What is a settlement crack?
A settlement crack is a crack in a structure caused by settlement: the compression of the ground beneath the foundation once the full weight of the building bears on it. Settlement is usually a one-off process that comes to rest in the first years after construction. A crack appears, but the structure remains stable. A settlement crack is therefore usually not serious and repair is mainly cosmetic.
Settlement, subsidence or shrinkage crack?
- Settlement crack: caused by settlement that stops. The crack does not keep growing.
- Subsidence crack: caused by ongoing, uneven sinking, for example due to a deteriorating foundation. The crack keeps widening and points to a structural problem.
- Shrinkage crack: caused by the material itself shrinking (concrete, mortar, plaster) as it cures or dries, unrelated to the foundation.
How to recognise it
In masonry, settlement cracks often run diagonally or in a stepped pattern through the joints, and they tend to start at the corners of window and door openings, where the wall is weakest. They often appear where parts of a building with different loads or foundations meet, such as an extension built against an existing house.
Application: monitoring and assessment
- Mark the ends of the crack with a pencil line and the date.
- Fix a crack monitor (tell-tale) across the crack and record the reading.
- Read it regularly, for example every three months for at least a year, so seasonal movement shows up.
- If the crack stays the same, it can be repaired. If it grows, call in a structural engineer.
Practical tips
- Only fill a crack once you are sure it has stopped moving, or the repair will crack again.
- For masonry, use a mortar that matches the existing joints.
- A movement joint between old and new work prevents many settlement cracks at extensions.
Related terms
- Crack
- Shrinkage crack
- Differential settlement
- Absolute settlement
- Settlement joint
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