Which San Antonio ZIP Codes Have the Most Foundation Problems?

Which San Antonio ZIP codes have the most foundation problems? The ones sitting on deep expansive clay, and in San Antonio that means the old core around downtown and the east, northeast, west, and southwest sides. 78208, just east of downtown, scores highest at 96 out of 99 in our open soil dataset. 78244 on the northeast side follows at 86, downtown's 78205 at 85, 78202 at 84, and 78237 on the west side at 83. Thirteen San Antonio ZIPs land in the High band and eighteen more in Elevated, so 31 of the city's 59 ZIPs, roughly half, sit on ground with High or Elevated shrink-swell potential. The score measures the soil, not your house, and the full table of all 59 is below.

If you found us through our sponsored article in MySA, some of the numbers in that piece have changed. We rescored every Texas ZIP on October 17, and the section on the rescore explains what moved and why. Roughly half of San Antonio's ZIPs still rate High or Elevated, and 78208 still leads the city.

How the San Antonio scores are built

The scores come from the dataset behind our foundation risk map. We start with USDA NRCS soil survey data, the same records anyone can pull up in the USDA's Web Soil Survey. For every soil mapped inside a ZIP we take its linear extensibility, the lab measure of how much a soil changes in length between wet and dry over the top 100 centimeters, and we weight each soil by the ground it actually covers in that ZIP. That area-weighted number, divided by 13.33 and multiplied by 100, with a floor of 5 and a ceiling of 99, is the score. A score of 72 or more is High, 52 to 71 is Elevated, 34 to 51 is Moderate, and anything under 34 is Lower.

San Antonio here means the 59 ZIPs whose primary postal city is San Antonio. Fifty-eight of them are in Bexar County and one, 78266, is in Comal County. All 59 carry a score. Scores updated October 2026, when we moved from sampling five points per ZIP to weighting every soil type by its actual area in the ZIP. The method, the Central Texas totals, and a free CSV of every row are on our foundation repair statistics page.

What changed after our sponsored article in MySA

On October 9 we published Before You Spend Thousands on Foundation Repairs in MySA's sponsored section. It is labeled as an ad and as provided by Motmot Foundation Repair because it is sponsored content that we wrote, not MySA news coverage. It walked San Antonio homeowners through checking their ZIP on our map before making a repair decision, and it listed the things worth documenting before an inspection. That advice still stands, and the longer version of it is further down this page.

Some of its numbers did not survive our October 17 rescore. The piece said 30 of the city's 59 ZIPs rated High or Elevated, split 23 High and 7 Elevated, with 13 Moderate and 16 Lower. It named 78208 and 78216 as the city's two ZIPs at 99, and after the rescore 78208 sits at 96 and 78216 at 61. Today 31 of the 59 rate High or Elevated, so roughly half still holds, but the mix is different. Thirteen are High, eighteen Elevated, twenty-six Moderate, and two Lower. 78208 still leads the city. 78216, the ZIP pictured on the map in that article, now sits in the Elevated band.

The scores moved because the method changed. The old method averaged soil readings at up to five points inside each ZIP. In a ZIP with mixed ground, five points can all land on the heaviest clay and push the score to the ceiling, or all land on rock or on loam that barely swells and drop it to the floor. 78216, with heavy clay over shallow limestone, was the first kind and fell from 99 to 61. 78252 and 78224 were the second kind and rose from 11 to 58 and 54. The new method weights every soil mapped in the ZIP by the ground it covers, so a mixed ZIP lands in the middle where it belongs. That is why 30 of the 59 San Antonio ZIPs changed band, 17 moving up and 13 moving down, and why the Moderate band grew from 13 ZIPs to 26.

The live risk map and our methodology page already show the new scores, and the table below comes from the same data. If you looked up your ZIP when the MySA piece ran, look it up again.

The old core and the east side carry the highest scores

The 13 High-band ZIPs ring downtown and run out to the east, northeast, west, and southwest. 78208 leads at 96, on soil averaging 12.8 percent linear extensibility, the highest reading in our Central Texas dataset. 78244 follows at 86 on 11.4 percent, 78205 scores 85 and 78202 scores 84, both on 11.3 percent, and 78237 scores 83 on 11.1 percent. 78225 scores 78, 78239 scores 76, four ZIPs tie at 75 (78207, 78215, 78219, and 78242), 78218 scores 74, and 78227 closes the band at 72.

The soil explains it. Most of these ZIPs are mapped mainly as Houston Black or Branyon clay, with Heiden the second soil in four of them. All three are Vertisols. Texas A&M AgriLife describes Vertisols as soils defined by smectite, a clay mineral that swells when wet and shrinks when dry, and points to the surface cracking it produces in long dry spells. In 78208, Houston Black covers 56 percent of the ZIP and Heiden another 27 percent. The USDA rates 88 percent of that ground very high for shrink-swell.

Ground like that moves a slab edge with the seasons. The edges dry and drop through August, the first big fall rains swell them back, and the drywall over the doors keeps the record. If your house is in one of these ZIPs, stair-step brick cracks and doors that stick by late summer are the patterns to watch for.

Mixed ground fills the Elevated band

Eighteen ZIPs score Elevated, from 67 down to 52. 78226 and 78235 lead the band at 67, 78201 scores 66, and 78204 and 78228 score 65. This is where San Antonio's ground gets mixed. Several of these ZIPs, 78201, 78209, 78212, and 78216 among them, sit where the clay gives way to the limestone of the Balcones Escarpment, and the USDA maps bedrock within reach under 28 to 56 percent of their ground. Those transition streets, where clay pockets sit over rock, produce some of the sharpest differential movement we measure. A house with two corners on rock and one on clay hinges every dry summer.

78216 is the clearest example, and it is the ZIP our MySA article pictured. No single soil dominates it. Lewisville clay covers about 15 percent, Houston Black about 14, Eckrant, a thin stony soil over limestone, about 13, and Heiden about 11. The USDA rates a third of the ZIP very high for shrink-swell and maps bedrock within reach under 28 percent of it. One lot there can sit on Heiden clay that swells hard and the next on limestone a foot down. The ZIP score splits the difference, so it cannot speak for one house.

The rest of the band reads the same way at lower intensity. 78209 around Alamo Heights scores 52 on a mix of Eckrant over limestone and Houston Black clay, with rock under more than half its ground. On the south and southwest sides, 78211 scores 62, 78243 scores 60, 78252 scores 58, and 78224 scores 54, with almost no rock in any of them. Expansive clay, mostly Houston Black, Lewisville, and Branyon, covers about half to seven tenths of each, going by the USDA shrink-swell classes. Much of the rest is Sunev, Loire, and similar loams that the USDA rates low for shrink-swell, from nearly a fifth of 78211 to nearly half of 78243. Lewisville also swells less than Houston Black. There is almost no limestone here to pull the average down, so the loam and the milder clay do it, and these ZIPs land a band below the core.

Limestone on the north side and sandier ground on the far south

Twenty-six ZIPs land in Moderate, from 51 down to 34, and two land in Lower. Most of the Moderate band is the north side. Out along and beyond Loop 1604, ZIPs like 78255, 78256, and 78261 score 34 on Eckrant and Brackett soils, thin stony ground over limestone, with bedrock mapped under 81 to 91 percent of each ZIP. Rock does not swell. When a slab moves up there, the cause is usually local, such as a clay pocket, a utility trench, fill around a pool deck, or water from a leak.

The north side has its own issue, and the soil details on our map show it. In 78258, a Moderate ZIP, the USDA still rates 84 percent of the ground very limited for houses without basements. The main limit it lists is hard bedrock near the surface, under about 94 percent of the ZIP, with shrink-swell second. Thin soil over limestone moves far less than clay, but it punishes bad drainage, so on those lots we look hardest at where the water goes.

The south edge of the city breaks the clay pattern too. 78264, at the far south end of Bexar County, scores 16, the lowest in San Antonio, on Aluf and other sandy soils that barely swell. The USDA rates about 70 percent of that ZIP not limited for houses. 78266, the one San Antonio ZIP in Comal County, scores 33 on thin, stony soil over limestone. Lower never means zero. A slab in either ZIP still moves when a drain line leaks, when downspouts dump against one corner, or when the lot was built up on poorly compacted fill.

All 59 San Antonio ZIP codes ranked

Every San Antonio ZIP, highest score first, with its band, its area-weighted linear extensibility, and the soil series that covers the most ground in it. Area is the direction of the ZIP's center from downtown, and Central means within about three miles of it. The most common soil often covers well under half the ZIP, so open the soil details on the map to see the full mix. Rock outcrop and other non-soil map units are left out of that column.

What a ZIP score can and cannot tell you about one house

A ZIP score is an average across thousands of lots. It tells you how hard the native soil in your part of town can push on a foundation. It does not tell you what your slab has done. Inside one High-band ZIP you will find houses that have stood square since the fifties next door to houses on their second round of repairs, because drainage, plumbing, trees, the age of the slab, and the quality of the original pad all sit on top of the soil map.

That is why we measure before we talk about repair. About a third of our inspections end with no repair needed, and that holds in high-scoring ZIPs too. Treat a High score as a reason to keep water away from the slab and to watch for early signs. Treat a Lower score as a lighter background force rather than a clean bill of health. The mapped soil covers only the top 100 centimeters, it is averaged across the ZIP, and fill brought in when a subdivision was built may not match the survey at all.

How to read your ZIP on the risk map

Open the foundation risk map and type your ZIP, your neighborhood, or your street address into the search box. Tap your ZIP and a panel shows its score, its band, and the main soil driver. That much answers the question most people arrive with.

For the rest, press See soil details. The map goes full screen and opens a drawer for that ZIP. It lists the soils mapped in the ZIP and the share of ground each one covers, shows how the ZIP splits across the USDA shrink-swell classes, and gives the USDA rating for houses with and without basements along with the main limits it names. Below that is a plain description of how the ground moves through the year and what you can do about it. Every value comes from the USDA soil survey, weighted by area across the ZIP.

Read those ratings together. In 78208 nearly all the ground is Vertisol clay, and the main limit the USDA names for houses is shrink-swell. In 78258 the main limit is bedrock near the surface. Both ZIPs show most of their ground as very limited for houses, for completely different reasons, and they ask different things of a homeowner. To go one step further, the USDA's Web Soil Survey lets you draw an area around your own block and read the soil map units under it.

What to write down before an inspection

Our MySA article listed four things to document before an inspection. This is how we would do each one from the inspector's side.

Photograph the crack with a ruler and a date. Take one wide shot that shows where the crack sits on the wall, then a close shot with a tape measure or ruler held across it. Put a pencil tick at each end of the crack and write the date beside it. Shoot the same spot from the same angle every few weeks. A crack that opens in a dry summer and tightens after rain is following the clay. A crack that only grows, and runs past your pencil ticks, is the one to have measured.

Watch where the water goes. Walk around the house during a real rain, not after it. Note every downspout that drops water at the slab, any corner where water stands, and any bed or patch of lawn that stays wet days after the rest dries. Guidance from the American Society of Civil Engineers puts downspout discharge at least five feet from the house, and builders rarely run them that far. Check where the AC condensate line and the sprinkler heads drain too. A wet spot that shows up in dry weather can mean a leak, and a leak under a slab on clay can lift part of the floor.

Write down which doors stick, and when. List the doors and windows by room. Note when each one started and whether it comes and goes. Look at the gap between the top of the door and the frame. A gap that tapers from one side to the other means the frame has racked. A door that drags in August and frees up after a wet winter is following the clay through its normal cycle. One that never comes back is worth measuring.

Mark where the floor changed. Note cracked tile, baseboards pulling away from the floor, trim that opened at a corner, and any spot where a marble rolls. Write down the room and take a photo. These are the places an inspector will want to put the level first, and your notes let the survey line up with what you have been living with.

What a measured inspection should record

A survey shows what the floor actually did, which a photo cannot. On our free inspection an ICC-certified inspector shoots a floor elevation survey of about 40 points across the slab, read in tenths of an inch, maps the cracks, and walks the drainage, usually in 60 to 90 minutes on site. You get written findings to keep, whether the answer is stable, monitor, or repair.

One survey is a snapshot. It shows where the floor sits today, not whether it is still moving, and some of what it shows is simply how the slab was poured. When the readings are borderline, the honest answer is often to fix the water and measure again in a few months, because two surveys taken a season apart show the trend. When the pattern calls for an engineering evaluation, we work with independent engineers. And when we do repair a house, it gets a yearly performance follow-up inspection, because clay this active deserves a recheck.

How to read a repair bid

A bid should explain your house. Ask every company for the elevation readings behind its plan, the number of piers with each location marked on a drawing, and which readings put a pier on each wall. A wall that measures level does not need one. When two bids differ, the difference is almost always the count, and a lower count is a smaller scope rather than a better deal.

Then read what is in and what is out. Drainage work, a plumbing test, the permit, an engineering letter, and putting the yard and the interior back together are sometimes included, sometimes listed separately, and sometimes missing. San Antonio requires a permit for structural foundation repair, so ask who pulls it. Ask whether the warranty transfers to the next owner and what voids it. Our San Antonio cost guide walks through what moves a bid.

If a plan leaves you unsure, get a second opinion. Ours is free. Bring the other company's scope and any readings that came with it, and we will re-shoot your floor elevations and tell you whether the plan matches them. Sometimes the honest answer is that it is a fair scope and you should hire them.

Using the map when you buy a house

For buyers the map is a starting point before you know anything about a particular house. A High-band ZIP tells you to read the foundation section of the inspection report closely and to ask the seller for every record. That means any earlier elevation surveys, the repair plan and pier log if the house was underpinned, the engineer's letter, the permit, and the warranty with its transfer terms. Do your measuring inside the option period, while you can still walk away. Our guides on foundation problems during the option period and buying a house with a previous foundation repair go through both in detail.

A high score cannot tell you an earlier repair failed, and a low score cannot tell you a house is sound. Only a measurement of the house itself can answer that.

If you live in San Antonio, or anywhere in Bexar, Comal, Guadalupe, Kendall, Medina, Bastrop, Caldwell, Hays, Travis, or Williamson County, the inspection is free. Bring your photos, your notes, and any old reports. Book online or call or text (210) 816-0034, and an inspector will measure your floors and give you the findings in writing, including when the answer is that nothing needs fixing.