California Climate Zone 11
Climate zone 11 covers the northern Sacramento Valley and the Sierra foothills above it. The Energy Commission assigns 111 of California's ZIP codes to it, making it the 12th largest of the sixteen.
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Where zone 11 is
The Energy Commission assigns 111 ZIP codes to zone 11 — about 4.1 per cent of every ZIP code it lists, and the 12th largest of the sixteen. Places in it include Chico, Redding, Roseville, Yuba City, Oroville and Auburn.
The zone is geographically contiguous — it occupies one continuous block of the state rather than being scattered. The ZIP codes fall in the prefix ranges 956xx, 957xx, 959xx, 960xx.
What drives compliance in zone 11
A genuine two-season zone: hot summers and cool winters mean both loads have to be designed for rather than one traded against the other. That makes heat pumps a natural fit, and it makes envelope decisions do double duty in a way they do not in a single-load zone.
Where zone 11 ends
Zone 11 begins where the Sacramento area ends. Roseville, Rocklin and Auburn are in it while Sacramento a short drive away is not, so the boundary falls close to the Placer County line and catches out anyone treating the whole metro as one assignment.
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.