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Appendix BK — COB CONSTRUCTION (MONOLITHIC ADOBE)

Section BK109 — THERMAL PERFORMANCE

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.

BK109.1 Thermal characteristics.

Cob walls shall be classified as mass walls in accordance with Section N1102.2.6 and shall meet the R -value requirements for mass walls in Table N1102.1.3.

BK109.2 Thermal resistance.

The unit R -value for cob walls with a density of 110 pounds per cubic foot (1762 kg/m [3] ) shall be R-0.22 (RSI 0.0387) per inch of cob thickness. The unit R -value for cob walls with a density of 75 pounds per cubic foot (1201 kg/m [3] ) shall be R-0.54 (RSI 0.095) per inch of cob thickness. Linear interpolation is permitted. Extrapolation is not permitted. Walls that vary in thickness along their height or length shall use the average thickness of the wall to determine its R -value. The thermal resistance values of air films and finish materials or additional insulation shall be added to the cob wall’s thermal resistance value to determine the Rvalue of the wall assembly. Cob density shall be measured at equilibrium moisture content.

BK109.3 Additional insulation.

Where insulating materials are added to the face of a cob wall, the combination of additional insulation and any associated connecting, weather-resisting or protective materials shall comply with Section BK104.1.2, Items 1 through 4.

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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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