey the drainage by gravity, subsoil drains shall discharge to an accessible sump provided with an approved automatic electric pump. The sump shall be not less than 15 inches (381 mm) in diameter, 18 inches (457 mm) in depth, and provided with a fitted cover. The sump pump shall have an adequate capacity to discharge water coming into the sump as it accumulates to the required discharge point, and the capacity of the pump shall be not less than 15 gallons per minute (gpm) (0.95 L/s). The discharge piping from the sump pump shall be not less than 1 [1] ⁄ 2 inches (40 mm) in diameter and have a union or other approved quick-disconnect assembly to make the pump accessible for servicing. 1101.6.3 Splash Blocks. For separate dwellings not serving continuously flowing springs or groundwater, the sump discharge pipe shall be permitted to discharge onto a concrete splash block with a minimum length of 24 inches (610 mm). This pipe shall be within 4 inches (102 mm) of the splash block and positioned to direct the flow parallel to the recessed line of the splash block.

    1101.6.4 Backwater Valve. Subsoil drains subject to backflow where discharging into a storm drain shall be provided with a backwater valve in the drain line so located as to be accessible for inspection and maintenance. 1101.6.5 Open Area. Nothing in Section 1101.6 shall prevent drains that serve either subsoil drains or areaways of a detached building from discharging to a properly graded open area, provided that:

    (1) They do not serve continuously flowing springs or groundwater.

    (2) The point of discharge is not less than 10 feet (3048 mm) from a property line.

  • CRC § 1805.4.1 High relevance — show source text

    The top of joints or the top of perforations shall be protected with an approved filter membrane material. The pipe or tile shall be placed on not less than 2 inches (51 mm) of gravel or crushed stone complying with Section 1805.4.1, and shall be covered with not less than 6 inches (152 mm) of the same material.

    1805.4.3 Drainage discharge. The floor base and foundation perimeter drain shall discharge by gravity or mechanical means into an approved drainage system that complies with the California Plumbing Code .

    Exception: Where a site is located in well-drained gravel or sand/gravel mixture soils, a dedicated drainage system is not required.

    SECTION 1806—PRESUMPTIVE LOAD-BEARING VALUES OF SOILS

    1806.1 Load combinations. The presumptive load-bearing values provided in Table 1806.2 shall be used with the allowable stress design load combinations specified in ASCE 7, Section 2.4 or the alternative allowable stress design load combinations of Section 1605.2. The values of vertical foundation pressure and lateral bearing pressure given in Table 1806.2 shall be permitted to be increased by one-third where used with the alternative allowable stress design load combinations of Section 1605.2 that include wind or earthquake loads.

    1806.2 Presumptive load-bearing values. The load-bearing values used in design for supporting soils and rock near the surface shall not exceed the values specified in Table 1806.2 unless data to substantiate the use of higher values are submitted and approved. Where the building official has reason to doubt the classification, strength or compressibility of the soil or rock, the requirements of Section 1803.5.2 shall be satisfied.

    Presumptive load-bearing values shall apply to materials with similar physical and engineering characteristics. Mud, organic silt and organic clays (OL, OH), peat (Pt) and undocumented fill shall not be assumed to have a presumptive load-bearing capacity unless data to substantiate the use of such a value are submitted.

    Exception: A presumptive load-bearing capacity shall be permitted to be used where the building official deems the load-bearing capacity is adequate for the support of lightweight or temporary structures.

    TABLE 1806.2—PRESUMPTIVE LOAD-BEARING VALUES Col2 Col3 Col4 Col5
    CLASS OF MATERIALS VERTICAL
    FOUNDATION
    PRESSURE
    (psf)    		 LATERAL
    BEARING PRESSURE
    (psf/ft below natural grade)    		 LATERAL SLIDING RESISTANCE LATERAL SLIDING RESISTANCE
    CLASS OF MATERIALS VERTICAL
    FOUNDATION
    PRESSURE
    (psf)    		 LATERAL
    BEARING PRESSURE
    (psf/ft below natural grade)    		 Coefficient of
    frictiona    		 Cohesion
    (psf)b
    1. Crystalline bedrock 12,000 1,200 0.70 —
    2. Sedimentary and foliated rock 4,000 400 0.35 —
    3. Sandy gravel and gravel (GW and GP) 3,000 200 0.35 —
    4.
  • CRC § 1804.6 High relevance — show source text
    1. In coastal high hazard areas, unless such fill is conducted or placed to avoid diversion of water and waves toward any building or structure.
    2. 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 § 3.1 High relevance — show source text

    2|1/3| |F/C-3-RC-2|31/4″|31/4″ deep (3540 psi) concrete deck;3/8″ main
    reinforcement bars at 51/2″ pitch with7/8″
    cover;3/8″ main reinforcement bars at 41/2″
    pitch perpendicular with1/2″ cover; 13′1″
    span restrained.|195
    psf|2 hrs|||7|1, 3, 4|2| |F/C-3-RC-3|31/4 ″|31/4″ deep (4175 psi) concrete deck;3/8″ main
    reinforcement bars at 51/2″ pitch with7/8″
    cover;3/8″ main reinforcement bars at 41/2″
    pitch perpendicular with1/2″ cover; 13′1″
    span restrained.|195
    psf|31
    min|||7|1, 5|1/2| |F/C-3-RC-4|31/4″|31/4″ deep (4355 psi) concrete deck;
    3/8″ main reinforcement bars at 51/2″ pitch
    with7/8″ cover;3/8″ main reinforcement bars
    at 41/2″ pitch perpendicular with1/2″ cover;
    13′1″ span restrained.|195
    psf|41
    min|||7|1, 5, 6|1/2|

    2025 CALIFORNIA EXISTING BUILDING CODE RESOURCE A-91

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

    RESOURCE A—GUIDELINES ON FIRE RATINGS OF ARCHAIC MATERIALS AND ASSEMBLIES

    TABLE 3.1—continued
    FLOOR/CEILING ASSEMBLIES—REINFORCED CONCRETE    		 Col2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10
    ITEM
    CODE    		 ASSEMBLY
    THICKNESS    		 CONSTRUCTION DETAILS PERFORMANCE PERFORMANCE REFERENCE NUMBER REFERENCE NUMBER REFERENCE NUMBER NOTES REC.
    HOURS
    ITEM
    CODE    		 ASSEMBLY
    THICKNESS    		 CONSTRUCTION DETAILS LOAD TIME PRE-BMS-92 BMS-92 POST-BMS-92 POST-BMS-92 POST-BMS-92
    F/C-3-RC-5 31/4″ 31/4″ thick (3800 psi) concrete deck;3/8″
    main reinforcement bars at 51/2″ pitch
    with7/8″ cover;3/8″ main reinforcement
    bars at 41/2″ pitch perpendicular with1/2″
    cover; 13′1″ span restrained.    		 195 psf 1 hr
    5 min    		 7 1, 5 1
    F/C-4-RC-6 41/4″ 41/4″ thick; 31/4″ (4000 psi) concrete deck;
    1″ sprayed asbestos lower surface;
  • 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).

Frequently asked questions

What if I already have a foundation without a perimeter drain?

If the foundation now retains earth and encloses below‑grade habitable space, the CRC requires drainage per § R405.1; corrective work should follow the same placement, bedding and discharge rules (or consult the building official for retrofit options) — § R405.1 .

Can I run the perimeter drain to the street gutter?

Drains must discharge to an approved drainage system (approved sewer, storm drain, daylight or other approved outlet). Local jurisdiction and plumbing code rules govern acceptable discharge points — § R405.1 and California Plumbing Code guidance .

Do I need a filter membrane over exterior drains?

Yes. The code requires that exterior perforated drains be covered with an approved filter membrane, and that gravel drains be covered with an approved filter membrane — § R405.1 .

Is a sump required for concrete foundations?

A sump requirement for concrete foundations is not stated in § R405.1 for concrete/masonry; however, wood foundations (R405.2.3) require a sump in non‑Group I soils. For concrete basements, a sump is commonly used where gravity discharge is not possible — see § R405.2.3 and the Plumbing Code for specifics .

How do I know if my site is Group I soil (exception to drainage)?

The CRC references Table R401.4.1(2) for Group I soils; that table was not included in the retrieved files here. Confirm soil classification via the table, geotechnical report, or the building official — § R405.1 Exception .

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Related in the CRC

When is dampproofing acceptable and when is waterproofing required for foundations?

What are the requirements for under‑floor (crawlspace) access, ventilation and clearances?

Foundation drainage, dampproofing/waterproofing and under‑floor spaces

California Residential Code