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Appendix BK — COB CONSTRUCTION (MONOLITHIC ADOBE)

Section BK101 — GENERAL

2025 California Residential Code (Title 24, Part 2.5) · 2025 edition · updated 2026-07-27 · California

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

BK101.1 Scope.

This appendix provides prescriptive and performance-based requirements for the use of natural cob as a building material. Buildings using cob walls shall comply with this code except as otherwise stated in this appendix.

BK101.2 Intent.

In addition to the intent described in Section R101.3, the purpose of this appendix is to establish minimum requirements for cob structures that provide flexibility in the application of certain provisions of the code, to permit the use of site-sourced and local materials, and to permit combinations of historical and modern techniques.

BK101.3 Tests and empirical evidence.

Tests for an alternative material, design or method of construction shall be in accordance with Section R104.2.2.5, and the building official shall have the authority to consider evidence of a history of successful use in lieu of testing.

BK101.4 Cob wall systems.

Cob wall systems include those shown in Figure BK101.4 and approved variations.

FIGURE BK101.4—TYPICAL COB WALL

BOND BM

PER SECTION BK106.9

ANCHORS, WHERE OCCUR, PER TABLES BK105.3, BK106.11(1) AND BK106.12

WALL TAPER ALLOWED

ONE OR BOTH SIDES PER SECTION BK106.5(1)

HORIZONTAL REINFORCING, WHERE OCCURS, PER TABLE BK106.11(1)

VERTICAL REINFORCING, WHERE OCCURS, PER TABLE BK106.11(1)

COB MATERIAL

PER SECTION BK103

ANCHORS, WHERE OCCUR, PER TABLE BK106.11(1)

SEPARATION FROM

FINISHED GRADE

PER SECTION BK105.4.4

FINISHED FLOOR LEVEL

VARIES

FINISHED GRADE

FOUNDATION AND STEM WALL

PER SECTION BK106.4

H
HEIGHT,
WALL
COB
F
V

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

APPENDIX BK — COB CONSTRUCTION (MONOLITHIC ADOBE)

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▸ Contents — 2025 California Residential Code (Title 24, Part 2.5)
2025 California Residential Code (Title 24, Part 2.5)
  1. Chapter 1 — ADMINISTRATION
  2. Chapter 2 — DEFINITIONS
  3. Chapter 3 — BUILDING PLANNING
  4. Chapter 4 — FOUNDATIONS
  5. Chapter 5 — FLOORS
  6. Chapter 6 — WALL CONSTRUCTION
  7. Chapter 7 — WALL COVERING
  8. Chapter 8 — ROOF-CEILING CONSTRUCTION
  9. Chapter 9 — ROOF ASSEMBLIES
  10. Chapter 10 — CHIMNEYS AND FIREPLACES
  11. Chapter 44 — REFERENCED STANDARDS
  12. Appendix AA — BOARD OF APPEALS
  13. Appendix AB — PERMIT FEES
  14. Appendix AC — RESERVED
  15. Appendix BA — RESERVED
  16. Appendix BB — TINY HOUSES
  17. Appendix BC — RESERVED
  18. Appendix BD — RESERVED
  19. Appendix BE — RADON CONTROL METHODS
  20. Appendix BF — PATIO COVERS
  21. Appendix BG — SOUND TRANSMISSION
  22. Appendix BH — AUTOMATIC VEHICULAR GATES
  23. Appendix BI — LIGHT STRAW-CLAY CONSTRUCTION
  24. Appendix BJ — STRAWBALE CONSTRUCTION
  25. ▸ Appendix BK — COB CONSTRUCTION (MONOLITHIC ADOBE)
    Overview
    1. Section BK101 — GENERAL
    2. Section BK102 — DEFINITIONS
    3. Section BK103 — MATERIALS, MIXING AND INSTALLATION
    4. Section BK104 — FINISHES
    5. Section BK105 — COB WALLS—GENERAL
    6. Section BK106 — COB WALLS—STRUCTURAL
    7. Section BK107 — COB FLOORS
    8. Section BK108 — FIRE RESISTANCE
    9. Section BK109 — THERMAL PERFORMANCE
    10. Section BK110 — REFERENCED STANDARDS
  26. Appendix BL — HEMP-LIME (HEMPCRETE) CONSTRUCTION
  27. Appendix BM — 3D-PRINTED BUILDING CONSTRUCTION
  28. Appendix BN — EXTENDED PLATE WALL CONSTRUCTION
  29. Appendix BO — EXISTING BUILDINGS AND STRUCTURES
  30. Appendix CA — RESERVED
  31. Appendix CB — RESERVED
  32. Appendix CC — RESERVED
  33. Appendix CD — RESERVED
  34. Appendix CE — RESERVED
  35. Appendix CF — RESERVED
  36. Appendix CG — NONSEWERED SANITATION SYSTEMS
  37. Appendix CH — PRIVATE SEWAGE DISPOSAL
  38. Appendix CI — SWIMMING POOL SAFETY ACT
  39. Appendix CJ — EMERGENCY HOUSING
  40. Appendix CK — AREAS PROTECTED BY THE FACILITIES OF THE CENTRAL…

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