Most cracks in a house are not subsidence. Buildings move seasonally with moisture in the ground, materials expand and contract with temperature, and normal settlement produces hairline cracking that is cosmetic rather than structural. Genuine subsidence, where the ground beneath the foundations actually moves downward, produces a more specific pattern of symptoms that tends to worsen over time rather than staying static. This guide sets out how to tell the difference, what to monitor if you are unsure, and what investigation and repair typically involve if subsidence is confirmed.
Why cracks happen at all
Buildings move continuously on a small scale. Clay soils shrink in dry summers and swell again in wet winters, timber and masonry expand and contract with temperature, and new extensions settle slightly as foundations bed in. None of this is necessarily a problem — it becomes significant when the movement is one-directional, ongoing, and linked to a specific cause such as ground shrinkage, a leaking drain, or a removed tree.
Tell-tale signs beyond the cracks themselves
Cracks are the most visible symptom, but other signs often appear alongside genuine subsidence and are worth checking for together rather than relying on cracking alone.
- Doors and windows binding or no longer closing square
- Wallpaper creasing at the junction between wall and ceiling
- Gaps opening up between a bay window and the main house wall
- Sloping floors that were previously level
- Cracks appearing on both internal and external leaves at the same location
Seasonal movement is a genuine clue
Subsidence linked to clay shrinkage typically worsens in late summer, when clay soils have dried out and shrunk the most, and can appear to close up slightly over winter as the ground rehydrates and swells back. If a crack visibly changes width through the seasons rather than staying static, that seasonal pattern is a meaningful indicator worth recording.
Using tell-tales to monitor movement
A tell-tale is a simple monitoring strip, often a small glass or plastic gauge, fixed across a crack to record any change in width or alignment over time. Photographing a crack against a ruler at regular intervals achieves a similar result. Monitoring over several months, ideally spanning a dry and a wet season, gives a far more reliable picture than a single snapshot.
Distinguishing settlement, thermal cracking, subsidence and heave
These four causes of cracking are often confused, but they tend to show different characteristics in terms of width, direction and location, summarised in the table below.
| Type | Typical width | Direction | Typical location |
|---|---|---|---|
| Settlement (normal) | Hairline, under 1mm | Diagonal or vertical, stable over time | New extensions, near openings, first year or two |
| Thermal/material movement | Hairline to 2mm | Often horizontal at material junctions | Render joints, movement joints, junctions between materials |
| Subsidence | 3mm and above, widening over time | Diagonal, often wider at top | Corners, bay windows, near trees or drains |
| Heave | Can be wide, sudden | Often vertical, floor lifting | Areas where a tree was recently removed or a leak saturated ground |
These are general indicators only. Crack width and pattern alone cannot confirm subsidence — a structural engineer's assessment is needed for a reliable diagnosis.
Common causes worth checking first
Before assuming the worst, check for straightforward causes nearby: a leaking drain saturating the ground under one corner of the house, a large tree that has been planted, removed, or grown significantly since the house was built, or recent nearby excavation work. Addressing the cause is usually part of any effective repair, not just treating the symptom.
Investigation and repair cost ranges
If subsidence is suspected, a structural engineer's assessment, sometimes alongside a drainage survey and trial pits, establishes the cause and extent before any repair is designed. Costs vary enormously depending on cause and severity, but indicative ranges are set out below.
| Stage | Typical indicative cost (UK) |
|---|---|
| Structural engineer's assessment | £500–£1,500 |
| Drainage survey (CCTV) | £200–£600 |
| Trial pits/site investigation | £1,000–£3,000 |
| Root cause remedy (drain repair, tree removal) | £500–£5,000+ |
| Localised underpinning | £4,000–£10,000 per affected area |
| Full underpinning of a wall section | £10,000–£30,000+ |
Figures are broad indicative UK ranges for 2026, vary considerably by cause, extent and region, and are not a substitute for a proper survey. A site visit and engineer's assessment are needed for a realistic figure.
When to involve your insurer
Most UK buildings insurance policies cover subsidence, though usually with a specific excess for subsidence claims. If you suspect subsidence, it is worth notifying your insurer early, since many will arrange or fund the initial investigation, and delaying can complicate a future claim.
What the insurance claim process usually involves
Once notified, most insurers appoint a loss adjuster to visit the property, review the crack patterns and any monitoring evidence you have, and commission a structural engineer's report if one has not already been done. This typically leads to a period of monitoring, often six to twelve months, to confirm whether movement is ongoing before any repair scheme is approved and funded. Keep dated photographs, tell-tale readings and correspondence organised from the outset, since a clear record speeds up the assessment considerably. Claims involving underpinning or root cause works such as tree removal can take a year or more from first notification to completed repair, so it is worth being realistic about timescales, particularly where the cause involves a tree that needs a formal removal agreement with a neighbour or the local authority.
- Notify your insurer as soon as subsidence is suspected, not after a full diagnosis
- Keep a dated log of cracks, photographs and any tell-tale readings
- Ask the insurer to confirm what the monitoring period covers before it starts