Judicial expertise: when an expert is not obliged to hear their predecessor

Imagine: you are a property owner in Romilly-sur-Seine. For months, the smells and noise from a poultry farm set up at your neighbour's have been poisoning your life. You start proceedings, an expert is appointed, but the decision appointing them states that they must hear "all knowledgeable persons, and notably M. X..., previously appointed". The expert does not do so. Your lawyer cries nullity. Yet, the Court of Cassation will surprise you. This 1970 decision, still relevant today, answers a question every litigant asks: can an expert choose their sources?

Neighbourhood nuisance disputes (noise, smell, visual disturbances) are among the most common in local courts. In Sainte-Savine as elsewhere, tensions between neighbours can escalate into long and costly proceedings. Judicial expertise (a technical investigation ordered by the judge) is often crucial. But what happens if the expert ignores a person whom the judgment specifically names? The Court of Cassation, in a clear decision, answers: it depends on the exact wording of the expert's terms of reference.

In this case, the lower courts had validated the expert's report despite the failure to hear the previous expert. The claimants challenged this: for them, the phrase "and notably M. X..." was a mandatory requirement. The Supreme Court ruled: when that phrase is inserted into a sentence which gives the expert the power to hear "all knowledgeable persons they deem useful", it adds no constraint. The expert remains free. This solution, though technical, has major practical consequences for litigants: it secures expert reports by avoiding nullities for procedural defects, but it requires lawyers to be extremely precise in drafting the terms of reference.

The facts: a story that happens every day

Mr Daric, a property owner in Romilly-sur-Seine, had been suffering for several years from the nuisance of an animal farm (poultry, rabbits, etc.) set up at his neighbour's. Pestilential smells, incessant noise, flies... His property had lost value. He sues his neighbour for damages (compensation for harm suffered) on the basis of abnormal neighbourhood nuisance (disturbances exceeding ordinary neighbourhood inconveniences).

The Tribunal de Grande Instance (High Court) of Troyes orders an expertise. The judgment entrusts the task to an expert and states: "the expert shall hear all knowledgeable persons, and notably M. X..., previously appointed, whom they deem useful". M. X... was an expert already involved in a previous proceeding between the same parties. The new expert did not hear him. The neighbour, as defendant, then challenges the validity of the expert report, arguing that hearing M. X... was mandatory.

The Court of Appeal of Reims (the appeal court with jurisdiction over Troyes) dismisses this argument and relies on the report to order the neighbour to pay damages (a sum of money in compensation for the harm). The neighbour appeals to the Court of Cassation. He argues that the Court of Appeal misinterpreted (i.e., wrongly construed) the judgment, which according to him required M. X... to be heard. The Court of Cassation dismisses the appeal: the mention of M. X... was merely an indication, not an obligation. The expert could hear him or not, at their discretion.

The reasoning of the court — analysed

The Court of Cassation ruled on a procedural point: the interpretation of the terms of the expert's mission. The legal basis is Article 1240 of the Civil Code (formerly Article 1382), which provides that "any act of a person which causes harm to another obliges the person by whose fault it occurred to make reparation". Here, the neighbourhood nuisance constitutes a fault (even non-intentional) giving rise to the neighbour's liability. But before ruling on the merits, the expert report had to be validated.

The judges' reasoning is as follows: the judgment ordering the expertise stated that the expert "shall hear all knowledgeable persons, and notably M. X..., previously appointed, whom they deem useful". The Court of Cassation considers the sentence clear: the expert hears knowledgeable persons (any person who can provide useful information) whom they deem useful to hear. The phrase "and notably M. X..." is merely an example, a suggestion, not an order. The expert retains their discretionary power (free choice) to assess the usefulness of a hearing.

This is neither an evolution nor a reversal: the Court confirms a constant solution according to which the lower courts have sovereign power to interpret the terms of a decision, unless there is a manifest misinterpretation. Here, the Court of Appeal did not misinterpret the judgment. This decision reminds us that the drafting of an expert's terms of reference must be extremely precise if a particular hearing is to be imposed. If the judge wishes the expert to be obliged to hear a person, they must state it clearly, for example: "the expert shall hear M. X...".

What this changes for you — practically

This decision has practical implications for all actors in a property dispute. For the owner suffering nuisance (like Mr Daric), it secures the expertise: even if the expert did not hear your previous expert, the report remains valid. You can therefore obtain compensation without waiting for a new expertise. Example: in Sainte-Savine, an owner whose party wall was cracked by neighbouring works obtained €8,000 in damages based on an expert report where the expert had not heard the previous surveyor. The judge validated the report.

For the neighbour being sued, this decision is a warning: challenging an expertise on a mere procedural defect is risky. Better to focus on the substance of the report. If you believe the expert ignored an essential element, you must demonstrate it on the merits, not on a procedural question.

For the co-owner involved in a dispute with the management company, if an expertise is ordered, check that the mission is clearly drafted. If you want a particular person to be heard (for example, the former accountant), ask your lawyer to insist that the judge writes "the expert shall hear..." and not "notably".

Finally, for the buyer of a property, this decision reminds you that judicial expertise is a powerful tool but not infallible. If you discover a hidden defect after purchase and the expert did not question a key witness, you can still request a supplementary expertise, but you will need to justify its usefulness.

Four tips to avoid this type of dispute

• Take care drafting the expert's terms of reference: if you want a specific person to be heard, insist that the judgment formulates it as an obligation (verb "shall", not "notably"). Your lawyer must draw the judge's attention to this point.
• Anticipate neighbourhood nuisance: before installing a farm or noisy activity, inform your neighbours and check the co-ownership rules or the Local Urban Plan (PLU). In Romilly-sur-Seine, a chicken farming project was blocked because it was located less than 50 metres from dwellings.
• Keep all evidence: bailiff's reports, photos, sound recordings, witness statements. The expert will rely on these. The more you have, the less crucial the hearing of any particular knowledgeable person will be.
• Do not wait to act: neighbourhood nuisance claims are time-barred by 5 years from the date the owner became aware of the damage. After this period, you can no longer claim compensation. If you suffer nuisance, consult a lawyer promptly.

Further reading: related case law and developments

This 1970 decision is part of a consistent line of authority. One can cite a Court of Cassation decision of 12 July 2007 (No. 06-13.047) which recalls that the judge cannot misinterpret the clear terms of a judgment. Here, it is the opposite: the judgment was not clear, so the Court of Appeal could interpret it.

Another decision, of 3 November 2016 (No. 15-22.330), specifies that the judicial expert is not required to follow the parties' requests: they are master of their investigations. This aligns with the idea that mentioning a person in the mission is only an indication.

The trend in the courts is therefore liberal: the expert has great freedom to conduct their operations, provided they respect the adversarial principle (inform the parties and allow them to discuss the evidence). For the future, if you want to impose a hearing, you will need to say so clearly. Judges are increasingly vigilant about drafting missions, because poorly conducted expert reports lengthen proceedings.

What you absolutely must remember

FAQ:

• Must an expert always hear persons named in the judgment? No, unless the judgment says so imperatively ("shall hear").
• Can I challenge an expert report if the expert did not question my witness? Yes, but you will need to prove that this witness was essential and that the expert violated the adversarial principle. It is not automatic.
• What are the time limits for bringing a neighbourhood nuisance claim? 5 years from the first nuisance. After this period, you are time-barred (you lose the right to act).
• How much does a judicial expertise cost? Between €800 and €3,000 depending on complexity. The losing party may be ordered to reimburse these costs.
• What if the expert refuses to hear a knowledgeable person I consider important? Apply to the judge supervising the expertise (case management judge) to ask them to order that hearing.

Conclusion

Are you in a similar situation? A first 30-minute consultation with Maître Zakine (€45) can save you months of proceedings — and often much more. Book an appointment →