What Causes Foundation Cracks?
Almost every foundation crack in the Kansas City area traces back to soil and water. Here is the chain of events, and why some houses crack and others on the same street do not.
Expansive clay soil
The soil across most of the metro is clay with a high shrink-swell rating. When it rains, the clay absorbs water and expands, pressing in on foundation walls and lifting parts of the structure. In a dry summer it loses that water, shrinks, and pulls away from the foundation, removing support.
That back-and-forth happens every year. Over time it works cracks into walls, floors, and the drywall above door and window openings.
Water in the wrong places
- Downspouts that discharge right next to the foundation
- A yard that slopes toward the house instead of away
- Poor or failed footing drains that no longer carry water off
- A plumbing or sewer leak slowly softening the soil under a footing
- Large trees pulling moisture out of the clay on one side of the house
Uneven moisture is worse than uniformly wet or uniformly dry soil, because it makes one part of the foundation move while the rest stays put. That differential movement is what cracks things.
Construction and age factors
Newer homes on graded subdivision lots often have deep backfill against the foundation that was never fully compacted. That soil keeps settling for years, and the foundation, garage floor, and patio settle with it.
Concrete also shrinks as it cures, so some hairline cracks appear in the first year and never move again. And a 70-year-old foundation has simply been through more wet-dry cycles than a 10-year-old one.
Why your house and not the neighbor’s
Two houses on the same block can sit on different amounts of fill, have different tree cover, different downspout setups, and different original construction quality. Small differences in how water reaches the soil add up to big differences in how much a foundation moves.
What to do next
Knowing the cause matters because the repair depends on it. A crack from settlement needs the settlement fixed. A crack from wall pressure needs the pressure relieved. A crack that is just a water path gets sealed. An inspection identifies which one you have.
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