Frost Line Depth in Sonoma County, CA: California Codes Range 0

No official local value

No official frost line depth is published for Sonoma County.

No verified code nearby; verified California codes range 0–30 in.

Source and how we checked

We searched this place’s own code and website and found no published frost line depth.

Climate: 31 nights a year at or below 32 °F (NOAA 1991–2020, Santa Rosa Sonoma Co Airport, 6.4 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

0–30 inrange of verified California codes
31nights a year at or below 32 °F
100%of nearby soil rated “none” for frost action (USDA)

Does Sonoma County have an official frost line depth?

No adopted frost line depth found for Sonoma County in its official documents (checked Oct 2026). No verified code lies near Sonoma County; the California codes we verified range from 0 to 30 in. Ask the building department for Sonoma County’s own number before you dig.

What frost line depth does Sonoma County use for footings under Table R301.2(1)?

Call 811 at least a few working days before you dig, so buried lines are marked.
Confirm the frost line depth with the Sonoma County building department.
Ask whether your project needs a permit (decks, larger sheds and footings usually do).
Dig below 30 in (the deepest verified state value) unless the building department tells you otherwise.
Book the footing inspection before you pour concrete.

How deep do footings, decks and water lines need to be in Sonoma County?

Drawn with the deepest California official value (30 in). Confirm Sonoma County’s own depth before you dig.

House or garage footing Deck footing Water service line Fence post

House or garage footing in Sonoma County: dig at least 30 in (76 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).

Using the nearby official value of 30 in until Sonoma County confirms its own
Project	Depth	Rule
House or garage footing	30 in	Below the frost line and at least 12 in deep (IRC R403.1.4)
Deck footing (attached)	30 in	Below the frost line and at least 12 in deep (IRC R507.3)
Water service line	36 in	6 in below the frost line and at least 12 in deep (IRC P2603.5)
Fence post bottom	30 in	No code rule; common practice is below the frost line

Work out posts, concrete and footing sizes with the fence post depth calculator or the deck footing calculator.

How cold does it get in Sonoma County?

Sonoma County never averages a low below freezing. 31 nights a year reach 32 °F or colder; Dec is coldest, with an average low of 36.9 °F.

NOAA 1991–2020 climate normals, Santa Rosa Sonoma Co Airport station, 6.4 mi away, elevation 114 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	37.5	39.4	41.4	43.2	46.6	50.1	51.7	51.9	49.6	45.5	40.1	36.9
High	57.9	61.7	65.1	69	74.7	81.8	83.5	84.1	83.4	77.1	65.4	57.5

Sonoma County has more freezing nights than 194 of the 208 other California places we track. The California median is 3. Coldest: El Dorado County; mildest: San Diego.

How likely is the soil in Sonoma County to heave?

None 100%

USDA rates the sampled soil around Sonoma County as 100% none for frost action (main soils: Hugo, Laughlin, Cibo).

USDA NRCS soil survey, 9 sample points within 2 mi. Higher frost action means more risk of heave; see frost heave.

Sonoma County at a glance

Frost line depth: No official local value
Population (2023 est.): 481,812
Mean annual temperature: 58.1 °F
ZIP codes (40): 94515 · 94574 · 94922 · 94923 · 94928 · 94931 · 94951 · 94952 · 94954 · 94972 · 95401 · 95403 · 95404 · 95405 · 95407 · 95409 · 95412 · 95419 · 95421 · 95425 · 95430 · 95431 · 95436 · 95439 · 95441 · 95442 · 95444 · 95446 · 95448 · 95450 · 95452 · 95462 · 95465 · 95471 · 95472 · 95476 · 95480 · 95486 · 95492 · 95497