Guide
Is it subsidence, or just cracking? How the difference is established
Updated
Cracking is common and most of it is not subsidence. Knowing which category you are probably in makes the next step calmer and cheaper.
The common causes of cracking that are not subsidence
- Thermal movement
- Materials expand and contract with temperature. Fine cracking that opens in cold weather and closes in warm weather, often at changes of material or around openings, is normal building behaviour.
- Shrinkage
- New plaster, new render and new masonry dry out and shrink. Hairline cracking in the first year or two after work is expected, not a fault.
- Settlement
- A new building or a new extension beds down into the ground under its own load. Settlement is normally short-lived and self-limiting, unlike subsidence, which is the ground moving away beneath a foundation that was previously stable.
- Lintel, wall-tie and sulphate problems
- Localised structural defects produce cracking that can look alarming but has a defined cause and a defined repair, with no ground investigation needed.
What tends to raise genuine concern
- Cracking that is getting wider over time rather than staying the same. Progression is the single most important observation, which is why monitoring exists.
- Cracks that are wider at one end than the other, typically wider at the top, and that run diagonally through the masonry rather than following the mortar joints.
- The same crack visible inside and outside in the same place, running through the full thickness of the wall.
- Doors and windows going out of square so they stick or will not latch, alongside the cracking.
- A plausible mechanism nearby: a large tree or hedge close to the building on a shrinkable clay soil, a suspected drain leak, or a recent excavation.
None of those on its own is a diagnosis. They are the reasons an engineer takes a case seriously, and the reasons a monitoring period may be recommended before anyone specifies a repair. Ground conditions matter here too: shrinkable clay soils behave very differently from sand or rock, and the British Geological Survey publishes research on shallow ground hazards including ground movement (BGS).
A sensible order of doing things
- Record what you have. Dated photographs with a ruler or coin in shot, noting where each crack is and how wide. This costs nothing and is the baseline everyone will ask for.
- Do not fill the cracks yet. Filling removes the evidence of whether they are still moving, which is the question that determines everything else.
- Tell your buildings insurer if you have cover and you suspect ground movement. Investigation and works are normally dealt with through a claim.
- Get a structural engineer's opinion if the insurer route does not apply, for example on a purchase. See what that report costs.
Nothing on this page is a diagnosis of your property, and nothing here is insurance or structural advice. An opinion on your building requires someone qualified to look at your building.