This case study is based on a real instruction. Names, addresses and identifying details have been changed, and figures rounded, to protect client confidentiality.

The situation

Our clients had an offer accepted on a three-bedroom Victorian mid-terrace house in Wimbledon at £1.1 million. Their mortgage valuer had flagged “evidence of structural movement” and recommended a specialist report. The estate agent was telling them it was “just settlement, all these houses have it”. They asked us to find out which it was.

What we found on inspection

There was stepped diagonal cracking to the front bay, widening towards the top, with associated distortion to the bay roof and a hairline continuation internally at the corner of the front room. Doors on the ground floor front were binding. Externally, a mature street tree sat approximately seven metres from the front elevation.

The subsoil across much of this part of SW19 is London Clay, which shrinks in dry conditions and swells when wet. Combined with the shallow foundations typical of 1890s terraced housing and a nearby mature tree with a high water demand, this is a well-recognised risk pattern.

So the agent was wrong. This was not simply “settlement”, a term properly reserved for the initial bedding-down of a structure shortly after construction. The pattern here was consistent with clay-related seasonal movement, and possibly with active subsidence.

Establishing whether the movement was live

The distinction between historic and progressive movement is the whole question, and it is not answered by looking at cracks alone. Our investigation covered:

• Crack characteristics. The main cracks were open, clean-edged and unfilled, with no accumulated paint or debris — indicating relatively recent movement rather than decades-old damage.
• Repair history. Two older cracks elsewhere on the elevation had been filled and painted over, and had reopened. Recurrence is a significant indicator.
• Adjoining properties. The neighbouring house showed a matching crack pattern on its shared bay, suggesting a common cause affecting the pair rather than an isolated defect.
• Drainage. A gully immediately adjacent to the bay was blocked and overflowing at the time of inspection. Leaking or blocked drains are one of the most common contributors to clay movement and one of the cheapest to rectify.
• Insurance history. We advised the buyers to require the sellers to disclose the full claims history for the property. This produced a previous subsidence claim on the neighbouring property, settled some years earlier, with partial underpinning to that property’s bay.

What we recommended

We did not recommend walking away, and we did not recommend proceeding regardless. We recommended a sequence:

1. A CCTV drainage survey to establish whether the defective gully and any below-ground drainage were contributing.
2. Level monitoring over a minimum of twelve months, spanning at least one full seasonal cycle, before any decision on structural intervention. Underpinning a property that does not need it is expensive, disruptive and permanently affects marketability.
3. A structural engineer’s opinion on the bay specifically, given the visible distortion to the bay roof.
4. Written confirmation from an insurer that cover would be available on normal terms, obtained before exchange rather than after.

That last point is frequently overlooked. A property with a subsidence history can become difficult and expensive to insure, and where an existing insurer has settled a claim, continuity of cover with that insurer is often the practical route. Establishing this before exchange, rather than discovering the position afterwards, is essential.

The outcome

The drainage survey confirmed a fractured section of clay drain beneath the front garden. The engineer’s view was that the bay movement was capable of stabilising once the drainage was repaired, and that monitoring rather than underpinning was the correct first response.

The buyers renegotiated a £15,000 reduction covering drainage repair, monitoring costs and making good, and obtained an insurance quotation on standard terms subject to the drainage works. They proceeded and completed. Monitoring over the following year showed no significant progression.

What to take from this

• “All these houses have cracks” is not a diagnosis. Some cracking is benign. Some is not. The difference is established by investigation, not by reassurance.
• Underpinning is rarely the first answer. Identifying and removing the cause — very often drainage or vegetation — resolves a large proportion of clay-related movement.
• Sort insurance before exchange. It is far harder to fix afterwards.
• Ask about the neighbours. Terraced and semi-detached properties share ground conditions, foundations and, frequently, problems.

Frequently asked questions

What is the difference between subsidence and settlement?

Settlement is the initial downward movement of a building as it beds into the ground shortly after construction, and is generally not a continuing problem. Subsidence is the downward movement of the ground beneath the foundations for other reasons — commonly clay shrinkage, vegetation, or leaking drains — and can be progressive. The distinction matters for insurance, cost and saleability.

Should I buy a house with subsidence?

It depends entirely on the cause, whether the movement is active, whether the cause can be removed, and whether insurance is available on acceptable terms. Many properties with historic, resolved movement are perfectly sound purchases. The decision should follow investigation, not precede it.

Does a building survey cover subsidence?

An RICS Level 3 building survey will identify evidence of structural movement, assess its likely cause and significance, and advise on what further investigation is required. It is not a structural engineer’s report, and where movement appears active a surveyor will usually recommend specialist input — as we did here.

Do trees cause subsidence?

Trees can contribute significantly on shrinkable clay soils, because they draw moisture from the ground and cause it to shrink. Proximity, species and water demand all matter. Removing a mature tree is not always the answer, since ground heave on rewetting can cause its own damage, and street trees are frequently protected in any event.

Concerned about cracking?

Blakes Chartered Surveyors carry out RICS Level 3 building surveys across south west London and Surrey, including properties with known or suspected structural movement. We will tell you plainly what we think is happening, what it is likely to cost, and what to do next.

Call 020 7373 7373 or email info@blakessurveyors.com.