Foundation repair · Bexar County County, TX
Drive from the north side of Bexar County to the south side and the ground under the houses changes three times.
Bexar County does not have one foundation problem, it has three, and the Balcones Fault Zone sorts them out. North and northwest of the escarpment, houses sit on thin soil over limestone that turns up 11 to 12 inches down. Through the middle they sit on Blackland Prairie clay that swells 17 percent between wet and dry, and south and southeast of that they sit on sand that barely swells at all. The USDA publishes its soil survey at the county level, which is what this page is for, and every number below comes out of survey area TX029.
The ground under Bexar County County
The ground under Bexar County, north side to south side
Bexar County is cut in half by the Balcones Fault Zone, and nearly every foundation difference in the county follows from that one structure. It is an arc of en echelon normal faults 10 to 60 km wide that trends east through Uvalde County into Bexar and then bends northeast toward Austin. USGS Water Supply Paper 1588, on the ground water geology of Bexar County, records individual faults or shatter zones traced as much as 25 miles with maximum displacement of at least 600 feet, and notes that in the central and southern parts of the county the rocks dip gulfward at gentle to moderately steep angles and are extensively faulted in the Balcones and Mexia fault zones. That fault zone stacks bands of ground running southwest to northeast across the county. North and northwest of the escarpment sits the Edwards Plateau, Cretaceous Edwards Limestone and Glen Rose Limestone, hard rock close to the surface, karst, and the Edwards Aquifer recharge zone. Through the middle, southeast of the escarpment, the section steps up into younger Cretaceous units, the Austin Chalk and then the Taylor Group, described in the literature as more than 600 feet of poorly exposed shelf marls, argillaceous limestones and shale or clay, followed by Navarro. Those marls and clays weather into the Blackland Prairie belt that follows the fault line from south of Bexar all the way to Dallas along I-35. South and southeast of that clay belt the Tertiary Wilcox Group and Carrizo Sand plus Pleistocene and Recent alluvium take over, and the soils turn sandy. The plain version. North Bexar hits rock in a foot, mid Bexar sits on clay that swells 17 percent, south Bexar sits on sand. Same county, three different repair problems, one fault zone explaining all of them.
North and northwest of the escarpment
Edwards Plateau ground, Edwards and Glen Rose Limestone with karst and the Edwards Aquifer recharge zone. The soil is thin, sometimes a foot of it, and the rock underneath is hard. Houses here rarely heave. They settle, and what makes them settle is usually the lot itself, cut on the uphill side and filled on the downhill side, with fill that was never going to behave like the rock beside it. Piers reach competent limestone fast on this side of the county. Drainage is the other half of the job, because water runs across rock instead of soaking into it.
The escarpment edge where deep clay sits on rock
This is the sharpest combination in the county. Anhalt carries the highest clay content anywhere in Bexar, 55 to 71 percent, with a linear extensibility of 15.9 percent and paralithic bedrock at 71 cm, about 28 inches. Deep clay over rock has nowhere to go but up and down, so the movement is severe and it is differential, meaning one corner lifts while the next one stays put. Doors that stick after a wet spring and swing free by August are the usual first complaint.
The clay belt through the middle of the county
Blackland Prairie vertisols weathered off the Austin Chalk, the Taylor Group marls and Navarro. Houston Black, Branyon and Lewisville all live in this band. The Houston Black Official Series Description records cracks 1.3 to 10 cm wide, half an inch to 4 inches, opening at 12 inches of depth in dry periods, and the soil is moderately well drained with very slow permeability, so it takes water in slowly and gives it up slowly. Slabs ride the seasons here. Perimeter beams drop in a dry summer, interiors dome, and a leaking sewer line under a slab will do in one year what weather does in ten. Piers in this band have to reach well past the active zone before they hold anything.
South and southeast toward the sand
Tertiary Wilcox Group and Carrizo Sand plus Pleistocene and Recent alluvium. Aluf is the marker soil, deep sand at 5 to 10 percent clay with a linear extensibility of 1.5 percent and no bedrock restriction to 203 cm. Houses out here are not shrink swell cases. They erode, they lose bearing under a footing, and they get into trouble when roof water and street drainage are allowed to run alongside the foundation. The work is usually drainage correction, french drains and restoring bearing, not chasing clay.
Straight from the soil survey
What the USDA maps under Bexar County County.
Seven series carry most of Bexar County. Every acreage, clay percentage and linear extensibility figure below came from USDA Soil Data Access for survey area TX029 at https://sdmdataaccess.sc.egov.usda.gov/ , queried on 2026-08-21, and that survey area covers 804,601 acres. Linear extensibility is the percent a sample changes in length between wet and dry, so read it as a swelling score. The values shown are the highest representative horizon value inside the Bexar map units for that series, not a whole profile average and not a reading from your lot. Depth to rock is the representative value for mapped components from the same survey, not a site specific measurement, which is why we still dig test holes before quoting pier depths.
| Soil series | Share of county | How much it swells | What that means for a foundation |
|---|---|---|---|
| Eckrant | 112,116 acres, about 13.9 percent of the 804,601 acres mapped in survey area TX029 | LEP ≈ 6.1% | Clay content runs 42 to 45 percent but lithic limestone shows up at 28 to 30 cm, which is 11 to 12 inches, so piers reach competent rock fast and the damage usually traces to cut and fill lots and thin soil over hard rock rather than swelling. |
| Houston Black | 74,984 acres, about 9.3 percent of the county | LEP ≈ 17% | The worst mover in Bexar at 54 to 55 percent clay with no bedrock restriction anywhere in the profile to 218 cm, roughly 86 inches, so slabs ride up and down with the seasons and piers have to go deep before they find anything that holds still. |
| Lewisville | 65,662 acres, about 8.2 percent of the county | LEP ≈ 7.5% | Deep clay at 41 to 46 percent with no bedrock restriction to 175 cm, but it moves noticeably less than Houston Black at similar clay content, which is why two houses a mile apart can behave very differently. |
| Brackett | 41,774 acres, about 5.2 percent of the county | LEP ≈ 3.2% | A shallow Hill Country soil at 28.5 to 30 percent clay with paralithic bedrock at 30 to 41 cm, which is 12 to 16 inches, so there is very little swelling and very little soil, and the failures here are settlement, fill and drainage rather than heave. |
| Aluf | 41,549 acres, about 5.2 percent of the county | LEP ≈ 1.5% | Deep South Texas Plains sand at just 5 to 10 percent clay with no bedrock restriction to 203 cm, so houses on it are not shrink swell victims, they are erosion, drainage and bearing capacity cases. |
| Branyon | 40,090 acres, about 5 percent of the county | LEP ≈ 13% | A second Blackland Prairie vertisol at 47 to 53 percent clay running deep to 203 cm with no rock to stop it, and it behaves close enough to Houston Black that we treat it the same way. |
| Anhalt | 3,996 acres | LEP ≈ 15.9% | The highest clay content in the county at 55 to 71 percent sitting on paralithic bedrock at 71 cm, about 28 inches, and deep clay directly on rock produces the sharpest differential movement because the soil has nowhere to go but up and down. |
Linear extensibility (LEP) is the USDA's measure of how much a soil changes volume between wet and dry. Higher numbers move houses.
Where we work in Bexar County County
The Bexar County County towns we cover.
Each one has its own page, because the ground changes inside this county and the local pattern is what matters when you are standing in the house.
- San AntonioThe only city here touching all three soil bands
- Alamo HeightsSits on the escarpment edge above the Olmos basin
- Balcones HeightsPostwar buildout where the escarpment gets its name
- Beacon HillNear north side bungalows built before the slab era
- Castle HillsEnclave on the north side where the clay thins
- ConverseNortheast farmland turned base housing after the war
- HelotesNorthwest of the escarpment, shallow soil over limestone
- King WilliamThe county's oldest stock, 1880s houses on crawl space
- Leon ValleyWest side slab era, Leon Creek runs through it
- Live OakBase corridor suburb, slab on grade from the start
- Mahncke ParkEast of downtown by Fort Sam, drainage and moisture
- Monte VistaThe rising ground north of downtown, 1900s mansions
- Olmos ParkBetween downtown and the north side, 1920s planned streets
- Shavano ParkFar north, rock close enough to hit while digging
- South San AntonioSouth side sand, erosion and drainage before swelling
- Stone OakNewest growth, cut and fill lots on hard rock
- Terrell HillsPrewar homes ringed entirely by San Antonio city limits
- Universal CityStraddles the Guadalupe County line by Randolph
- Windcrest1960s subdivision laid out inside Loop 410 northeast
- WoodlawnWest side prewar, crawl space work rather than slabs
What gets built here, and when
Every building era in San Antonio sits somewhere in this county
Bexar County has no single housing era, and the stock sorts by neighborhood rather than by decade. Once you know which ring of the city you are standing in, the foundation type and the failure pattern follow. The oldest stock sits in the near downtown neighborhoods, King William, Monte Vista, Beacon Hill, Mahncke Park and Woodlawn. Those houses are predominantly pier and beam on masonry or cedar piers over crawl spaces, which is why the work there is releveling, crawl space repair and moisture control far more often than piering. The 1940s through 1960s expansion filled the ring inside Loop 410 and the corridors around the military bases, Randolph on the northeast near Converse, Universal City and Live Oak, and Lackland and the former Kelly on the west and south sides. That is the era when San Antonio moved to slab on grade, typically thin and lightly reinforced by current standards, and those are the slabs that show up cracked when they happened to land in the clay belt. The enclave cities, Alamo Heights, Terrell Hills, Olmos Park, Castle Hills and Balcones Heights, are largely 1920s through 1950s, so a single street can hold both systems. On the far north side the newer subdivisions are slabs poured on cut and fill over shallow rock, which is a different failure again. The city pages cover what all of that looks like block by block.
Permits in Bexar County County
Who signs off on a foundation repair here.
Your address falls under one of three jurisdictions in this county, San Antonio, one of the suburban or enclave cities, or unincorporated Bexar County, and they are not the same process. Inside San Antonio city limits the Development Services Department issues a dedicated foundation repair permit, applied for through the BuildSA portal. The application separates full repair from partial repair, separates slab on grade or concrete foundation from concrete post, pier and beam, and asks for the number of posts or piers. San Antonio is explicit about engineering. The application states that an Engineer's Assumption Letter is required to be submitted at the time of application, and that all foundation repairs require the submittal of an engineer's inspection letter to clear the foundation inspection. The city publishes a template letter that the Engineer of Record must sign, seal and date, and only letters from the Engineer of Record are accepted. Two things follow from that for a homeowner. First, our inspectors are ICC certified, not engineers and not PE, so when a San Antonio permit calls for a sealed letter the engineer is a separate party you engage, and we build to that engineer's plan. Second, that process stops at the city limit. The suburban and enclave cities each run their own building departments and set their own requirements, and an unincorporated address falls to the county, where floodplain and on site sewage requirements can still apply. We call the office with jurisdiction over your address before anything is scheduled rather than assuming the San Antonio process carries over. Fees change often enough that we do not print them, and the permit office will quote the current ones.
Costs, warranty and inspections
The straight numbers in Bexar County County.
Straight answers
Foundation questions people ask in Bexar County County.
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