Wisconsin / Clark County
Score 56 · elevated · #3 of 72 in WI
Crawl space moisture in Clark County, WI
76% of Clark County's soil falls in hydrologic group D or a dual D group: clays and high water tables that shed water slowly. Where a seasonal water table is reported — 97% of acres — it averages 0.8 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 0.8 ft
- 2Wet soils 49%
- 3Moisture score 56
- 4EPA radon zone 2
Reading the Clark County soil survey
The score of 56 combines four parts, each from the USDA survey: wet drainage classes contribute 54.2 points of 100 on their own scale, group D soils 50.4, a shallow water table 85.6, and flooding 2.9; the weights are on the methodology page. The dominant hydrologic group is C/D (56% of acres): D when undrained, C 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 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 Wisconsin
Clark County ranks 3 of 72 Wisconsin counties, 23 points above the state median of 33. Only 2 other counties in the state score higher. Statewide, 32% of mapped soil is in the wet drainage classes; here it is 49%, half again the state figure or more. After moderately well drained, the next most common class is somewhat poorly drained at 34%.
Flooding. 2% of acres with a flooding class are rated frequent; 1.5% 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 2. The zone is a county-level prediction; EPA says elevated levels occur in every zone and every home should be tested.
Near Clark County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area WI019; drainage covers 99% of 780,224 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.