Title 24 Reports in Sonoma County

Zone 1 is the unusual part

Most of California's population lives in zones 3 through 15. Zone 1 is the cold, wet, fog-bound coastal assignment, and it covers a thin strip of the far north coast — of which the Sonoma coast is the southern reach. Eleven of the county's ZIP codes sit in it.

That matters because zone 1 is a heating-dominated zone in a state where most compliance thinking is about cooling. A design carried over from Santa Rosa, half an hour inland, is built around a different problem.

Where the line falls

The split follows how far the marine layer reaches inland. The coast and the lower river valley are zone 1; once the terrain rises and the fog stops arriving reliably, the county becomes zone 2 — which is the larger share by some distance, 27 of the 38 ZIP codes we derive for the county, and includes Santa Rosa, Petaluma, Rohnert Park, Sonoma and Healdsburg.

What it means for a report

Zone 2 is a mild mixed climate where both heating and cooling matter and neither dominates outright. Zone 1 pushes the calculation toward envelope and heating performance. Two projects twenty miles apart in this county are assessed against genuinely different targets, so the ZIP check is not a formality here.

Example ZIP codes and their zones

Derived from the Energy Commission's ZIP-to-climate-zone table, with county membership taken from the U.S. Census Bureau's 2020 ZCTA-to-county relationship file:

• Climate zone 1 — 94922, 94923, 95412, 95421, 95450 and 6 more
• Climate zone 2 — 94928, 94931, 95401, 95404, 95476 and 22 more

ZIP codes that cross the county line

A ZIP code is a postal boundary, not a county boundary, and several here fall on both sides of one. Where that happens we do not treat the county as settling the question:

• 94515 — about 51% within Sonoma County, the remainder in Napa 49%
• 95425 — about 68% within Sonoma County, the remainder in Mendocino 32%

For an address in one of these, the climate zone still comes from the ZIP code, which is assigned by the Energy Commission regardless of the county line. What the split affects is which jurisdiction issues the permit — worth confirming before a submittal.

Finding the zone for your own project

The zone is set by the project's location and confirmed from the ZIP code against the Energy Commission's published table — not from the county name and not from the nearest large town. Because Sonoma County contains more than one zone, that check decides which set of numbers a report is written against.

Give us the project address and we determine the zone as part of preparing the report. It is the first thing established, because every insulation, glazing and equipment figure downstream depends on it.

City and unincorporated permitting

A project inside a city's limits is permitted by that city. A project on unincorporated land is permitted by the county instead, and the two can run different submittal processes even where the energy requirements are identical. The California Energy Code is statewide — what changes locally is the climate zone the site falls in and how the jurisdiction wants the compliance documents presented.

Climate zones in Sonoma County

Sonoma County contains California climate zones 1 and 2. The zone drives the insulation, glazing and equipment performance a report has to demonstrate, and it is confirmed from the project ZIP code against the Energy Commission's published table.