California Climate Zones Explained: Which Title 24 Requirements Apply to Your Building

California Climate Zones Explained: Which Title 24 Requirements Apply to Your Building

TL;DR: California has 16 climate zones defined by the California Energy Commission (CEC). Title 24 fenestration requirements — including SHGC and U-factor thresholds for window film — vary by climate zone, and a single county can span multiple zones. This guide explains the 16 zones, lists their representative cities, and tells you which Title 24 prescriptive requirements apply where. Use the CEC's ZIP-lookup tool for any specific property, because borders straddle individual streets.

Why climate zones matter for Title 24

California is one of the only US states that has its own climate zone system separate from the federal IECC zones, and the difference is meaningful. The CEC's 16-zone map reflects the state's geographic and climatic diversity — from cool marine north coast to low-elevation desert to cold mountain — and Title 24 Part 6 prescriptive requirements are calibrated to that diversity.

For window film, the practical implication is this: the SHGC and U-factor thresholds your project must meet are not a single national number. They depend on the climate zone of the building's address. A film specification that's over-compliant on the coast (CZ 3, Oakland) may be non-compliant inland (CZ 9, Burbank) — even though the two cities are about 380 miles apart.

The first step on any California commercial window film project is confirming the climate zone. The second is reading the prescriptive requirements for that zone. This guide is about both.

How CEC climate zones differ from federal climate zones

You'll occasionally see Title 24 documentation referencing federal IECC climate zones (Zone 3B, 3C, etc.) alongside the CEC 16-zone system. For Title 24 Part 6 compliance, the CEC 16-zone system is the controlling map. Federal zones are referenced for cross-state energy code comparisons but do not govern California building permits.

The CEC zones are based on heating degree days, cooling degree days, solar gain, coastal vs inland exposure, and elevation. This is why one California county can span multiple zones — Los Angeles County alone covers CZ 6 (coastal), CZ 8 (inland LA/OC), CZ 9 (hot inland), CZ 14 (high desert), and CZ 16 (mountain). A single project's zone assignment can swing the prescriptive SHGC and U-factor requirements significantly.

The 16 California climate zones

The 16 CEC zones, with representative city, climate character, and the major California cities and counties that fall in each:

CZ 1 — Cool Marine North Coast

Rep city: Arcata. Character: Persistently cool, foggy, maritime-influenced. Major cities: Eureka, Crescent City, Fort Bragg. Counties: Del Norte, Humboldt, parts of Mendocino. CZ 1 has the lightest cooling load in the state. Title 24 solar control requirements are the least demanding here, but window film is still useful for fade prevention and UV protection — California's strongest UV-driven product demand sits here for furniture and floor preservation rather than heat reduction.

CZ 2 — Mild North Coast Inland

Rep city: Santa Rosa. Character: Mild, with greater day-to-night temperature swings than CZ 1. Major cities: Santa Rosa, Petaluma, Napa. Counties: Sonoma, Napa, inland Marin. Moderate cooling load. Wine country and hospitality applications are common — comfort-driven film installs in tasting rooms and west-facing inn windows.

CZ 3 — Mild Bay Area Coastal

Rep city: Oakland. Character: Cool to mild year-round. Marine layer influence. Major cities: San Francisco, Oakland, Berkeley, San Mateo, Fremont, Monterey, Santa Cruz. Counties: San Francisco, Alameda (west), San Mateo, Monterey, Santa Cruz. The classic "mild Bay Area" zone. Cooling load is real but modest. Most commercial film installs here are driven by glare control and tenant comfort rather than absolute heat reduction.

CZ 4 — Bay Area Inland / Santa Clara Valley

Rep city: San Jose. Character: Mild with warmer summer afternoons than CZ 3. Major cities: San Jose, Sunnyvale, Palo Alto, Mountain View. Counties: Santa Clara, inland San Mateo, parts of Alameda. Silicon Valley climate. Heavy commercial office and corporate campus inventory. Cooling load picks up in CZ 4 noticeably vs CZ 3 — a meaningful Title 24 distinction even within "Bay Area."

CZ 5 — Cool Central Coast

Rep city: Santa Maria. Character: Cool with persistent ocean influence. Major cities: Santa Maria, San Luis Obispo, parts of Santa Barbara County coast. Counties: San Luis Obispo, parts of Santa Barbara.

CZ 6 — Mild South Coast (LA Basin Coastal)

Rep city: Torrance. Character: Mild Mediterranean, marine moderation. Major cities: Santa Monica, Long Beach, Torrance, Huntington Beach, Newport Beach, El Segundo. Counties: Coastal LA, coastal OC. The LA Basin coastal zone. Significant commercial inventory. Cooling load moderate but driven hard by west-facing afternoon sun on dense glass facades.

CZ 7 — Mild South Coast (San Diego)

Rep city: San Diego. Character: Mild marine. Major cities: San Diego, Chula Vista, Oceanside, Carlsbad, Coronado. Counties: San Diego (coastal). Climate twin to CZ 6 but with more consistent year-round mildness. Hospitality, biotech corridor, and military-adjacent commercial.

CZ 8 — Warm Inland LA / OC

Rep city: Fullerton. Character: Warmer than coastal zones; reduced marine moderation. Major cities: Fullerton, Anaheim, Santa Ana (inland portions), Garden Grove. Counties: Inland Orange County, parts of LA County south. The first zone where Title 24 SHGC requirements become a serious design constraint. West-facing glass without solar control treatment becomes a comfort and energy problem.

CZ 9 — Hot Inland LA (San Fernando Valley)

Rep city: Burbank. Character: Hot inland, dry summer afternoons regularly above 95°F. Major cities: Burbank, Glendale, Pasadena, North Hollywood, Sherman Oaks, Studio City, Encino. Counties: San Fernando Valley portion of LA County, parts of east LA. Heavy commercial inventory. CZ 9 is where window film delivers some of its strongest measurable cooling savings in California, and where prescriptive Title 24 requirements meaningfully constrain glazing-heavy designs.

CZ 10 — Hot Inland SoCal (Inland Empire)

Rep city: Riverside. Character: Hot inland with limited marine moderation; summer highs frequently above 100°F. Major cities: Riverside, San Bernardino, Redlands, Corona, Ontario. Counties: Riverside, San Bernardino (west). The Inland Empire. Large commercial warehouse and logistics inventory plus growing office and retail. Cooling cost reduction from window film is among the highest economic returns in California here.

CZ 11 — Hot North Valley

Rep city: Red Bluff. Character: Hot summers, cold winters. Major cities: Red Bluff, Chico, Redding (lower elevation). Counties: Tehama, Butte, Shasta (valley).

CZ 12 — Hot Central Valley

Rep city: Sacramento. Character: Hot dry summers, cool foggy winters. Major cities: Sacramento, Stockton, Modesto, Davis, Roseville, Elk Grove. Counties: Sacramento, San Joaquin, Stanislaus, Yolo. State capital. Heavy government and institutional commercial inventory. Hot summer afternoons drive Title 24 SHGC requirements similar to CZ 9.

CZ 13 — Very Hot Central Valley

Rep city: Fresno. Character: Very hot summers (frequently 105°F+), substantial cooling load. Major cities: Fresno, Bakersfield, Visalia, Merced. Counties: Fresno, Kern, Tulare, Madera, Merced. Some of the hottest cooling-loaded commercial markets in California. Single-pane existing glass in CZ 13 typically requires both window film and supplementary measures to meet Title 24 — performance pathway is common here.

CZ 14 — High Desert

Rep city: Palmdale. Character: Hot dry summers, cold winters, large diurnal swings. Major cities: Palmdale, Lancaster, Victorville, Barstow, Hesperia. Counties: Northern LA, San Bernardino (high desert), parts of Kern. Hot summer, cold winter — Title 24 here requires both SHGC and U-factor attention. Single-pane glass benefits dramatically from high-performance Low-E film.

CZ 15 — Low / Hot Desert

Rep city: Palm Springs. Character: The hottest zone in California. Summer highs above 110°F are routine. Major cities: Palm Springs, Palm Desert, Indio, La Quinta, El Centro, Imperial. Counties: Imperial, eastern Riverside. CZ 15 sees the most aggressive Title 24 SHGC requirements in California. Resort, hospitality, retail, and government commercial inventory. Window film is a near-universal recommendation for west and south-facing glass on existing buildings.

CZ 16 — Cold Mountain

Rep city: Blue Canyon (Sierra Nevada). Character: Cold winters, heavy snow, cool summers. Major cities: South Lake Tahoe, Truckee, Mammoth Lakes, Big Bear Lake. Counties: Mountain portions of El Dorado, Placer, Mono, Inyo, San Bernardino (mountain). Title 24 in CZ 16 is driven primarily by heating load. U-factor (winter heat loss) matters more than SHGC. Low-E window film with high U-factor improvement is the typical film recommendation here.

How to find the climate zone for any California address

The CEC publishes a Climate Zone Tool by ZIP that lets you look up the zone for any California property. This is the authoritative source — use it, not a city-name approximation, because borders can run through individual streets. Los Angeles County alone spans CZ 6, 8, 9, 14, and 16, and we've seen a single project's two buildings sit in different zones because of where the parcel line falls.

For commercial projects spanning multiple zones (a portfolio with buildings in different parts of the state), each building's compliance is calculated separately for its own zone.

Title 24 prescriptive requirements by climate zone — the structure

Title 24 prescriptive SHGC and U-factor requirements for fenestration come from Table 140.3-B for nonresidential and high-rise residential and Table 150.1-A for low-rise residential (single-family and low-rise multifamily). The tables differentiate by climate zone (CZ 1-16), vertical fenestration vs skylight, Window-to-Wall Ratio (WWR) for nonresidential, and building type and orientation.

Widely reported 2025 cycle values for residential (Table 150.1-A): Maximum U-factor 0.30 (area-weighted average); Maximum SHGC 0.23 in regulated climate zones (historically CZ 2, 4, 6-15). Nonresidential prescriptive thresholds are more granular — the table differentiates further by orientation and WWR. The 2025 cycle tightened vertical fenestration U-factors in cooler and inland zones (a meaningful change for designers who used to lean on prescriptive in CZ 3-7).

Specific per-zone numeric values in Tables 140.3-B and 150.1-A should be pulled from the 2025 CEC PDF before any project quote. Web search results occasionally still reflect prior cycles, and prescriptive cells were updated as of the January 1, 2026 effective date. The CEC's restructured 2025 Energy Code PDF is the live authority.

How window film fits across the climate zone spectrum

The right film for a California commercial project varies significantly by zone:

• CZ 1-3 (cool to mild): Light solar control is sufficient. High VLT clear films (XPEL Vision Clear View Plus 70, 3M Affinity, similar) preserve aesthetics while delivering glare and UV control.

• CZ 4-7 (mild to warm): Mid-tier solar control. Moderate VLT (50-70%) films with TSER in the 55-65% range.

• CZ 8-12 (warm to hot inland and Central Valley): Significant solar control needed. Lower VLT or higher-performance spectrally-selective films (Clear View Plus 40, 3M Prestige 50, LLumar SelectPro CTX 50).

• CZ 13-15 (very hot to desert): Maximum-performance solar control. Spectrally-selective films at moderate VLT plus consideration of reflective options (Dual Reflective Series, Silver Series). Often combined with performance pathway modeling for Title 24 compliance.

• CZ 16 (cold mountain): Low-E films for heating retention. U-factor improvement matters more than SHGC reduction here.

The right specification for any project is a function of zone + occupancy + design intent + Title 24 pathway. The above is a starting framework; the actual product specification happens per project.

Common questions

Q: Which climate zone is Los Angeles in? A: Los Angeles County spans CZ 6, 8, 9, 14, and 16. The City of Los Angeles itself covers CZ 6 (coastal LA), CZ 8 (parts of South and East LA), and CZ 9 (San Fernando Valley). Use the CEC ZIP-lookup tool for any specific address.

Q: Which climate zone is San Diego in? A: San Diego is primarily CZ 7 (coastal) and parts of CZ 10 (inland east San Diego County).

Q: Which climate zone is the Bay Area in? A: The Bay Area spans CZ 3 (coastal SF, Oakland, Berkeley, San Mateo) and CZ 4 (Silicon Valley inland — San Jose, Sunnyvale, Palo Alto).

Q: Which climate zone is Sacramento in? A: Sacramento is CZ 12.

Q: Which climate zone is Palm Springs in? A: Palm Springs is CZ 15 — the lowest, hottest desert zone in California with the most aggressive Title 24 cooling requirements.

Q: Do climate zones ever change? A: Rarely. The CEC's 16-zone system has been stable for decades. Climate zone reassignment for a given ZIP only happens during major CEC updates and is publicly announced.

Q: Does my project's climate zone affect window film warranty? A: Generally no. Manufacturer warranties are based on product type and installation quality, not climate zone. That said, hotter zones place greater thermal stress on glass — proper film selection by zone reduces the risk of thermal stress cracks on weak glass.

California Climate Zones Explained

Get a zone-specific Title 24 assessment

If you have a commercial project anywhere in California, the fastest path to a compliant film specification is a site visit. We'll confirm the climate zone, pull the prescriptive thresholds, measure the existing glass, and recommend the film that meets your Title 24 target at the right cost. Book a Free Climate-Zone-Specific Title 24 Assessment at https://www.rapidwindowtinting.com/price-and-appointments.