Delaware / Sussex County
Score 41 · elevated · #2 of 3 in DE
Crawl space moisture in Sussex County, DE
Sussex County scores elevated because several moderate signals stack up rather than one dominant one. Where a seasonal water table is reported — 67% of acres — it averages 1.5 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 1.5 ft
- 2Wet soils 44%
- 3Moisture score 41
- 4EPA radon zone 3
Reading the Sussex County soil survey
The score of 41 combines four parts, each from the USDA survey: wet drainage classes contribute 49.1 points of 100 on their own scale, group D soils 29.8, a shallow water table 51.7, and flooding 10.1; the weights are on the methodology page. The dominant hydrologic group is A (43% of acres): high infiltration, low runoff (sands, gravels).
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 Sussex County. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Sussex County against the rest of Delaware
Sussex County ranks 2 of 3 Delaware counties, level with the state median of 41. Only 1 other county in the state score higher. Statewide, 40% of mapped soil is in the wet drainage classes; here it is 44%. After well drained, the next most common class is moderately well drained at 20%.
Flooding. 3.1% of acres with a flooding class are rated frequent; 1.2% of acres with a flooding class are rated occasional. Flood-prone soils are a minority here, concentrated along streams; the score mostly reflects what happens between floods.
What it means for a crawl space here
In an elevated county the soil supplies more moisture than average, but a vented crawl space can work if the ground is covered: the code lets vent area drop from 1 sq ft per 150 to 1 per 1500 with a Class I vapor retarder on the ground, which is an admission of how much moisture comes from below. Grading, gutters and a ground cover usually decide whether a crawl space here stays dry before any decision about sealing it.
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 Sussex County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area DE005; drainage covers 80% of 626,600 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.