Cowlitz County, WA Frost Line Depth: 12 in

Verified

12in

30 cm · 1 ft

Set in the building code Cowlitz County has adopted.

Source and how we checked

Document: co.cowlitz.wa.us

Climate: 41 nights a year at or below 32 °F (NOAA 1991–2020, Longview, 11.8 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

0 of 1nearby verified codes use the same depth
41nights a year at or below 32 °F
79%of nearby soil rated “none” for frost action (USDA)

How deep is the frost line in Cowlitz County?

"{confirmed quote}". Footings, piers and other permanent supports must reach at least this depth (IRC R403.1.4.1).

Who sets the frost line depth in Cowlitz County?

Washington leaves the frost line depth to each city or county, and Cowlitz County fills it in when it adopts the residential code. The value above comes from Cowlitz County’s own document on co.cowlitz.wa.us. See how Washington sets frost line depth.

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

House or garage footing Deck footing Water service line Fence post

House or garage footing in Cowlitz 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 Cowlitz 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 Cowlitz County?

Cowlitz County never averages a low below freezing. 41 nights a year reach 32 °F or colder; Feb is coldest, with an average low of 34.7 °F.

NOAA 1991–2020 climate normals, Longview station, 11.8 mi away, elevation 12 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	35.1	34.7	37.5	40.4	45.3	49.5	53.4	53.3	49.6	44.1	38.6	34.8
High	47.7	52	56.9	62.1	68.8	72.9	79.3	80.4	75.7	64	53	46.6

Cowlitz County has fewer 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 Cowlitz County use?

One official code near Cowlitz County is verified.

Official frost line depths near Cowlitz County
Place	Verified frost line	Distance
Pierce County	18 in	64 mi away

How likely is the soil in Cowlitz County to heave?

None 79%High 21%

USDA rates the sampled soil around Cowlitz County as 79% none, 21% high for frost action (main soils: Hazeldell, Olympic, Jonas).

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 Cowlitz County?

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

Cowlitz County at a glance

Frost line depth: 12 in
Population (2023 est.): 112,864
Mean annual temperature: 53.2 °F
ZIP codes (12): 98581 · 98601 · 98603 · 98609 · 98611 · 98616 · 98625 · 98626 · 98632 · 98645 · 98649 · 98674