Louisiana / LaSalle Parish
Score 43 · elevated · #52 of 64 in LA
Crawl space moisture in LaSalle Parish, LA
60% of LaSalle 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 — 61% of acres — it averages 1.5 ft below grade, shallow enough to reach a typical crawl-space footing.
- 1Water table 1.5 ft
- 2Wet soils 36%
- 3Moisture score 43
- 4EPA radon zone n/a
Reading the LaSalle Parish soil survey
The score of 43 combines four parts, each from the USDA survey: wet drainage classes contribute 38.9 points of 100 on their own scale, group D soils 52.2, a shallow water table 47.3, and flooding 24.7; the weights are on the methodology page. The dominant hydrologic group is C/D (37% of acres): D when undrained, C 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 LaSalle Parish. Venting cannot fix that; it needs drainage — a perimeter drain to daylight or a sump — before any liner goes down.
LaSalle Parish against the rest of Louisiana
LaSalle Parish ranks 52 of 64 Louisiana counties, 19 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 36%, 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 27%.
Flooding. 17.8% of acres with a flooding class are rated frequent; 10% of acres with a flooding class are rated occasional; 4.4% 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. Ponding — water standing at the surface with nowhere to go — affects 2.3% 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.
Near LaSalle Parish by score
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey area LA059; drainage covers 95% of 424,100 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.