Frost Line Depth in Brentwood, California
- Brentwood’s adopted code
- Checked Oct 2026
- Sources
Verified
30in
76 cm · 2 ft 6 in
Set in the building code Brentwood has adopted.
Source and how we checked
Document: ecode360.com
Climate: 7 nights a year at or below 32 °F (NOAA 1991–2020, Antioch Pumping Plt #3, 3.8 mi).
Checked Oct 2026. Report a correction
How deep is the frost line in Brentwood?
Brentwood's building authority sets the frost line depth at 30 in (76 cm). Footings, piers and other permanent supports must reach at least this depth (IRC R403.1.4.1).
Who sets the frost line depth in Brentwood?
California leaves the frost line depth to each city or county, and Brentwood fills it in when it adopts the residential code. The value above comes from Brentwood’s own document on ecode360.com. See how California sets frost line depth.
How deep do footings, decks and water lines need to be in Brentwood?
House or garage footing in Brentwood: 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 Brentwood?
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Brentwood never averages a low below freezing. 7 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 40.3 °F.
NOAA 1991–2020 climate normals, Antioch Pumping Plt #3 station, 3.8 mi away, elevation 60 ft.
Monthly temperatures as a table
| °F | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Low | 40.3 | 43.9 | 46.6 | 49.5 | 54.3 | 59 | 60.6 | 60.3 | 58.7 | 54.2 | 46.2 | 40.4 |
| High | 55.7 | 60.8 | 66.5 | 72.1 | 79 | 86.3 | 91.4 | 90.2 | 86.7 | 77.5 | 64.6 | 55.8 |
Brentwood has more freezing nights than 122 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 Brentwood use?
5 official codes near Brentwood are verified; each links to its document.
| Place | Verified frost line | Distance |
|---|---|---|
| Dublin | 12 in | 18 mi away |
| Palo Alto | 5 in | 44 mi away |
| Campbell | 12 in | 47 mi away |
| Turlock | 12 in | 56 mi away |
| Santa Cruz | 12 in | 69 mi away |
How likely is the soil in Brentwood to heave?
USDA rates the sampled soil around Brentwood as 100% none for frost action (main soils: Capay, Rincon, Kimball).
USDA NRCS soil survey, 9 sample points within 2 mi. Higher frost action means more risk of heave; see frost heave.
How do you confirm the frost line before you dig in Brentwood?
Brentwood at a glance
- Frost line depth
- 30 in
- County
- Contra Costa County
- Population (2023 est.)
- 65,126
- Mean annual temperature
- 62.5 °F
- ZIP codes (1)
- 94513