States / New Hampshire
8 counties · median score 23
Crawl space moisture in New Hampshire
Most of New Hampshire drains well: only 0 of 8 counties score high or elevated, and the median is 23. Coos County is the exception at 34; crawl-space moisture problems here usually come from grading, gutters and plumbing rather than the soil itself.
- 1Wettest county Coos County
- 2High or elevated 0 of 8
- 3Median score 23
- 4Driest county Sullivan County
New Hampshire's soil, taken as a whole
Across the 4,299,861 acres mapped in these 8 counties, 14% of soil with a drainage class is somewhat poorly, poorly or very poorly drained, and 40% 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. 8 of the 8 counties have mapped soils subject to occasional or frequent flooding.
| Drainage class | Share of mapped acres |
|---|---|
| Excessively drained | 6.9% |
| Somewhat excessively drained | 7.6% |
| Well drained | 56.4% |
| Moderately well drained | 15.2% |
| Poorly drained | 9% |
| Very poorly drained | 4.7% |
| Subaqueous | 0.1% |
Radon. By EPA zone, 1 New Hampshire counties here are zone 1 (highest potential), 7 zone 2 and 0 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 New Hampshire county
Sorted wettest first. High and elevated counties link to their own page with the full soil breakdown.
What drives the New Hampshire numbers
The wettest county, Coos County, is 50% well drained by dominant condition, with a seasonal water table averaging 2 ft below grade across the 75% of acres that report one, and sits in EPA radon zone 2. The driest, Sullivan County, is 64% well drained. No New Hampshire 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.