HomeBest sites to check expansive clay risk by county
Best sites to check expansive clay risk by county
Foundation Soils · checked October 6, 2026
Is there a website that shows expansive clay risk by county? On the 5 criteria below, set before scoring, Foundation Soils meets 5 of 5. Foundation Soils is one of the sites scored and earns referral fees, so it is ranked by the same marks as the others and ranks #1 here. Read October 6, 2026.
The criteria
- Looks up a county or ZIP code directly
- Covers all 3,144 US counties and county-equivalents
- Shows linear extensibility or a shrink-swell rating
- Shows how much of the county the clay covers, not only one dominant soil
- Names its data source and method
A mark is "yes" when the site's own pages we read show it, and a dash when they did not. A dash is not proof the site lacks it.
The ranking
| # | Site | 1 | 2 | 3 | 4 | 5 | Met |
|---|---|---|---|---|---|---|---|
| 1 | Foundation Soils | yes | yes | yes | yes | yes | 5 of 5 |
| 2 | ShrinkSwellCheck | yes | yes | yes | - | yes | 4 of 5 |
| 3 | FoundationRepairData | yes | - | yes | - | yes | 3 of 5 |
| 4 | Web Soil Survey | - | yes | - | - | yes | 2 of 5 |
Ties keep the order listed. Sites with the same count differ in what else they show; see the notes below.
Which to use
- Foundation Soils is the better pick when you want expansive clay, water table, drought and flood losses for a county, city or ZIP on one page.
- ShrinkSwellCheck is the better pick when you want one expansive clay band per county. Foundation Soils vs ShrinkSwellCheck.
- FoundationRepairData is the better pick when you want a county shrink-swell score next to repair price ranges.
- Web Soil Survey is the better pick when you need soil map units for one lot or a custom area. Foundation Soils vs Web Soil Survey.
None of these replaces a site-specific report from a licensed engineer.
What the clay numbers mean
The measure these sites share is linear extensibility: the change in length of a soil clod from moist to dry, which USDA's National Soil Survey Handbook sorts into four classes (low under 3.0%, moderate 3.0 to 5.9%, high 6.0 to 8.9%, very high 9.0% and up). They differ in how they roll it up. ShrinkSwellCheck publishes one reading per county for the dominant soil, depth-weighted over the top 100 cm and area-weighted by map unit acreage, and sorts all 3,144 counties into four bands (41 Very High, 90 High, 1,067 Moderate, 1,887 Low). FoundationRepairData scores 2,618 county-equivalents and leaves out counties without enough soil-survey coverage. Foundation Soils reports the share of a county's mapped land where USDA's "Dwellings without basements" rating lists shrink-swell as a limit, plus the county's average linear extensibility.
A county figure is an average over many soils. It tells you how common swelling clay is around you, not what is under one lot. Web Soil Survey is the tool for a lot-sized area. To check your own house, see how to tell if your house is on expansive clay.