California Title 24 Part 6: Envelope Requirements

Title 24 Part 6 applies to all new residential construction and major alterations in California, with prescriptive R-values and U-factors that vary across 16 California-specific climate zones.

California operates under its own state energy code — Title 24 Part 6, the Building Energy Efficiency Standards — administered by the California Energy Commission (CEC). Title 24 is updated on a 3-year cycle; the 2025 edition (Title 24, Part 6) became effective January 1, 2026 and applies to permits submitted on or after that date. Permits submitted before Jan 1, 2026 vest under the 2022 edition. Title 24 supersedes the IECC for all California construction, and its prescriptive R-values, U-factors, and SHGC limits track the IECC closely but with different climate-zone definitions and additional requirements like Quality Insulation Installation (QII), photovoltaic mandates, and battery storage requirements for new homes.

California uses 16 of its own climate zones (CZ 1 through CZ 16), not the 8 IECC zones. CZ 6 (coastal Los Angeles) and CZ 7 (San Diego coast) are the warmest; CZ 16 (Mono County, eastern Sierra) is the coldest. The mapping between California climate zones and IECC climate zones is approximate — for example, CZ 12 (Sacramento) corresponds roughly to IECC Zone 3B, and CZ 16 corresponds to IECC Zone 6B. Always use the California climate zone for Title 24 compliance and the IECC zone for any non-California reference.

This guide consolidates the 2025 Title 24 Part 6 prescriptive envelope requirements, the cool-roof rules unique to California, the QII mandate, and the photovoltaic and battery requirements that apply to new construction. It links into the insulation and roofing calculators with California-specific presets. Note that local jurisdictions in California (San Francisco, Berkeley, Marin County, others) have adopted "reach codes" that exceed Title 24 — always check the local AHJ.

2025 Title 24 Prescriptive Envelope by California Climate Zone

2025 Title 24 Part 6 Section 150.1 sets prescriptive envelope requirements that vary across the 16 California climate zones. Wood-frame wall R-values range from R-13 cavity (CZ 6, 7, 8, 9 — coastal LA, San Diego, Long Beach, San Bernardino coastal) up to R-21 cavity + R-5 ci (CZ 16 — Mono County alpine). Ceiling R-values are R-30 to R-38 in mild coastal zones and R-49 to R-60 in cold and Central Valley zones. Slab insulation (R-0 to R-15 depending on zone) and basement walls (R-0 to R-15 ci) round out the envelope picture. Title 24 prescriptive numbers are the floor — most builders pursue the performance path or HERS-tested compliance to optimize cost. The cells in the table below are illustrative for orientation; the 2025 cycle values must be verified against the CEC Reference Appendix JA4 before permitting.

Cool-Roof Requirements

Title 24 Part 6 §150.1(c) mandates cool-roof products for low-slope roofs (≤2:12) in CZ 13 and 15 (Central Valley and inland Southern California) and recommends them in other zones. Required values for low-slope roofs in those zones: 3-year aged solar reflectance ≥0.63 and thermal emittance ≥0.75, OR an SRI (Solar Reflectance Index) ≥75. For steep-slope roofs (>2:12), CZ 10–15 require aged reflectance ≥0.20 and emittance ≥0.75 (or SRI ≥16). The low-slope thresholds tightened to 0.63 / 0.75 / SRI 75 with the 2016 Title 24 update; the older 0.55 / 0.75 / SRI 64 values are no longer compliant. The Cool Roof Rating Council (CRRC) maintains the directory of qualifying products. Title 24 also accepts radiant-barrier roof decks as an alternative compliance path in some zones.

Quality Insulation Installation (QII)

California Title 24 includes a Quality Insulation Installation (QII) protocol that goes beyond standard installation grading. QII requires HERS-Rater verification of insulation Grade I per RESNET 301 — meaning batts cut to fit, no compression at electrical boxes or plumbing, no missing sections at top plates, and no air gaps behind cavity insulation. Title 24 prescriptive paths in many California climate zones credit QII with a wall-R reduction or U-factor relaxation. QII is the single biggest installation-quality requirement in U.S. residential construction and has driven California batt installers to a much higher standard than the rest of the country.

Photovoltaic and Battery Requirements

Beginning with the 2019 Title 24 update and continuing in 2022, all new low-rise residential construction in California must include a photovoltaic system sized to offset annual electricity use. The 2022 update extended the requirement to multifamily and certain non-residential buildings. The 2022 code also adds a battery-storage requirement for many new homes — typically 5 to 10 kWh of storage paired with the PV system. Solar carports and ground-mount alternatives are permitted on lots where roof orientation cannot accommodate the required system. While not strictly an envelope requirement, the PV mandate interacts with envelope decisions because better envelope performance reduces the required PV size.

Window U-Factor and SHGC

Title 24 fenestration limits vary by climate zone but generally require U-factor ≤0.30 and SHGC ≤0.23 in cooling-dominated zones (CZ 6–15). Cold zones (CZ 16) follow IECC Zone 6 rules: U-0.30, no SHGC limit. Skylights are limited to U-0.55. Site-built fenestration and metal-framed assemblies have separate U-factor categories. NFRC certification labels are required for all glazing — without an NFRC sticker, the window cannot be installed. California also limits west-facing glazing area in the prescriptive path: more than 20% of conditioned floor area in west-facing fenestration triggers performance-path compliance.