North Carolina / Tyrrell County
Score 72 · high · #2 of 100 in NC
Crawl space moisture in Tyrrell County, NC
98% of Tyrrell County's mapped soil is somewhat poorly to very poorly drained, which means ground that stays wet near the surface for significant periods. Where a seasonal water table is reported — 65% of acres — it averages 0.2 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 0.2 ft
- 2Wet soils 98%
- 3Moisture score 72
- 4EPA radon zone 3
Reading the Tyrrell County soil survey
The score of 72 combines four parts, each from the USDA survey: wet drainage classes contribute 97.9 points of 100 on their own scale, group D soils 60.5, a shallow water table 62.7, and flooding 17.8; the weights are on the methodology page. The dominant hydrologic group is B/D (36% of acres): D when undrained, B when drained.
A water table under two feet is the single most important number here. A crawl-space floor is usually 18 to 36 inches below the joists and often below outside grade, so in a wet season groundwater can stand at or above the crawl-space floor across much of Tyrrell County. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Tyrrell County against the rest of North Carolina
Tyrrell County ranks 2 of 100 North Carolina counties, 55 points above the state median of 17. Only 1 other county in the state score higher. Statewide, 30% of mapped soil is in the wet drainage classes; here it is 98%, half again the state figure or more. After very poorly drained, the next most common class is poorly drained at 12%.
Flooding. 6.6% of acres with a flooding class are rated frequent; 56.2% of acres with a flooding class are rated rare. That is a large flood-prone share; a crawl space in the floodplain needs flood vents under most local floodplain ordinances, which is a separate rule from R408 and can rule out a fully sealed design.
What it means for a crawl space here
In a high county, the model-code default of a vented crawl space over bare earth works against the soil: outside air brings humidity in all summer, and the ground underneath keeps supplying moisture from below. The R408 alternative — an unvented crawl space with a sealed vapor retarder lapped 6 inches and turned 6 inches up the stem wall, plus conditioned or exhaust air at 1 cfm per 50 sq ft or a dehumidifier — is built for exactly this. If the water table is shallow, drainage comes first.
Radon. EPA radon zone 3. The zone is a county-level prediction; EPA says elevated levels occur in every zone and every home should be tested.
Near Tyrrell County by score
All 100 North Carolina counties
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area NC177; drainage covers 65% of 383,143 mapped acres); EPA Map of Radon Zones, county table (June 2024 JSON); IRC R408.3 Unvented crawl space, as adopted in S.C. Code Regs. 8-1221 (LII). Checked 2026-10-23.