Mississippi / Harrison County
Score 37 · moderate · #36 of 82 in MS
Crawl space moisture in Harrison County, MS
Harrison County scores moderate: no single wet-soil signal dominates its mapped acres. Where a seasonal water table is reported — 82% of acres — it averages 2.1 ft below grade.
- 1Water table 2.1 ft
- 2Wet soils 30%
- 3Moisture score 37
- 4EPA radon zone 3
Reading the Harrison County soil survey
The score of 37 combines four parts, each from the USDA survey: wet drainage classes contribute 36.4 points of 100 on their own scale, group D soils 27.5, a shallow water table 56.1, and flooding 19.1; the weights are on the methodology page. The dominant hydrologic group is B (34% of acres): moderate infiltration.
At 2.1 ft the seasonal water table is usually below a crawl-space floor, but the 82% of acres that report one are by definition the wettest parts of the county; on those lots, a wet spring can bring water close to the footings.
Harrison County against the rest of Mississippi
Harrison County ranks 36 of 82 Mississippi counties, 2 points above the state median of 35. That places it in the middle range, nationally and for the state. Statewide, 35% of mapped soil is in the wet drainage classes; here it is 30%, below the state figure — the score here comes from a shallow water table rather than drainage class alone. After well drained, the next most common class is moderately well drained at 22%.
Flooding. 12.3% of acres with a flooding class are rated frequent; 7.3% of acres with a flooding class are rated occasional; 3.4% 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 moderate county the soil record is mixed rather than uniformly wet, so conditions vary from lot to lot. Where the lot drains, the model-code default — a vented crawl space with 1 sq ft of net vent per 150 sq ft of floor, or 1 per 1500 with a Class I vapor retarder on the ground — is a reasonable starting point; where the sections above point to a shallow water table or flood-prone soil on your lot, plan as for an elevated county. Either way, check the site first: grading that falls away from the foundation, gutters and downspouts that discharge well clear of it, and a ground cover over bare earth. A wet crawl space in a moderate county points to one of those 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 Harrison County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area MS047; drainage covers 98% of 382,343 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.