Subsidence is the downward movement of the ground under a building’s foundations, usually because clay has dried and shrunk or a leaking drain has softened or washed away the soil. Most house cracks are not subsidence, and the cracks that matter most are those that are new, getting wider, wider at the top than the bottom, or more than about 3 mm across. If you suspect subsidence, photograph and date the cracks, contact your buildings insurer, and have a chartered structural engineer inspect the property before any repair is chosen.
Subsidence, settlement, heave or landslip: what is the difference?
These words get used loosely, but they describe different things, and the difference changes what happens next. A surveyor who writes “historic settlement” in a mortgage report is saying something quite different from an insurer’s engineer who confirms “subsidence”.
| Term | What is happening | Typical pattern |
|---|---|---|
| Subsidence | The ground supporting the foundations moves downwards, for example clay shrinking or soil washed out by a leaking drain | Can continue or recur, often seasonally on clay |
| Settlement | The building compresses the ground beneath its own weight | Usually early in a building’s life, and usually stops |
| Heave | The ground moves upwards, typically as clay swells after a large tree is removed or the ground is saturated | Can lift part of a house and crack it in the opposite direction to subsidence |
| Landslip | Ground on a slope moves downhill, taking foundations with it | Linked to sloping plots, retaining walls and water |
Definitions here follow the RICS consumer guide on subsidence and NHBC Standards chapter 4.2. Only an engineer’s inspection, and sometimes investigation and monitoring, can say which one, if any, is affecting a particular house.
What causes subsidence in Liverpool and Merseyside homes?
The RICS consumer guide names two main causes: shrinkable clay soils drying out in long dry spells or because trees and shrubs draw moisture from them, and leaking drains or water mains softening or washing away soil, most often in sandy or gravelly ground. RICS cites Which? as saying tree roots cause about 70% of cases.
Clay, trees and dry summers
The British Geological Survey describes much of the Liverpool district as covered by glacial till, commonly called boulder clay. Clay soils change volume as their moisture content changes. NHBC Standards list oak, poplar, willow, elm, hawthorn and eucalyptus among the high water demand species, with most other broad-leaved trees moderate. For new foundations, NHBC uses a zone of influence of roughly 1.25 times the mature height for high-demand trees, 0.75 times for moderate and 0.5 times for low. Older houses were not built to those rules, which is why a mature tree a few metres from a 1930s bay can matter.
Felling a large tree on clay is not a cure. The ground can take years to rehydrate and swell, causing heave. Any tree work should follow advice from an arboriculturist and the engineer, and protected trees need council consent first.
Leaking drains and sandy ground
Along the Sefton and north Wirral coasts there is blown and dune sand, and fine sandy soils are easily washed away by a leaking drain. Old clay drainage pipes crack and lose joints over time, and a slow leak can soften clay or carry fines away for years before cracking shows. A CCTV drain survey is the normal way to check. Since 1 October 2011, shared private sewers and lateral drains beyond a property boundary have been the responsibility of the water company in England, which for Merseyside is United Utilities; the homeowner stays responsible for drains within their own boundary that serve only their property.
Made ground, soft deposits and mining
Parts of the city region include poorly compacted made ground, backfilled former clay pits dug for brickmaking, and softer alluvium or peat. These can compress under load. Parts of St Helens lie on the former Lancashire Coalfield; the free GOV.UK service “Find out if a property is affected by coal mining” shows whether a mining report is advised for a postcode. Mining subsidence claims go to the Mining Remediation Authority, formerly the Coal Authority.
Which cracks matter, and which are cosmetic?
BRE Digest 251 grades crack damage from category 0 to 5. BRE describes categories 0, 1 and 2, cracks up to about 5 mm, as aesthetic damage that usually needs only redecoration. Categories 3 and 4 are serviceability damage, affecting weather-tightness and the operation of doors and windows. Category 5 is stability damage that is likely to need structural intervention.
| BRE category | Type of damage | What it usually means |
|---|---|---|
| 0–2 | Aesthetic | Hairline to fine cracks, usually redecoration, though growth over time still matters |
| 3–4 | Serviceability | Wider cracks, doors and windows sticking, possible water getting in; repairs to the structure are likely |
| 5 | Stability | Severe damage where structural intervention is likely to be needed |
Width is not the only factor. A crack that keeps getting wider is more significant than one that has stayed the same for years, which is why monitoring matters. RICS says cracks that appear suddenly and are wider than 3 mm are the main cause for concern.
What do common crack patterns often point to?
Patterns help an engineer form a view, but none of them is a diagnosis on its own. These are the patterns that most often prompt a call:
- Tapering cracks wider at the topOften linked to part of the building dropping away, as with subsidence at a corner or under a bay.
- Cracks continuing below the damp-proof courseCracks that run down into below-ground masonry are commonly associated with foundation movement rather than surface shrinkage.
- Diagonal cracks from window and door cornersOpenings are weak points, so movement often shows there first; a failed lintel can produce similar cracks without any ground movement.
- A crack where an extension meets the houseOften a sign the two parts are on different foundations and moving differently.
- Horizontal cracks every few coursesRegular horizontal cracking in mortar, roughly every six courses, is often linked to corroding wall ties rather than the ground.
- A wall bulging or leaning outCan come from failed ties, missing restraint at floors or roof, roof spread or foundation movement.
Several of these are not ground problems at all. Corroded ties call for wall tie replacement, and cracking above openings may point to lintel replacement rather than anything to do with the foundations. That is why the cause is found by inspection, not guessed from a photo.
What other signs suggest subsidence?
- doors and windows that start sticking or jamming for no clear reason;
- wallpaper rippling or tearing at the joins, especially where walls meet ceilings;
- a new slope in a solid floor, or skirting boards pulling away;
- a bay window, porch or conservatory pulling away from the main walls;
- cracks that reopen after redecoration, particularly after a dry summer.
What should you do if you notice cracks?
- Record them. Photograph each crack with a ruler or coin beside it, write the date and measure the widest point. Repeat every few weeks.
- Note other changes. Write down doors or windows that start sticking and when.
- Contact your buildings insurer if you suspect subsidence. The insurer and its loss adjuster decide on investigation, monitoring and repairs.
- Do not fill and paint over the cracks. The way a crack changes is evidence an engineer needs, and hiding past movement from an insurer, buyer or lender causes serious problems later.
- Leave trees alone for now. Do not fell or heavily prune without advice, and check with your council whether a tree is protected or in a conservation area.
- Keep gutters and drains working, and do not start building work near the affected area.
- Get a chartered structural engineer to inspect, through your insurer if a claim is involved or privately if not.
If cracks open quickly, a wall leans noticeably, or a doorway or ceiling looks unsafe, keep people away from the area and get urgent professional advice. The council’s building control (dangerous structures) team deals with dangerous buildings. If movement damages a gas pipe and you smell gas, leave and call the National Gas Emergency Service on 0800 111 999.
How is the cause of movement found?
An engineer starts with a structural survey: the crack pattern, the age and construction of the house, trees, drains, extensions and the lie of the land. Where that is not enough, investigation follows. Trial pits show the depth and condition of the footings and whether roots are present; soil samples tell the engineer how shrinkable the clay is; a CCTV survey checks the drains. Our page on soil and site investigation covers these in more detail.
Monitoring is often the deciding step. RICS notes cracks may need measuring for around 12 months or longer to tell seasonal movement on clay from progressive movement. Tell-tale gauges, calibrated crack-width studs and level surveys are typical, and crack and movement monitoring gives the engineer readings through a full wet and dry cycle.
What are the repair options?
For most houses the order is: remove the cause, let the ground stabilise, then repair. Drains are repaired or relined; vegetation is managed on expert advice; and once readings show the building has stopped moving, the damage is put right through structural crack repair, sometimes with helical bar stitching to tie cracked masonry together. Crack repair does not stop ongoing foundation movement, so it only comes after the cause has been dealt with.
Underpinning is for cases where the cause cannot be removed, the footings are too shallow for the ground, or movement will continue without it. RICS says fewer than 5% of affected properties need it and that the Institution of Structural Engineers recommends it only as a last resort. When it is needed, the engineer chooses between methods such as mass concrete, mini-piles, beam and base or resin injection, and the work needs Building Regulations approval. Our main page on underpinning in Liverpool explains the methods, and the underpinning cost guide covers what drives the price.
Buying or selling a house with past subsidence
Past movement does not make a house unsellable, but it has to be disclosed and explained. Buyers’ surveyors and solicitors will usually ask for the engineer’s reports, details of the cause and how it was dealt with, any Building Control completion certificate, and, after an insurance repair, the certificate of structural adequacy that the insurer’s engineer often provides. Insurers commonly ask about past subsidence too. If you are buying, a structural engineer’s inspection can tell you whether cracks look historic or active before you commit. In terraces and semis, any future underpinning will usually need the Party Wall etc. Act 1996 to be considered, as explained on our party walls and underpinning page.
When should you call a professional?
Call for advice if cracks are new, growing, wider than about 3 mm, wider at the top than the bottom, or accompanied by sticking doors and windows or sloping floors, or if a buyer, lender or insurer has raised movement. You do not need to know what is causing it; that is the engineer’s job. As a contractor offering local underpinning and subsidence repair across Merseyside, we can talk through what you have seen, visit, and recommend the investigation that makes sense before any repair is decided.
Worried about cracks in your home?
Call 07777 659786 and tell us where the cracks are, roughly how wide, whether they are changing, and whether an insurer or buyer is involved. We will explain the sensible next step, which is often investigation rather than repair.
Frequently asked questions
How do I know if a crack is subsidence?
You cannot tell for certain from the crack alone. Warning signs include cracks that are new or widening, wider at the top, more than about 3 mm, running below the damp-proof course, or appearing with sticking doors and windows. A chartered structural engineer has to inspect, and sometimes monitor, before anyone can say whether ground movement is the cause.
Are hairline cracks in a new extension a problem?
Fine cracks in new plaster are very common as materials dry out and the structure beds in, and BRE treats damage up to about 5 mm as aesthetic. Keep an eye on them. If a crack keeps widening, appears where the extension meets the house, or doors start sticking, have it looked at by an engineer.
Does subsidence get worse in summer?
On shrinkable clay it often does. Long dry spells and trees drawing water from the soil make clay shrink, so cracks can open in late summer and partly close again over a wet winter. That seasonal pattern is one reason monitoring often runs for around 12 months, so the engineer can see a full cycle.
Should I cut down a tree near my house?
Not without advice. Removing a large tree on clay can let the ground swell and cause heave, which can be as damaging as the original shrinkage. Speak to your insurer if a claim is involved, follow an arboriculturist’s and engineer’s advice, and check with your council whether the tree is protected or in a conservation area.
Will my insurance cover subsidence?
Buildings insurance usually covers subsidence damage to the home, according to the ABI, with a higher excess than standard claims. Garden walls, patios and drives are usually only covered if damaged at the same time as the house. Contact your insurer first: it decides on investigation and the repair, and no contractor can promise a claim will be accepted.
Can cracks be repaired without fixing the foundations?
Often yes. Most subsidence is resolved by dealing with the cause, such as a leaking drain, letting the ground stabilise and then repairing the masonry and plaster. Repairing cracks before the cause is known, though, risks them reopening and hides evidence an engineer needs, so the order matters.