Missouri / Holt County
Score 35 · moderate · #67 of 113 in MO
Crawl space moisture in Holt County, MO
Holt County scores moderate: no single wet-soil signal dominates its mapped acres. Where a seasonal water table is reported — 47% of acres — it averages 1.8 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 1.8 ft
- 2Wet soils 39%
- 3Moisture score 35
- 4EPA radon zone 1
Reading the Holt County soil survey
The score of 35 combines four parts, each from the USDA survey: wet drainage classes contribute 36.2 points of 100 on their own scale, group D soils 39.6, a shallow water table 34.3, and flooding 18.8; the weights are on the methodology page. The dominant hydrologic group is C (36% of acres): slow infiltration (clay layers).
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 on the soils that report a water table — about 47% of Holt County's acres. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Holt County against the rest of Missouri
Holt County ranks 67 of 113 Missouri counties, 4 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 39%. After well drained, the next most common class is somewhat poorly drained at 19%.
Flooding. 6.9% of acres with a flooding class are rated frequent; 7.6% of acres with a flooding class are rated occasional; 36.6% 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. Holt County is in EPA radon zone 1, the highest predicted potential. A sealed crawl space and a radon system share most of their parts — the liner, the sealed seams, a fan — so if you are encapsulating, test for radon first and design both together. EPA itself says the zone map is not a reason to skip testing in zones 2 and 3.
Near Holt County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area MO087; drainage covers 100% of 300,685 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.