Frost Line Depth in Thurston County, Washington
- 4 verified codes nearby
- Checked Oct 2026
No official local value
No official frost line depth is published for Thurston County.
Nearby official codes require 12–18 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: 77 nights a year at or below 32 °F (NOAA 1991–2020, Olympia Airport, 4.3 mi).
Checked Oct 2026. Report a correction
Does Thurston County have an official frost line depth?
No adopted frost line depth found for Thurston County in its official documents (checked Oct 2026). The nearest official values, from codes we verified, are 12 to 18 in. Use the deepest of them until the building department confirms Thurston County’s own number.
What frost line depth does Thurston County use for footings under Table R301.2(1)? Is it 18 in, like Pierce County?
How deep do footings, decks and water lines need to be in Thurston County?
Drawn with the deepest nearby official value (18 in). Confirm Thurston County’s own depth before you dig.
House or garage footing in Thurston County: dig at least 18 in (46 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).
| Project | Depth | Rule |
|---|---|---|
| House or garage footing | 18 in | Below the frost line and at least 12 in deep (IRC R403.1.4) |
| Deck footing (attached) | 18 in | Below the frost line and at least 12 in deep (IRC R507.3) |
| Water service line | 24 in | 6 in below the frost line and at least 12 in deep (IRC P2603.5) |
| Fence post bottom | 18 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 Thurston County?
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Thurston County never averages a low below freezing. 77 nights a year reach 32 °F or colder; Feb is coldest, with an average low of 32.3 °F.
NOAA 1991–2020 climate normals, Olympia Airport station, 4.3 mi away, elevation 188 ft.
Monthly temperatures as a table
| °F | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Low | 33.2 | 32.3 | 34.5 | 37.5 | 43 | 47.4 | 50.7 | 50.5 | 46.2 | 40.5 | 35.8 | 32.8 |
| High | 46 | 49.1 | 53.7 | 58.9 | 66.1 | 70.8 | 77.6 | 78 | 72.1 | 60.2 | 50.6 | 44.9 |
Thurston County has more freezing nights than 31 of the 47 other Washington places we track. The Washington median is 54. Coldest: Chelan County; mildest: Lakewood.
What frost line depth do towns near Thurston County use?
4 official codes near Thurston County are verified; each links to its document.
| Place | Verified frost line | Distance |
|---|---|---|
| Pierce County | 18 in | 33 mi away |
| Mason County | 12 in | 33 mi away |
| Bremerton | 12 in | 42 mi away |
| Cowlitz County | 12 in | 52 mi away |
How likely is the soil in Thurston County to heave?
USDA rates the sampled soil around Thurston County as 89% none, 11% low for frost action (main soils: Alderwood, Everett, Puget).
USDA NRCS soil survey, 9 sample points within 2 mi. Higher frost action means more risk of heave; see frost heave.
Thurston County at a glance
- Frost line depth
- No official local value
- Population (2023 est.)
- 299,003
- Mean annual temperature
- 50.5 °F
- ZIP codes (16)
- 98501 · 98502 · 98503 · 98505 · 98506 · 98512 · 98513 · 98516 · 98530 · 98531 · 98556 · 98568 · 98576 · 98579 · 98589 · 98597