California Climate Zone 3
Climate zone 3 covers the bay shore and the central coast, moderated by the ocean year round. The Energy Commission assigns 276 of California's ZIP codes to it, making it the 3rd largest of the sixteen.
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Where zone 3 is
The Energy Commission assigns 276 ZIP codes to zone 3 — about 10.2 per cent of every ZIP code it lists, and the 3rd largest of the sixteen. Places in it include San Francisco, Oakland, Berkeley, Hayward, San Mateo, Santa Cruz, Salinas and Monterey.
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 939xx, 940xx, 941xx, 944xx, 945xx, 946xx, 947xx, 948xx, 949xx, 950xx.
What drives compliance in zone 3
Neither heating nor cooling is severe, so the calculation is usually decided by the envelope and the glazing rather than by equipment capacity. That makes zone 3 a comparatively forgiving assignment — but it also means the margin often comes from window performance and area, which is where a glass-heavy design gets caught.
Where zone 3 ends
Zone 3 reaches from Marin down to Monterey, and on the peninsula its southern boundary tracks the Santa Clara County line rather than the terrain — Menlo Park is zone 3, Palo Alto next door is not. Inland, the Oakland-Berkeley hills separate it from the valley zone behind.
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 3
Zone 3 sets no SHGC, no west-facing glass limit and no cool roof in Table 150.1-A, and its column matches zone 5 cell for cell: U-0.27 windows, R-30 ceilings under both attic options, a radiant barrier and R-6 attic ducts.
Cities we cover in zone 3
6 of our city guides cover places in this zone.
- Title 24 in San Francisco
- Title 24 in Oakland
- Title 24 in Fremont
- Title 24 in Salinas
- Title 24 in Santa Cruz
- Title 24 in Hayward
County guides: Title 24 in Alameda County, Title 24 in San Mateo County, Title 24 in San Francisco County.