Does my area have expansive clay soil?

USDA measures linear extensibility, the lab number behind shrink-swell risk, for the dominant soil in every US county. Type a county to see its reading and what it means for a foundation - free, no guessing, sourced straight from USDA's own Soil Data Access.

If you're already seeing this, don't wait for the county lookup to tell you why:

Stair-step cracksDiagonal, following brick or block mortar joints rather than running straight

Doors that stickSeasonally, worse after a wet spell followed by a dry one

Floors that slopeUneven in one part of the house, not the whole structure

Gaps that moveAround window and door frames, opening and closing with the weather

None of these proves expansive soil alone. Two or more, in a county that reads "High" or "Very High" below, is the pattern worth a real answer for.

Check your county's reading

3,144 US counties, straight from USDA's own soil survey - or just type your ZIP.

The four bands USDA's data sorts every county into

Measured as linear extensibility - how much the soil swells wet and shrinks dry:

41Very High≥9% - usually needs an engineered foundation

90High6-9% - can crack a standard foundation without moisture control

1067Moderate3-6% - standard foundations usually hold, drainage still matters

1887Low<3% - the easiest starting point

Orleans Parish, LA carries this site's most-constrained reading - see its page for what that looks like in practice.

The number that actually decides anything

Not the soil class by itself - what it costs to find out for certain, against what it costs to have skipped that:

Geotechnical report, one lot	$1,000–$5,000
Foundation repair, after damage	$5,000–$15,000

In a "High" or "Very High" county, that gap is the whole argument for spending a few thousand dollars now rather than finding out from the cracks.

This is a county-level figure, area-weighted across a whole county's surveyed soil - not a reading for one address. A site-specific geotechnical report is still what an engineer or a permit application actually requires; this exists to set expectations before that, not replace it.

Browse all 3,144 counties by state

The question this site answers

Before paying $2,700 for a site-specific geotechnical report, most people want a rough sense of whether their area's soil is the expansive-clay kind that damages foundations. USDA already measures it: its Soil Survey Geographic (SSURGO) database records linear extensibility, the lab measurement behind shrink-swell risk, for the dominant soil in every US county. ShrinkSwellCheck reports that county-level reading straight from USDA's Soil Data Access, no guessing.

A county figure, not a permit

This is the county-wide, area-weighted reading - useful for a first read before you buy land, plan a build, or decide whether cracking you're already seeing has a geological explanation. It is not a substitute for a site-specific geotechnical report, which is what an engineer or a permit application actually requires.