Tennessee / Cannon County
Score 22 · moderate · #22 of 88 in TN
Crawl space moisture in Cannon County, TN
51% of Cannon County's soil falls in hydrologic group D or a dual D group: clays and high water tables that shed water slowly. Where a seasonal water table is reported — 29% of acres — it averages 1.7 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 1.7 ft
- 2Wet soils 4%
- 3Moisture score 22
- 4EPA radon zone 2
Reading the Cannon County soil survey
The score of 22 combines four parts, each from the USDA survey: wet drainage classes contribute 11.1 points of 100 on their own scale, group D soils 48.6, a shallow water table 21.5, and flooding 3.9; the weights are on the methodology page. The dominant hydrologic group is D (33% 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 on the soils that report a water table — about 29% of Cannon County's acres. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Cannon County against the rest of Tennessee
Cannon County ranks 22 of 88 Tennessee counties, 10 points above the state median of 12. That puts it in the wettest quarter of the state. Statewide, 9% of mapped soil is in the wet drainage classes; here it is 4%, below the state figure — the score here comes from heavy group D soils rather than drainage class alone. After well drained, the next most common class is moderately well drained at 24%.
Flooding. 0.6% of acres with a flooding class are rated frequent; 5.4% of acres with a flooding class are rated occasional; 0.1% 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 2. The zone is a county-level prediction; EPA says elevated levels occur in every zone and every home should be tested.
Near Cannon County by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area TN015; drainage covers 100% of 170,000 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.