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California's 16 building climate zones, explained

Title 24 splits California into 16 building climate zones. What they are, why they matter for your project and how to find yours.

The California Energy Commission divides the state into 16 building climate zones based on weather. Your zone is one of the first facts any Title 24 calculation needs.

Why the zone matters

  • Prescriptive requirements, like insulation levels and window performance, differ by zone.
  • Performance calculations use a weather file for your zone, so the same house can pass in one zone and fall short in another.

Finding your zone

The CEC publishes the zone for each ZIP code. A few ZIP codes cross zone boundaries; for those, confirm the zone for the exact address with the CEC's climate zone map or your building department.