Foundation cracks and settlement: when to call a geotechnical engineer
Sticking doors, sloping floors, widening cracks: how to tell ordinary shrinkage from soil movement, what to record before the visit and how a foundation investigation finds the cause.
Most concrete foundations have some cracks. Concrete shrinks as it cures, and fine vertical cracks that stay the same width are common. Soil movement is different: it tends to show up as cracks that grow, cracks in several places at once, and doors or floors that move out of level. Finding out which one you have is the job of an engineer.
Signs that point to soil movement
- cracks that widen over weeks or months, or that are wider at one end;
- stair-step cracks in block or brick walls;
- doors and windows that start to stick or no longer latch;
- sloping floors or gaps between the floor and the baseboards;
- a wall that leans or bulges inward;
- cracks that appeared after a very dry summer, a wet spring, nearby excavation or a plumbing leak.
Possible causes in the soil
- consolidation of soft clay or poorly compacted fill under the footings;
- clay soils that shrink in drought and swell when wet, sometimes made worse by large trees near the house;
- frost heave where footings are too shallow or poorly drained;
- water: leaking pipes, poor grading or downspouts that discharge against the foundation;
- slope movement on sites near ravines or riverbanks.
Before the visit
- Photograph each crack with a ruler or tape for scale, and date the photos.
- Mark the ends of the cracks with a pencil to see whether they grow.
- Note when doors started sticking and any recent work, leak or drought.
- Check that downspouts and grading send water away from the house.
How a foundation investigation works
A structural engineer looks at the building; a geotechnical engineer looks at the ground. The geotechnical investigation may include boreholes or test pits next to the foundation, laboratory tests and groundwater readings. The report explains the cause and gives options, such as drainage improvements, underpinning or piers, with the data the repair contractor and the structural engineer need.
Starting with the investigation avoids paying for a repair that does not address the cause. If a wall is bulging or the cracks are moving fast, call a professional promptly.
Describe the cracks in the form and local geotechnical firms get back to you. Building an addition on the same foundation? Read soils reports and building permits.