You have just bought a 52-square-metre apartment in Paris, and your architect tells you it measures barely 48. Four square metres have vanished between the deed and the tape measure, and at Paris prices that gap is worth tens of thousands of euros. For a foreign buyer, this is one of the most disorienting discoveries in French real estate law: the surface area written in the notarised deed is not a marketing figure, it is a legal warranty, and when it is wrong by more than a small statutory margin, the buyer can force the seller to give part of the price back. This guide explains how the French loi Carrez (mandatory private-area measurement rule) works, how the surface is legally computed, which of the two remedies applies to your situation, and what three recent rulings of the Cour de cassation (Supreme Court for civil matters) change in practice.

The framework sits in a single provision, Article 46 of Law No. 65-557 of 10 July 1965, introduced by the so-called loi Carrez (Law No. 96-1107 of 18 December 1996). Every preliminary contract and every deed selling a condominium lot must state the private surface area of the lot, computed under strict statutory rules. If the mention is missing, the buyer alone can seek nullity of the preliminary contract within a short deadline. If the stated area exceeds the real area by more than one twentieth, the buyer can demand a proportional price reduction within one year of the authenticated deed. The two actions obey different clocks, different thresholds and different strategies, and confusing them is the costliest mistake a foreign buyer can make. The Third Civil Chamber of the Cour de cassation polices each detail, and its recent published rulings refine the rules on nullity, on what counts as private area, and on who ultimately pays.

I. The warranty: how the area is computed and what the seller guarantees

Before any remedy comes the measurement itself. The loi Carrez does not protect every purchase: it applies only to sales of lots in buildings under condominium (copropriété, co-ownership) status. A detached house sold as such falls outside the rule, as do lots smaller than eight square metres, which are simply ignored. For everything else sold as a condominium lot, the deed must carry the number, and that number must be computed the way the statute commands, not the way an estate agent paces out rooms.

A. The statutory measurement: closed rooms, 1.80 metres, and mandatory deductions

The legal definition counts only the floor area of enclosed and covered premises with a ceiling height of at least 1.80 metres, after deducting the surfaces occupied by walls, partitions, steps and stairwells, ducts, and door and window recesses. In substance, only the floor surface of closed, covered rooms at least 1.80 metres high counts, after deducting the surfaces occupied by walls, partitions, steps and stairwells, shafts and door and window recesses, as Decree No. 97-532 of 23 May 1997 defining the private area of a co-ownership lot provides. Areas under sloping ceilings below 1.80 metres, balconies, terraces, loggias, cellars, garages and parking spaces are not private area, even when they plainly add value to the flat. A 20-square-metre terrace does not add a single Carrez metre, and a mezzanine under the roof counts only for the portion high enough to stand in.

Three practical consequences follow for the foreign buyer. First, the seller is not obliged to hire a professional surveyor: the statute imposes no duty to use a certified diagnostiqueur (property surveyor) for the Carrez measurement, unlike the asbestos, lead or energy surveys of the technical file. Many sellers measure themselves or reuse an old certificate, which is precisely where errors creep in. Second, the buyer cannot rely on the floor area shown on listing portals or on the condominium règlement de copropriété (co-ownership by-laws): only the figure stated in the preliminary contract and repeated in the authenticated deed triggers the warranty. Third, the relevant state of the premises is assessed at the sale, not at some earlier administrative description, a point the courts have now settled, as Section II explains. A buyer who commissions an independent measurement between the compromis de vente (preliminary sale agreement) and the final deed negotiates from strength: if the gap already exceeds the tolerance, the price can be renegotiated before completion instead of litigated after it.

Foreign buyers should also understand what the rule does not do. It does not punish a flat that is simply larger than announced: where the real area exceeds the stated area, the excess gives rise to no price supplement, and the seller has no action against the buyer. The statute plays one way only, in favour of the buyer, and within a tolerance band described in the next section. Nor does the rule dispense the buyer from the ordinary hidden-defects regime: a surface shortfall and a structural defect are two different claims with two different deadlines, and the boundary between them matters enormously, as developed below. Readers unfamiliar with the purchase sequence itself may usefully consult our companion overview alongside this guide through a real estate practice handling foreign buyers in Paris, before turning to the remedies.

B. Two sanctions, two clocks: nullity for a missing mention, price reduction beyond one twentieth

The statute organises two distinct actions, and each has its own trigger and its own guillotine deadline. The first action punishes the absence of any surface mention. Where the preliminary contract states no private area at all, the buyer alone may seek nullity of that preliminary contract. The nullity action must be brought within one month of the authenticated deed of sale: once the final deed is signed with the area stated in it, the right to attack the preliminary contract for the missing mention lapses. This is a short, brutal forfeiture, and it runs even if the buyer only discovers the omission later. The nullity is relative, meaning only the buyer can invoke it, never the seller seeking to escape a sale he regrets.

The second action, by far the most litigated, is the price-reduction claim. Where the real private area is more than one twentieth smaller than the area stated in the deed, the seller must, at the buyer’s request, accept a price reduction proportional to the shortfall. A 5 per cent tolerance protects the seller against trivial discrepancies: a 50-square-metre flat that truly measures 48 is within tolerance and gives no claim, while one that measures 47 opens the full proportional remedy. The statute states the rule in one sentence: “Si la superficie est inférieure de plus d’un vingtième à celle exprimée dans l’acte, le vendeur, à la demande de l’acquéreur, supporte une diminution du prix proportionnelle à la moindre mesure.” In English: where the area is more than one twentieth below the area stated in the deed, the seller must, at the buyer’s request, accept a proportional price reduction. The reduction is strictly proportional, computed on the sale price: the buyer has one year from signature of the deed to claim it, as Article 46 of Law No. 65-557 of 10 July 1965 provides. The one-year period is a forfeiture period, not a mere limitation: once it expires, the claim is dead, whatever the excuse. No good faith or bad faith inquiry is required; the action is purely objective, comparing two numbers.

The arithmetic deserves a worked example, because foreign buyers often misprice their claim. Take a Paris flat bought for 600,000 euros on the basis of 60 square metres stated in the deed, where an independent survey establishes 55 square metres of true private area. The shortfall is 5 square metres out of 60, or 8.33 per cent, well beyond the one-twentieth threshold. The proportional reduction equals 5/60 of the price, or 50,000 euros. Registration duties and the notary’s proportional fees follow the price downward, which adds several thousand euros of recovery. Conversely, a 58.5-square-metre reality against 60 stated gives a 2.5 per cent gap: inside tolerance, no claim at all, and a lawsuit would fail and cost money. Measuring early, with a surveyor who applies the statutory deductions rather than a commercial estimate, is therefore the single highest-value step a buyer can take, and it must be taken inside the one-year window.

II. How the courts apply the rule: nullity, surface disputes and who pays

Three published rulings of the Third Civil Chamber now frame almost every Carrez dispute: one on the nullity action that rejects contractual shortcuts, one on how the surface is assessed when the paper description and the physical reality diverge, and one on the liability of the architect who delivers a building smaller than his own plans. Together they draw a coherent picture: formalism protects the buyer at the preliminary stage, physical reality governs at the measurement stage, and professionals with a full mission cannot hide behind the absence of a specific measuring task.

A. Nullity is strictly policed and the surface follows physical reality

The nullity action for a missing mention looks simple on paper but generated years of litigation over one question: can the parties cure the omission before the final deed by signing a side document? In a 2018 published ruling, buyers had signed a private preliminary agreement for two apartments and a cellar with no surface stated, then signed a measurement certificate marked “taken note of”, and refused to complete. The appeal court treated the signed certificate as a contractual add-on curing the defect and ordered the buyers to pay the penalty clause. The Cour de cassation quashed that analysis entirely, holding that “seule la signature de l’acte authentique constatant la réalisation de la vente mentionnant la superficie de la partie privative du lot ou de la fraction de lot entraîne la déchéance du droit à engager ou à poursuivre une action en nullité de la promesse ou du contrat qui l’a précédée, fondée sur l’absence de mention de cette superficie” In English: only signature of the authenticated deed completing the sale, stating the private area of the lot, extinguishes the right to bring or continue a nullity action against the earlier contract for lack of that mention. Neither an undated certificate, nor signatures beside a “taken note of” formula, nor a supposed contractual addendum can substitute for the authenticated deed (Cass. 3e civ., 22 November 2018, No. 17-23.366, published in the Bulletin). For the foreign buyer, the message is operational: if the compromis states no area, do not sign informal measurement papers thinking they fix or waive anything, and calendar the one-month nullity window from the final deed rather than from discovery.

The second ruling answers the mirror question: when the deed and the by-laws call a room a cellar but it is physically used as a storeroom joined to the shop above, which description governs the measurement? A buyer company had purchased a lot described as shop plus cellar and sued for a price reduction, arguing the basement, labelled a cellar in both the by-laws and the deed, had to be excluded. The appeal court included it, and the Cour de cassation rejected the appeal, holding that “il y avait lieu de prendre en compte le bien tel qu’il se présentait matériellement au moment de la vente” In English: taken into account the property as it physically presented itself at the time of the sale. The basement, directly connected by an internal staircase to the ground-floor room and fitted out as a reserve, counted toward the private area although neither the by-laws nor the deed had been amended, and the alleged flood-prone character of the room was an inoperative argument once the physical use was established (Cass. 3e civ., 2 October 2013, No. 12-21.918, published in the Bulletin). The lesson cuts both ways for foreign parties. A buyer hoping to exclude an awkward basement from the area, to manufacture a shortfall, will fail if the room is in fact usable private space at completion. Symmetrically, a seller cannot shelter behind an outdated label in the by-laws to defend an overstated area: what the surveyor sees and measures on the day governs, room by room, metre by metre.

These two rulings combine into a practical timeline. At the preliminary stage, check that the area is stated and distrust any informal cure. Between preliminary and final deed, verify the physical configuration room by room, because labels do not decide the measurement. After completion, measure promptly under the statutory method and compare against the one-twentieth threshold inside the one-year forfeiture. Each step has its own deadline, and missing any one of them converts a winning file into a lost cause.

B. Who ultimately pays: the seller first, the architect on a full mission, and the hidden-defects boundary

The price reduction is owed by the seller, and the seller cannot pass the loss to the buyer by invoking his own good faith: the action is objective, and even a seller who relied in good faith on a surveyor’s certificate must refund the proportional overprice. The seller’s only recourse is then against whoever supplied the wrong figure, typically the surveyor or agent, in a separate warranty claim. That separation matters for foreign buyers suing from abroad: the buyer sues the French seller within the one-year forfeiture, and the seller’s downstream claim against his surveyor does not extend the buyer’s deadline by a single day. Sue the right defendant, in the right court, inside the right year.

The most significant recent development extends liability one step further up the chain, to the design professional. In a November 2024 published ruling, a developer had entrusted an architect with a complete project-management mission for a residential building, and one delivered lot came out smaller than the architect’s own plans provided. The appeal court rejected the developer’s indemnity claim because no specific measuring or surface-computation mission had been entrusted to the architect. The Cour de cassation quashed that reasoning, holding that the architect “était tenu de veiller à une exécution conforme aux prévisions contractuelles et aux plans établis, même en l’absence de mission particulière portant sur le mesurage des surfaces” In English: the architect was bound to ensure performance consistent with the contractual projections and the established plans, even without any specific mission covering surface measurement. A complete mission necessarily includes supervision of execution, and supervision includes delivering the promised surfaces (Cass. 3e civ., 7 November 2024, No. 23-12.315, published in the Bulletin). For buyers of new or newly renovated flats, this ruling opens a second target where the seller is insolvent or the developer has vanished: the architect on a full mission answers for the missing metres under the former Article 1147 of the Civil Code, now the general contract-liability regime.

Finally, the Carrez action must be distinguished from the hidden-defects warranty, because the two regimes attract different defendants and, critically, different clocks. The Civil Code provides that “Le vendeur est tenu de la garantie à raison des défauts cachés de la chose vendue qui la rendent impropre à l’usage auquel on la destine, ou qui diminuent tellement cet usage que l’acheteur ne l’aurait pas acquise, ou n’en aurait donné qu’un moindre prix, s’il les avait connus.” In English: the seller warrants hidden defects that render the property unfit for its intended use, or so impair that use that the buyer would not have bought, or would have paid less, had he known. That is the garantie des vices cachés (hidden-defects warranty), and it covers concealed structural or technical flaws, not a shortfall in stated area (Article 1641 of the Civil Code). Its deadline runs two years from discovery of the defect: “L’action résultant des vices rédhibitoires doit être intentée par l’acquéreur dans un délai de deux ans à compter de la découverte du vice.” In English: the action for redhibitory defects must be brought within two years of discovery of the defect (Article 1648 of the Civil Code). A damp cellar with hidden subsidence is a vice claim within two years of discovery; a flat 8 per cent smaller than the deed states is a Carrez claim within one year of the deed, full stop. Pleading the wrong regime loses the right case on the wrong clock, and courts will not reclassify an out-of-time Carrez claim as a hidden defect.

For the Paris and Île-de-France buyer, five operational points close the file. First, jurisdiction: surface disputes go to the judicial court of the property’s location, so a Paris flat means proceedings in Paris, in French, with exhibits translated where needed. Second, evidence: commission a surveyor’s report applying the statutory deductions expressly, keep the preliminary contract, the deed, the listing and the by-laws, and photograph ceiling heights and configurations before any renovation alters them. Third, negotiation leverage: a documented shortfall above the threshold, raised before the one-year expiry, regularly settles, because sellers know the action is objective and fee-shifting punishes resistance. Fourth, money flows: the recovered reduction lowers the transfer-tax base, and the notary’s duties are recalculated, so instruct the notary early rather than discovering the adjustment at tax time. Fifth, cross-border follow-through: rental income and any eventual resale remain taxable in France for non-residents under their own regimes, so coordinate the price-reduction recovery with your tax position without letting tax analysis delay the forfeiture deadline. Throughout, documented support from a real estate team acting for foreign owners in Paris keeps the measurement, the demand letter and the filing sequenced inside the one-year guillotine.

Conclusion

A French condominium deed guarantees its own number: where the private area is missing, the buyer alone can seek nullity within one month of the final deed, and no informal signed certificate cures the omission; where the area falls short by more than one twentieth, the buyer recovers a proportional price reduction within one unforgiving year. The courts measure physical reality at the sale rather than paper labels, and the architect on a complete mission answers for delivering less than his plans promised. For the foreign buyer in Paris, the discipline is simple: verify the mention in the preliminary contract, measure independently under the statutory method, compare against the 5 per cent threshold, and act inside the year. Four square metres at Paris prices pay for a great deal of diligence.

Need a quick opinion on your case

If your French flat measures less than your deed states, or your preliminary contract omits the surface area, a telephone consultation within 48 hours with a lawyer of the firm clarifies your deadline and your recoverable amount. Call +33 6 46 60 58 22 or write via our contact page with your deed and any measurement report.