A new flat, once sold, turns out to be several square metres smaller than on the plans. The client (maître de l’ouvrage), which had the building constructed and sold the flat, turns against the architect, who objects that the contract included no measuring assignment. On 7 November 2024, the Third Civil Chamber of the Cour de cassation (French supreme court for civil and commercial matters) rejected that defence for an architect with a full assignment (mission complète), and accepted that the client may claim a lost profit (manque à gagner) or, at the very least, a lost chance (perte de chance) of selling for more.
The facts
In 2010, a company entrusted an architect with project management (maîtrise d’œuvre, the design and supervision of the works) for the construction of a building; a société civile de construction vente (SCCV, a company formed to build and sell property) later took over its rights. Lot no. 18, sold after completion, showed a shortfall of at least 6.70 m² against the expected area of 73 m². The client sued the architect for compensation.
After a first quashing (Cass. 3e civ., 16 February 2022, appeal no. 20-22.778), the Bordeaux Court of Appeal, to which the case had been sent back, ruled on 1 December 2022. It reversed the first-instance judgment insofar as that judgment had declared the measurement certificate drawn up by a third-party company unenforceable against the architect (inopposable), then dismissed the claim for compensation. In its view, the architect, holding a full basic assignment but no additional assignment for measurement or the “calculation of floor areas” (loi Carrez), could not be blamed for any breach. Nor could the client claim, under the guise of compensation, the refund of part of the price. Finally, since the SCCV did not establish that it would necessarily have sold its unit for €30,731 more with the expected area, its loss could only be a lost chance; the Court of Appeal concluded that the claim failed outright, including the alternative request for a court-ordered expert appraisal (expertise judiciaire).
The decision
The Cour de cassation partly quashed the decision (Cass. 3e civ., 7 November 2024, appeal no. 23-12.315, reported), upholding three of the client’s four complaints. Only the part of the decision reversing the first-instance judgment on the measurement certificate escaped the quashing.
The architect’s duty. Under article 1147 of the Civil Code (contractual liability), in its wording prior to the ordinance of 10 February 2016, the Court noted that the architect’s full assignment “necessarily included supervising the execution of the works, so that the architect was bound to ensure that the works were carried out in accordance with the contractual provisions and the plans drawn up, even in the absence of a specific assignment covering the measurement of floor areas” (translated from the French). The Court did not itself rule on whether there was a breach.
Lost profit. Under the same article, the Court held that “the client may claim compensation for a lost profit resulting from the non-conformity of the work with the contractual provisions if it is attributable to a contractor” (locateur d’ouvrage, a professional bound to the client by a contract for works, such as the builder or the architect). By objecting that the refund of part of the price is not a recoverable loss, the Court of Appeal breached that text.
Lost chance. Under articles 4 and 5 of the Code of Civil Procedure, which define what the judge must decide, the Court held that “the judge may not refuse to compensate a lost chance of avoiding a loss, whose existence the judge has found, on the ground that only full compensation for that loss was claimed”. The Court of Appeal therefore could not dismiss the whole claim because the SCCV sought the entire price difference.
The rejection of the request for an expert appraisal was quashed as a consequence. Except for the point on the certificate, the case was sent back to the Poitiers Court of Appeal, which must rule again on the architect’s liability and, if established, on the loss.
What this changes for valuation
Two measures of the loss, to be presented together. The lost profit is the entire difference between the price the planned area would have fetched and the price obtained; the lost chance is only a fraction of it, which a judge who finds it must compensate even when only the entire difference is claimed. The report therefore values the unit at the date of the sale with the planned area and with the actual area, and presents the gap as a loss suffered by the seller, not as a share of the price to be refunded. It then gathers evidence on the probability of a sale at the higher price: market conditions, pace of sales in the scheme, discounts on comparable units. Surveyor cases draw the same line: the full loss for asbestos or termites, a lost chance for a wrong energy performance certificate (DPE).
The missing square metre is not an average square metre. Spread over the minimum shortfall of 6.70 m² found by the Court of Appeal, the €30,731 price difference relied on by the SCCV gives just under €4,600 per square metre, an indicative figure, since the decision does not say on which area it was calculated. The unit price adopted, which depends on whether the lost area shrinks a room or changes the type of home, must be justified. The comparison method (Charte de l’expertise en évaluation immobilière, the French property valuation charter, 6th edition, November 2025, Title III, ch. 2, §2.1), which favours transaction prices, relies here first on the sales completed within the scheme, adjusted for floor, aspect and type of home, then on those in the area; the price list, a mere asking price, can be used only by estimating the gap with likely sale prices and justifying the adjustment (§2.1.2).
Compare areas of the same kind. The plans, the deed of sale and a measurement certificate do not always rest on the same definition of floor area; the Charte distinguishes statutory areas and contractual areas (Title III, ch. 3). The report therefore measures the unit under each definition at stake and states the origin and date of each measurement used, since here the certificate relied on against the architect was itself in dispute. The liability of the surveyor (diagnostiqueur, the technician who prepares the statutory pre-sale reports) towards the buyer belongs to another dispute: Wrong Carrez measurement: the surveyor can be liable to the buyer.
What the valuer takes from it
- An architect with a full assignment must ensure that the work conforms to the plans, even without a measuring assignment.
- The client may claim a lost profit if the non-conformity is attributable to a contractor; the report quantifies it at the date of the sale.
- A lost chance once found must be compensated; the report provides the evidence to measure its probability.
- The missing square metre is valued first by comparison with sales completed within the scheme, not at the unit’s average price.
- The report states the origin, date and definition of each floor area measurement.
Further reading
The Property loss of value page describes the assignment and its fee. The guide Producing a valuation in a French court: which format to choose? and the glossary entries préjudice immobilier, surface Carrez and méthode par comparaison complement this article. On the area certified at the sale: Wrong Carrez measurement: the surveyor can be liable to the buyer. On the same theme: Builders’ liability in France: legal grounds and awards and Sale annulled for noise: a lost capital gain must be certain. The decision is available on Légifrance.
What next
Is the flat as built smaller than on the plans?
I measure the unit under each applicable definition and compare the result with the plans. I then put a value on the shortfall, lost profit or lost chance, based on sales within the scheme and verifiable comparable sales.
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