Michigan / Mackinac County
Score 53 · elevated · #20 of 79 in MI
Crawl space moisture in Mackinac County, MI
58% of Mackinac 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 — 68% of acres — it averages 0.2 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 0.2 ft
- 2Wet soils 58%
- 3Moisture score 53
- 4EPA radon zone 3
Reading the Mackinac County soil survey
The score of 53 combines four parts, each from the USDA survey: wet drainage classes contribute 54.7 points of 100 on their own scale, group D soils 58.5, a shallow water table 66.2, and flooding 0.4; the weights are on the methodology page. The dominant hydrologic group is A/D (35% of acres): D when undrained, A 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 across much of Mackinac County. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Mackinac County against the rest of Michigan
Mackinac County ranks 20 of 79 Michigan counties, 16 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 58%. After very poorly drained, the next most common class is well drained at 24%.
Flooding. No mapped soil in Mackinac County carries a flooding frequency above "none", so the score here is about water held in and under the soil rather than water arriving over it. Ponding still affects 2.2% of acres.
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 Mackinac County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area MI097; drainage covers 93% of 698,937 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.