A few missing square metres are enough to start a dispute: between a buyer and the seller, between a developer and the architect, between the buyer and the surveyor who certified the floor area. Two rulings of the Third Civil Chamber of the Cour de cassation (the French supreme court for civil and commercial matters), one reported in November 2024, the other handed down in March 2026, clarify who answers for the shortfall and what loss can be claimed. In both cases, the value of the missing square metre is at the centre of the debate.
The loi Carrez rule
Article 46 of the law of 10 July 1965 on co-owned buildings, known as the loi Carrez, requires the private floor area of a co-ownership lot to be stated in any sale. If the actual area is more than one twentieth smaller than the area stated, the buyer may claim a proportional reduction of the price, within one year of the deed. The decree of 23 May 1997 lists the areas to be excluded: floor space under a ceiling height of less than 1.80 metres, cellars, garages and parking spaces.
First ruling: the architect answers for the plans he drew
A property development company had entrusted an architect with a full project management assignment, from preliminary studies to assistance at handover. One lot was delivered with a shortfall of at least 6.70 square metres against the planned area. The developer sued the architect. The Bordeaux Court of Appeal, ruling after a first remittal, had rejected the claim on the ground that the architect had no measuring assignment.
The Cour de cassation quashed that decision (Cass. 3e civ., 7 November 2024, appeal no. 23-12.315, reported decision). The architect in charge of supervising the works “was bound to ensure that they were carried out in accordance with the contractual provisions and the plans drawn up” (translated from the French), regardless of any measuring assignment (article 1147, now 1231-1, of the Civil Code). On the loss, the Court held that “the client may claim compensation for a lost profit resulting from the non-conformity of the work” and that the judge “may not refuse to compensate a lost chance” once he finds one, here the chance of selling at a better price. The case was sent to the Poitiers Court of Appeal.
Second ruling: the surveyor answers to the buyer for his measurement
By a deed of 25 April 2017, a third-floor flat, with a toilet on the landing, a former maid’s room on the fifth floor and a cellar, had been sold for €270,000. The surveyor (diagnostiqueur, the certified technician who prepares the statutory pre-sale reports) had certified a floor area of 60.07 square metres. The buyers sued the sellers for a price reduction and the surveyor for damages. The Versailles Court of Appeal had held that the toilet on the landing and the maid’s room had to be counted, “the area of these rooms not being subject to any statutory or regulatory exclusion from the scope of article 46 of the law of 10 July 1965” (translated from the French), but had dismissed the claim against the surveyor.
The Cour de cassation approved the first point and quashed the second (Cass. 3e civ., 5 March 2026, appeal no. 23-13.288). By dismissing the surveyor’s liability despite the measuring error, the Court of Appeal had breached article 1240 of the Civil Code, under which any act of a person that causes damage to another obliges the person at fault to make it good. The sellers were released from the proceedings. The claim against the surveyor goes to another Court of Appeal.
What the expert quantifies
A square metre does not have a single price. The price reduction under article 46 is proportional: the sale price multiplied by the missing area divided by the area declared. But the loss recoverable in liability, that of the developer against the architect or of the buyer against the surveyor, is measured differently: what the property would have been worth with the promised area, less what it is actually worth. Depending on the layout, a maid’s room on the fifth floor without a lift and a toilet on the landing are not worth the average square metre price of the flat. The report establishes a value per square metre for each type of area, from comparable sales.
A developer’s lost profit is calculated from the price list. For a new-build lot, the loss is the difference between the price the planned area would have fetched, according to the marketing price list and the sales made in the scheme, and the price actually obtained. The lost chance is then expressed as a fraction of that difference, according to the probability that the sale would have gone through at the higher price.
Measure before arguing. The Charte de l’expertise en évaluation immobilière (the French property valuation charter) devotes a chapter to areas and floor areas, and distinguishes cadastral area, statutory areas and contractual areas (6th edition, November 2025, Title III, chapter 3), with weighting recommendations (chapters 4 and 6). A valuation report begins with a survey of the areas under each applicable definition. That is often where the shortfall is explained, between habitable area, loi Carrez area and the area on the plans.
Further reading
The Property loss of value page describes how a loss of value is quantified, the timescale and the fee. On the same theme: The seller is deemed to know the value and the area of the property and Incorrect energy certificate: the surveyor owes a lost chance to negotiate the price. The rulings are available on Légifrance: 7 November 2024 and 5 March 2026.
What next
The actual floor area does not match the one announced?
I measure, I compare with the applicable rules (loi Carrez, plans, contract) and I put a value on the shortfall: price reduction, lost profit or lost chance, with verifiable comparables per square metre.
Free quote, by email or by phone. No commitment before the quote is accepted. Fees are never linked to the value of the property (Charte de l’expertise, Title I, §2.1).
