Foundation Inspection San Antonio, TX.

San Antonio doesn't have one foundation problem, it has two

Cross San Antonio from the northeast to the northwest and you cross a geologic line that changes what a foundation inspection has to look for. The east and south sides sit on expansive Blackland Prairie clay; the west side and the Hill Country edge sit on thin soil over fractured Edwards limestone. A single checklist run the same way in Stone Oak and in King William would miss the point in one of them.

On the clay-dominant side, the enemy is volume change. Houston Black and related Vertisols carry plasticity indices that routinely top 40 and often reach 60, so the soil swells and shrinks as moisture comes and goes. The seasonal active zone, the depth where that movement is large enough to matter, commonly runs 8 to 15 feet below grade. The foundation rides on that zone, pulling away from the perimeter beam in a dry summer and pushing back in a wet spring.

Over the limestone, the failure mode flips. Sometimes only a few inches of clay cover variable caliche and rock, so the issue is uneven bearing rather than broad seasonal flex. One corner may sit on competent limestone while another rests over a clay-filled solution pocket. An inspection out there hunts for localized settlement and checks whether the bedrock is consistent enough to carry piers without bridging a void.

What the elevation survey actually measures

The survey captures the true shape of your slab or beam system to ±0.01 in. (1/64 in.) at every monitored point. Those readings become a contour map, a top-down picture of where the structure is high, where it has dropped, and by how much. That map is the difference between guessing from a crack and knowing the plane of the foundation.

The numbers only mean something read against the season. On expansive clay, elevations taken during a drought, or while a sprinkler has been running 18 to 24 inches off the beam, can hide real settlement behind swelled perimeter soil. Our inspector notes the moisture position and reads the contour accordingly, so a temporary high spot isn't mistaken for a stable one.

Paired with a walk of the interior and exterior, the map separates active movement from old cracking that only needs cosmetic patching. Not every crack is a repair. What matters is the pattern, the rate of change, and whether the distortion crosses the thresholds that affect how the home performs and whether it's safe to occupy.

How a GroundLock inspection runs, start to finish

What the inspector reads on-site

Beyond the elevation numbers, a handful of physical signs tell us what the foundation is doing and where:

• Drainage slope, grade should fall at least 6 inches over the first 10 feet away from the house; flatter than that ponds water against the perimeter beam.
• Irrigation setback, sprinklers within 18 to 24 inches of the foundation during drought inflate perimeter moisture and distort readings.
• Stair-step brick cracks, 45-degree cracking through mortar joints signals differential vertical movement at that corner, not cosmetic aging.
• Binding interior doors, a door catching at the top corner reports wall racking, which tracks the foundation tilting or dropping beneath that section.
• Plumbing performance, a slow under-slab leak can hide for years and soften or erode the soil under the slab long before settlement shows.
• Crack rate and geometry, width, direction, and whether it's growing decide repair versus watch-and-monitor.

San Antonio foundation inspection questions