1. Stair-step cracks in block or brick
Cracks that follow the mortar joints diagonally, like a staircase, indicate differential movement rather than simple curing shrinkage. In a concrete-block basement wall, a stair-step crack near the corner is the classic St. Louis symptom of soil pressure or settlement.
Measure the width with a crack gauge or a business card edge. Under 1/8 inch and stable is monitoring territory. Over 1/4 inch, displaced horizontally, or widening over a season warrants a professional evaluation.
2. Horizontal cracks or a bowing wall
A horizontal crack running along the middle of a basement wall is the most serious of these signs, because it indicates lateral soil pressure rather than vertical settlement. Hold a string line or a long level against the wall; a bow of more than about an inch across the wall height is significant.
This pattern shows up in the metro after wet springs, particularly where downspouts discharge next to the foundation and the backfill soil stays saturated.
3. Doors and windows that stick seasonally
Humidity swells wood, so a door that sticks in August and behaves in January may just be a door. What matters is a door that no longer latches at all, a visible gap that tapers from top to bottom, or window sashes that bind on one side only.
Check the gap around the door in the frame. A wedge-shaped gap, wide at one corner and tight at the other, points to frame racking rather than seasonal wood movement.
4. Sloping or uneven floors
Set a marble or a golf ball on the floor in several rooms. Consistent rolling in the same direction is worth measuring properly with a 4-foot level and shims. Roughly a half inch of slope over 10 feet is a common threshold that professionals treat as meaningful.
In older St. Louis homes with original wood joists over a basement, some deflection is expected. New slope, or slope that has changed since you moved in, is the real signal.
5. Gaps at trim, ceilings, and exterior brick
Look for separation between crown molding and the ceiling, baseboards pulling away from walls, and gaps opening between the brick veneer and window or door frames outside. Caulk that repeatedly tears open at the same joint is telling you the joint is moving.
Also inspect the chimney. A chimney leaning away from the house or a widening gap at the flashing is a structural observation, not a roofing one.
6. Water in the basement that is new
Efflorescence, the white powdery mineral deposit on block walls, means water is moving through the masonry. New dampness at the cove joint where the wall meets the floor, or a sump pump that suddenly runs far more than it used to, indicates a change in how water reaches the foundation.
Before assuming structural work is needed, check grading and drainage. Downspouts should discharge at least 4 to 6 feet from the wall, and soil should slope away roughly 6 inches over the first 10 feet. Fixing drainage first is standard practice and sometimes ends the problem.
7. Crumbling concrete or exposed rebar
Spalling concrete, flaking surfaces, and visible rust staining indicate moisture reaching reinforcement. Once rebar corrodes it expands and accelerates the damage, so this is not a wait-and-see item.
On piers and porch supports, tap the concrete with a hammer. A hollow sound over a broad area suggests delamination beneath the surface.
Who to call, and in what order
For an unbiased assessment, a Missouri-licensed professional engineer performing a structural evaluation typically charges $400 to $800 in this market and does not sell the repair. Foundation repair contractors usually inspect for free, which is useful, but the inspection is also a sales call.
If more than one of these signs is present, or a single sign is severe, getting the engineer report first gives you a scope document that repair bids can be compared against. Ask any contractor for their approach, warranty terms, and whether the warranty is transferable, and confirm their license and insurance directly with the issuing authority.
Frequently asked questions
Are all foundation cracks serious?
No. Thin vertical cracks under 1/8 inch in poured concrete are commonly shrinkage from curing and are often only a water-entry concern. Width, direction, displacement, and change over time are what separate cosmetic from structural.
How do I monitor a crack myself?
Mark the ends with a pencil, write the date, and measure the width at a marked point. Photograph it with a ruler in frame every three months. A crack that has not changed in a year behaves very differently from one that grows each spring.
Does homeowners insurance cover foundation repair?
Typically not when the cause is soil movement, settling, or long-term water intrusion, which are standard exclusions. Damage from a sudden covered event such as a plumbing line burst may be treated differently. Read your policy exclusions.
Sources and further reading
Price ranges in this guide come from quotes and invoices shared with STL Home Pros by St. Louis area homeowners and contractors. Technical and climate references are listed below.
About the author
Nick Cascani is a New York native who has called St. Louis home for the last few years. He believes getting professional home service should be simple and convenient, and he writes these guides to help local homeowners make confident decisions about their HVAC, plumbing, and foundation projects.
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