California Climate Zone 1
Climate zone 1 covers the far north coast — the wettest and one of the coolest assignments in the state, and the only zone confined to the redwood coast. The Energy Commission assigns 55 of California's ZIP codes to it, making it the 14th largest of the sixteen.
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Where zone 1 is
The Energy Commission assigns 55 ZIP codes to zone 1 — about 2.0 per cent of every ZIP code it lists, and the 14th largest of the sixteen. Places in it include Crescent City, Eureka, Arcata and Fort Bragg.
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 949xx, 954xx, 955xx.
What drives compliance in zone 1
Heating dominates here and cooling barely registers. On the far north coast the design problem is keeping heat in through a long wet winter, so insulation levels, air tightness and heating equipment efficiency carry the calculation. Solar heat gain is rarely the constraint it is further south, and west-facing glazing is far less of a liability.
Where zone 1 ends
Zone 1 is the only assignment confined to the redwood coast. It gives way to zone 2 a short distance inland and to the mountain zone in the Siskiyous, so its boundaries are set by how far the marine influence reaches rather than by any administrative line.
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.