The mechanism

McKinney sits on the Blackland Prairie — expansive clay soils with a high proportion of smectite minerals, which are the ones that hold water between their layers and physically change volume as that water comes and goes.

Wet season, clay absorbs water and swells. Dry season, it releases water and shrinks. Vertical movement of two to four inches across a lot within a single year is unremarkable here. Some sites do more.

A slab poured on that soil rides it. In an ordinary year the movement is gentle, roughly uniform, and reverses. Drought breaks the pattern: soil dries much deeper than usual, shrinkage is much larger, and because drying doesn’t happen evenly around a house, the movement becomes differential. Differential is what breaks things.

Why one corner and not the whole house

A house drying out uniformly on all sides would drop as a unit and you’d likely never notice. That basically never happens.

• South and west exposures dry faster and deeper than shaded north sides
• A large tree pulls hundreds of gallons a day from one quadrant
• Irrigated beds hold moisture the bare side yard doesn’t
• Slab perimeter dries from the edge inward while the center stays damp longer
• Driveways and patios shield the soil beneath them from evaporation
• Neighbors who water heavily change your soil moisture at the property line

Every one of those creates a moisture gradient. Enough gradient across enough distance and the slab has to bend.

The lag

This is the part that confuses people.

Clay dries from the surface downward, and it’s slow. The deep soil actually supporting your foundation loses moisture months after the drought begins. Then the structure has to move far enough for something brittle — mortar, drywall, tile — to fail.

So the crack you notice in November traces to a dry June. Calls spike in late summer and stay elevated into winter, and a severe drought year produces damage that keeps surfacing well into the following year. North Texas has been through several of these in recent memory — 2011 and 2023 both produced pronounced waves — and the pattern repeats.

Which is why “we made it through the summer fine” isn’t reassuring yet.

The rebound is also a problem

When the rain finally returns, desiccated clay rehydrates and swells — sometimes with real force, and sometimes faster than it shrank.

Some houses recover most of what they lost, cracks partially close, and doors start working again. Others don’t, because soil under the slab center rewets on a different schedule than the perimeter, or because a section that dropped has since been supported by soil that settled into the gap and now can’t go back up.

Heave can be as damaging as settlement, and it’s the specific reason removing a large tree near a house isn’t the automatic fix people assume. See root barriers for that discussion.

Newer homes aren’t exempt

A common assumption is that modern post-tension slabs in the newer subdivisions north and west of town are immune. They aren’t.

Post-tension construction makes a slab better at resisting cracking as it bends. It doesn’t stop the soil underneath from moving. On top of that, rapidly developed areas often have engineered fill that continues consolidating for years, and new landscaping has no established root systems or mature irrigation patterns to stabilize moisture.

Homes three to eight years old in fast-growing parts of Collin County show up on our schedule regularly. Different failure mode, same soil.

What to do during a dry summer

• Water the foundation, consistently. A soaker hose loop twelve to eighteen inches out, run daily in July and August. Full schedule in our watering guide.
• Water all four sides. Partial coverage manufactures the gradient you’re trying to avoid.
• Check the trees. Anything large within its own height of the house deserves attention before August, not after.
• Photograph your cracks with a date. Put a coin or a ruler next to them. Growth over time is the diagnostic, and memory is unreliable.
• Don’t panic at the summer gap. Soil pulling back from the slab edge is normal shrinkage and usually closes with the rain.
• Get a baseline survey. An elevation survey now is worth far more later, because it turns next year’s reading into a rate rather than a number.

Should you repair during a drought?

Reasonable people disagree here.

The argument for waiting: soil is at its driest and the house at its lowest, so piering now locks in a position that might have partially recovered on its own once rain returned. You may install more piers than you needed.

The argument for acting: piers reach depths where seasonal moisture barely matters, so the support is stable regardless of when it goes in, and waiting lets damage accumulate.

Practically — if damage is significant and getting worse, repair. If it’s mild and you’re mid-drought, correct drainage, start watering, document with photos, and re-survey after a wet season before committing. That’s not a stalling tactic. It’s often the honest answer, and it’s saved people the entire cost of a job.