South Carolina / Horry County
Score 59 · elevated · #8 of 46 in SC
Crawl space moisture in Horry County, SC
61% of Horry 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 — 94% of acres — it averages 1 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 1 ft
- 2Wet soils 61%
- 3Moisture score 59
- 4EPA radon zone 3
Reading the Horry County soil survey
The score of 59 combines four parts, each from the USDA survey: wet drainage classes contribute 66.6 points of 100 on their own scale, group D soils 45.8, a shallow water table 79.3, and flooding 15; the weights are on the methodology page. The dominant hydrologic group is A/D (32% of acres): D when undrained, A 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 Horry County. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Horry County against the rest of South Carolina
Horry County ranks 8 of 46 South Carolina counties, 34 points above the state median of 25. That puts it in the wettest quarter of the state. Statewide, 34% of mapped soil is in the wet drainage classes; here it is 61%, half again the state figure or more. After poorly drained, the next most common class is moderately well drained at 25%.
Flooding. 14.8% of acres with a flooding class are rated frequent. 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 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 Horry County by score
All 46 South Carolina counties
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area SC051; drainage covers 99% of 732,900 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.