HyreFoundation
Find a Foundation Professional

HyreFoundation tools

Expansive soil map lookup

Find your lot in USDA Web Soil Survey, read one number, and see what class of shrink-swell soil you are on.

An expansive soil map lookup tells you whether the soil mapped under your house shrinks and swells. Look up your address in the USDA NRCS Web Soil Survey, read the linear extensibility percent (LEP), and enter it here.

Under NRCS bands, less than 3% is low, 3 to 6% moderate, 6 to 9% high and 9% or more very high. We hold no county data of our own; the number comes from USDA.

Expansive soil lookup

Find your lot in USDA Web Soil Survey, read one number, and see what class of shrink-swell soil you are on.

Soil Properties and Qualities → Soil Physical Properties → Linear Extensibility.

— Shrink-swell class
— What it means
— Plasticity index
— What to do

What this assumed —

Map-scale soil data, not a test of your lot.

How to find your number in Web Soil Survey

  • Open Web Soil Survey and find your address

    Use the Address search on the Area of Interest tab, then draw a box around your lot with the AOI tool.

  • Open Soil Data Explorer

    Go to Soil Properties and Qualities, then Soil Physical Properties, then Linear Extensibility.

  • View rating

    Read the value for the map unit under your house. If two units meet near the house, note both.

  • Enter it here

    The tool classes it with the NRCS bands. Keep a screenshot for any engineer you hire.

What a soil map can and cannot tell you

A soil map is the right first look. Expansive clay swells when wet and shrinks when dry. The Colorado Geological Survey reports such soils can expand 10% or more as they wet, and exert pressures of up to 30,000 pounds per square foot. See why foundations move and expansive clay soil.

It is not a lot test. Map units cover large areas, and builders bring in fill. For repair or new work, a geotechnical engineer tests the soil at your site. The plasticity index from that report says more than any map.

The national map exists too. The USGS published a swelling clays map of the conterminous United States in 1989. It is a regional picture; Web Soil Survey is finer.

Questions this calculator answers

How do I know if my soil is expansive?
Look up your address in USDA Web Soil Survey and read the linear extensibility rating. Moderate (3% or more) and above can damage buildings. A soil test at your site is the only lot-specific answer.
What does linear extensibility mean?
The percent change in length of a soil clod between moist and oven-dry. NRCS uses it to rate shrink-swell potential from low to very high.
Is there an expansive soil map by county?
USDA Web Soil Survey maps soil properties nationwide by map unit, finer than county. We do not publish county tables of our own.
What can I do if I live on expansive soil?
Keep moisture around the house even: working gutters, downspouts carried away, grade sloping away and no flooding or drought at the foundation edge.
Does expansive soil mean my foundation will fail?
No. Many houses on expansive clay perform well, especially when designed for it and kept at steady moisture.

Sources and methodology

Figures dated 26 October 2026. Last reviewed .

Related

Find a Foundation Professional Back to the homepage