Frostline.info

Frost line depth in Pierce County, Washington

Frost reaches about 13 inches in typical soil across Pierce County, from 11″ in the mildest ZIP code to 25″ in the coldest. Codes in this climate commonly set footing depth at 12 to 18 inches.

Moderate frost
Estimated frost depth
13″
typical silt/loam soil
Typical code footing depth
12–18″
rule of thumb for this climate
Design freezing index
166
°F-days, 100-year winter
ZIP codes covered
51
#29 of 39 counties in WA (1 = deepest)
13″ 0″12″24″36″ ground frozen
Est. frost (typical soil) Typical code footing depth Clay–sand range

Frost depth by soil type

Soil typeEst. frost depth
Sand / gravel (drains well)16″
Silt / loam (typical yard soil)13″
Clay (holds water)11″

County average. Methodology.

Verify before you dig. These are climate-based estimates. The legally required frost depth is the figure your building department publishes in its IRC Table R301.2 (climatic and geographic design criteria). Call the Pierce County building or permitting office in Washington and call 811 before digging.

Frost depth by ZIP code in Pierce County

ZIPCityEst. frostCode range
98303Anderson Island11″12–18″
98304Ashford25″24–36″
98321Buckley13″12–18″
98323Carbonado13″12–18″
98327Dupont12″12–18″
98328Eatonville15″12–18″
98329Gig Harbor11″12–18″
98330Elbe20″18–30″
98332Gig Harbor11″12–18″
98333Fox Island11″12–18″
98335Gig Harbor11″12–18″
98338Graham14″12–18″
98349Lakebay11″12–18″
98351Longbranch11″12–18″
98354Milton12″12–18″
98360Orting14″12–18″
98371Puyallup12″12–18″
98372Puyallup13″12–18″
98373Puyallup14″12–18″
98374Puyallup14″12–18″
98375Puyallup14″12–18″
98387Spanaway13″12–18″
98388Steilacoom12″12–18″
98390Sumner13″12–18″
98391Bonney Lake13″12–18″
98394Vaughn11″12–18″
98402Tacoma11″12–18″
98403Tacoma11″12–18″
98404Tacoma12″12–18″
98405Tacoma11″12–18″
98406Tacoma11″12–18″
98407Tacoma11″12–18″
98408Tacoma11″12–18″
98409Tacoma11″12–18″
98413Tacoma11″12–18″
98418Tacoma11″12–18″
98421Tacoma11″12–18″
98422Tacoma11″12–18″
98424Fife12″12–18″
98433Tacoma12″12–18″
98439Lakewood12″12–18″
98443Tacoma12″12–18″
98444Tacoma12″12–18″
98445Tacoma13″12–18″
98446Tacoma13″12–18″
98465Tacoma11″12–18″
98466Tacoma11″12–18″
98467University Place12″12–18″
98498Lakewood12″12–18″
98499Lakewood12″12–18″
98580Roy14″12–18″

What this means for your project in Pierce County

Deck footings & piers

Footings must bear below the frost line and at least 12″ below undisturbed ground. For planning in this area, budget for holes around 18″ deep until your permit office confirms the exact figure.

Fence posts

Set posts at least one-third of their above-ground height. Where frost heave is a problem, carry concrete footings below the frost line (about 13″ here in typical soil) and bell or taper the bottom.

Water & irrigation lines

Bury supply lines below the frost depth. Your water utility or plumbing code sets the minimum cover; add a margin below the estimate above for unusually cold winters.

Slabs & frost-protected foundations

Frost-protected shallow foundations (IRC R403.3) use the 100-year air freezing index — 166 °F-days here — to size perimeter insulation, letting footings sit shallower than the frost line.

Weather stations used

NOAA weather stationDistance100-yr AFI
Puyallup 2 W Exp Sta, WA5 mi160
Tacoma City Hall, WA5 mi117
Mc Millin Reservoir, WA8 mi204
Kent, WA17 mi148

Nearby counties

Common questions

What is the frost line depth in Pierce County?

About 13 inches in typical soil, based on NOAA's 100-year air freezing index. Across the county's ZIP codes the estimate runs from 11 to 25 inches.

How deep should footings be in Pierce County, Washington?

Codes in climates like this commonly require 12 to 18 inches. The Pierce County building department publishes the required frost depth in its adopted code (IRC Table R301.2).

Does frost depth vary within Pierce County?

Yes. Estimates differ by 14 inches between the coldest and mildest ZIP codes, mostly from latitude and elevation. Check your own ZIP below.