How do I know whether cracking is serious?

Width alone is a poor guide. A surveyor looks at the pattern, where the crack runs relative to openings and structure, whether it is tapering, and whether it is progressive. Where movement may be active, monitoring or a structural engineer's involvement is recommended.

Do I need a chemical damp-proof course?

Frequently not. Injection treats one specific cause. Bridged cavities, raised ground levels, failed rainwater goods and condensation are far more common in practice, and none of them are cured by injecting a wall.

Is thermal imaging proof of a defect?

No. It shows temperature differences, which can indicate missing insulation, air leakage or moisture. It is supporting evidence, interpreted with other findings, not a standalone diagnosis.

Can a building surveyor sign off structural work?

No. Structural design and calculations are the work of a structural engineer, and statutory sign-off sits with building control.

Building surveyor (building pathology and defect diagnosis)

Building surveyors: diagnosing what is actually wrong

Building surveyors diagnose defects: damp, cracking, roof failure, timber decay and movement. See how a diagnosis is reached.

Ask KJ about this property concern 01706 318200

Last reviewed 31 August 2026

What does a building surveyor do when something is wrong with a building?

A building surveyor investigates defects and explains their cause, not just their appearance. The discipline is building pathology: reading the symptom, testing it against how the building was constructed and how it is used, and separating the underlying cause from the visible damage. The output is a diagnosis, a recommended remedy and, where the visual limit is reached, a referral to the right specialist.

At a glance

Symptom versus cause: Damp on a wall is a symptom. Rain penetration, condensation and rising damp need different remedies.
Independent of remedial contractors: A surveyor with nothing to sell has no reason to recommend an unnecessary treatment.
Evidence used: Visual inspection, moisture readings, construction history and, where justified, thermal imaging or drainage CCTV.
Honest limits: Where a defect needs calculation, sampling or opening up, the report says so rather than guessing.

Why misdiagnosis is so common

Most defect reports in circulation are written by companies who sell the remedy. That is not automatically wrong, but it does explain why so many walls end up chemically injected when the real problem was a bridged cavity, a raised external ground level or a blocked gutter.

An independent diagnosis starts from the building: age, wall construction, ventilation, heating pattern and what has been altered. The same stain means different things in a solid-walled Victorian terrace and a 1990s cavity-walled semi.

Cracking and movement

Most cracking is not structurally significant. What matters is pattern, width, location and whether it is progressive. Thermal and moisture movement, settlement of new work, and subsidence all leave different signatures.

Where movement may be active or the building's stability is in question, the surveyor's job is to say so, recommend monitoring or investigation, and refer the structural design questions to a structural engineer. Structural calculations and engineering design are the engineer's work, not the surveyor's.

Water: the cause of most of it

Roof coverings, flashings, gutters, downpipes, flat-roof detailing, render cracks and failed pointing account for a large share of the defects found in older housing. Below ground, a collapsed or leaking drain can wash out ground beneath a foundation.

That is why an investigation often starts outside and above the reported problem, rather than at the wet patch itself.

What a good defect report contains

A statement of what was inspected and how; the evidence recorded; the most likely cause with the reasoning; alternatives that were considered and ruled out; the recommended remedy in order of priority; and a clear line on what still needs specialist investigation.

Who this is for

A good fit if

Owners with damp, cracking, mould or a leak nobody has been able to trace
Buyers whose survey recommended further investigation of a specific defect
Landlords responding to a tenant complaint about damp and mould
Anyone holding a remedial quotation they are not sure they need

Not the right choice if

Structural design, calculations or a formal structural stability opinion — that requires a structural engineer
Emergency make-safe works, which need a contractor on site first
Sampling and analysis of asbestos-containing materials, which requires an accredited specialist

Damp, mould and timber

Damp survey

Independent diagnosis separating penetrating damp, condensation and rising damp.

Condensation and mould survey

Ventilation, heating and thermal bridging assessed together.

Timber and rot survey

Wet rot, dry rot and the moisture source keeping it alive.

Woodworm survey

Whether infestation is active and whether treatment is justified.

Crack and movement survey

Pattern, width and progression assessed before anyone talks about underpinning.

Subsidence investigation

Cause, contributing factors and the evidence an insurer will expect.

Structural survey report

Detailed condition reporting where stability has been questioned.

Cavity wall tie survey

Corroded ties, horizontal cracking and the bulging that follows.

Roof survey

Coverings, flashings, structure and the detailing that usually fails first.

Drone roof inspection

Close visual inspection where safe access is not practical.

Render and external wall survey

Cracked, hollow or inappropriate render trapping moisture in the wall.

Chimney survey

Stack condition, flaunching, flues and redundant stacks left in place.

Drainage CCTV survey

Camera survey of below-ground drainage, often the missing piece.

Thermal imaging survey

Thermal patterns used as supporting evidence, never as proof on their own.

What to do before you spend anything

The order matters more than the money.

1.Record the symptom over time
Dated photographs, when it appears, and whether it follows rain, cold weather or use of a room. This evidence shortens the investigation.
2.Get the diagnosis before the quotation
A remedial quotation assumes a cause. If the cause is wrong, the work is wasted however well it is carried out.
See how a damp diagnosis works
3.Act on the priority order, not the loudest symptom
Rainwater goods and roof detailing first, internal redecoration last. Fixing the finish before the cause simply resets the clock.

When to bring in a specialist

Structural calculations, stability opinions, underpinning design and movement monitoring — structural engineer
Asbestos identification and sampling — accredited asbestos specialist
Electrical installation condition — a qualified electrician
Trees, root activity and shrinkable clay soils — arboricultural consultant
Insurance claims and policy cover — your insurer and broker

Common questions

Limitations and sources

Diagnosis is based on a visual inspection of accessible areas plus any measurements taken on the day, and cannot describe concealed construction.
Meter readings on wall surfaces are indicative, not definitive; they are interpreted alongside construction and use, never in isolation.
KJ can discuss a defect in general terms online, but until a surveyor has inspected the building, nothing said is a professional opinion on your property.

Source: RICS · checked August 2026

Source: UK Government · checked August 2026

Source: Historic England · checked August 2026

Last reviewed 31 August 2026.

Where to go next

a full survey rather than a single defect — If you are buying, a whole-building report is usually the better starting point.
the same defect in commercial premises — Repair liability then depends on the lease as well as the building.
damage you believe a neighbour's work caused — Where notifiable works are involved, the Act provides its own route.

Describe the defect to KJ

Photographs help. Say when it appears, how long it has been there and what has already been tried.

KJonline

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Hi, I'm KJ. Tell me about the property or the surveying advice you need and I'll help you work out the right next step.

KJ gives general guidance only and has not inspected your property. A professional opinion follows an inspection by a surveyor.