Title 24 Reports in Solano County

A lopsided split

Only three of the fifteen ZIP codes we derive for Solano County sit in zone 3, and they are all on the western edge at the Carquinez Strait — the Vallejo waterfront, where the bay's influence still reaches. Everything else, twelve ZIP codes, is zone 12.

That is worth knowing in the specific direction it runs. A project anywhere in Fairfield, Vacaville, Suisun City, Benicia's inland side, Dixon or Rio Vista is a zone 12 project. Assuming bay-area mildness across this county is the error to avoid, because the county stops being coastal very quickly.

The gap between the two is real

Zone 3 is a mild marine climate. Zone 12 is a Central Valley climate with hot summers and genuinely cold winter nights. The county sits at the point where the bay stops moderating the interior, and the transition is compressed into a few miles.

Which side of it you are on

Because the zone 3 area is small and specific, this is a county where the ZIP check resolves quickly — but it has to be made. The answer is zone 12 for most addresses and zone 3 for a few, and the consequence of getting it backwards is a calculation built for the wrong climate.

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 3 — 94589, 94590, 94592
• Climate zone 12 — 94510, 94533, 94534, 95687, 95688 and 7 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:

• 95620 — about 76% within Solano County, the remainder in Yolo 24%
• 94571 — about 82% within Solano County, the remainder in Sacramento 18%

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 Solano 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 Solano County

Solano County contains California climate zones 3 and 12. 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.