States / Pennsylvania
67 counties · median score 25
Crawl space moisture in Pennsylvania
Most of Pennsylvania drains well: only 12 of 67 counties score high or elevated, and the median is 25. Mercer County is the exception at 65; crawl-space moisture problems here usually come from grading, gutters and plumbing rather than the soil itself.
- 1Wettest county Mercer County
- 2High or elevated 12 of 67
- 3Median score 25
- 4Driest county Lancaster County
Pennsylvania's soil, taken as a whole
Across the 29,005,952 acres mapped in these 67 counties, 16% of soil with a drainage class is somewhat poorly, poorly or very poorly drained, and 48% of acres report a seasonal water table within about two metres. That is a middling figure: wet ground is common in valleys and lowlands but far from universal. 67 of the 67 counties have mapped soils subject to occasional or frequent flooding.
| Drainage class | Share of mapped acres |
|---|---|
| Excessively drained | 0.7% |
| Somewhat excessively drained | 4.5% |
| Well drained | 54% |
| Moderately well drained | 24.5% |
| Somewhat poorly drained | 9.7% |
| Poorly drained | 5.9% |
| Very poorly drained | 0.7% |
Radon. By EPA zone, 49 Pennsylvania counties here are zone 1 (highest potential), 17 zone 2 and 1 zone 3. With most of the state in zone 1, any crawl-space sealing project here should start with a radon test and be designed to take a radon fan.
Every Pennsylvania county
Sorted wettest first. High and elevated counties link to their own page with the full soil breakdown.
What drives the Pennsylvania numbers
The wettest county, Mercer County, is 42% somewhat poorly drained by dominant condition, with a seasonal water table averaging 0.8 ft below grade across the 88% of acres that report one, and sits in EPA radon zone 2. The driest, Lancaster County, is 87% well drained. 3 Pennsylvania counties reach the high tier, where poorly drained soils, group D clays and a shallow water table occur together.
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.