Frost Line Depth in Polk County, OR: 12 in (Oregon rule)

State-set value

12in

30 cm · 1 ft

12 in (Oregon rule)

Set by the state: Oregon Residential Specialty Code Table R301.2(1), Polk County.

Source and how we checked

Polk County does not publish its own value; the state rule applies.

Document: codes.iccsafe.org

Climate: 70 nights a year at or below 32 °F (NOAA 1991–2020, Falls City 2 Ssw, 5.2 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

2 of 2nearby verified codes use the same depth
70nights a year at or below 32 °F
89%of nearby soil rated “low” for frost action (USDA)

How deep is the frost line in Polk County?

Oregon sets the frost footing depth for Polk County 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 Polk County?

Oregon writes this depth into its statewide residential code, so Polk County’s building department enforces the state’s number rather than setting its own. See how Oregon sets frost line depth.

How deep do footings, decks and water lines need to be in Polk County?

House or garage footing Deck footing Water service line Fence post

House or garage footing in Polk County: dig at least 12 in (30 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).

Minimum depths in Polk County with a 12 in frost line
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 Polk County?

Polk County never averages a low below freezing. 70 nights a year reach 32 °F or colder; Jan is coldest, with an average low of 32.9 °F.

NOAA 1991–2020 climate normals, Falls City 2 Ssw station, 5.2 mi away, elevation 690 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	32.9	33.2	35	37.5	42.6	46.6	50.2	50.4	47.5	42.5	36.6	33.2
High	45	49.2	53.4	57.7	65.1	70.3	79.9	80.7	74.9	62.4	50.9	44.9

Polk County has more freezing nights than 15 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 Polk County use?

2 official codes near Polk County are verified; each links to its document.

Official frost line depths near Polk County
Place	Verified frost line	Distance
Corvallis	12 in	24 mi away
Marion County	12 in	40 mi away

How likely is the soil in Polk County to heave?

Low 89%

USDA rates the sampled soil around Polk County as 11% none, 89% low for frost action (main soils: Honeygrove, Jory, Rickreall).

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 Polk County?

Call 811 at least a few working days before you dig, so buried lines are marked.
Confirm the frost line depth with the Polk County building department.
Ask whether your project needs a permit (decks, larger sheds and footings usually do).
Dig below 12 in unless the building department tells you otherwise.
Book the footing inspection before you pour concrete.

Polk County at a glance

Frost line depth: 12 in (Oregon rule)
Population (2023 est.): 89,805
Mean annual temperature: 50.9 °F
ZIP codes (11): 97101 · 97304 · 97338 · 97344 · 97347 · 97351 · 97361 · 97370 · 97371 · 97378 · 97396