Title 24 Reports in Marin County

Two coastlines, not one

Marin has a bay shore on its east side and an open Pacific shore on its west, and the two behave differently enough to sit in different zones. Fifteen of the twenty-nine ZIP codes we derive for the county are zone 2 and fourteen are zone 3 — an unusually even split.

Zone 2 covers the sheltered eastern corridor along the bay: San Rafael, Novato, Larkspur, Corte Madera and the towns along the freeway. Zone 3 covers the coastal side and the southern tip — Bolinas, Stinson Beach, Point Reyes Station, Inverness, Tiburon and Sausalito.

The ridge between them

The dividing feature is the ridge that runs down the spine of the county. East of it the bay side is warmer and more sheltered; west of it the Pacific side takes the full marine influence, with fog and wind and a narrower temperature range.

That makes the county unusually easy to get wrong from a map, because the two sides are physically close. Places a few miles apart across the ridge are in different zones.

What it changes

Both are mild by California standards and neither is cooling-dominated, so the difference is smaller here than in a valley-to-mountain county. But zone 2 carries more summer warmth and zone 3 more persistent marine cooling, and the compliance figures follow accordingly.

Example ZIP codes and their zones

Derived from the Energy Commission's ZIP-to-climate-zone table, with county membership taken from the U.S. Census Bureau's 2020 ZCTA-to-county relationship file:

• Climate zone 2 — 94901, 94903, 94904, 94945, 94947 and 10 more
• Climate zone 3 — 94920, 94924, 94937, 94965, 94970 and 9 more

ZIP codes that cross the county line

A ZIP code is a postal boundary, not a county boundary, and several here fall on both sides of one. Where that happens we do not treat the county as settling the question:

• 94952 — about 51% within Marin County, the remainder in Sonoma 49%

For an address in one of these, the climate zone still comes from the ZIP code, which is assigned by the Energy Commission regardless of the county line. What the split affects is which jurisdiction issues the permit — worth confirming before a submittal.

Finding the zone for your own project

The zone is set by the project's location and confirmed from the ZIP code against the Energy Commission's published table — not from the county name and not from the nearest large town. Because Marin County contains more than one zone, that check decides which set of numbers a report is written against.

Give us the project address and we determine the zone as part of preparing the report. It is the first thing established, because every insulation, glazing and equipment figure downstream depends on it.

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 is statewide — what changes locally is the climate zone the site falls in and how the jurisdiction wants the compliance documents presented.

Climate zones in Marin County

Marin County contains California climate zones 2 and 3. 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.