Spokane County, WA Frost Line Depth: 24 in

Verified

24in

61 cm · 2 ft

Set in the building code Spokane County has adopted.

Source and how we checked

Document: spokanecounty.gov

Climate: 123 nights a year at or below 32 °F (NOAA 1991–2020, Spokane Felts Fld, 5.8 mi).

Checked Oct 2026. Report a correction

Footings Deck Water line Fence post

123nights a year at or below 32 °F
61%of nearby soil rated “low” for frost action (USDA)

How deep is the frost line in Spokane County?

Spokane County's building authority sets the frost line depth at 24 in (61 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 Spokane County?

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

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

House or garage footing Deck footing Water service line Fence post

House or garage footing in Spokane County: dig at least 24 in (61 cm). Below the frost line and at least 12 in deep (IRC R403.1.4).

Minimum depths in Spokane County with a 24 in frost line
Project	Depth	Rule
House or garage footing	24 in	Below the frost line and at least 12 in deep (IRC R403.1.4)
Deck footing (attached)	24 in	Below the frost line and at least 12 in deep (IRC R507.3)
Water service line	30 in	6 in below the frost line and at least 12 in deep (IRC P2603.5)
Fence post bottom	24 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 Spokane County?

Average lows are at or below freezing from Nov to Mar. 123 nights a year reach 32 °F or colder; Dec is coldest, with an average low of 25.7 °F.

NOAA 1991–2020 climate normals, Spokane Felts Fld station, 5.8 mi away, elevation 1,953 ft.

Monthly temperatures as a table

°F	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Low	25.8	26.7	31.7	36.6	44.1	50.4	56	54.5	46.8	38	30.7	25.7
High	37.8	42.5	51.3	59.6	69.7	75.8	87.1	86.2	76	60.3	45.1	36.9

Spokane County has more freezing nights than 41 of the 47 other Washington places we track. The Washington median is 54. Coldest: Chelan County; mildest: Lakewood.

How likely is the soil in Spokane County to heave?

Low 61%Moderate 35%

USDA rates the sampled soil around Spokane County as 61% low, 35% moderate, 4% high for frost action (main soils: Marble, Rockly, Opportunity).

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 Spokane County?

Call 811 at least a few working days before you dig, so buried lines are marked.
Confirm the frost line depth with the Spokane County building department.
Ask whether your project needs a permit (decks, larger sheds and footings usually do).
Dig below 24 in unless the building department tells you otherwise.
Book the footing inspection before you pour concrete.

Spokane County at a glance

Frost line depth: 24 in
Population (2023 est.): 551,455
Mean annual temperature: 49.8 °F
ZIP codes (48): 99001 · 99003 · 99004 · 99005 · 99006 · 99008 · 99009 · 99011 · 99012 · 99013 · 99014 · 99016 · 99018 · 99019 · 99020 · 99021 · 99022 · 99023 · 99025 · 99026 · 99027 · 99029 · 99030 · 99031 · 99032 · 99033 · 99036 · 99037 · 99039 · 99110 · 99156 · 99170 · 99201 · 99202 · 99203 · 99204 · 99205 · 99206 · 99207 · 99208 · 99212 · 99216 · 99217 · 99218 · 99223 · 99224 · 99251 · 99258