Ohio / Clark County
Score 38 · moderate · #55 of 88 in OH
Crawl space moisture in Clark County, OH
Clark County scores moderate: no single wet-soil signal dominates its mapped acres. Where a seasonal water table is reported — 62% of acres — it averages 1.3 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 1.3 ft
- 2Wet soils 38%
- 3Moisture score 38
- 4EPA radon zone 1
Reading the Clark County soil survey
The score of 38 combines four parts, each from the USDA survey: wet drainage classes contribute 37.9 points of 100 on their own scale, group D soils 39.4, a shallow water table 50.3, and flooding 3.2; the weights are on the methodology page. The dominant hydrologic group is C (33% of acres): slow infiltration (clay layers).
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 Clark County. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Clark County against the rest of Ohio
Clark County ranks 55 of 88 Ohio counties, 8 points below the state median of 46. That places it in the middle range, nationally and for the state. Statewide, 44% of mapped soil is in the wet drainage classes; here it is 38%, 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 very poorly drained at 24%.
Flooding. 0% of acres with a flooding class are rated frequent; 5% of acres with a flooding class are rated occasional; 0.9% of acres with a flooding class are rated rare. 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 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. Clark County is in EPA radon zone 1, the highest predicted potential. A sealed crawl space and a radon system share most of their parts — the liner, the sealed seams, a fan — so if you are encapsulating, test for radon first and design both together. EPA itself says the zone map is not a reason to skip testing in zones 2 and 3.
Near Clark County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area OH023; drainage covers 96% of 256,883 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.