What is differential settlement?
Differential settlement is the uneven sinking of a building or part of it relative to the rest. In Dutch this is called verzakking. Every building sinks a little after construction: this is called settlement. As long as everything sinks evenly, that is usually not a problem. You speak of differential settlement when one part sinks more or faster than another. The structure is then pulled out of true, and stresses and cracks develop.
Causes
- Shallow foundations on compressible ground: peat and soft clay are slowly compressed under load.
- Deteriorated timber piles: when the groundwater level drops, the heads of timber piles dry out and pile rot can occur.
- Drying out of clay: in dry summers clay shrinks, especially under the external walls and close to trees.
- Uneven loading or foundations: an extension on a different foundation from the main house often settles differently.
- Works nearby: excavations, dewatering or vibrations can disturb the ground under a foundation.
Recognising it
Look out for the following signs:
- Stepped or diagonal cracks in masonry, often running from the corners of windows and doors.
- Doors and windows that start to stick or no longer close properly.
- Sloping floors (check with a spirit level or a marble).
- A joint between an extension and the main house that keeps getting wider.
In practice
- Measure first, then repair: a crack does not tell you whether the settlement is still continuing. Have the cracks and levels monitored for a while (crack monitors, level surveys) before you decide.
- Have a foundation survey carried out by a specialist firm if you suspect timber piles or a shallow foundation on soft ground.
- Do not just fill cracks cosmetically: as long as the cause has not been removed, it will crack again.
- Expect substantial costs for foundation repair: in the Netherlands these quickly run into tens of thousands of euros per home. Sometimes municipal schemes or a loan through the Fonds Duurzaam Funderingsherstel (the Dutch fund for sustainable foundation repair) are available; ask your municipality.
Related terms
- Settlement
- Absolute settlement
- Foundation repair
- Pile rot
- Crack
- Foundation survey
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