Michigan / Mason County
Score 29 · moderate · #52 of 79 in MI
Crawl space moisture in Mason County, MI
Mason County scores moderate: no single wet-soil signal dominates its mapped acres. Where a seasonal water table is reported — 43% of acres — it averages 1 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 1 ft
- 2Wet soils 36%
- 3Moisture score 29
- 4EPA radon zone 3
Reading the Mason County soil survey
The score of 29 combines four parts, each from the USDA survey: wet drainage classes contribute 31.8 points of 100 on their own scale, group D soils 26, a shallow water table 36.4, and flooding 3.7; the weights are on the methodology page. The dominant hydrologic group is A (54% 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 43% of Mason County's acres. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Mason County against the rest of Michigan
Mason County ranks 52 of 79 Michigan counties, 8 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 36%, below the state figure — the score here comes from flooding and ponding rather than drainage class alone. After well drained, the next most common class is excessively drained at 26%.
Flooding. 3.7% of acres with a flooding class are rated frequent. Flood-prone soils are a minority here, concentrated along streams; the score mostly reflects what happens between floods. Ponding — water standing at the surface with nowhere to go — affects 4.6% of acres.
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 Mason County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area MI105; drainage covers 96% of 326,970 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.