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Appendix BL — HEMP-LIME (HEMPCRETE) CONSTRUCTION

Section BL106 — 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.

BL106.1 Mass walls.

Walls with hemp-lime infill shall be classified as mass walls in accordance with Section N1102.2.5 (R402.2.5) and shall meet the R-value requirements for mass walls in Table N1102.1.3 (R402.1.3), when their heat capacity ( C ) is greater than or equal to 6 Btu/ft [2] × °F (123 kJ/m [2] × K) in Equation BL-1.

Equation BL-1 C = ρ × t × 0.299 Btu/lb × °F

where:

C = Heat capacity (Btu/ft [2] × °F).

ρ = Density of hemp-lime infill (pounds per cubic foot).

t = Thickness of hemp-lime infill (feet).

BL106.2 Thermal resistance.

Hemp-lime has the unit thermal resistance values in accordance with Table BL106.2. Alternatively, the unit R-value of hemp-lime shall be determined with one of the following tests by an approved laboratory: ASTM C177 ASTM C518, ASTM C1114 or ASTM C1363. Test results from a specific hemp-lime mix shall be permitted to be used for multiple projects.

TABLE BL106.2—THERMAL RESISTANCE OF HEMP-LIMEa

DENSITY (pounds per cubic foot) R-VALUE (ft2× °F × h/Btu per inch of thickness)
12.5 R-2.10
15 R-1.86
20 R-1.54
25 R-1.20
For SI: 1 pound per cubic foot = 1.6 kg/m3.
a. Linear interpolation is permitted. Extrapolation is not permitted.

BL106.3 Density measurement.

Hemp-lime density shall be measured based on approved test samples as follows:

  1. Three samples of the proposed hemp-lime mix shall be placed moist to completely fill a 6-inch by 6-inch by 12-inch (152 mm × 152 mm × 305 mm) form, a 6-inch (152 mm) diameter by 12-inch (305 mm) length form or other approved form, following the application method and procedure that will be used during construction.
  2. Samples shall be removed from the forms within 24 hours after hemp-lime placement or per the binder manufacturer’s specifications.
  3. Samples shall be cured/dried for a minimum of 14 days in indoor ambient conditions before density determination.

APPENDIX BL-10 2025 CALIFORNIA RESIDENTIAL CODE

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

APPENDIX BL — HEMP-LIME (HEMPCRETE) CONSTRUCTION

  1. Density shall be determined by Equation BL-2.

Equation BL-2 ρ = w/V

where:

ρ = Density of hemp-lime infill (pounds per cubic foot).

w = Weight of hemp-lime infill sample (pounds).

V = Volume of hemp-lime sample (cubic feet).

BL106.4 Compliance with Section R302.10.1.

Hemp-lime infill shall meet the requirements for insulation materials in Section R302.10.1 for flame spread index and smoke-developed index as tested in accordance with ASTM E84.

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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)
  26. ▸ Appendix BL — HEMP-LIME (HEMPCRETE) CONSTRUCTION
    Overview
    1. Section BL101 — GENERAL
    2. Section BL102 — DEFINITIONS
    3. Section BL103 — HEMP-LIME CONSTRUCTION
    4. Section BL104 — FINISHES
    5. Section BL105 — FIRE RESISTANCE
    6. Section BL106 — THERMAL PERFORMANCE
    7. Section BL107 — MECHANICAL PERFORMANCE
    8. Section BL108 — REFERENCED STANDARDS
  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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