Frost Line Depth in Napa, California
- 4 verified codes nearby
- Checked Oct 2026
No official local value
No official frost line depth is published for Napa.
Nearby official codes require 5–30 in (4 verified codes).
Source and how we checked
We searched this place’s own code and website and found no published frost line depth.
Climate: 12 nights a year at or below 32 °F (NOAA 1991–2020, Napa State Hospital, 2.4 mi).
Checked Oct 2026. Report a correction
Does Napa have an official frost line depth?
No adopted frost line depth found for Napa in its official documents (checked Oct 2026). The nearest official values, from codes we verified, are 5 to 30 in. Use the deepest of them until the building department confirms Napa’s own number.
What frost line depth does Napa use for footings under Table R301.2(1)? Is it 30 in, like Brentwood?
How deep do footings, decks and water lines need to be in Napa?
Drawn with the deepest nearby official value (30 in). Confirm Napa’s own depth before you dig.
House or garage footing in Napa: dig at least 30 in (76 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).
| 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 Napa?
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Napa never averages a low below freezing. 12 nights a year reach 32 °F or colder; Dec is coldest, with an average low of 39.7 °F.
NOAA 1991–2020 climate normals, Napa State Hospital station, 2.4 mi away, elevation 35 ft.
Monthly temperatures as a table
| °F | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Low | 40.1 | 41.9 | 43.6 | 45.6 | 49.9 | 53.7 | 55.5 | 55.5 | 53.4 | 49.3 | 43.6 | 39.7 |
| High | 58.6 | 63.2 | 67.5 | 72.1 | 76.6 | 82.3 | 83.3 | 83.7 | 84.4 | 78.1 | 66.2 | 58.5 |
Napa has more freezing nights than 146 of the 208 other California places we track. The California median is 3. Coldest: El Dorado County; mildest: San Diego.
What frost line depth do towns near Napa use?
4 official codes near Napa are verified; each links to its document.
How likely is the soil in Napa to heave?
USDA rates the sampled soil around Napa as 100% none for frost action (main soils: Haire, Bressa, Cole).
USDA NRCS soil survey, 9 sample points within 2 mi. Higher frost action means more risk of heave; see frost heave.
Napa at a glance
- Frost line depth
- No official local value
- County
- Napa County
- Population (2023 est.)
- 77,492
- Mean annual temperature
- 60.2 °F
- ZIP codes (3)
- 94503 · 94558 · 94559