Proving a defect: what evidence holds before a judge
Proving a construction defect before a Belgian judge does not consist of showing that a defect exists — an iPhone photo does that. It is about demonstrating that this defect, on this date, at this place, results from a fault attributable to the contractor, and that it engages his contractual or ten-year liability. This legal qualification requires an enforceable chain of evidence combining dated photos, official records, adversarial expertise and contractual documentation. A well-visible but poorly documented defect loses 80% of its evidential force in procedure. This page synthesises the construction of a solid defect evidence file, from amateur finding to expert report.
Why legal proof is built, not merely observed
In Belgian law, the burden of proof falls on the plaintiff — it is the buyer or owner who must demonstrate the fault, the prejudice, and the causal link. The contractor does not have to prove his innocence; it is up to you to prove his fault.
Yet construction defects present three particularities that complicate proof: they evolve over time (a crack propagates, an infiltration spreads), they can be masked by the contractor after reception (filling, painting), and they often involve technical questions the judge is not equipped to settle alone.
Hence the necessity of an evidential chain combining several natures of evidence, hierarchised by increasing evidential force: amateur photos < registered letter < bailiff record < amicable expertise < judicial expertise. The higher the stake, the further down the chain you must go.
The photographic chain: to handle with rigour
Your photos have little intrinsic value: any modern smartphone produces them, and their authenticity can be contested (tampered date, recropping, retouching). For them to become enforceable defect evidence, they must satisfy five cumulative criteria:
- Preserved EXIF metadata: date, time, GPS, device model. Systematically activate geolocation.
- Visible scale: ruler, tape measure or reference object in the frame.
- Contextual localisation: a wide shot situating the photo in the room, then a close-up of the defect.
- Written referencing in a letter or report dated from the same period. An isolated photo is weak; a photo annexed to a registered letter of the same day is strong.
- Double storage: cloud + local disk. Data losses are frequent after several years.
A photo sent by WhatsApp or SMS loses all its EXIF metadata during compression; its evidential value is divided by ten. Always transfer by email attachment or store directly from the device.
For evolving defects (cracks, infiltrations), take photos dated at regular intervals (D+0, D+30, D+90) with adhesive crack gauges: this demonstrates the evolving character of the disorder, key element to qualify a ten-year liability.
The bailiff record: strong evidence outside procedure
The bailiff record for defects is the strongest evidence accessible outside judicial procedure. The judicial bailiff is a ministerial officer: his official report stands as authentic until inscription of forgery (a rare and heavy procedure).
Procedure: you contact a bailiff, set an appointment (generally within 5 to 10 days), the bailiff visits the property, observes, measures, photographs with his professional equipment, and drafts an authentic report delivered within 5 to 15 days. The authentic report timestamps the facts, identifies the places and defects, without legal qualification (the bailiff observes, he does not judge).
Cost: 180 to 400 € depending on complexity and travel. Pricing regulated by the FPS Justice. Profitable investment from 3,000 € of potential stake. Find a competent bailiff in the directory of the National Chamber of Judicial Bailiffs (huissiersdejustice.be).
Limitation: the bailiff observes the apparent state, he does not expertise technically. To qualify the cause of a crack or impute a defect to an execution fault, a technical expert is needed in addition.
The adversarial technical expertise
The adversarial amicable expertise brings together the technical expert, the buyer and the contractor (and his insurer if applicable) on the property. The expert observes, measures, possibly samples (material samples for laboratory analysis), audits the contractual documents, and issues a technical opinion on the cause and attribution of the disorder.
Evidential force: an adversarial expertise report signed in an adversarial manner (or notified to the contractor who refused to participate) has a very high evidential force before a judge. In more than 70% of cases, the report is enough to reach a transactional agreement without judicial procedure — the contractor prefers to negotiate rather than expose himself to a trial he knows is lost.
Cost: 800 to 3,500 € depending on complexity, surface, number of disorders, travel and laboratory analyses. It is more expensive than a bailiff record, but infinitely cheaper than a judicial procedure (8,000 to 25,000 €) and the normal step between amicable and contentious.
If the contractor refuses adversarial expertise, you can carry out a documented unilateral expertise — less powerful but useful to support a formal notice or request a subsequent judicial expertise. See judicial construction expertise.
Case study: 14,200 € obtained without procedure thanks to expertise
A representative case followed by the firm in 2025: house received in 2023, infiltrations in the kitchen wall appeared at T+18 months. The contractor, contacted, denies any execution defect and invokes an “unforeseeable exterior infiltration”.
Sequence undertaken by the owner:
- Bailiff record (220 €) at T+18 + 7 days, photographic documentation of damage.
- Adversarial technical amicable expertise by the firm (1,100 €) at T+18 + 30 days. Report: sealing defect of the south window lintel, characterised execution fault, attributable to the contractor under perfect completion guarantee and then two-year warranty.
- Formal notice annexing the two reports (see formal notice to contractor).
- Contractor reaction within 15 days: acknowledgement of the fault, proposal of complete repair + compensation for material damage.
Result: 14,200 € of works and compensation obtained without procedure, file closed in 70 days. Total cost of evidence: 1,320 €. Ratio: 10.8 € recovered for 1 € invested in evidence.
Pitfalls to avoid in building the file
- Photos without context: near-zero evidential value.
- No record or expertise on stake > 3,000 €: fragile file.
- Communication by telephone only: no trace.
- Waiting too long: prescription, evidence degradation, unavailable witnesses.
- Mixing minor and major defects: dilutes the file’s strength.
- Refusing adversarial expertise: closes the amicable route and forces judicial.
What to do upon suspicion of defect
The efficient reflex upon suspicion of defect: document immediately (photos, measurements, crack gauges), send a registered observational letter without precipitous legal qualification, and mobilise an expertise within 30 days. The Mon Etat Des Lieux firm offers its defects expertise service producing a circumstantial technical report that is enforceable, a solid basis for formal notice, mediation or court. For the detection phase, see also detecting defects. Request a free quote within 24 hours.