Missouri / Polk County
Score 31 · moderate · #77 of 113 in MO
Crawl space moisture in Polk County, MO
Polk County scores moderate: no single wet-soil signal dominates its mapped acres. Where a seasonal water table is reported — 58% of acres — it averages 2.2 ft below grade.
- 1Water table 2.2 ft
- 2Wet soils 9%
- 3Moisture score 31
- 4EPA radon zone 2
Reading the Polk County soil survey
The score of 31 combines four parts, each from the USDA survey: wet drainage classes contribute 23.6 points of 100 on their own scale, group D soils 45.6, a shallow water table 38.8, and flooding 9.1; the weights are on the methodology page. The dominant hydrologic group is C (47% of acres): slow infiltration (clay layers).
At 2.2 ft the seasonal water table is usually below a crawl-space floor, but the 58% 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.
Polk County against the rest of Missouri
Polk County ranks 77 of 113 Missouri counties, 8 points below the state median of 39. That places it in the middle range, nationally and for the state. Statewide, 32% of mapped soil is in the wet drainage classes; here it is 9%, below the state figure — the score here comes from flooding and ponding rather than drainage class alone. After moderately well drained, the next most common class is well drained at 40%.
Flooding. 8.4% of acres with a flooding class are rated frequent; 1.2% of acres with a flooding class are rated occasional; 0.1% 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. 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 Polk County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area MO167; drainage covers 100% of 411,296 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.