Missouri / Audrain County
Score 80 · high · #1 of 113 in MO
Crawl space moisture in Audrain County, MO
98% of Audrain 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 — 99% of acres — it averages 0.9 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 0.9 ft
- 2Wet soils 98%
- 3Moisture score 80
- 4EPA radon zone 2
Reading the Audrain County soil survey
The score of 80 combines four parts, each from the USDA survey: wet drainage classes contribute 90.1 points of 100 on their own scale, group D soils 88.6, a shallow water table 84.4, and flooding 7.3; the weights are on the methodology page. The dominant hydrologic group is D (72% 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 Audrain County. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Audrain County against the rest of Missouri
Audrain County ranks 1 of 113 Missouri counties, 41 points above the state median of 39. Only no other county in the state scores higher. Statewide, 32% of mapped soil is in the wet drainage classes; here it is 98%, half again the state figure or more. After poorly drained, the next most common class is somewhat poorly drained at 25%.
Flooding. 5.1% of acres with a flooding class are rated frequent; 3.1% of acres with a flooding class are rated occasional; 1.8% 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 high county, the model-code default of a vented crawl space over bare earth works against the soil: outside air brings humidity in all summer, and the ground underneath keeps supplying moisture from below. The R408 alternative — an unvented crawl space with a sealed vapor retarder lapped 6 inches and turned 6 inches up the stem wall, plus conditioned or exhaust air at 1 cfm per 50 sq ft or a dehumidifier — is built for exactly this. If the water table is shallow, drainage comes first.
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 Audrain County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area MO007; drainage covers 100% of 446,285 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.