Michigan / Allegan County
Score 36 · moderate · #41 of 79 in MI
Crawl space moisture in Allegan County, MI
50% of Allegan 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 — 52% of acres — it averages 0.9 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 0.9 ft
- 2Wet soils 50%
- 3Moisture score 36
- 4EPA radon zone 3
Reading the Allegan County soil survey
The score of 36 combines four parts, each from the USDA survey: wet drainage classes contribute 41.5 points of 100 on their own scale, group D soils 30, a shallow water table 44.8, and flooding 4.5; the weights are on the methodology page. The dominant hydrologic group is A (38% of acres): high infiltration, low runoff (sands, gravels).
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 52% of Allegan County's acres. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Allegan County against the rest of Michigan
Allegan County ranks 41 of 79 Michigan counties, 1 points below the state median of 37. That places it in the middle range, nationally and for the state. Statewide, 45% of mapped soil is in the wet drainage classes; here it is 50%. After somewhat poorly drained, the next most common class is excessively drained at 28%.
Flooding. 4.1% of acres with a flooding class are rated frequent; 1.9% 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 3. The zone is a county-level prediction; EPA says elevated levels occur in every zone and every home should be tested.
Near Allegan County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area MI005; drainage covers 97% of 539,680 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.