The short answer
Yes — suspected subsidence is exactly the kind of problem a chartered structural engineer exists to diagnose. Cracks alone don't prove subsidence; many are harmless shrinkage or thermal movement. An engineer inspects the cracks, the building and the ground, works out the likely cause (clay shrinkage near trees, a leaking drain washing out soil, made-up ground, or simply old settlement), and judges whether the movement is active or historic. They may recommend a period of monitoring before any repair. If your home is insured, subsidence is usually a claim, and the insurer will appoint their own engineer or loss adjuster — but an independent engineer protects your interests. Underpinning is a last resort, not an automatic answer.
The word 'subsidence' triggers panic, but most cracks aren't it, and even real subsidence rarely needs the drastic fix people fear. The engineer's first job is diagnosis, not repair. Here's how it works.
Subsidence & cracks
- Engineer neededYes — to diagnose
- First stepInspection, not repair
- Common causesClay/trees, drains, made ground
- Often advisedMonitoring before action
- InsuranceUsually a claim; insurer engages own engineer
Not every crack is subsidence
Most cracks in a home are cosmetic. New plaster shrinks, materials expand and contract with temperature and humidity, and a settling house produces fine hairline cracks that never get worse. Subsidence specifically means the ground beneath the foundations is moving downwards or sideways, taking the foundation with it — and that produces a distinct pattern: cracks that are wider at the top than the bottom (or vice versa), diagonal, wider than about 3mm, that pass through both inside and outside walls, and that are getting worse over time. Doors and windows sticking, and gaps opening between an extension and the main house, can be further signs.
Because the signs overlap with harmless movement, the engineer's value is telling them apart. Replacing or underpinning on a misdiagnosis wastes large sums; ignoring genuine progressive movement risks the structure. That judgement — active versus historic, structural versus cosmetic — is the core of the engineer's report.
Finding the cause
If movement is real, the engineer's next task is the cause, because the cause dictates the cure. Common UK causes include:
- Clay shrinkage: shrinkable clay soils dry out and shrink in hot, dry spells, especially where trees or large shrubs draw moisture from the ground near the foundations. This is the most common cause in much of England.
- Leaking drains: a cracked drain or water main can wash fine soil away from under the foundation (sometimes called 'wash-out'), creating voids.
- Made-up or poorly compacted ground: fill or soft ground beneath part of the building can settle unevenly.
- Trees removed (heave): removing a large tree can let clay re-swell, causing the opposite problem — upward movement.
The engineer may arrange trial holes to inspect the foundations, a drain survey, and soil tests, then often recommends monitoring (measuring the cracks over months, sometimes a full year, to see if they are still moving). Acting only after monitoring confirms active movement avoids unnecessary work.
Insurance, the report, and what gets fixed
Subsidence is a standard peril on most UK buildings insurance policies. If you suspect it, contact your insurer early: they typically appoint their own engineer or loss adjuster to investigate, and the policy may cover the cost of investigation and any necessary repair (subject to your subsidence excess, which is often higher than the standard excess). Many homeowners also commission an independent structural engineer so they have an opinion that isn't the insurer's, particularly if there's any disagreement about cause or scope.
The fixes are usually less dramatic than people fear. If the cause is a tree, managed pruning or removal may stabilise the ground. If it's a leaking drain, repairing the drain may be enough. Underpinning — deepening or strengthening the foundations — is a genuine last resort used only where the movement is significant and won't otherwise stop. An engineer who jumps straight to underpinning without diagnosing the cause should be questioned.
| Cause | Typical first response | Underpinning? |
|---|---|---|
| Tree/clay shrinkage | Manage or remove tree; monitor | Only if movement persists |
| Leaking drain | Repair drain; monitor | Rarely needed |
| Made-up ground | Assess extent; targeted repair | Sometimes |
| Historic settlement | Cosmetic repair only | No |
Indicative responses by cause. Sources: RICS and Subsidence Support guidance; insurer practice.
When to call an engineer about cracks
You don't need an engineer for every hairline crack, but you should get one in if cracks are wider than about 3mm, diagonal, getting visibly worse, appear on both the inside and outside of the same wall, or are accompanied by sticking doors and windows or a gap opening up where an extension meets the house. Cracks that suddenly appear after a hot dry summer, near a large tree, or after a drain problem are also worth a professional look. A structural engineer's inspection and report typically costs in the region of a few hundred pounds and is the fastest route to a clear answer — whether that's 'cosmetic, leave it', 'monitor for six months', or 'here is the cause and here is the proportionate fix'. It is also the document a buyer's surveyor or solicitor will want if you sell, so keeping the report on file pays off later.
It helps to understand why monitoring is so often the engineer's first recommendation rather than an immediate repair, because homeowners sometimes read a 'wait and watch' answer as the engineer being unhelpful. The opposite is true: clay-related subsidence is seasonal, worsening through a hot dry summer as the ground shrinks and partly recovering in a wet winter as it re-swells, so a crack measured once tells you very little. By fitting tell-tales or taking careful measurements across a full cycle of seasons, the engineer can distinguish movement that is still active from movement that has stopped — and that single distinction decides whether you need a few hundred pounds of cosmetic repair or a major intervention. Acting too early, before monitoring has confirmed the movement is genuinely progressive, is how people end up paying for underpinning that was never needed. A patient, evidence-led diagnosis protects both the building and your money, and it is exactly the discipline that separates a chartered structural engineer's assessment from a builder's guess at a crack.
Frequently asked questions
Are all cracks a sign of subsidence?
No — most cracks are harmless shrinkage, thermal movement or finished historic settlement. Subsidence cracks tend to be diagonal, wider than about 3mm, present on both sides of a wall, and getting worse over time. A structural engineer can tell the difference.
Should I tell my insurer about suspected subsidence?
Yes. Subsidence is a standard peril on most UK buildings insurance, and the insurer will usually appoint their own engineer or loss adjuster to investigate. Contact them early; the policy may cover investigation and repair, though the subsidence excess is often higher than normal.
Will I need underpinning?
Usually not. Underpinning is a last resort used only where movement is significant and won't stop once the cause is addressed. Many cases are resolved by managing a tree, repairing a leaking drain, or simply monitoring confirmed-historic cracks. An engineer should diagnose the cause before recommending underpinning.
Sources & further reading
- RICS — subsidence and your home
- Institution of Structural Engineers — find an engineer
- HomeOwners Alliance — subsidence guide
Figures on this page are typical UK ranges drawn from published sources and depend on your specific project. They are guidance, not a quotation.