States / Washington
36 counties · median score 12
Crawl space moisture in Washington
Most of Washington drains well: only 0 of 36 counties score high or elevated, and the median is 12. Island County is the exception at 39; crawl-space moisture problems here usually come from grading, gutters and plumbing rather than the soil itself.
- 1Wettest county Island County
- 2High or elevated 0 of 36
- 3Median score 12
- 4Driest county Adams County
Washington's soil, taken as a whole
Across the 28,069,986 acres mapped in these 36 counties, 6% of soil with a drainage class is somewhat poorly, poorly or very poorly drained, and 18% of acres report a seasonal water table within about two metres. That is a dry figure; wet soils here are confined to river bottoms and wetlands. 34 of the 36 counties have mapped soils subject to occasional or frequent flooding.
| Drainage class | Share of mapped acres |
|---|---|
| Excessively drained | 2.5% |
| Somewhat excessively drained | 6.7% |
| Well drained | 74.2% |
| Moderately well drained | 11.2% |
| Somewhat poorly drained | 2.3% |
| Poorly drained | 2.5% |
| Very poorly drained | 0.7% |
Radon. By EPA zone, 6 Washington counties here are zone 1 (highest potential), 14 zone 2 and 16 zone 3. EPA says to test regardless of zone; a sealed crawl space is the cheapest moment to add radon venting if a test calls for it.
Every Washington county
Sorted wettest first. High and elevated counties link to their own page with the full soil breakdown.
What drives the Washington numbers
The wettest county, Island County, is 37% somewhat excessively drained by dominant condition, with a seasonal water table averaging 0.9 ft below grade across the 85% of acres that report one, and sits in EPA radon zone 3. The driest, Adams County, is 98% well drained. No Washington county reaches the high tier.
The score is a guide to the soil, not to a house: a well-graded lot with working gutters in a high county can have a dry crawl space, and a bad downspout can flood one in a low county. The R408 calculator sizes venting or encapsulation for any footprint.
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted; EPA Map of Radon Zones, county table (June 2024 JSON). Checked 2026-10-23.