Permits & Code
Energy code (Title 24) for small homes
The 2025 California Energy Code, in effect for permits from January 1, 2026, sets wall, window, ventilation and solar rules by climate zone. Hempcrete walls can count as mass walls.
| Item | Requirement | Notes |
|---|---|---|
| Mass wall with exterior insulation | U-0.125 / R-8 in CZ 1–15; U-0.077 / R-13 in CZ16 | A 12-inch hempcrete wall at 12.5–15 pcf is about R-22 to R-25 |
| Framed wall | U-0.048 (U-0.065 in CZ 6–7) | Metal framing uses framing factors of 25% at 16 in and 22% at 24 in on center (JA4) |
| Window U-factor (maximum) | 0.27 in CZ 1–5, 11–14, 16; 0.30 in CZ 6–10, 15 | Homes of 500 sq ft or less in CZ5 may use 0.30; mandatory area-weighted maximum 0.40 |
| Window SHGC (maximum) | 0.23 in CZ 2, 4, 6–14; 0.20 in CZ15 | |
| Solar PV | Smaller of roof area × 18 W/sq ft or the Table 150.1-C formula | No PV if under 80 sq ft of solar-access roof or under 1.8 kWdc |
| Battery-ready wiring | Required with electrical service of 125 A or more | §150.0(s) |
MicroHom's reading of Table 150.1-A and related sections. An energy consultant must confirm which category a hempcrete assembly falls under.
Solar sizes and costsHempcrete R-values
Sources
- 2025 CRC Appendix BL, Section BL106 Thermal Performance. Checked Oct 17, 2026.
- Energy Code Ace, 2025 fenestration and envelope requirements. Checked Oct 17, 2026.
- Energy Code Ace, 2025 Reference Appendix JA4 (U-factors, framing factors). Checked Oct 17, 2026.
- California Energy Commission, 2025 Single-Family Residential Compliance Manual. Checked Oct 17, 2026.
- California Energy Commission, 2025 Energy Code Support Center: single-family solar PV FAQ. Checked Oct 17, 2026.
- 2025 California Energy Code, Section 150.1 (gocodebook). Checked Oct 17, 2026.
- California Energy Commission, What's New for 2025: Single-Family. Checked Oct 17, 2026.
Last updated Oct 18, 2026. Each source above was checked on the date shown.