Title 24 Reports in the North Bay

Marin, Sonoma, Napa and Solano counties are four neighbours with different zone pictures, a fire-rebuild history and two Marin cities with their own energy ordinances.

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Where the North Bay starts and stops

The Metropolitan Transportation Commission gives Marin, Napa, Solano and Sonoma one commissioner each, and this guide uses those four. The five counties around the bay are in the Bay Area guide. Mendocino and Lake, sometimes called North Bay, are in the Northern California guide. Solano also faces east along Interstate 80, which is why its zones include 12.

Four counties, four zone stories

Across the four counties, 52 ZIP codes are in zone 2, 17 in zone 3, 12 in zone 12 and 11 in zone 1. Sonoma holds zones 1 and 2, with Santa Rosa in zone 2. Marin holds 2 and 3. Solano holds zones 3 and 12: Vallejo is mostly zone 3, Fairfield zone 12. Napa, which has no page yet, is zone 2.

Zone 2 asks for U-0.27 windows with SHGC 0.23, a radiant barrier and R-38 ceilings. It is the only zone below zone 8 that requires charge verification on a new air conditioner. Total glazing is capped at 20 percent of floor area, 480 square feet on a 2,400 square foot house, and in zone 2 west-facing glass at 5 percent, or 120. Zone 3 has no west cap. A design over the caps moves to the performance method.

Fire and wine country

CAL FIRE records 5,636 structures destroyed in the 2017 Tubbs Fire in Napa and Sonoma counties. A rebuild meets the code in force when the application is submitted, now the 2025 Energy Code; see the wildfire rebuild guide. Tasting rooms and cellars follow winery and brewery projects.

Local rules

Two North Bay cities, both in Marin, have ordinances approved by the Energy Commission for the 2025 code, Corte Madera and San Rafael, each covering single-family additions and alterations of 500 square feet or more. Sonoma, Napa and Solano have none on the list. See what a reach code is.

Every county, city and zone in the North Bay

Three county pages and two city pages are live, each noted with its zones.

The locations page shows the other regions, and the counties page lists every county.

Order a North Bay report

Whether it is a hillside addition in Marin or a barrel hall in Sonoma, send the plans and the address. An ADU report is from $199, a residential report from $245 and multi-family from $345. Revisions are unlimited, and the 24-hour rush costs $95 more.

From $199 · ready in 2–3 days

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