The short answer
There is no single answer for Round Rock, and that is the useful thing to know before you call anyone. The Handbook of Texas describes the Balcones Escarpment dividing Williamson County along the Jarrell–Georgetown–Round Rock line — a line drawn through this city by name. Soils change across it: in the Handbook’s summary, blackland east, limey west. So a house on the east side of Round Rock and a house on the west side are sitting on two different problems, and the right repair for one is the wrong repair for the other.
The line runs through town
Most places are on one side of a geological boundary or the other. Round Rock is the place the boundary is named after when geographers draw it, which means the two sides of town are not a subtlety here — they are the main fact about the ground.
East of the line is Blackland Prairie clay. The soil that defines it, Houston Black, is described by the USDA as having high shrink-swell potential, opening cracks 1/2 to 4 inches wide at a foot down in dry weather. Clay that moves that much carries a slab edge with it.
West of the line the soil is thinner and sits over stone. The Georgetown series, whose type location is in the same county, formed in clay loams and clays over Edwards formation limestone. Where rock is close to the surface, a slab can bear on something that does not move at all — and move anyway where the soil above the rock is deeper on one side of the house than the other.
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Which side of town are you on?
This matters for the work, not just the geology:
- Depth. On deep clay, piers have to pass the zone where seasonal moisture still swells and shrinks the soil, or the house settles again on the next dry summer. On shallow rock, a pier reaches bearing much sooner.
- The failure you see. Clay tends to drop a perimeter corner in a drought and push it back up after heavy rain, so cracks open and close with the seasons. Shallow rock tends to produce differential movement that arrives once and stays.
- What watering does. Keeping the soil evenly damp helps on clay and does very little where the slab is on stone. The ASCE Texas Section guidelines put it carefully: clients should be told that keeping near uniform soil moisture on all sides may be beneficial, and warned against overdoing it.
- Drainage either way. Both sides want water leaving the house. The same guidelines recommend a slope of 5 percent (6 inches in 10 feet) away from the foundation for the first ten feet, where that can be managed.
What is not known
We would rather be plain about the limits than draw a line we cannot source:
- The published boundary is a county-scale description. No map we could open shows which Round Rock streets fall on which side, and the transition on the ground is unlikely to be a clean edge.
- There is no soil survey tied to Round Rock’s neighborhoods, so this page does not claim one.
- There is no Round Rock cost figure anywhere we could find. The numbers below are metro-wide and national.
What settles it for your house is specific to your house: an elevation survey, a soil log if the contractor takes one, and cracks photographed and dated over a few months. A metro average cannot tell you which side of an escarpment your slab is on.
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A city of early-2000s slabs
Census estimates count 51,143 housing units in Round Rock, with a median build year of 2002. 55% went up in 2000 or later and only 11% before 1980, and detached single-family houses make up 64% of the stock.
A housing stock that young has a particular pattern. Most of these slabs have now been through several of Central Texas’s dry summers, and the first real movement often shows up a decade or two in — late enough that the builder’s warranty may have lapsed, early enough that owners assume a new house cannot have a foundation problem. Trees planted when the subdivision was built are also now large enough to draw water from under a slab edge, which the ASCE guidelines name as a cause of soil shrinkage under a foundation.
What repairs cost here
No guide publishes a Round Rock number. Angi’s Austin page says prices in the metro commonly fall between $3,822–$9,809, and a foundation inspection averages $600 nationally.
Per-pier figures are where the two sides of town show up in a quote. Olshan, a contractor, lists drilled piers for slab foundations at $765–$1,100 per pier and steel push piers at $990–$1,350 per pier. Multiply either by the number of piers a plan calls for and the design matters more than the unit price — which is why the first thing worth paying for is the measurement, not the piers. The cost page breaks down how a quote adds up, the slab repair page covers settled edges, heave and leaks, and why foundations move here explains the same escarpment split across the whole metro.