Title 24 Reports in the Bay Area

Three climate zones cover the five core Bay Area counties, and the line between them runs through backyards. This guide shows what separates them and where local rules apply.

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The nine counties, split in two

The Metropolitan Transportation Commission names nine Bay Area counties. This guide takes the five around the bay: Alameda County, Contra Costa County, San Francisco County, San Mateo County and Santa Clara County. Marin, Napa, Solano and Sonoma are in the North Bay guide. Concord and Fairfield, on the Interstate 80 corridor toward Sacramento, are zone 12, like Sacramento.

Three zones, three kinds of project

Of the Bay Area's 208 ZIP codes, 110 are in zone 3 (San Francisco, Oakland, Fremont), 58 in zone 4 (San Jose, Sunnyvale) and 40 in zone 12, behind the East Bay hills. For a new house, windows are U-0.27 in all three. Zone 3 sets no solar heat gain limit and no west cap, with R-30 ceilings; zones 4 and 12 allow SHGC 0.23 with R-38 ceilings. Only zone 12 also needs a whole-house fan, a cool roof and air-conditioner charge verification. With one dwelling, the equation alone owes no PV below about 1,080 square feet in zone 3, 1,010 in zone 4 and 650 in zone 12.

Local rules

Three of the Energy Commission's ten approved ordinances for the 2025 code are here: Menlo Park, Mountain View and Palo Alto, mostly about altering cooling systems in existing homes. Sunnyvale's code adds an air-conditioner replacement rule for zone 4. The Building Standards Commission reports that AB 130 froze most new local residential amendments from 1 October 2025 to 1 June 2031, so read what a reach code is and ask the building department.

Typical projects

Infill ADUs, second-story additions, SB 9 lot splits, townhomes and offices.

Every county, city and zone in the Bay Area

Five county pages and seven city pages are live, each noted with its zones.

See the locations page for the other regions and the counties page for every county.

Order a Bay Area report

Start with the project address, because the zone can change between neighbouring cities. Prices begin at $199 for ADUs, $245 for residential work and $345 for multi-family; revisions are unlimited, and a rush in 24 hours adds $95.

From $199 · ready in 2–3 days

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