Marion County, OR Frost Line Depth: 12 in

Verified

12in

30 cm · 1 ft

Set in the building code Marion County has adopted.

Source and how we checked

Document: co.marion.or.us

Climate: 85 nights a year at or below 32 °F (NOAA 1991–2020, Silver Creek Falls, 4 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

1 of 1nearby verified codes use the same depth
85nights a year at or below 32 °F
100%of nearby soil rated “low” for frost action (USDA)

How deep is the frost line in Marion County?

Marion County'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 Marion County?

Oregon sets frost line depth in its state code, and Marion County’s own document lists the value above (co.marion.or.us). See how Oregon sets frost line depth.

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

House or garage footing Deck footing Water service line Fence post

House or garage footing in Marion 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 Marion 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 Marion County?

Marion County never averages a low below freezing. 85 nights a year reach 32 °F or colder; Dec is coldest, with an average low of 32.5 °F.

NOAA 1991–2020 climate normals, Silver Creek Falls station, 4 mi away, elevation 1,350 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	32.7	32.9	34	36.9	42	45.8	50.2	49.9	45.8	40.5	35.9	32.5
High	42.7	45.4	49.8	54.7	62.8	67.6	76.3	76.1	70.1	57.8	47.1	41.6

Marion County has more freezing nights than 18 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 Marion County use?

One official code near Marion County is verified.

Official frost line depths near Marion County
Place	Verified frost line	Distance
Corvallis	12 in	41 mi away

How likely is the soil in Marion County to heave?

Low 100%

USDA rates the sampled soil around Marion County as 100% low for frost action (main soils: Kinney, McCully).

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 Marion County?

Call 811 at least a few working days before you dig, so buried lines are marked.
Confirm the frost line depth with the Marion 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.

Marion County at a glance

Frost line depth: 12 in
Population (2023 est.): 346,741
Mean annual temperature: 48.8 °F
ZIP codes (28): 97002 · 97020 · 97026 · 97032 · 97071 · 97137 · 97301 · 97302 · 97303 · 97305 · 97306 · 97310 · 97317 · 97325 · 97342 · 97346 · 97350 · 97352 · 97358 · 97360 · 97362 · 97373 · 97375 · 97381 · 97383 · 97384 · 97385 · 97392