Frost Line Depth in Tacoma, Washington
- Tacoma’s adopted code
- Checked Oct 2026
- Sources
Verified
12in
30 cm · 1 ft
Set in the building code Tacoma has adopted.
Source and how we checked
Document: cms.tacoma.gov
Climate: 27 nights a year at or below 32 °F (NOAA 1991–2020, Tacoma #1, 2.3 mi).
Checked Oct 2026. Report a correction
How deep is the frost line in Tacoma?
Tacoma's building authority sets the frost line depth at 12 in (30 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 Tacoma?
Washington leaves the frost line depth to each city or county, and Tacoma fills it in when it adopts the residential code. The value above comes from Tacoma’s own document on cms.tacoma.gov. Pierce County, which covers the unincorporated land around Tacoma, uses 18 in, so check which one issues your permit. See how Washington sets frost line depth.
How deep do footings, decks and water lines need to be in Tacoma?
House or garage footing in Tacoma: dig at least 12 in (30 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).
| Project | Depth | Rule |
|---|---|---|
| House or garage footing | 12 in | Below the frost line and at least 12 in deep (IRC R403.1.4) |
| Deck footing (attached) | 12 in | Below the frost line and at least 12 in deep (IRC R507.3) |
| Water service line | 18 in | 6 in below the frost line and at least 12 in deep (IRC P2603.5) |
| Fence post bottom | 12 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 Tacoma?
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Tacoma never averages a low below freezing. 27 nights a year reach 32 °F or colder; Dec is coldest, with an average low of 36.9 °F.
NOAA 1991–2020 climate normals, Tacoma #1 station, 2.3 mi away, elevation 25 ft.
Monthly temperatures as a table
| °F | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Low | 37.4 | 37.4 | 40.1 | 43.7 | 49.1 | 53.4 | 57.2 | 57 | 53 | 46.6 | 40.5 | 36.9 |
| High | 48.1 | 50.3 | 54.7 | 59.8 | 66.5 | 71.1 | 76.8 | 76.9 | 70.7 | 60.7 | 52.4 | 47.3 |
Tacoma has fewer freezing nights than 41 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 Tacoma use?
4 official codes near Tacoma are verified; each links to its document.
| Place | Verified frost line | Distance |
|---|---|---|
| Pierce County | 18 in | 20 mi away |
| Bremerton | 12 in | 23 mi away |
| Redmond | 12 in | 34 mi away |
| King County | 12 in | 34 mi away |
How likely is the soil in Tacoma to heave?
USDA rates the sampled soil around Tacoma as 100% none for frost action (main soils: Alderwood, Everett, Kitsap).
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 Tacoma?
Tacoma at a glance
- Frost line depth
- 12 in
- County
- Pierce County
- Population (2023 est.)
- 222,906
- Mean annual temperature
- 53.7 °F
- ZIP codes (19)
- 98402 · 98403 · 98404 · 98405 · 98406 · 98407 · 98408 · 98409 · 98416 · 98418 · 98421 · 98422 · 98424 · 98444 · 98445 · 98465 · 98466 · 98467 · 98499