California climate zones
California’s 58 counties fall in 7 IECC 2021 climate zones: 2B (1), 3B (25), 3C (14), 4B (8), 4C (2), 5B (6), 6B (2).
Zone 2B: hot-dry
Attic target R49 (ENERGY STAR)Imperial County (Hot-dry)
Zone 3B: warm-dry
Attic target R49 (ENERGY STAR)Butte County (Hot-dry) · Colusa County (Hot-dry) · Contra Costa County (Hot-dry) · Fresno County (Hot-dry) · Glenn County (Hot-dry) · Kern County (Hot-dry) · Kings County (Hot-dry) · Los Angeles County (Hot-dry) · Madera County (Hot-dry) · Merced County (Hot-dry) · Orange County (Hot-dry) · Placer County (Hot-dry) · Riverside County (Hot-dry) · Sacramento County (Hot-dry) · San Bernardino County (Hot-dry) · San Diego County (Hot-dry) · San Joaquin County (Hot-dry) · Shasta County (Hot-dry) · Solano County (Hot-dry) · Stanislaus County (Hot-dry) · Sutter County (Hot-dry) · Tehama County (Hot-dry) · Tulare County (Hot-dry) · Yolo County (Hot-dry) · Yuba County (Hot-dry)
Zone 3C: warm-marine
Attic target R49 (ENERGY STAR)Alameda County (Marine) · Marin County (Marine) · Mendocino County (Marine) · Monterey County (Marine) · Napa County (Marine) · San Benito County (Marine) · San Francisco County (Marine) · San Luis Obispo County (Marine) · San Mateo County (Marine) · Santa Barbara County (Marine) · Santa Clara County (Marine) · Santa Cruz County (Marine) · Sonoma County (Marine) · Ventura County (Marine)
Zone 4B: mixed-dry
Attic target R60 (ENERGY STAR)Amador County (Mixed-dry) · Calaveras County (Mixed-dry) · El Dorado County (Mixed-dry) · Inyo County (Mixed-dry) · Lake County (Mixed-dry) · Mariposa County (Mixed-dry) · Trinity County (Mixed-dry) · Tuolumne County (Mixed-dry)
Zone 4C: mixed-marine
Attic target R60 (ENERGY STAR)Del Norte County (Marine) · Humboldt County (Marine)
Zone 5B: cool-dry
Attic target R60 (ENERGY STAR)Lassen County (Cold) · Modoc County (Cold) · Nevada County (Cold) · Plumas County (Cold) · Sierra County (Cold) · Siskiyou County (Cold)
Zone 6B: cold-dry
Attic target R60 (ENERGY STAR)Alpine County (Cold) · Mono County (Cold)