Title 24 Reports in Santa Clara County
Santa Clara County is entirely one climate zone. Every ZIP code in it, from Palo Alto down to Gilroy, carries the same assignment.
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One zone, and the boundary is the county line
This is unusual for a county of this size and population. There is no internal split to resolve: Palo Alto, Mountain View, Sunnyvale, Santa Clara, San Jose, Milpitas, Campbell, Cupertino, Los Gatos, Morgan Hill and Gilroy all sit in the same zone, as does unincorporated land including Mount Hamilton.
What makes it more striking is that the zone boundary tracks the county line rather than the terrain. Menlo Park, just over the line in San Mateo County, is a different zone from Palo Alto next door. Fremont in Alameda County is a different zone from Milpitas. Scotts Valley in Santa Cruz County is a different zone from Los Gatos.
What that is worth
Inside the county the zone question is settled and needs no investigation. Immediately outside it, the answer changes — so the risk here is not ambiguity within the county but carrying a Santa Clara assumption across the line into a neighbouring one.
A firm working the whole peninsula or the whole bay is working in more than one zone even though every job feels like the same market.
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 itself is statewide — what changes locally is the climate zone the site falls in and how the jurisdiction wants the compliance documents presented.
The zone is confirmed from the project address as a matter of course, but in this county the answer does not change from one address to the next.
Climate zone in Santa Clara County
Santa Clara County contains California climate zone 4. 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.