Hidden building defect discovered: investigate without losing evidence

1. A later-visible problem is not an established cause

Start with what you actually observe: location, extent, date and conditions. For example, note moisture occurring only after driving rain or a crack widening over several weeks. Avoid a confident diagnosis in the first notification when there has been no investigation. A leaking floor may have several causes; the location of the damage is not automatically where the error occurred.

Distinguish a defect in the original work from misuse, insufficient maintenance and damage caused by later intervention. Similar symptoms may have different causes. The expert therefore needs information about changes since completion. Honestly identify other businesses that worked there and your own alterations. A missing detail may later weaken an otherwise technically plausible conclusion.

2. Record what exists before it changes

Take overview and detail photographs with dates and identifiable locations. Keep original files and a measurement or observation log for recurring symptoms. Record who was present and what each person saw themselves. Retain messages in which the contractor explains connections, materials or previous repair attempts. Unconnected images without locations or a chronology are difficult to assess.

Also collect drawings, calculations, product information, maintenance instructions and the completion report. A consumer dossier may show what was actually built and which materials were used. IPLO distinguishes it from documents supplied to the authority. The statutory dossier rules do not automatically apply to agreements made before 1 January 2024, and parties may have made different arrangements. A missing dossier does not itself prove the cause of a leak.

3. Report suspicion and invite joint investigation

Report the problem promptly to the contractual contractor even before the final cause is known. Explain what you discovered, when and why further investigation appears necessary. Request a response and offer a practical inspection appointment. ACM ConsuWijzer recommends recording a specific complaint about defective work and allowing the business an opportunity to resolve it.

Separate the initial investigation from a later repair instruction. Allowing the contractor to investigate does not require acknowledging that you bear the cost or accept the diagnosis. Agree permissible openings before inspection. In a substantial financial dispute, discuss reservations with a lawyer and ensure investigation discussions do not delay a necessary complaint or other deadline.

Keep a separate limitation calendar alongside prompt notification. Article 7:761 BW generally time-bars a claim for a defect in completed work two years after the complaint. If you gave the contractor a period to remove the defect, limitation starts after that repair period, or earlier when the contractor says it will not repair. Record the complaint, repair deadline and any refusal. This is separate from whether the defect was reported promptly enough.

For structures, article 7:761 also provides an absolute period of twenty years from completion. During investigation or repair promised by the contractor, a statutory extension may apply under paragraph 3’s conditions; not every discussion automatically creates another two years. Before a possible expiry, assess timely interruption of limitation or proceedings. An ongoing telephone conversation, new inspection or insurer’s file is not itself a safe reason to disregard limitation.

4. Organise destructive investigation with a clear protocol

Ask the expert which question must be answered and why opening up is necessary. First consider whether less invasive measurements provide enough information. If destructive investigation is needed, record the locations, method and documentation. Give the contractor a reasonable opportunity to attend or respond unless a specific emergency makes delay impossible.

Photograph the overview, successive steps and details encountered. Retain removed materials potentially relevant to the cause, identifying their origin and date. The report should distinguish observations, inferences and unanswered questions. A technical conclusion without an explained method is harder to test. Where the parties fundamentally disagree, the lawyer can assess a joint investigation or procedural evidence measure.

5. Limit acute damage without needlessly erasing causes

Active leakage or suspected structural danger may make waiting irresponsible. Obtain appropriate technical assistance and limit further damage. Record as much as safely possible before intervention and immediately inform the contractor why it is necessary. Explain why an appointment weeks later was not a responsible alternative. Safety and damage limitation require an actual assessment, not a standard waiting period.

Separate emergency measures from permanent repair. Temporary sealing or securing a room need not mean replacing the whole structure. Ask the person doing the work to explain the findings and necessity of each intervention in the invoice and report. Spending does not automatically make costs recoverable. Necessity, extent, cause and liability must still be capable of proof later.

6. Assess liability with date and findings

For construction agreements made from 1 January 2024, IPLO explains article 7:758(4) BW: the contractor is liable for defects undiscovered at completion unless they are not attributable to it. The rule is not limited to something literally invisible. A visible but undiscovered defect may also fall within it. The contractor must substantiate non-attributability.

Completion may be assessed differently under older agreements. Discuss the exact contract date, what was known at completion and the applicable terms rather than relying only on the label “hidden defect”. Consumers cannot be disadvantaged by departures from the new protection. Meanwhile the technical report must supply the facts: the defective element, relevant requirement or agreement and why another cause is less plausible.

7. Fictional example: condensation or faulty connection

Soraya discovers moisture behind a new cupboard wall after renovation. The contractor mentions insufficient ventilation, while an installer suspects a leaking connection. She wants the whole wall removed. Her lawyer advises collecting observations, drawings and maintenance information first, then proposing a focused joint inspection. An expert determines the opening needed to investigate both explanations.

The opening is photographed step by step and a removed connection is kept. The report describes the condition found and a further measurement still needed. Soraya arranges temporary protection against further damage. Only then does she discuss repair, responsibility and costs with her lawyer. The fictional example illustrates building evidence; it does not predict which party would win a comparable dispute.

8. Checklist before opening or final repair

Give your lawyer and expert a short, coherent chronology. A clear investigation question and controlled first intervention usually provide more useful information than substantial repairs without anyone recording the original condition.

• Collect the contract date, completion report, drawings and available material and maintenance information.
• Keep dated photographs, observations and an overview of subsequent work or earlier repairs.
• Provide the notification, contractor’s reply and a proposal for access and investigation.
• Prepare a plan identifying locations, attendees, photography and retention of relevant components.
• Justify emergency measures, permanent repair and their costs separately.