Missouri / Franklin County
Score 34 · moderate · #70 of 113 in MO
Crawl space moisture in Franklin County, MO
Franklin County scores moderate: no single wet-soil signal dominates its mapped acres. Where a seasonal water table is reported — 65% of acres — it averages 2.2 ft below grade.
- 1Water table 2.2 ft
- 2Wet soils 10%
- 3Moisture score 34
- 4EPA radon zone 2
Reading the Franklin County soil survey
The score of 34 combines four parts, each from the USDA survey: wet drainage classes contribute 25.1 points of 100 on their own scale, group D soils 44.4, a shallow water table 43.5, and flooding 15.1; the weights are on the methodology page. The dominant hydrologic group is C (52% of acres): slow infiltration (clay layers).
At 2.2 ft the seasonal water table is usually below a crawl-space floor, but the 65% 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.
Franklin County against the rest of Missouri
Franklin County ranks 70 of 113 Missouri counties, 5 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 10%, below the state figure — the score here comes from a shallow water table rather than drainage class alone. After moderately well drained, the next most common class is well drained at 40%.
Flooding. 12.2% of acres with a flooding class are rated frequent; 4.2% of acres with a flooding class are rated occasional; 2.1% 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.
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 Franklin County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area MO071; drainage covers 100% of 595,226 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.