Frost Line Depth in Whatcom County, Washington
- Whatcom County’s adopted code
- Checked Oct 2026
- Sources
Verified
18in
46 cm · 1 ft 6 in
Set in the building code Whatcom County has adopted.
Source and how we checked
Document: whatcomcounty.us
Climate: 102 nights a year at or below 32 °F (NOAA 1991–2020, Upper Baker Dam, 14.7 mi).
Checked Oct 2026. Report a correction
How deep is the frost line in Whatcom County?
Whatcom County's building authority sets the frost line depth at 18 in (46 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 Whatcom County?
Washington leaves the frost line depth to each city or county, and Whatcom County fills it in when it adopts the residential code. The value above comes from Whatcom County’s own document on whatcomcounty.us. See how Washington sets frost line depth.
How deep do footings, decks and water lines need to be in Whatcom County?
House or garage footing in Whatcom 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 Whatcom County?
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Average lows are at or below freezing from Dec to Mar. 102 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 28.9 °F.
NOAA 1991–2020 climate normals, Upper Baker Dam station, 14.7 mi away, elevation 690 ft.
Monthly temperatures as a table
| °F | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Low | 28.9 | 29.1 | 31.8 | 35.8 | 41.9 | 46.9 | 50.9 | 51.3 | 47.3 | 40.6 | 34.2 | 29.8 |
| High | 37.9 | 42.4 | 47.9 | 55.8 | 63.7 | 67.5 | 74.4 | 75.3 | 68.6 | 55.7 | 43.8 | 37.3 |
Whatcom County has more freezing nights than 34 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 Whatcom County use?
4 official codes near Whatcom County are verified; each links to its document.
| Place | Verified frost line | Distance |
|---|---|---|
| Marysville | 18 in | 55 mi away |
| Snohomish County | 18 in | 55 mi away |
| Lake Stevens | 12 in | 59 mi away |
| Everett | 18 in | 63 mi away |
How likely is the soil in Whatcom County to heave?
USDA rates the sampled soil around Whatcom County as 43% low, 52% moderate, 5% high for frost action (main soils: Typic Vitricryands, Andic Dystrocryepts, Lithic Dystrocryepts).
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 Whatcom County?
Whatcom County at a glance
- Frost line depth
- 18 in
- Population (2023 est.)
- 231,919
- Mean annual temperature
- 47.5 °F
- ZIP codes (18)
- 98220 · 98225 · 98226 · 98229 · 98230 · 98237 · 98240 · 98244 · 98247 · 98248 · 98262 · 98264 · 98266 · 98276 · 98281 · 98283 · 98284 · 98295