Why Your Foundation Moved
Expansive clay is the culprit under most damaged American foundations. But whether it damaged your house by getting wetter or by getting drier decides everything you should do about it.
Expansive clay can change volume by a significant fraction as its moisture content changes, and that movement is what lifts and drops United States foundations - it is not the weight of the house.
In wet-trigger regions of the United States, prevention costs almost nothing: downspout extensions running water six to ten feet from the wall, and attention to large trees close to the house.
In drought-trigger regions, prevention is the reverse and equally cheap: a soaker hose laid 18 inches out from the footing, run slowly and evenly during dry spells, for under $40.
The wet trigger
Clay takes on water and expands. If it expands unevenly - saturated at one corner where a downspout discharges, dry under the middle of the house - the foundation is pushed up in one place and not another, and something has to crack.
Large mature trees complicate this in the other direction. A big tree draws a serious volume of water out of the ground every day through summer, drying the soil on that side of the house specifically. The result is the same: differential movement.
The drought trigger
In a climate with hard dry summers the dominant movement is shrinkage. The perimeter dries fastest because edges lose moisture from two directions, so the clay under the footing pulls away while the soil under the centre of the house stays put. The house settles at the edges - and diagonal cracks appear at door and window corners, because that is where stress concentrates.
You can often see this with your own eyes at the end of a dry summer: a visible gap between the soil and the foundation wall, sometimes wide enough to drop a coin into.
Why this changes what you should do
| Wet trigger | Drought trigger | |
|---|---|---|
| What to look at | Downspouts, grading, large trees | Soil pulling away from the footing in late summer |
| Prevention | Move roof water away; watch root proximity | Water the perimeter evenly during dry spells |
| Worst season for damage | After prolonged wet periods | Late summer after a dry spell |
| What makes it worse | Concentrated water at one corner | Watering one side and not another |
| Cost of prevention | $50-300 in downspout extensions | Under $40 for a soaker hose |
Notice that the wrong prevention actively harms you. Watering unevenly in a drought region moves one part of the house and not another, which is worse than doing nothing at all.
Because both cycles partly reverse - cracks narrow again when the season turns - American homeowners systematically under-react. The useful discipline is photographing the same cracks with a date twice a year.
Common questions
How do I know which trigger applies to my house?
Walk the perimeter at the end of a dry summer. A visible gap between soil and footing points to the shrinkage trigger. Persistent saturation at one corner, or a very large tree within about its own height of the house, points to the wet one. An engineer will tell you in one visit.
Does a plumbing leak look the same?
It can, and it is worth ruling out because it changes both the fix and whether insurance applies. The clue is location: leak-driven movement is usually concentrated near a bathroom or kitchen rather than following the perimeter.
Are newer houses safer?
Not reliably. Newly graded lots sometimes have fill that has not fully consolidated, and young landscaping means less established root systems moderating soil moisture. Age of house is a poor predictor; soil type and drainage are much better ones.
Get a local opinion
Describe what you are seeing and when it changes through the year. One independent local contractor will tell you whether this needs an engineer now or watching for a season. No charge, no obligation.
Or call (877) 701-2518