You find a crack, you look it up, and within four minutes the internet has told you your house is falling down and uninsurable. For the subsidence UK homeowner in 2026, the reality is more boring and much better than that: most cracks are not subsidence, most subsidence cases are not underpinned, and the damage a badly handled claim does to a sale is usually worse than the damage the movement itself did.
The short answer
Subsidence is downward movement of the ground beneath your foundations, usually caused by clay soil shrinking in dry weather, a tree drawing water from that clay, or a leaking drain washing soil away. It is covered by standard buildings insurance, subject to a much higher excess than a normal claim. The insurer’s route is almost always investigate, monitor for a period, then fix the cause - underpinning is the last resort, not the first response.
The important thing to get right at the start is whether you have subsidence at all.
What subsidence is, and what it is not
Three different kinds of movement produce cracks, and they get confused constantly.
Settlement is a new building - or a new extension - compressing the ground under its own weight and finding its level. It happens in the first few years, then stops. Cracks from settlement are usually fine, vertical or near-vertical, and stable.
Thermal and moisture movement is the whole building expanding and contracting with the seasons. It produces hairline cracks in plaster, cracks that open in winter and close in summer, and cracking around the junctions of different materials. It is not a structural problem.
Subsidence is the ground itself moving downward, unevenly, taking part of the foundation with it. Because one part of the building drops and another does not, the wall tears. That is why the classic subsidence crack has a specific shape.
There is also heave, which is the opposite: clay swelling as it regains moisture, often after a large tree is removed. Heave pushes upward and can do as much damage as subsidence.
The warning signs worth acting on
No single sign is diagnostic. The pattern is what matters.
Diagonal, stepped cracking that follows the mortar beds in brickwork, running roughly at 45 degrees, typically starting at a weak point such as a window or door opening.
Cracks wider at one end than the other - usually wider at the top, tapering downward.
Width above about 3mm, and particularly cracks you can push a coin into. Hairline crazing in plaster is not this.
The same crack inside and outside, in corresponding positions.
Doors and windows sticking or dropping out of square in one part of the house but not others.
Rippling wallpaper at wall and ceiling junctions where there is no damp.
Movement that is getting worse, particularly after a long dry summer.
Risk factors that make subsidence more plausible: shrinkable clay soil, a mature tree or large shrub within roughly its own mature height of the building, a known drain problem, a history of mining or made-up ground, and an older property with shallow foundations. Two or three of those together plus a stepped crack is the combination that justifies a phone call.
The first thing to do - and it is not phone the insurer
Before you notify anyone, start a record. Photograph every crack with a ruler or a coin in shot for scale, and photograph it again from the same position every two weeks. Write the date on each one. A dated series of photographs showing whether a crack is moving is worth more to a loss adjuster than any description you can give them, and it is the single thing homeowners most often fail to produce.
While you are doing that, check the obvious cause. A leaking drain, a broken gully, a downpipe discharging into the ground beside the wall, or a soakaway that has failed will wash fine material out of the soil and is a very common trigger. It is also the cheapest possible outcome, because fixing the drain frequently fixes the movement.
What an insurance claim actually involves
Buildings insurance in the UK covers subsidence as standard, but the process is unlike any other claim.
Notify your insurer, not a builder. If you commission structural works yourself before notifying, you risk the claim. The insurer appoints a loss adjuster, who usually appoints a structural engineer.
Expect a high excess. Subsidence carries a separate, substantially higher excess than the rest of your policy - commonly a four-figure sum. Check your schedule before you notify, because on a small crack the excess can exceed the likely cost of repair, in which case a claim may not be in your interest at all.
Expect monitoring. The engineer will typically install telltales or survey levels and monitor movement across at least one full seasonal cycle - often twelve months, sometimes longer. This feels like nothing happening. It is not. Distinguishing live movement from historic movement is the entire question, and no competent engineer will underpin without it.
Expect cause removal before structural works. If the cause is a tree, the answer may be pruning or a managed reduction rather than felling - removing a mature tree from clay can cause heave, which is a bigger problem than the one you started with. If the cause is a drain, the drain is repaired. In a large share of cases, that is where it ends: cause removed, movement stops, cracks repaired cosmetically, no underpinning.
Underpinning is the last option. It is disruptive, expensive, and it creates a permanent stiff point in a building that can generate new movement elsewhere. Good engineers avoid it where the cause can be removed instead.
At the end, ask for a certificate of structural adequacy and the full engineer’s report and monitoring data. Those documents are what you will hand a future buyer, and they are worth more than the repair itself.
What it does to your sale
This is where homeowners lose real money, and usually not for the reason they expect.
A properly investigated, properly repaired, properly documented subsidence claim is not a disaster. An undocumented crack that a buyer’s surveyor finds first is. The difference is not structural, it is informational. A buyer facing a full engineer’s report, monitoring data and a certificate of structural adequacy is buying a known, closed problem. A buyer whose surveyor flags “evidence of historic movement, further investigation recommended” on a house with no paperwork is buying an open-ended risk, and will price it like one or walk. The single most valuable thing you can do for your future sale price is keep the file - and the second is to stop treating the word subsidence as something to be managed with silence.
Practically, you should expect to disclose. The property information form asks directly about structural problems and insurance claims, and answering it inaccurately is a serious problem rather than a negotiating tactic. You should also expect the insurance to matter: a property with a subsidence history is harder to insure with a new insurer, though specialist underwriters exist and an existing insurer will normally continue cover. Tell your buyer early that the policy can be discussed with the incumbent insurer - it removes the objection before it becomes a price cut.
What to do in the next 30 minutes
Photograph every crack, inside and out, with a coin or ruler in shot and today’s date recorded.
Measure the widest point of the worst crack and write the figure down.
Walk the outside of the house and check every downpipe, gully and drain cover for leaks or standing water.
Note the distance from the house to any mature tree, and identify the species if you can.
Find your buildings insurance schedule and read the subsidence excess before you decide whether to notify.
Set a calendar reminder to repeat the photographs in two weeks from the same spot.
That photo series is the whole thing, and it only works if you can find the earlier pictures months later. Home+ gives you a free, date-stamped place to log each crack against the property and to keep the engineer’s report, monitoring data and certificate of structural adequacy in one file for the day you sell. Photo-log cracks in Home+ from the first one, not the fifth.
FAQ
Is every diagonal crack subsidence? No. Diagonal stepped cracking is the characteristic pattern, but thermal movement, lintel failure and historic settlement all produce diagonal cracks too. The pattern, the width, whether it appears inside and out, and whether it is changing over time are what separate them.
Does buildings insurance cover subsidence? Standard UK buildings policies cover subsidence, heave and landslip as standard, subject to a separate and much higher excess. Check your schedule for the figure before you notify.
Will my house be underpinned? Probably not. The usual route is investigate, monitor across a seasonal cycle, then remove the cause - most often a drain repair or tree management. Underpinning is reserved for cases where movement continues after the cause has been addressed.
Should I cut down the tree? Not without advice. Removing a mature tree from shrinkable clay can cause heave as the soil rehydrates, which can be more damaging than the subsidence. It may also be protected by a TPO or a conservation area designation. Get the engineer’s view first.
Can I still sell a house that has had subsidence? Yes, and people do routinely. What determines whether you sell at a normal price is the quality of the documentation: engineer’s report, monitoring records, evidence the cause was removed, and a certificate of structural adequacy.
Do I have to tell a buyer about a past claim? The property information form asks about structural movement and insurance claims and must be answered honestly. Take the wording of your answers from your conveyancer rather than deciding yourself what counts.
