R401 General — 2025 California Residential Code
California Residential Code (Title 24, Part 2.5) · 2025 edition · updated 2026-09-26 · California
CBSC: official editions, supplements and errata
Italicized text is a California amendment to the model code, as printed in the official publication.
Cite as: 2025 California Residential Code (Title 24, Part 2.5) § R401 · Effective January 1, 2026 · Official source: Building Standards Commission
R401.1 Application.¶
The provisions of this chapter shall control the design and construction of the foundation and foundation spaces for buildings. In addition to the provisions of this chapter, the design and construction of foundations in flood hazard areas as established by Table R301.2 shall meet the provisions of Section R306. Wood foundations shall be designed and installed in accordance with AWC PWF.
Exception: The provisions of this chapter shall be permitted to be used for wood foundations only in the following situations:
- In buildings that have not more than two floors and a roof.
- Where interior basement and foundation walls are constructed at intervals not exceeding 50 feet (15 240 mm) .
Wood foundations in Seismic Design Category D 0, D 1 or D 2 shall be designed in accordance with accepted engineering practice.
R401.2 Requirements.¶
Foundation construction shall be capable of accommodating all loads in accordance with Section R301 and of transmitting the resulting loads to the supporting soil. Fill soils that support footings and foundations shall be designed, installed and tested in accordance with accepted engineering practice.
Note: See Section R301.1.1.1 for limited-density owner-built rural dwellings.
R401.3 Drainage.¶
Surface drainage shall be diverted to a storm sewer conveyance or other approved point of collection that does not create a hazard. Lots shall be graded to drain surface water away from foundation walls. The grade shall fall not fewer than 6 inches (152 mm) within the first 10 feet (3048 mm).
Exception: Where lot lines, walls, slopes or other physical barriers prohibit 6 inches (152 mm) of fall within 10 feet (3048 mm), drains or swales shall be constructed to ensure drainage away from the structure. Impervious surfaces within 10 feet (3048 mm) of the building foundation shall be sloped not less than 2 percent away from the building.
R401.4 Soil tests.¶
Where quantifiable data created by accepted soil science methodologies indicate expansive soils, compressible soils, shifting soils or other questionable soil characteristics are likely to be present, the building official shall determine whether to require a soil test to determine the soil’s characteristics at a particular location. This test shall be done by an approved agency using an approved method. Where the seismic design category in accordance with Section R301.2.2.1 is C or greater and where soil testing is performed, the geotechnical report shall include the determination of the site class and the short-period spectral response acceleration, S DS, in accordance with Section 1613 of the California Building Code . The seismic design category shall be assigned in accordance with Table R301.2.2.1.1.
R401.4.1 Geotechnical evaluation. In lieu of a complete geotechnical evaluation, the load-bearing values in Table R401.4.1(1) and the soil classifications in Table R401.4.1(2) shall be assumed.
TABLE R401.4.1(1)—PRESUMPTIVE LOAD-BEARING VALUES OF FOUNDATION MATERIALSa
| ** CLASS OF MATERIAL** | ** LOAD-BEARING PRESSURE** (pounds per square foot) |
|---|---|
| Crystalline bedrock | 12,000 |
| Sedimentary and foliated rock | 4,000 |
| Sandy gravel and/ |
3,000 |
| Sand, silty sand, clayey sand, silty gravel and clayey gravel (SW, SP, SM, SC, GM and GC) | 2,000 |
| Clay, sandy, silty clay, clayey silt, silt and sandy siltclay (CL, ML, MH and CH) | 1,500b |
| For SI: 1 pound per square foot = 0.0479 kPa. a. Where soil tests are required by Section R401.4, the allowable bearing capacities of the soil shall be part of the recommendations. b. Where the building official determines that in-place soils with an allowable bearing capacity of less than 1,500 psf are likely to be present at the site, the allowable bearing capacity shall be determined by a soils investigation. |
FOUNDATIONS
TABLE R401.4.1(2)—PROPERTIES OF SOILS CLASSIFIED ACCORDING TO THE UNIFIED SOIL CLASSIFICATION SYSTEM
| ** SOIL** GROUP |
** UNIFIED SOIL** CLASSIFICATION SYSTEM SYMBOL |
** SOIL DESCRIPTION** | ** USDA** TEXTURAL SOIL CLASSIFICATION |
** DRAINAGE** CHARACTERISTICSa |
** FROST** HEAVE POTENTIAL |
** VOLUME CHANGE** POTENTIAL EXPANSIONb |
|---|---|---|---|---|---|---|
| Group I | GW | Well-graded gravels, gravel sand mixtures, little or no fines |
N/A | Good | Low | Low |
| Group I | GP | Poorly graded gravels or gravel sand mixtures, little or no fines |
N/A | Good | Low | Low |
| Group I | SW | Well-graded sands, gravelly sands, little or no fines |
N/A | Good | Low | Low |
| Group I | SP | Poorly graded sands or gravelly sands, little or no fines |
Sand | Good | Low | Low |
| Group I | GM | Silty gravels, gravel-sand-silt mixtures |
N/A | Good | Medium | Low |
| Group I | SM | Silty sand, sand-silt mixtures | Loamy sand, sandy loam |
Good | Medium | Low |
| Group II | GC | Clayey gravels, gravel-sand-clay mixtures |
N/A | Medium | Medium | Low |
| Group II | SC | Clayey sands, sand-clay mixture | Sandy clay loam, sandy clay |
Medium | Medium | Low |
| Group II | ML | Inorganic silts and very fine sands, rock flour, silty or clayey fine sands or clayey silts with slight plasticity |
Silt, silt loam | Medium | High | Low |
| Group II | CL | Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, lean clays |
Loam, clay loam, silty clay loam |
Medium | Medium | Medium to Low |
| Group III | CH | Inorganic clays of high plasticity, fat clays |
Clay, silty clay | Poorc | Medium | High |
| Group III | MH | Inorganic silts, micaceous or diatomaceous fine sandy or silty soils, elastic silts |
N/A | Poorc | High | High |
| Group IV | OL | Organic silts and organic silty clays of low plasticity |
N/A | Poorc | Medium | Medium |
| Group IV | OH | Organic clays of medium to high plasticity, organic silts |
N/A | Unsatisfactoryc | Medium | High |
| Group IV | Pt | Peat and other highly organic soils | N/A | Unsatisfactoryc | Medium | High |
| For SI: 1 inch = 25.4 mm. N/ a. The percolation rate for good drainage is over 4 inches per hour, medium drainage is 2 inches to 4 inches per hour, and poor is less than 2 inches per hour. b. Soils with a low potential expansion typically have a plasticity index (PI) of 0 to 15, soils with a medium potential expansion have a PI of 10 to 35 and soils with a high potential expansion have a PI greater than 20. c. Unsuitable as backfill material. |
R401.4.1.1 General and where required for applications listed in Section 1.8.2.1.1 regulated by the Department of Housing and Community Development. Foundations and soils investigations shall be conducted in conformance with Health and Safety Code Sections 17953 through 17957 as summarized below.
R401.4.1.1.1 Preliminary soil report. Each city, county, or city and county shall enact an ordinance which requires a prelimi- nary soil report, prepared by a civil engineer who is registered by the state. The report shall be based upon adequate test borings or excavations, of every subdivision, where a tentative and final map is required pursuant to Section 66426 of the Government Code.
The preliminary soil report may be waived if the building department of the city, county or city and county, or other enforce- ment agency charged with the administration and enforcement of the provisions of Section R401.4.1.1, shall determine that, due to the knowledge such department has as to the soil qualities of the soil of the subdivision or lot, no preliminary analysis is
necessary.
R401.4.1.1.2 Soil investigation by lot, necessity, preparation and recommendations. If the preliminary soil report indicates the presence of critically expansive soils or other soil problems which, if not corrected, would lead to structural defects, such ordinance shall require a soil investigation of each lot in the subdivision.
The soil investigation shall be prepared by a civil engineer who is registered in this state. It shall recommend corrective action which is likely to prevent structural damage to each dwelling proposed to be constructed on the expansive soil.
4-4 2025 CALIFORNIA RESIDENTIAL CODE
FOUNDATIONS
R401.4.1.1.3 Approval, building permit conditions, appeal. The building department of each city, county or city and county, or other enforcement agency charged with the administration and enforcement of the provisions of this code, shall approve the soil investigation if it determines that the recommended action is likely to prevent structural damage to each dwelling to be constructed. As a condition to the building permit, the ordinance shall require that the approved recom- mended action be incorporated in the construction of each dwelling. Appeal from such determination shall be to the local appeals board.
R401.4.1.1.4 Liability. A city, county, or city and county or other enforcement agency charged with the administration and enforcement of the provisions of Section R401.4.1.1, is not liable for any injury which arises out of any act or omission of the city, county or city and county, or other enforcement agency, or a public employee or any other person under Section R401.4.1.1.1, R401.4.1.1.2 or R401.4.1.1.3.
R401.4.1.1.5 Alternate procedures. The governing body of any city, county, or city and county may enact an ordinance prescribing an alternate procedure which is equal to or more restrictive than the procedures specified in Sections R401.4.1.1.1, R401.4.1.1.2 and R401.1.1.3.
R401.4.2 Compressible or shifting soil. Instead of a complete geotechnical evaluation, where top or subsoils are compressible or shifting, they shall be removed to a depth and width sufficient to ensure stable moisture content in each active zone and shall not be used as fill or stabilized within each active zone by chemical, dewatering or presaturation.
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