Expansive Soil in Louisiana: County Ratings
25 of the 64 rated counties in Louisiana have a dominant shrink-swell rating of High or Very High. Each rating below is the NRCS shrink-swell class covering the largest share of the county's mapped soil acres, computed from USDA SSURGO data. Open a county for the full class breakdown and what it means for a slab foundation.
| County | Dominant class | High + Very High share | Survey coverage |
|---|---|---|---|
| Acadia Parish | Moderate | 24% | 99% |
| Allen Parish | Low | 2% | 100% |
| Ascension Parish | Very High | 51% | 94% |
| Assumption Parish | Very High | 76% | 91% |
| Avoyelles Parish | Very High | 62% | 96% |
| Beauregard Parish | Low | 15% | 99% |
| Bienville Parish | Low | 23% | 98% |
| Bossier Parish | Moderate | 49% | 96% |
| Caddo Parish | Low | 45% | 92% |
| Calcasieu Parish | Low | 32% | 93% |
| Caldwell Parish | Low | 27% | 97% |
| Cameron Parish | Very High | 72% | 61% * |
| Catahoula Parish | Very High | 55% | 93% |
| Claiborne Parish | Low | 17% | 98% |
| Concordia Parish | Very High | 83% | 88% |
| De Soto Parish | High | 63% | 98% |
| East Baton Rouge Parish | Moderate | 9% | 87% |
| East Carroll Parish | Very High | 70% | 93% |
| East Feliciana Parish | Low | 1% | 98% |
| Evangeline Parish | Moderate | 25% | 97% |
| Franklin Parish | Low | 21% | 96% |
| Grant Parish | Low | 29% | 96% |
| Iberia Parish | Low | 40% | 87% |
| Iberville Parish | Very High | 61% | 92% |
| Jackson Parish | Low | 10% | 98% |
| Jefferson Parish | Very High | 87% | 42% * |
| Jefferson Davis Parish | Moderate | 41% | 98% |
| LaSalle Parish | Low | 30% | 95% |
| Lafayette Parish | Low | 10% | 98% |
| Lafourche Parish | Very High | 70% | 66% * |
| Lincoln Parish | Low | 0% | 99% |
| Livingston Parish | Moderate | 39% | 87% |
| Madison Parish | Very High | 78% | 94% |
| Morehouse Parish | Low | 34% | 98% |
| Natchitoches Parish | High | 57% | 97% |
| Orleans Parish | Very High | 89% | 32% * |
| Ouachita Parish | Low | 29% | 94% |
| Plaquemines Parish | Very High | 67% | 30% * |
| Pointe Coupee Parish | Moderate | 25% | 92% |
| Rapides Parish | Low | 35% | 96% |
| Red River Parish | Low | 34% | 95% |
| Richland Parish | Low | 30% | 97% |
| Sabine Parish | Low | 50% | 86% |
| St. Bernard Parish | Very High | 89% | 33% * |
| St. Charles Parish | Very High | 79% | 59% * |
| St. Helena Parish | Low | 0% | 99% |
| St. James Parish | Very High | 78% | 91% |
| St. John the Baptist Parish | Very High | 78% | 56% * |
| St. Landry Parish | Moderate | 44% | 98% |
| St. Martin Parish | Very High | 66% | 88% |
| St. Mary Parish | Very High | 79% | 68% * |
| St. Tammany Parish | Low | 6% | 73% * |
| Tangipahoa Parish | Low | 1% | 84% |
| Tensas Parish | Very High | 85% | 93% |
| Terrebonne Parish | Very High | 67% | 54% * |
| Union Parish | Low | 8% | 97% |
| Vermilion Parish | Very High | 62% | 69% * |
| Vernon Parish | Low | 26% | 99% |
| Washington Parish | Low | 0% | 98% |
| Webster Parish | Low | 33% | 96% |
| West Baton Rouge Parish | Very High | 52% | 93% |
| West Carroll Parish | Low | 14% | 99% |
| West Feliciana Parish | Low | 17% | 93% |
| Winn Parish | Low | 13% | 99% |
* Less than 80% of this county's map acres have completed soil survey data; treat its rating as provisional.
How these ratings are computed
Ratings come from USDA NRCS SSURGO soil survey data: for each soil component we take the maximum linear extensibility percent (lep_r) in the top 100 cm, apply the NRCS Handbook Part 618 class limits (Low under 3 percent, Moderate 3 to 6, High 6 to 9, Very High 9 and above), assign map units by plurality of component percent, and roll acres up to the county. Full details on the methodology section of the lookup page. A county rating is not a parcel-level geotechnical assessment.