Does Your Area Have Expansive Soil? Look It Up by ZIP Code

Expansive soil is clay that swells when wet and shrinks when dry, and that movement is one of the most common causes of slab foundation damage. Enter your ZIP code to see the USDA shrink-swell rating for your county's soils, or browse every rated county by state below. A 1973 ASCE study (Jones and Holtz) estimated expansive soils cause more annual property damage in the US than floods and tornadoes combined.

Check your ZIP code

Enter a 5-digit ZIP code to see the USDA shrink-swell rating for your county's soils.

Expansive soil across the US

Of the 3,109 counties rated so far, here is how the dominant shrink-swell class breaks down:

Very High 103 counties
High 287 counties
Moderate 766 counties
Low 1,953 counties

Top 25 counties by Very High expansive soil share

Ranked by the share of mapped soil acres in the NRCS Very High shrink-swell class.

#	County	State	Very High share	Dominant class
1	Lyman County	South Dakota	93%	Very High
2	Stanley County	South Dakota	92%	Very High
3	Tensas Parish	Louisiana	83%	Very High
4	Concordia Parish	Louisiana	80%	Very High
5	Madison Parish	Louisiana	78%	Very High
6	Rockwall County	Texas	78%	Very High
7	St. James Parish	Louisiana	78%	Very High
8	Sharkey County	Mississippi	75%	Very High
9	Assumption Parish	Louisiana	74%	Very High
10	Audrain County	Missouri	69%	Very High
11	Dewey County	South Dakota	68%	Very High
12	Collin County	Texas	68%	Very High
13	Fillmore County	Nebraska	67%	Very High
14	Leflore County	Mississippi	67%	Very High
15	Issaquena County	Mississippi	66%	Very High
16	Shelby County	Missouri	65%	Very High
17	Tunica County	Mississippi	65%	Very High
18	St. Martin Parish	Louisiana	65%	Very High
19	East Carroll Parish	Louisiana	63%	Very High
20	Humphreys County	Mississippi	62%	Very High
21	Navarro County	Texas	61%	Very High
22	Chambers County	Texas	60%	Very High
23	Brazoria County	Texas	60%	Very High
24	Iberville Parish	Louisiana	59%	Very High
25	Monroe County	Missouri	59%	Very High

Browse expansive soil ratings by state

Alaska 22 counties
Alabama 67 counties
Arkansas 75 counties
Arizona 14 counties
California 57 counties
Colorado 63 counties
Connecticut 8 counties
District of Columbia 1 counties
Delaware 3 counties
Florida 67 counties
Georgia 159 counties
Hawaii 5 counties
Iowa 99 counties
Idaho 41 counties
Illinois 102 counties
Indiana 92 counties
Kansas 105 counties
Kentucky 120 counties
Louisiana 64 counties
Massachusetts 12 counties
Maryland 24 counties
Maine 16 counties
Michigan 83 counties
Minnesota 87 counties
Missouri 114 counties
Mississippi 82 counties
Montana 55 counties
North Carolina 100 counties
North Dakota 53 counties
Nebraska 93 counties
New Hampshire 10 counties
New Jersey 21 counties
New Mexico 33 counties
Nevada 17 counties
New York 62 counties
Ohio 88 counties
Oklahoma 77 counties
Oregon 34 counties
Pennsylvania 67 counties
Rhode Island 5 counties
South Carolina 46 counties
South Dakota 66 counties
Tennessee 95 counties
Texas 254 counties
Utah 28 counties
Virginia 127 counties
Vermont 14 counties
Washington 35 counties
Wisconsin 72 counties
West Virginia 54 counties
Wyoming 21 counties

Methodology: what we compute and where the data comes from

Every rating on this site is derived from the USDA NRCS SSURGO soil survey database (Soil Survey Geographic Database), accessed through the NRCS Soil Data Access service. Here is exactly what we compute:

Per-component metric. For each soil component we take the maximum linear extensibility percent (the SSURGO lep_r representative value) among horizons whose top depth falls within 0 to 100 cm of the surface.
Class limits. We apply the NRCS National Soil Survey Handbook Part 618 linear extensibility classes to that value: Low under 3 percent, Moderate 3 to under 6, High 6 to under 9, Very High 9 and above. These are NRCS's own class limits, not ours.
Map unit class. Component classes are weighted by component percent (comppct_r); each map unit takes the class holding the plurality of component percent.
County rollup. Map unit acres are summed per class across the county. The dominant class is the one covering the largest share of mapped soil acres, excluding unmapped (NOTCOM) and water map units. The percentages shown are shares of mapped acres.
Coverage honesty. Each county page reports what share of its map acres have completed soil survey data. Counties under 80 percent coverage carry an incomplete data caveat, and we keep them out of our sitemap. The 80 percent line is our own editorial gate, not a soil science claim.

Sources: USDA Natural Resources Conservation Service, SSURGO (Soil Survey Geographic Database) via Soil Data Access; USDA NRCS National Soil Survey Handbook, Part 618 (linear extensibility classes); HUD USPS ZIP-county crosswalk for ZIP matching. A county rating is not a parcel-level geotechnical assessment.

Expansive soil FAQ

What is expansive soil?

Expansive soil is clay-rich ground that swells when it absorbs water and shrinks as it dries. That repeated volume change moves the ground under a house, and slab foundations are especially exposed because they sit directly on the soil. A 1973 ASCE study (Jones and Holtz) estimated expansive soils cause more annual property damage in the US than floods and tornadoes combined.

How is my county's rating calculated?

We compute each rating from USDA NRCS SSURGO soil survey data. For every soil component we take the maximum linear extensibility percent (lep_r) among horizons starting within 0 to 100 cm of the surface, apply the NRCS National Soil Survey Handbook Part 618 class limits (Low under 3 percent, Moderate 3 to 6, High 6 to 9, Very High 9 and above), assign each map unit the class holding the plurality of component percent, and roll map unit acres up to the county. The rating shown is the class covering the largest share of the county's mapped soil acres.

Does a High or Very High county rating mean my house will have foundation problems?

No. The rating is a county-level rollup of soil survey data, not a parcel-level geotechnical assessment. Soils vary lot to lot, and construction quality, drainage, and moisture management matter as much as the clay itself. A geotechnical engineer or foundation professional can assess your specific lot.

Can I look up expansive soil by ZIP code?

Yes. Enter a 5-digit ZIP code in the lookup above and we match it to its county using the HUD USPS ZIP-county crosswalk, showing the county that holds the largest share of the ZIP's residential addresses. Where a ZIP spans several counties, the result notes the others it touches.