Cour d'appel de Rouen, RG 25/01677 (Copilot analysis)

What happened

Two homeowners in Normandy complained that water was entering the basement of their house after their neighbors had their garden and driveway rebuilt in May and June 2024. They sought an order in summary proceedings before the judicial court of Le Havre requiring the neighbors to stop the infiltration. On April 22, 2025, the summary judge rejected their claims and ordered them to pay damages and costs. They appealed.

On appeal, the homeowners relied on several kinds of evidence: a leak investigation with dye tracing by an assessor appointed by their insurer, a private expert's report, correspondence from the city's sanitation service, and bailiff's reports of the site. They also relied on an analysis produced with an AI system. The judgment records their argument that "l'analyse du second écrit par l'IA de microsoft Co-pilot", the Microsoft Copilot analysis of the neighbors' contractor's second written statement, confirmed that the works caused the infiltration and did not conform to trade standards.

What the court did

On February 11, 2026, the court reversed the summary order in full. It found that rainwater falling on the rebuilt driveway ran past the drainage channel into the lawn and then into the buried basement wall, and it ordered the neighbors to have corrective drainage works carried out within six months, under a daily penalty of 200 euros, and to pay 5,000 euros toward the homeowners' costs.

The court was precise about what it relied on. Causation, it said, followed "de la concordance des éléments probants suivants (constats, avis techniques émanant de professionnels), ce que n'est pas l'analyse effectuée par le biais de l'intelligence artificielle produite par les appelants": from the agreement of the evidence listed, bailiff's reports and technical opinions from professionals, which the analysis produced by the appellants by means of artificial intelligence is not. It then listed the professional evidence item by item and did not mention the Copilot analysis again.

Where it stands

The judgment was delivered on February 11, 2026. A further appeal to the Cour de cassation was not located as of October 8, 2026. The party names are pseudonymized in the published text, as is standard for French judgments.

The court did not exclude the AI analysis as inadmissible or criticize the parties for offering it. It classified it. A technical opinion from a professional counts toward causation; a chatbot's reading of a contractor's letter does not. The party who offered it won anyway, on the other evidence.

The obligation it engaged

The matter sits under expert witnesses because the court drew the line the Standard draws. Clause 2, non-delegation, holds that the opinion and its basis belong to the expert. The court treated the AI analysis as something other than an opinion because no professional stood behind it, and it gave weight to the evidence that did have a professional author.

Clause 4, checkability before adoption, explains why. Each professional item could be tested: the dye trace by repeating it, the site reports against the site. A summary generated from a contractor's letter could be checked only against the letter, which the court already had.

Sources

• Cour de cassation (Judilibre open data) · February 11, 2026
  CA Rouen, 11 février 2026, n° 25/01677
• Damien Charlotin, AI evidence database · October 8, 2026
  AI evidence cases

What could not be confirmed

The full text was read through a third-party API copy of the Judilibre record (Pappers Justice), because the Cour de cassation's page requires JavaScript. Translations of quoted passages are this record's own. The database's description of the matter as concerning 'AI expertise on rain patterns' does not match the judgment, which concerns a Copilot analysis of a contractor's statement.