California Climate Zones by County
California's 58 counties span climate zones 2B to 6B under the 2021 International Energy Conservation Code (IECC). Zone 3B is the most common, with 25 of the 58. For reference, San Diego, Los Angeles and Sacramento are in zone 3B and San Francisco is in 3C.
Insulation minimums for each zone in California
| Zone | Counties | Attic | Wood-frame walls | Floors over unheated space | Basement walls |
|---|---|---|---|---|---|
| 2B | 1 | R-49 | R-13, or R-10ci | R-13 | None required |
| 3B | 25 | R-49 | R-20, or 13+5ci, or R-15ci | R-19 | R-5ci or R-13 |
| 3C | 14 | R-49 | R-20, or 13+5ci, or R-15ci | R-19 | R-5ci or R-13 |
| 4B | 8 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-19 | R-10ci or R-13 |
| 4C | 2 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-30 | R-15ci, or R-19, or 13+5ci |
| 5B | 6 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-30 | R-15ci, or R-19, or 13+5ci |
| 6B | 2 | R-60 | R-30, or 20+5ci, or 13+10ci, or R-20ci | R-30 | R-15ci, or R-19, or 13+5ci |
Minimums from the 2021 IECC (Table R402.1.3). Many areas still enforce an older edition, so check with your local building department. See sources.
Which energy code California uses
California enforces the 2025 Building Efficiency Standards for homes (in effect since Jan 2026). Source: US Department of Energy, September 2026. Local governments can adopt newer codes or amendments. See every state's energy code.
What changed from the 2018 map
None of California's counties changed zone between the 2018 and 2021 maps.
Every county in California
| Name | Zone (2021) | Zone (2018) | Details |
|---|---|---|---|
| Alameda County | 3C | 3C | Insulation → |
| Alpine County | 6B | 6B | Insulation → |
| Amador County | 4B | 4B | Insulation → |
| Butte County | 3B | 3B | Insulation → |
| Calaveras County | 4B | 4B | Insulation → |
| Colusa County | 3B | 3B | Insulation → |
| Contra Costa County | 3B | 3B | Insulation → |
| Del Norte County | 4C | 4C | Insulation → |
| El Dorado County | 4B | 4B | Insulation → |
| Fresno County | 3B | 3B | Insulation → |
| Glenn County | 3B | 3B | Insulation → |
| Humboldt County | 4C | 4C | Insulation → |
| Imperial County | 2B | 2B | Insulation → |
| Inyo County | 4B | 4B | Insulation → |
| Kern County | 3B | 3B | Insulation → |
| Kings County | 3B | 3B | Insulation → |
| Lake County | 4B | 4B | Insulation → |
| Lassen County | 5B | 5B | Insulation → |
| Los Angeles County | 3B | 3B | Insulation → |
| Madera County | 3B | 3B | Insulation → |
| Marin County | 3C | 3C | Insulation → |
| Mariposa County | 4B | 4B | Insulation → |
| Mendocino County | 3C | 3C | Insulation → |
| Merced County | 3B | 3B | Insulation → |
| Modoc County | 5B | 5B | Insulation → |
| Mono County | 6B | 6B | Insulation → |
| Monterey County | 3C | 3C | Insulation → |
| Napa County | 3C | 3C | Insulation → |
| Nevada County | 5B | 5B | Insulation → |
| Orange County | 3B | 3B | Insulation → |
| Placer County | 3B | 3B | Insulation → |
| Plumas County | 5B | 5B | Insulation → |
| Riverside County | 3B | 3B | Insulation → |
| Sacramento County | 3B | 3B | Insulation → |
| San Benito County | 3C | 3C | Insulation → |
| San Bernardino County | 3B | 3B | Insulation → |
| San Diego County | 3B | 3B | Insulation → |
| San Francisco County | 3C | 3C | Insulation → |
| San Joaquin County | 3B | 3B | Insulation → |
| San Luis Obispo County | 3C | 3C | Insulation → |
| San Mateo County | 3C | 3C | Insulation → |
| Santa Barbara County | 3C | 3C | Insulation → |
| Santa Clara County | 3C | 3C | Insulation → |
| Santa Cruz County | 3C | 3C | Insulation → |
| Shasta County | 3B | 3B | Insulation → |
| Sierra County | 5B | 5B | Insulation → |
| Siskiyou County | 5B | 5B | Insulation → |
| Solano County | 3B | 3B | Insulation → |
| Sonoma County | 3C | 3C | Insulation → |
| Stanislaus County | 3B | 3B | Insulation → |
| Sutter County | 3B | 3B | Insulation → |
| Tehama County | 3B | 3B | Insulation → |
| Trinity County | 4B | 4B | Insulation → |
| Tulare County | 3B | 3B | Insulation → |
| Tuolumne County | 4B | 4B | Insulation → |
| Ventura County | 3C | 3C | Insulation → |
| Yolo County | 3B | 3B | Insulation → |
| Yuba County | 3B | 3B | Insulation → |
Source: Pacific Northwest National Laboratory, Guide to Determining Climate Zone by County: Building America and IECC 2021 Updates (2022).
Frequently asked questions
What climate zone is California?
California spans IECC climate zones 2B to 6B; zone 3B is the most common. Find your county in the table above, or search by ZIP code.
How much attic insulation do I need in California?
In California, the 2021 IECC calls for R-49 and R-60 in the attic, depending on the zone. The table near the top of this page lists each zone's minimums.
What energy code does California use?
California enforces the 2025 Building Efficiency Standards for homes (in effect since Jan 2026). Source: US Department of Energy, September 2026. Local governments can adopt newer codes or amendments.
More for California: Last frost dates in California · California planting zones · Frost line depth by state