Louisiana / Natchitoches Parish
Score 49 · elevated · #44 of 64 in LA
Crawl space moisture in Natchitoches Parish, LA
71% of Natchitoches Parish'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 — 70% of acres — it averages 1.6 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 1.6 ft
- 2Wet soils 40%
- 3Moisture score 49
- 4EPA radon zone 3
Reading the Natchitoches Parish soil survey
The score of 49 combines four parts, each from the USDA survey: wet drainage classes contribute 40.6 points of 100 on their own scale, group D soils 70, a shallow water table 53.1, and flooding 19; the weights are on the methodology page. The dominant hydrologic group is D (60% 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 across much of Natchitoches Parish. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
Natchitoches Parish against the rest of Louisiana
Natchitoches Parish ranks 44 of 64 Louisiana counties, 13 points below the state median of 62. Wetter counties exist in Louisiana, but the soil here still sits well above the national middle. Statewide, 64% of mapped soil is in the wet drainage classes; here it is 40%, below the state figure — the score here comes from heavy group D soils rather than drainage class alone. After moderately well drained, the next most common class is well drained at 28%.
Flooding. 13.3% of acres with a flooding class are rated frequent; 5% of acres with a flooding class are rated occasional; 13.2% of acres with a flooding class are rated rare. That is a large flood-prone share; a crawl space in the floodplain needs flood vents under most local floodplain ordinances, which is a separate rule from R408 and can rule out a fully sealed design.
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 Natchitoches Parish by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area LA069; drainage covers 97% of 832,000 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.