San Antonio to Austin corridor

Is your ZIP code built on soil that moves?

Foundation damage in Central Texas is mostly soil. Expansive clay swells when wet and shrinks in drought, and the more it moves, the more it pushes on your slab. This map looks up any ZIP code in the United States and scores it from real USDA soil shrink-swell data. Our free inspection is offered from San Antonio to Austin only. Hover or tap your area to see its risk, the main driver, and what to read about it.

The Foundation Risk Map is © Motmot Foundation Repair and licensed under CC BY-NC-ND 4.0. You’re welcome to share it, embed it, or link to it with credit to Motmot Foundation Repair (motmotfoundationrepair.com). You may not sell it, charge for access to it, or publish a modified version.

Attribution line: Foundation Risk Map · Motmot Foundation Repair, https://motmotfoundationrepair.com/foundation-risk-map/ (CC BY-NC-ND 4.0)

Want the numbers instead of the picture? Download the Central Texas data behind this map, the scores for our 333 Central Texas ZIPs as a free CSV, with the statistics we computed from it. The dataset is licensed separately under CC BY 4.0 (reuse with credit, commercial use OK); the map application above stays CC BY-NC-ND.

Buying a house anywhere in the US? The foundation repair permit finder shows which office issues building permits at the address, its flood zone, and permit records for the cities that publish them. Before you hire anyone to fix what the map warns about, our contractor licensing guide shows what a contractor has to hold in dozens of Texas cities and most states.

How to read the risk map

Every ZIP is shaded by the shrink-swell potential of all its soils, weighted by area, using the USDA’s linear-extensibility measure of how much the ground expands when it soaks up water and contracts when it dries out. Darker areas sit on high-plasticity clays like Houston Black and Ferris; lighter areas sit on shallow limestone or sandier soils that barely move. The risk isn’t evenly spread across San Antonio and Central Texas. South and east of downtown San Antonio, and out across the Blackland Prairie toward the I-35 corridor, the clay is deep and active. North of the Balcones Escarpment (Stone Oak, the Hill Country edge, and much of the limestone north side), the ground is steadier, and the movement you do see is usually local (a leaking line, poor drainage, or fill around a slab) rather than the whole footprint. We rank all 59 San Antonio ZIPs, with the soil under each, in which San Antonio ZIP codes have the most foundation problems, and the Travis County ZIPs in Austin ZIP codes with the most foundation problems. If you came here from our sponsored article in MySA, some San Antonio scores changed when we rescored on October 17, 2026, and this section explains what moved and why. The same deep corridor clay is what our crews measure day to day in foundation repair in New Braunfels, Kyle, and Buda along I-35. Where the shading runs darkest, a repair usually has to reach below the clay entirely, which is why deep foundation piers are the common answer in those ZIPs.

How each ZIP is scored

The score comes from one USDA number, linear extensibility, or LEP. LEP is the percent a soil changes in length between wet and dry, so a higher LEP means ground that moves more. For each ZIP we take every USDA SSURGO soil map unit inside the ZIP boundary, read its LEP over the top 100 cm, weighted by the share of each soil component in the unit, and then weight each map unit by its area inside the ZIP. The score is that LEP divided by 13.33, times 100, capped so it runs from 5 to 99. A score of 72 to 99 is High, 52 to 71 is Elevated, 34 to 51 is Moderate, and 5 to 33 is Lower. The score describes the ground across the whole ZIP, not any one lot. A ZIP is scored only when at least half of its soil area is rated (open water and bare rock are left out), so downtown cores that are mostly unrated urban land show no score. Scores were updated in October 2026, when we moved from sampling five points per ZIP to weighting every soil type by its actual area in the ZIP.

What a high-risk reading actually means

A high score means the soil under your ZIP is capable of moving a slab enough to crack drywall, rack doors, and separate brick, not that your specific house is damaged. Soil sets the odds; drainage, plumbing leaks, tree roots, watering habits, and the original build quality decide whether that potential ever turns into movement. Plenty of homes on high-risk clay stay flat for decades because their drainage and moisture stay even. The map is a screening tool: use it to understand the ground you’re on, spot the seasonal pattern (clay swells in a wet spring and shrinks hard in an August drought), and know which of our drought and heavy-rain guides apply to your area.

The only way to turn an odds reading into a real answer for your address is a measured look. A free foundation inspection shoots your floor elevations, maps any cracks, and reviews drainage and moisture, so you know whether your slab is actually moving, or whether the ground under your ZIP just could. If you want the raw source behind the shading, it comes from the USDA’s public Web Soil Survey, and our Texas clay soil guide explains the science in plain English. We publish the foundation risk data by ZIP as an open CSV too, so you can read the score, the band, and the soil measurement behind any ZIP in the corridor yourself.