Iowa / Lee County
Score 56 · elevated · #18 of 99 in IA
Crawl space moisture in Lee County, IA
56% of Lee 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 — 77% of acres — it averages 1.2 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 1.2 ft
- 2Wet soils 56%
- 3Moisture score 56
- 4EPA radon zone 1
Reading the Lee County soil survey
The score of 56 combines four parts, each from the USDA survey: wet drainage classes contribute 54.3 points of 100 on their own scale, group D soils 67.7, a shallow water table 62.9, and flooding 11.7; the weights are on the methodology page. The dominant hydrologic group is D (52% 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 Lee County. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Lee County against the rest of Iowa
Lee County ranks 18 of 99 Iowa counties, 9 points above the state median of 47. That puts it in the wettest quarter of the state. Statewide, 44% of mapped soil is in the wet drainage classes; here it is 56%. After somewhat poorly drained, the next most common class is poorly drained at 26%.
Flooding. 5.7% of acres with a flooding class are rated frequent; 8.7% of acres with a flooding class are rated occasional; 3.9% 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 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. Lee 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 Lee County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area IA111; drainage covers 95% of 345,300 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.