BasementSoil

Washington: basement moisture and foundation risk by county

39 counties, ranked by our combined index. Highest combined risk is Pierce County (51), lowest is Mason County (21). The worst soil for foundation cracks specifically is in Clallam County.

Where in Washington the ground is worse

Every county in the state, coloured by the soil values below. Click a county to open its report; switch what the colour means with the buttons. The pattern is geology, not administration — risk stops at the edge of a physiographic region, not at a county line.

Adams County, WA — combined 35/100, moisture 33, movement 41, water table 30Asotin County, WA — combined 35/100, moisture 34, movement 40, water table 30Benton County, WA — combined 30/100, moisture 34, movement 23, water table 30Chelan County, WA — combined 28/100, moisture 29, movement 26, water table 30Clallam County, WA — combined 49/100, moisture 36, movement 92, water table 16Clark County, WA — combined 38/100, moisture 47, movement 20, water table 46Columbia County, WA — combined 29/100, moisture 34, movement 20, water table 30Cowlitz County, WA — combined 41/100, moisture 43, movement 20, water table 66Douglas County, WA — combined 33/100, moisture 32, movement 36, water table 30Ferry County, WA — combined 33/100, moisture 32, movement 36, water table 30Franklin County, WA — combined 26/100, moisture 35, movement 22, water table 16Garfield County, WA — combined 32/100, moisture 32, movement 43, water table 16Grant County, WA — combined 28/100, moisture 34, movement 17, water table 30Grays Harbor County, WA — combined 49/100, moisture 35, movement 83, water table 30Island County, WA — combined 48/100, moisture 47, movement 35, water table 66Jefferson County, WA — combined 44/100, moisture 44, movement 28, water table 66King County, WA — combined 41/100, moisture 46, movement 31, water table 46Kitsap County, WA — combined 37/100, moisture 43, movement 23, water table 46Kittitas County, WA — combined 27/100, moisture 28, movement 32, water table 16Klickitat County, WA — combined 41/100, moisture 44, movement 32, water table 46Lewis County, WA — combined 39/100, moisture 48, movement 21, water table 46Lincoln County, WA — combined 35/100, moisture 33, movement 41, water table 30Mason County, WA — combined 21/100, moisture 28, movement 16, water table 16Okanogan County, WA — combined 26/100, moisture 30, movement 17, water table 30Pacific County, WA — combined 45/100, moisture 34, movement 82, water table 16Pend Oreille County, WA — combined 30/100, moisture 35, movement 22, water table 30Pierce County, WA — combined 51/100, moisture 47, movement 33, water table 82San Juan County, WA — combined 24/100, moisture 27, movement 25, water table 16Skagit County, WA — combined 47/100, moisture 46, movement 24, water table 82Skamania County, WA — combined 46/100, moisture 47, movement 29, water table 66Snohomish County, WA — combined 35/100, moisture 43, movement 17, water table 46Spokane County, WA — combined 28/100, moisture 35, movement 18, water table 30Stevens County, WA — combined 31/100, moisture 32, movement 29, water table 30Thurston County, WA — combined 44/100, moisture 44, movement 27, water table 66Wahkiakum County, WA — combined 47/100, moisture 38, movement 82, water table 16Walla Walla County, WA — combined 34/100, moisture 30, movement 42, water table 30Whatcom County, WA — combined 46/100, moisture 47, movement 19, water table 82Whitman County, WA — combined 31/100, moisture 31, movement 43, water table 16Yakima County, WA — combined 26/100, moisture 27, movement 21, water table 30
  • Low (0–27)
  • Moderate (28–49)
  • Elevated (50–74)
  • High (75–100)

County boundaries: US Census TIGER (public domain), simplified for display. Colours are our index from USDA SSURGO fields where loaded, otherwise from our regional model — each county page states which. How the index is calculated.

CountyIndexMoistureCracksWater tableRegion
Pierce County51473382Puget Sound and Willamette Lowland
Clallam County49369216Pacific Coast Ranges
Grays Harbor County49358330Pacific Coast Ranges
Island County48473566Puget Sound and Willamette Lowland
Skagit County47462482Puget Sound and Willamette Lowland
Wahkiakum County47388216Pacific Coast Ranges
Skamania County46472966Puget Sound and Willamette Lowland
Whatcom County46471982Puget Sound and Willamette Lowland
Pacific County45348216Pacific Coast Ranges
Jefferson County44442866Puget Sound and Willamette Lowland
Thurston County44442766Puget Sound and Willamette Lowland
Cowlitz County41432066Puget Sound and Willamette Lowland
King County41463146Puget Sound and Willamette Lowland
Klickitat County41443246Puget Sound and Willamette Lowland
Lewis County39482146Puget Sound and Willamette Lowland
Clark County38472046Puget Sound and Willamette Lowland
Kitsap County37432346Puget Sound and Willamette Lowland
Adams County35334130Columbia Plateau and Palouse
Asotin County35344030Columbia Plateau and Palouse
Lincoln County35334130Columbia Plateau and Palouse
Snohomish County35431746Puget Sound and Willamette Lowland
Walla Walla County34304230Columbia Plateau and Palouse
Douglas County33323630Columbia Plateau and Palouse
Ferry County33323630Columbia Plateau and Palouse
Garfield County32324316Columbia Plateau and Palouse
Stevens County31322930Columbia Plateau and Palouse
Whitman County31314316Columbia Plateau and Palouse
Benton County30342330Columbia Plateau and Palouse
Pend Oreille County30352230Columbia Plateau and Palouse
Columbia County29342030Columbia Plateau and Palouse
Chelan County28292630Sierra Nevada and Cascades
Grant County28341730Columbia Plateau and Palouse
Spokane County28351830Columbia Plateau and Palouse
Kittitas County27283216Sierra Nevada and Cascades
Franklin County26352216Columbia Plateau and Palouse
Okanogan County26301730Columbia Plateau and Palouse
Yakima County26272130Sierra Nevada and Cascades
San Juan County24272516Sierra Nevada and Cascades
Mason County21281616Sierra Nevada and Cascades

Values from USDA NRCS SSURGO where available, otherwise our regional model — each county page states which. Methodology.

The physiographic regions inside Washington

State lines are political; soil follows geology. These are the distinct ground types inside Washington and why each behaves the way it does.

Columbia Plateau and Palouse

Deep permeable loess on rolling hills, with basalt below. Water table deep, shrink-swell low. Loess is erodible and can settle under load when saturated, so a broken downspout does more damage here than the climate does.

16 counties: Adams County, Asotin County, Benton County, Columbia County, Douglas County, Ferry County, Franklin County, Garfield County, Grant County, Lincoln County, Okanogan County, Pend Oreille County, Spokane County, Stevens County, Walla Walla County, Whitman County

Puget Sound and Willamette Lowland

The one part of the West where basements are genuinely common — and the reason they leak is glacial: dense Vashon till under a permeable cap perches water just above it through the wet season. Volume change is low. Drainage, and hillside seepage, decide everything.

14 counties: Clark County, Cowlitz County, Island County, Jefferson County, King County, Kitsap County, Klickitat County, Lewis County, Pierce County, Skagit County, Skamania County, Snohomish County, Thurston County, Whatcom County

Sierra Nevada and Cascades

Coarse material over rock. Volume change is minimal and drainage is good; the seasonal problem is snowmelt arriving at foundations faster than it can be led away, not a water table.

5 counties: Chelan County, Kittitas County, Mason County, San Juan County, Yakima County

Pacific Coast Ranges

Some of the most expansive soils in North America sit here, on some of the least stable slopes. Winter rain saturates clay-rich colluvium and it moves — which is why hillside foundation work on the California and Oregon coast is engineered rather than standardised.

4 counties: Clallam County, Grays Harbor County, Pacific County, Wahkiakum County

Page data updated