Michigan / Isabella County
Score 41 · elevated · #34 of 79 in MI
Crawl space moisture in Isabella County, MI
55% of Isabella 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 — 55% of acres — it averages 0.7 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 0.7 ft
- 2Wet soils 55%
- 3Moisture score 41
- 4EPA radon zone 3
Reading the Isabella County soil survey
The score of 41 combines four parts, each from the USDA survey: wet drainage classes contribute 44.3 points of 100 on their own scale, group D soils 44.9, a shallow water table 49.4, and flooding 1.7; the weights are on the methodology page. The dominant hydrologic group is C/D (33% of acres): D when undrained, C when drained.
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 55% of Isabella County's acres. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Isabella County against the rest of Michigan
Isabella County ranks 34 of 79 Michigan counties, 4 points above the state median of 37. Wetter counties exist in Michigan, but the soil here still sits well above the national middle. Statewide, 45% of mapped soil is in the wet drainage classes; here it is 55%. After somewhat poorly drained, the next most common class is well drained at 32%.
Flooding. 1.3% of acres with a flooding class are rated frequent; 0.8% of acres with a flooding class are rated occasional. 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 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. EPA radon zone 3. The zone is a county-level prediction; EPA says elevated levels occur in every zone and every home should be tested.
Near Isabella County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area MI073; drainage covers 98% of 369,849 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.