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Chapter 18 — SOILS AND FOUNDATIONS

Section 1804A

California Building Code (Title 24, Part 2) · 2022 edition · updated 2026-09-12 · California

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

EXCAVATION, GRADING AND FILL

1804 A .1 Excavation near foundations. Excavation for any purpose shall not reduce vertical or lateral support for any foundation or adjacent foundation without first underpinning or protecting the foundation against detrimental lateral or vertical movement, or both, in accordance with Section 1803 A .5.7.

1804 A .2 Underpinning. Where underpinning is chosen to provide the protection or support of adjacent structures, the underpinning system shall be designed and installed in accordance with provisions of this chapter and Chapter 33.

1804 A .2.1 Underpinning sequencing. Underpinning shall be installed in a sequential manner that protects the neighboring structure and the working construction site. The sequence of installation shall be identified in the approved construction documents.

1804 A .3 Placement of backfill. The excavation outside the foundation shall be backfilled with soil that is free of organic material, construction debris, cobbles and boulders or with a controlled low-strength material (CLSM). The backfill shall be placed in lifts and compacted in a manner that does not damage the foundation or the waterproofing or dampproofing material.

Exception: CLSM need not be compacted.

1804 A .4 Site grading. The ground immediately adjacent to the foundation shall be sloped away from the building at a slope of not less than 1 unit vertical in 20 units horizontal (5percent slope) for a minimum distance of 10 feet (3048 mm)

18A-6 2022 CALIFORNIA BUILDING CODE

Copyright © 2022 by, or licensed to, International Code Council, Inc. (ALL RIGHTS RESERVED); licensed to California Building Standards Commission pursuant to License Agreement. No further reproductions is authorized. Any unauthorized reproduction or distribution is a violation of the federal copyright act and the license agreement, and subject to civil and criminal penalties thereunder.

measured perpendicular to the face of the wall. If physical obstructions or lot lines prohibit 10 feet (3048 mm) of horizontal distance, a 5-percent slope shall be provided to an approved alternative method of diverting water away from the foundation. Swales used for this purpose shall be sloped not less than 2 percent where located within 10 feet (3048 mm) of the building foundation. Impervious surfaces within 10 feet (3048 mm) of the building foundation shall be sloped not less than 2 percent away from the building.

Exceptions:

  1. Where climatic or soil conditions warrant, the slope of the ground away from the building foundation shall be permitted to be reduced to not less than 1 unit vertical in 48 units horizontal (2-percent slope).

  2. Impervious surfaces shall be permitted to be sloped less than 2 percent where the surface is a door landing or ramp that is required to comply with Section 1010 A .1.4, 1012 A .3 or 1012 A .6.1.

The procedure used to establish the final ground level adjacent to the foundation shall account for additional settlement of the backfill.

1804 A .5 Grading and fill in flood hazard areas. In flood hazard areas established in Section 1612 A .3, grading, fill, or both, shall not be approved:

  1. Unless such fill is placed, compacted and sloped to minimize shifting, slumping and erosion during the rise and fall of flood water and, as applicable, wave action.

  2. In floodways, unless it has been demonstrated through hydrologic and hydraulic analyses performed by a registered design professional in accordance with standard engineering practice that the proposed grading or fill, or both, will not result in any increase in flood levels during the occurrence of the design flood.

  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 A .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 A .

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 A .6.

1804 A .7 Controlled low-strength material (CLSM). Where shallow foundations will bear on controlled low

SOILS AND FOUNDATIONS

strength material (CLSM), the CLSM shall comply with the provisions of an approved geotechnical report, as set forth in Section 1803 A .

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▸Contents — California Building Code (Title 24, Part 2)
California Building Code (Title 24, Part 2)
  1. Chapter 2 — DEFINITIONS AND ABBREVIATIONS
  2. Appendix G — FLOOD-RESISTANT
  3. Appendix L — EARTHQUAKE RECORDING
  4. Appendix M — TSUNAMI-GENERATED
  5. Appendix N — REPLICABLE
  6. Appendix O — PERFORMANCE-BASED
  7. Chapter 1 — SCOPE AND ADMINISTRATION
  8. Chapter 3 — OCCUPANCY CLASSIFICATION AND USE
  9. Chapter 4 — SPECIAL DETAILED REQUIREMENTS BASED ON OCCUPANCY A…
  10. Chapter 5 — GENERAL BUILDING HEIGHTS AND AREAS
  11. Chapter 6 — TYPES OF CONSTRUCTION
  12. Chapter 7 — FIRE AND SMOKE PROTECTION FEATURES
  13. Chapter 7A — MATERIALS AND CONSTRUCTION
  14. Chapter 8 — INTERIOR FINISHES
  15. Chapter 9 — FIRE PROTECTION AND LIFE SAFETY SYSTEMS
  16. Chapter 10 — MEANS OF EGRESS
  17. Chapter 11A — HOUSING ACCESSIBILITY
  18. Chapter 11B — ACCESSIBILITY TO PUBLIC BUILDINGS, PUBLIC ACCOMM…
  19. Chapter 12 — INTERIOR ENVIRONMENT
  20. Chapter 14 — EXTERIOR WALLS
  21. Chapter 15 — ROOF ASSEMBLIES AND ROOFTOP STRUCTURES
  22. Chapter 16 — STRUCTURAL DESIGN
  23. Chapter 16A — STRUCTURAL DESIGN
  24. Chapter 17 — SPECIAL INSPECTIONS AND TESTS
  25. ▸Chapter 18 — SOILS AND FOUNDATIONS
    Overview
    1. Section 1801
    2. Section 1802
    3. Section 1803
    4. Section 1804
    5. Section 1805
    6. Section 1806
    7. Section 1807
    8. Section 1808
    9. Section 1809
    10. Section 1810
    11. Section 1811
    12. Section 1812
    13. Section 1813
    14. Section 1801A
    15. Section 1802A
    16. Section 1803A
    17. Section 1804A
    18. Section 1805A
    19. Section 1806A
    20. Section 1807A
    21. Section 1808A
    22. Section 1809A
    23. Section 1810A
    24. Section 1811A
    25. Section 1812A
    26. Section 1813A
  26. Chapter 19 — CONCRETE
  27. Chapter 20 — ALUMINUM
  28. Chapter 21 — MASONRY
  29. Chapter 22 — STEEL
  30. Chapter 23 — WOOD
  31. Chapter 24 — GLASS AND GLAZING
  32. Chapter 25 — GYPSUM BOARD, GYPSUM PANEL PRODUCTS AND PLASTER
  33. Chapter 26 — PLASTIC
  34. Chapter 27 — ELECTRICAL
  35. Chapter 28 — MECHANICAL SYSTEMS
  36. Chapter 30 — ELEVATORS AND CONVEYING SYSTEMS
  37. Chapter 31 — SPECIAL CONSTRUCTION
  38. Chapter 31B — PUBLIC POOLS
  39. Chapter 31C — RADIATION
  40. Chapter 31D — FOOD ESTABLISHMENTS
  41. Chapter 31F — MARINE OIL TERMINALS
  42. Chapter 32 — ENCROACHMENTS INTO THE PUBLIC RIGHT-OF-WAY
  43. Chapter 33 — SAFEGUARDS DURING CONSTRUCTION
  44. Chapter 35 — REFERENCED STANDARDS
  45. Appendix A — EMPLOYEE QUALIFICATIONS
  46. Appendix B — BOARD OF APPEALS
  47. Appendix C — GROUP U – AGRICULTURAL BUILDINGS
  48. Appendix D — FIRE DISTRICTS
  49. Appendix F — RODENTPROOFING
  50. Appendix H — SIGNS
  51. Appendix I — PATIO COVERS
  52. Appendix J — GRADING
  53. Appendix K — GROUP R-3 AND GROUP R-3.1 OCCUPANCIES
  54. Appendix P — EMERGENCY HOUSING

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