States / Idaho
33 counties · median score 12
Crawl space moisture in Idaho
Most of Idaho drains well: only 0 of 33 counties score high or elevated, and the median is 12. Benewah County is the exception at 25; crawl-space moisture problems here usually come from grading, gutters and plumbing rather than the soil itself.
- 1Wettest county Benewah County
- 2High or elevated 0 of 33
- 3Median score 12
- 4Driest county Bonneville County
Idaho's soil, taken as a whole
Across the 23,686,737 acres mapped in these 33 counties, 5% of soil with a drainage class is somewhat poorly, poorly or very poorly drained, and 10% 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. 32 of the 33 counties have mapped soils subject to occasional or frequent flooding.
| Drainage class | Share of mapped acres |
|---|---|
| Excessively drained | 1.3% |
| Somewhat excessively drained | 4% |
| Well drained | 85.6% |
| Moderately well drained | 4.1% |
| Somewhat poorly drained | 2.6% |
| Poorly drained | 1.8% |
| Very poorly drained | 0.6% |
Radon. By EPA zone, 15 Idaho counties here are zone 1 (highest potential), 17 zone 2 and 1 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 Idaho county
Sorted wettest first. High and elevated counties link to their own page with the full soil breakdown.
What drives the Idaho numbers
The wettest county, Benewah County, is 57% well drained by dominant condition, with a seasonal water table averaging 1.4 ft below grade across the 50% of acres that report one, and sits in EPA radon zone 1. The driest, Bonneville County, is 98% well drained. No Idaho 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.