Frost Line Depth in San Mateo, California
- 5 verified codes nearby
- Checked Oct 2026
No official local value
Frost rarely reaches the ground in San Mateo.
Nearby official codes require 5–30 in (5 verified codes).
Footings still go at least 12 in (30 cm) below undisturbed ground (IRC R403.1.4).
Source and how we checked
We searched this place’s own code and website and found no published frost line depth.
Climate: 0 nights a year at or below 32 °F (NOAA 1991–2020, San Francisco International Airport, 5.1 mi).
Checked Oct 2026. Report a correction
Does San Mateo have an official frost line depth?
No adopted frost line depth found for San Mateo 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 San Mateo’s own number.
What frost line depth does San Mateo use for footings under Table R301.2(1)? Is it 5 in, like Palo Alto?
How deep do footings, decks and water lines need to be in San Mateo?
Drawn with the deepest nearby official value (30 in). Confirm San Mateo’s own depth before you dig.
House or garage footing in San Mateo: 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 San Mateo?
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
San Mateo never averages a low below freezing. 0 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 44.5 °F.
NOAA 1991–2020 climate normals, San Francisco International Airport station, 5.1 mi away, elevation 8 ft.
Monthly temperatures as a table
| °F | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Low | 44.5 | 46.1 | 47.6 | 49.1 | 51.6 | 53.6 | 55.3 | 56.4 | 55.9 | 53.4 | 48.5 | 44.6 |
| High | 58 | 60.8 | 63.4 | 65.6 | 68.3 | 71.5 | 72.6 | 73.4 | 74.8 | 72.3 | 64.3 | 58.2 |
San Mateo has fewer freezing nights than 166 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 San Mateo use?
5 official codes near San Mateo are verified; each links to its document.
| Place | Verified frost line | Distance |
|---|---|---|
| Palo Alto | 5 in | 15 mi away |
| Dublin | 12 in | 25 mi away |
| Campbell | 12 in | 28 mi away |
| Brentwood | 30 in | 41 mi away |
| Santa Cruz | 12 in | 43 mi away |
How likely is the soil in San Mateo to heave?
USDA rates the sampled soil around San Mateo as 100% none for frost action (main soils: Urban land, Orthents, Novato).
USDA NRCS soil survey, 9 sample points within 2 mi. Higher frost action means more risk of heave; see frost heave.
San Mateo at a glance
- Frost line depth
- No official local value
- County
- San Mateo County
- Population (2023 est.)
- 101,327
- Mean annual temperature
- 58.7 °F
- ZIP codes (5)
- 94010 · 94401 · 94402 · 94403 · 94404