Austin ZIP Codes With the Most Foundation Problems

Which Austin ZIP codes have the most foundation problems? Five tie for the highest risk score in Travis County. 78702, 78721, 78722, 78723, and 78757 each score 99 out of 99 in our open soil dataset, and they share one cause, deep expansive clay with a measured linear extensibility of 17 percent, the strongest shrink-swell reading in the county. Del Valle's 78617 and northeast Austin's 78754 sit right behind at 98, 78724 scores 96, and a band of 90s takes in Pflugerville's 78660, Manor's 78653, and southeast Austin's 78741 and 78747. This is the full Travis County picture, drawn from the same public dataset we give away, so every number here is one you can check.

How the scores are built

The dataset behind this article is the one that powers our interactive foundation risk map. We take USDA NRCS SSURGO soil survey data, pull the linear extensibility for the soils mapped in each ZIP code, and scale it to a score from 0 to 99. Linear extensibility is the soil lab's measure of shrink-swell, the percent a soil column changes dimension between moist and dry. Clay at 17 percent can change size by roughly a sixth as the seasons swing, and a slab riding on it gets pushed and dropped a little differently every year.

The corridor dataset covers 333 ZIP codes from San Antonio up through the Austin area, and 48 of them fall in Travis County. Two of those, downtown's 78701 and the university's 78712, carry no score because the survey lacks usable soil data for those blocks, so we left them blank rather than guess. The other 46 sort into four bands. Twelve score High, one sits alone in Elevated, seventeen land in Moderate, and sixteen come in Lower. The full CSV is a free download on the map page, so you can check any figure in this article against the source.

The east side owns the top of the table

Every High-band ZIP in Travis County shares the same driver in the dataset, expansive shrink-swell clay. The five 99s, 78702, 78721, 78722, and 78723 along with 78757, all carry the county's top soil reading at 17 percent linear extensibility. Four of the five sit east and northeast of I-35, on the edge of the Blackland Prairie, the deep clay belt that runs the length of the corridor. The one that surprises people is 78757, up in Crestview and Allandale on the west side of the highway. The clay pays no attention to the freeway line, and the soil survey says that pocket of north-central Austin moves as much as anything on the east side.

Behind the 99s, Del Valle's 78617 and northeast Austin's 78754 score 98 on clay measured at 16.5 percent, and 78724 scores 96 at 15.1 percent. The rest of the High band lands at 90, Manor's 78653, Pflugerville's 78660, and southeast Austin's 78741 and 78747, each on readings near 12 percent. If your home sits in any of these twelve ZIPs, the ground under it is doing real seasonal work, and stair-step brick cracks and doors that start sticking by late summer show up here more than anywhere else in the county.

The middle of the county moves with the seasons

One ZIP holds the Elevated band by itself. 78705, the neighborhoods around the university, scores 68 on 9 percent clay, movement strong enough to matter and noticeably calmer than the east side. Below it, seventeen ZIPs make up the Moderate band with scores from 34 to 39, and here the dataset's listed driver changes from expansive clay to seasonal clay movement. The band runs through north-central and north Austin, 78752, 78753, and 78756 at 39, 78751 at 38, 78727 and 78749 at 37, and it reaches south through 78745 at 36 and 78748 at 34. Soil readings here sit near 5 percent, less than a third of what the 99 ZIPs carry. Houses in this band still crack, but the movement tends to track wet and dry years rather than grind through every single season.

West Austin sits on limestone

The Lower band is a west-side story. Sixteen Travis ZIPs score 33 or under, and the dataset lists the same driver for every one of them, thin soils over limestone and drainage. The lowest score in the county belongs to 78704 at 11, on soil measured at just 1.5 percent. Five ZIPs score 14, 78730, 78733, 78735, 78737, and 78759. Tarrytown's 78703, Westlake's 78746, and northwest Austin's 78731 come in at 23, and so do Lakeway's 78734 and Bee Cave's 78738. Out there the ground is mostly rock under a thin skin of soil, and rock does not swell.

Lower never means zero. Slabs in these ZIPs still move when a drain line leaks, when downspouts dump against one corner, or when a lot was built up on poorly compacted fill. What the score says is that the native soil is supplying very little of the force. When something moves out west, the cause is usually water you can find and fix.

What a score means for your house

A ZIP score describes the mapped soil, not your slab. Inside one high-band ZIP you'll find houses that have stood square since the sixties next door to homes on their second round of repairs, because trees, drainage, plumbing, slab age, and the quality of the original grading all sit on top of the soil map. That's why we measure before we ever talk repair. About a third of our inspections end with no repair needed, high-band ZIPs included, and homes we have repaired get a yearly performance follow-up inspection as standing practice, because clay this active deserves a recheck.

If the elevation survey does find movement worth fixing, the numbers stay knowable. Steel and hybrid piers run $600 to $1,000 each, and the pier count, not the ZIP code, is what sets the bill. The full pricing picture for the city is in our guide to what foundation repair costs in Austin, and the neighborhoods we work, from the east-side clay to the limestone hills, are on our Austin service area page. If you want the number for your own address rather than your ZIP, the inspection is free, and it comes with a floor elevation survey that shows what the soil has actually done to your slab.