How can I find out if my land has expansive soil?

Start with the free USDA Web Soil Survey, then confirm with a lab test if the results look risky. Web Soil Survey lets you outline your parcel and view building site ratings such as Dwellings Without Basements, plus a soil property called linear extensibility, which measures shrink-swell potential. For a definite answer, a geotechnical lab tests samples. Texas' TB 10-01 bulletin explains the IRC criteria used to call soil expansive, including a plasticity index of 15 or more (ASTM D4318) and an expansion index above 20 (ASTM D4829). Mapped soil data is a screening tool, not a site-specific test, so a geotechnical engineer should confirm before you pick a foundation on suspect ground.

Check your local rule. This varies by state, county or city. Your permitting office has the final word; the official lookup pages below show you who that is.

Sources

• Web Soil Survey Interpretations by CategoryUSDA Natural Resources Conservation Service
• IHB Technical Bulletin TB 10-01: Foundations on Expansive SoilsTexas Department of Licensing and Regulation
• Web Soil Survey: Soil Data Explorer Tab guideUSDA Natural Resources Conservation Service