California Climate Zone 12

Climate zone 12 covers the Sacramento and northern San Joaquin valleys, plus the inland East Bay — the largest zone in the state. The Energy Commission assigns 375 of California's ZIP codes to it, making it the largest of the sixteen.

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Where zone 12 is

The Energy Commission assigns 375 ZIP codes to zone 12 — about 13.9 per cent of every ZIP code it lists, and the largest of the sixteen. Places in it include Sacramento, Stockton, Modesto, Fairfield, Davis, Walnut Creek, Livermore and Merced.

The zone spans a wide swathe of the state, which is why two projects in it can be well over a hundred miles apart. The ZIP codes fall in the prefix ranges 936xx, 942xx, 945xx, 952xx, 953xx, 956xx, 957xx, 958xx, 959xx.

What drives compliance in zone 12

Hot dry summers and cool damp winters give this zone real demand in both directions, with cooling usually the larger of the two. Because it covers so much of the state's inland population, it is also the zone where duct leakage in older housing most often decides whether an alteration passes verification.

Where zone 12 ends

The largest zone in the state, covering about one in seven of every California ZIP code. It runs from Solano County through Sacramento and down the northern San Joaquin Valley, and it also reaches over the East Bay hills to take in Walnut Creek, Livermore and Pleasanton.

Boundaries follow conditions rather than administrative lines, so the assignment is resolved from the project ZIP code rather than inferred from the city on the drawings.

The 2025 Standards in zone 12

Zone 12 differs from zone 11 in one row of Table 150.1-A: concrete raised floors need U-0.138 with R-4, a line only zone 15 shares. Windows stay at U-0.27 and SHGC 0.23.

Cities we cover in zone 12

6 of our city guides cover places in this zone.

County guides: Title 24 in Sacramento County, Title 24 in Contra Costa County, Title 24 in San Joaquin County.