Appendix BL — HEMP-LIME (HEMPCRETE) CONSTRUCTION
BL106 Thermal Performance — 2025 California Residential Code
California Residential Code (Title 24, Part 2.5) · 2025 edition · updated 2026-10-19 · California
CBSC: official editions, supplements and errata
Italicized text is a California amendment to the model code, as printed in the official publication.
Cite as: 2025 California Residential Code (Title 24, Part 2.5) § BL106 · Effective January 1, 2026 · Official source: Building Standards Commission
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/ |
|---|---|
| 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/ 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:
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.
Samples shall be removed from the forms within 24 hours after hemp-lime placement or per the binder manufacturer’s specifications.
Samples shall be cured/dried for a minimum of 14 days in indoor ambient conditions before density determination.
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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