Frost Line Depth in Washington County, Oregon
- Washington County’s adopted code
- Checked Oct 2026
- Sources
Verified
12in
30 cm · 1 ft
12 in Below 500 ft, 18 in Above
Set in the building code Washington County has adopted.
Source and how we checked
Document: washingtoncountyor.gov
Climate: 61 nights a year at or below 32 °F (NOAA 1991–2020, Forest Grove, 2 mi).
Checked Oct 2026. Report a correction
How deep is the frost line in Washington County?
Washington County's building authority sets the frost line depth at 12 in (30 cm) below 500 ft elevation and 18 in (46 cm) at or above it. Footings, piers and other permanent supports must reach at least this depth (IRC R403.1.4.1).
Who sets the frost line depth in Washington County?
Oregon sets frost line depth in its state code, and Washington County’s own document lists the value above (washingtoncountyor.gov). See how Oregon sets frost line depth.
How deep do footings, decks and water lines need to be in Washington County?
House or garage footing in Washington County: 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 Washington County?
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Washington County never averages a low below freezing. 61 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 32.6 °F.
NOAA 1991–2020 climate normals, Forest Grove station, 2 mi away, elevation 180 ft.
Monthly temperatures as a table
| °F | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Low | 32.6 | 33.1 | 35.9 | 39.2 | 45.3 | 49.7 | 53.8 | 53.5 | 48.7 | 41.6 | 36.3 | 32.8 |
| High | 45 | 49.4 | 54.6 | 60.1 | 68.1 | 73.1 | 81.4 | 82.2 | 76.1 | 63.3 | 50.9 | 44 |
Washington County has more freezing nights than 12 of the 22 other Oregon places we track. The Oregon median is 54. Coldest: Deschutes County; mildest: Lincoln County.
What frost line depth do towns near Washington County use?
2 official codes near Washington County are verified; each links to its document.
| Place | Verified frost line | Distance |
|---|---|---|
| Marion County | 12 in | 52 mi away |
| Corvallis | 12 in | 69 mi away |
How likely is the soil in Washington County to heave?
USDA rates the sampled soil around Washington County as 23% none, 77% low for frost action (main soils: Woodburn, Amity, Verboort).
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 Washington County?
Washington County at a glance
- Frost line depth
- 12 in Below 500 ft, 18 in Above
- Population (2023 est.)
- 598,865
- Mean annual temperature
- 52.1 °F
- ZIP codes (32)
- 97003 · 97005 · 97006 · 97007 · 97008 · 97035 · 97056 · 97062 · 97064 · 97070 · 97078 · 97106 · 97109 · 97113 · 97116 · 97117 · 97119 · 97123 · 97124 · 97125 · 97132 · 97133 · 97140 · 97144 · 97210 · 97219 · 97221 · 97223 · 97224 · 97225 · 97229 · 97231