Clark County, WA Frost Line Depth: 12 in

Verified

12in

30 cm · 1 ft

Set in the building code Clark County has adopted.

Source and how we checked

Document: clark.wa.gov

Climate: 70 nights a year at or below 32 °F (NOAA 1991–2020, Battle Ground, 2.1 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

1 of 1nearby verified codes use the same depth
70nights a year at or below 32 °F
56%of nearby soil rated “moderate” for frost action (USDA)

How deep is the frost line in Clark County?

Clark 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 Clark County?

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

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

House or garage footing Deck footing Water service line Fence post

House or garage footing in Clark 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 Clark 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 Clark County?

Average lows are at or below freezing from Dec to Feb. 70 nights a year reach 32 °F or colder; Feb is coldest, with an average low of 31.7 °F.

NOAA 1991–2020 climate normals, Battle Ground station, 2.1 mi away, elevation 284 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	31.9	31.7	34.6	37.9	43.3	47.3	50.6	50.2	45.6	39.9	35.4	31.9
High	46.1	50.4	54.7	59.7	66.5	71.1	78.6	79.6	74.5	62.5	51.6	45.1

Clark County has more freezing nights than 28 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 Clark County use?

One official code near Clark County is verified.

Official frost line depths near Clark County
Place	Verified frost line	Distance
Cowlitz County	12 in	31 mi away

How likely is the soil in Clark County to heave?

None 33%Moderate 56%

USDA rates the sampled soil around Clark County as 33% none, 56% moderate, 11% high for frost action (main soils: Hesson, Olympic, Hockinson variant).

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 Clark County?

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

Clark County at a glance

Frost line depth: 12 in
Population (2023 est.): 521,150
Mean annual temperature: 50.9 °F
ZIP codes (20): 98601 · 98604 · 98606 · 98607 · 98629 · 98642 · 98660 · 98661 · 98662 · 98663 · 98664 · 98665 · 98671 · 98674 · 98675 · 98682 · 98683 · 98684 · 98685 · 98686