These four words get used as if they were synonyms, and they are not. They describe different mechanisms, they produce different evidence, and they lead to entirely different responses - one of which is very often to do nothing at all. Getting the distinction wrong is expensive in both directions: unnecessary underpinning is a large bill and a permanent mark on a property's history, while genuine progressive movement left alone gets worse.
This page is the hub the symptom pages link back into. If you have arrived here from a crack, a sloping floor or a sticking door, this is the framework an engineer fits that symptom into.
The four mechanisms
| What is happening | Typical cause | Does it stop? | |
|---|---|---|---|
| Settlement | The ground compresses under the building's own weight | A new building bedding in; a new extension loading ground beside an older structure | Yes - usually within the first years, and then it is finished |
| Subsidence | The ground moves down away from the foundations for a reason unrelated to the building's load | Clay shrinkage, washout into a defective drain or culvert, collapse of a void, dissolution of soluble strata | Only when the cause is removed |
| Heave | The ground swells and pushes the foundations up | Clay rehydrating after a large tree is removed; frost; certain chemical reactions in fill | Slowly - clay rehydration can run for years |
| Landslip | Sloping ground moves sideways as well as down | Steep ground, water, loading or excavation at the wrong point on a slope | Not without intervention |
Why settlement is the reassuring one
Settlement is normal. Every building settles into the ground it is built on, and older buildings on shallow foundations settled a great deal. It is one of the main reasons Victorian terraces have floors that slope and door frames that are no longer square.
The important property of settlement is that it finishes. Once the ground beneath a foundation has compressed under the load, it stops compressing, and the building sits where it has ended up. The cracking that accompanied it gets decorated over and stays decorated over. A survey that concludes 'historic settlement, stable' is a good outcome, and it is the most common conclusion we reach.
Differential settlement is the version that causes visible damage - one part of a building settling more than another, typically where an extension of a different weight and different foundation meets an older structure. That is why so much cracking appears at the junction between old and new rather than in the middle of a wall.
Subsidence: the word everyone reaches for
Subsidence is ground movement caused by something other than the building. The mechanism matters because it determines the remedy:
- Clay shrinkage - shrinkable clay drying out, usually with a tree or large shrub involved. The dominant mechanism in South East England and a real but smaller factor across Yorkshire.
- Washout - water from a defective drain, culvert or watercourse carrying fine material out from beneath a foundation. Common, local, and comparatively cheap to fix once identified.
- Void collapse - ground settling into shallow mine workings or a shaft. The Yorkshire mechanism, and site-specific rather than general.
- Made ground settlement - fill of variable composition and compaction consolidating unevenly, which is really a foundation design problem rather than subsidence proper.
- Dissolution - soluble strata such as gypsum dissolving, which around Ripon can produce genuine sinkholes and is confined to a small area.
Note what is not on that list: a crack. Cracking is evidence that something moved. It is not a diagnosis, and it cannot tell you on its own which of these mechanisms - if any - is in play.
Heave: the one that catches people out
Heave is the opposite of clay shrinkage and it is frequently caused by trying to solve it. Remove a mature tree from shrinkable clay and the soil that the tree had been drying out for decades gradually rehydrates and swells, lifting whatever is founded on it. The movement is slow, it can continue for years, and the damage pattern is different from subsidence.
This is why an engineer will not simply tell you to cut down the tree. On the wrong soil, removing a large tree close to a shallow-founded building can cause more damage than leaving it, and the sensible answer is often managed reduction rather than removal.
How an engineer tells them apart
By evidence, in a sequence, with the cheap stages first:
- Damage classification - the pattern, width and direction of cracking, judged against the BRE Digest 251 damage categories rather than by eye
- Direction of movement - whether the evidence says something dropped, rose, or moved sideways, which separates subsidence from heave from landslip immediately
- Corroborating evidence - floor levels, door and window fit, external distortion, fractured service pipes
- Age - decorated-over, dirt-filled cracking against fresh, clean-edged cracking, and whether previous repairs have themselves moved
- Desk study - geology, mining records, historic mapping, watercourses and drainage
- Drainage testing, because washout is common and cheap to rule in or out
- Vegetation survey where clay is a candidate - species, distance, mature height
- Monitoring across a full seasonal cycle, which is what actually establishes whether movement is progressive or cyclical
- Trial pits and, only where justified, ground investigation
Monitoring is the stage people want to skip and the one that most often decides the case. Ground and building movement varies through the year, so a record spanning an autumn and a spring tells you something that a single visit in July cannot.
What this means for you
If you have cracking and you have arrived at this page having typed the word subsidence, the most likely outcome is that you do not have it. Thermal movement, shrinkage, lintel deflection, wall tie corrosion, roof spread, an unsupported alteration and historic settlement between them account for the large majority of the damage we are asked to investigate.
We do not carry out repairs and we take no commission from anyone who does, so 'this is stable, leave it alone' is an answer we are free to give and give often. Where movement is genuinely progressive, establishing the mechanism is what makes the remedy proportionate - and underpinning is a last resort, not a first response.
Frequently asked questions
Is settlement the same as subsidence?
No. Settlement is the ground compressing under the building's own weight - normal, expected, and it finishes. Subsidence is the ground moving down for a reason unrelated to the building's load, and it continues until the cause is dealt with. Insurance policies treat them very differently, which is one reason the distinction matters.
Can a building have both?
Yes, and older properties often show historic settlement plus a separate, later problem such as a leaking drain washing out ground locally. That is exactly why an engineer looks for what is still moving rather than cataloguing everything that ever moved.
How long does it take to tell the difference?
Sometimes one visit, where the evidence is clear and the cracking is plainly decades old. Where it is not clear, monitoring across a full seasonal cycle is what settles it - months rather than days. No engineer can shorten a season, and anyone offering a definitive answer on progressive movement from a single summer visit is guessing.
Should I cut down the tree?
Not without advice. On shrinkable clay, removing a mature tree close to a shallow-founded building can cause heave that does more damage than the shrinkage did. Managed reduction is often the better answer, and the decision should follow an assessment rather than precede it.
Is underpinning the answer?
Rarely, and it should be the last option considered rather than the first. Repairing a leaking drain, managing vegetation, replacing a failed lintel, re-tying a cavity wall, or establishing through monitoring that the movement finished years ago all resolve far more cases than underpinning does.