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Appendix AT — SOLAR-READY PROVISIONS—DETACHED ONE- AND

Section AU103

California Residential Code (Title 24, Part 2.5) · 2022 edition · updated 2026-09-12 · California

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

AU103.1 Clay subsoil.

Clay subsoil for a cob mix shall be acceptable if the mix it produces meets the requirements of Section AU103.4.

TYPICAL COB WALL

APPENDIX AU-2 2022 CALIFORNIA RESIDENTIAL 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.

AU103.2 Sand.

Sand or other aggregates such as, but not limited to, gravel, pumice and lava rock, when added to cob mixes, shall yield a mix that meets the requirements of Section AU103.4.

AU103.3 Straw.

Straw for cob mixes shall be from wheat, rice, rye, barley or oat, or similar reinforcing fibers with similar performance. Before mixing, the straw or other reinforcing fibers shall be dry to the touch and free of visible decay.

AU103.4 Mix proportions.

Cob mixes shall be of any proportions of refined clay or clay subsoil, added sand (if any) and straw that produce a dried mix that passes the shrinkage test in accordance with Section AU103.4.1, complies with the compressive strength requirements of Section AU106.6 and complies with the modulus of rupture requirements of Section AU106.7.

AU103.4.1 Shrinkage test for cob mixes. Each proposed cob mix of different mix proportions shall be placed moist to completely fill a 24-inch by 3 1 /2-inch by 3 1 /2-inch (610 mm by 89 mm by 89 mm) wooden form on a plastic or paper slip sheet and dried to ambient moisture conditions, or oven dried. The total shrinkage of the length shall not exceed 1 inch (25 mm), as measured from the dried edges of the material to the insides of the form. Cracks in the sample greater than 1 /16 inch (1.5 mm) shall first be closed manually. The shrinkage test shall be shown to the building official for approval before placement of the cob mix onto walls

AU103.5 Mixing.

The clay subsoil, sand and straw for cob shall be thoroughly mixed by manual or mechanical means with water sufficient to produce a mix of a plastic consistency capable of bonding of successively placed layers or lifts.

AU103.6 Installation.

Cob shall be installed on the wall in lifts of a height that supports itself with minimal slumping.

AU103.7 Dry joints.

Each layer of cob shall be prevented from drying until the next layer is installed, to ensure bonding of successive layers. The top of each layer shall be kept moist and malleable with one or more of the following methods:

  1. Covering with a material that prevents loss of or holds moisture.

  2. Covering with a material that shades it from direct sun.

  3. Wetting.

Where dry joints are unavoidable, the previous layer shall be wetted prior to application of the next layer.

AU103.8 Drying holes.

Where holes to facilitate drying are used, such holes shall be of any depth and not exceeding 3 /4 inch (19 mm) in diameter on the face of cob walls. Drying holes shall not be spaced closer than 10 hole-diameters. Drying holes shall not be placed in braced wall panels. The design load on load-bearing walls with drying holes shall not exceed 90 percent of the allowable bearing capacity as determined in accordance with Section AU106.8. Drying holes shall be filled with cob before final inspection.

AU103.9 Adding roof loads to walls.

Roof and ceiling loads shall not be added until walls are sufficiently dry to support them without compressing.

APPENDIX AU—COB CONSTRUCTION (MONOLITHIC ADOBE)

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▸Contents — California Residential Code (Title 24, Part 2.5)
California Residential Code (Title 24, Part 2.5)
  1. Chapter 2 — DEFINITIONS AND ABBREVIATIONS
  2. Appendix AF — RADON CONTROL
  3. Appendix AI — PRIVATE SEWAGE
  4. Appendix AJ — EXISTING
  5. Appendix AK — SOUND
  6. Appendix AO — AUTOMATIC
  7. Appendix AR — LIGHT STRAW-CLAY
  8. Appendix AS — STRAWBALE
  9. Appendix AU — COB CONSTRUCTION
  10. Appendix AV — BOARD
  11. Appendix AW — 3D-PRINTED BUILDING
  12. Chapter 1 — SCOPE AND APPLICATION
  13. Chapter 3 — BUILDING PLANNING
  14. Chapter 4 — FOUNDATIONS
  15. Chapter 5 — FLOORS
  16. Chapter 6 — WALL CONSTRUCTION
  17. Chapter 7 — WALL COVERING
  18. Chapter 8 — ROOF-CEILING CONSTRUCTION
  19. Chapter 9 — ROOF ASSEMBLIES
  20. Chapter 10 — CHIMNEYS AND FIREPLACES
  21. Chapter 44 — REFERENCED STANDARDS
  22. Appendix AH — PATIO COVERS
  23. Appendix AL — PERMIT FEES
  24. Appendix AQ — TINY HOUSES
  25. ▸Appendix AT — SOLAR-READY PROVISIONS—DETACHED ONE- AND
    Overview
    1. Section AT101 — (RB101)
    2. Section AT102 — (RB102)
    3. Section AT103 — (RB103)
    4. Section AU101
    5. Section AU102
    6. Section AU103
    7. Section AU104
    8. Section AU105
    9. Section AU106
    10. Section AU107
    11. Section AU108
    12. Section AU109
    13. Section AU110
    14. Section AV101
    15. Section AW101
    16. Section AW102
    17. Section AW103
    18. Section AW104
    19. Section AW105
    20. Section AW106
  26. Appendix AX — SWIMMING POOL SAFETY ACT
  27. Appendix AY — AREAS PROTECTED BY THE FACILITIES
  28. Appendix AZ — EMERGENCY HOUSING

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