Kansas / Wilson County
Score 49 · elevated · #9 of 105 in KS
Crawl space moisture in Wilson County, KS
82% of Wilson 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 — 61% of acres — it averages 1.4 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 1.4 ft
- 2Wet soils 37%
- 3Moisture score 49
- 4EPA radon zone 2
Reading the Wilson County soil survey
The score of 49 combines four parts, each from the USDA survey: wet drainage classes contribute 40.3 points of 100 on their own scale, group D soils 79.7, a shallow water table 47.3, and flooding 10.7; the weights are on the methodology page. The dominant hydrologic group is D (70% of acres): very slow infiltration, high runoff (clays, high water table).
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 Wilson County. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Wilson County against the rest of Kansas
Wilson County ranks 9 of 105 Kansas counties, 36 points above the state median of 13. That puts it in the wettest quarter of the state. Statewide, 8% of mapped soil is in the wet drainage classes; here it is 37%, half again the state figure or more. After moderately well drained, the next most common class is somewhat poorly drained at 31%.
Flooding. 1.7% of acres with a flooding class are rated frequent; 14.6% of acres with a flooding class are rated occasional; 0.7% 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. Ponding — water standing at the surface with nowhere to go — affects 3.2% of acres.
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 Wilson County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area KS205; drainage covers 99% of 368,058 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.