33 counties mapped. On average, 1% of Washington county soil area is high shrink-swell clay (USDA SSURGO).
Higher percentages mean more of a county's mapped soil is shrink-swell clay that expands and contracts with moisture. This is county-scale exposure, not a diagnosis of any single home — but it tells you whether soil movement belongs on your radar.
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Before you call a foundation company →| County | Tier | High-risk % | Moderate % |
|---|---|---|---|
| Lewis | Moderate | 8% | 27% |
| Kittitas | Low | 5% | 29% |
| Pierce | Low | 4% | 6% |
| Cowlitz | Low | 4% | 34% |
| Skamania | Low | 4% | 12% |
| Spokane | Low | 4% | 22% |
| Thurston | Low | 3% | 21% |
| Clark | Low | 3% | 39% |
| Whitman | Low | 3% | 39% |
| Klickitat | Low | 2% | 34% |
| Yakima | Low | 2% | 20% |
| Whatcom | Low | 1% | 10% |
| Clallam | Low | 1% | 29% |
| Jefferson | Low | 1% | 40% |
| Snohomish | Low | 1% | 11% |
| Lincoln | Low | 1% | 8% |
| Stevens | Low | 1% | 8% |
| Douglas | Low | 1% | 16% |
| Skagit | Low | 1% | 10% |
| King | Low | 0% | 6% |
| Mason | Low | 0% | 13% |
| Kitsap | Low | 0% | 6% |
| Columbia | Low | 0% | 18% |
| Adams | Low | 0% | 0% |
| Franklin | Low | 0% | 2% |
| Grant | Low | 0% | 3% |
| Island | Low | 0% | 20% |
| San Juan | Low | 0% | 28% |
| Benton | Low | 0% | 0% |
| Garfield | Low | 0% | 7% |
| Okanogan | Low | 0% | 3% |
| Pend Oreille | Low | 0% | 13% |
| Walla Walla | Low | 0% | 6% |
Risk metrics are computed from USDA SSURGO soil survey data (linear extensibility of soil components, area-weighted by county). Soil varies lot to lot — this is county-scale context, not a substitute for a site-specific geotechnical or structural assessment.