I. The Carrez guarantee: what your French deed must state
You have just bought a twenty-square-metre studio in the 11th arrondissement, or a two-bedroom flat in Boulogne-Billancourt, and the figure printed in your title deed looks generous. A few months later, an architect draws up plans for a kitchen refit and tells you the flat is two square metres smaller than the deed says. In Paris, where each square metre routinely changes hands for more than ten thousand euros, that gap is not a detail: it is a five-figure overpayment. French law gives you a dedicated remedy for exactly this situation, and it works very differently from the general law of hidden defects.
Every sale of a condominium unit in France must state the private floor area of the lot. That rule comes from the loi Carrez, the nickname practitioners give to Article 46 of the Law of 10 July 1965 on co-ownership, as amended in December 1996. The mechanism is strict, arithmetic and fast: shortfalls above a fixed threshold give rise to a proportional price reduction, but the claim must be brought within one year of the final deed. For a foreign buyer who discovers the problem from abroad, the trap is not the substance of the right, which is generous, but the timetable and the proof, which are unforgiving. A Paris court applied both sides of that coin in a judgment of 9 April 2026 that every buyer should read before commissioning a second measurement.
A. The mandatory area statement and the 5% trigger
Article 46 requires that every unilateral promise of sale and every deed completing or recording the sale of a condominium lot mention the superficie de la partie privative (private floor area) of that lot. The statute refers the measurement method itself to the implementing decree designated in Article 47 of the same Law, which is the Decree of 17 March 1967 examined in the next section. The sanction for a total omission is severe: the buyer can seek annulment of the deed on the sole ground that no area is stated. That nullity action is distinct from the price-reduction action, and the two follow different clocks, as explained in Part II.
Once an area is stated, the statute applies a one-way tolerance. If the real area turns out to be larger than the figure in the deed, the seller cannot claim a penny more: the excess gives rise to no price supplement. If the real area is smaller, the buyer has a claim only where the shortfall exceeds one-twentieth, in other words 5%, of the stated figure. A shortfall of exactly 5% or less gives no right to anything; a shortfall of 5.01% opens the full proportional remedy. Article 46 of the Law of 10 July 1965 expresses it as follows: « 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. » That sentence is the entire economics of the claim, and it is worth reading twice: the seller bears a reduction proportional to the missing area, at the buyer’s request, as soon as the shortfall passes the twentieth threshold. The text was read on the official Légifrance page of Article 46 of the Law of 10 July 1965.
The computation itself is mechanical. Divide the purchase price by the area stated in the deed to obtain the price per square metre, multiply by the real area, and subtract the result from the price paid. Take a concrete Paris example. You buy a flat for 485,000 euros with a stated area of 52 square metres, and a later court-supervised measurement establishes 48.5 square metres. The shortfall is 3.5 square metres, or 6.7%, which clears the 5% threshold. The reduced price is (485,000 ÷ 52) × 48.5 = 452,403.85 euros, so the seller owes you the difference: 32,596.15 euros. On a small Paris studio the same arithmetic bites hard. In the Paris case decided on 9 April 2026, the buyer had paid 132,900 euros for the bare property with 15 square metres stated, and argued for 13 square metres actual, computing 132,900 − [(132,900 ÷ 15) × 13] = 17,720 euros of reduction. The court did not quarrel with the arithmetic, which follows directly from the statutory proportionality; it rejected the claim on proof, a point developed below, and that distinction is precisely what foreign buyers must grasp.
Three practical consequences follow from the one-way design. First, the seller can never turn the tables: a deed that understates the flat enriches the buyer, and the buyer keeps the benefit. Second, the threshold is assessed against the figure stated in the final authentic deed, not against the preliminary contract, so always compare the final acte authentique (notarial deed of sale) figure with reality. Third, the debtor of the reduction is the seller personally, even where the wrong figure came from the estate agent’s brochure or the surveyor’s certificate. The statute says the seller bears the reduction, and any recourse by the seller against the person who measured wrongly is a separate dispute that does not delay your claim. In the leading loggia case discussed below, the sellers had themselves joined the estate agency and the measuring firm to the proceedings, which shows where that secondary liability sits: between the seller and its providers, not as a shield against the buyer.
Foreign buyers sometimes confuse this action with the guarantee against vices cachés (hidden defects). The two are independent. A surface shortfall is not a defect in the thing sold; it is a breach of a statutory measurement guarantee with its own one-year clock. The Civil Code defines the hidden-defects guarantee separately: « 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. » That is Article 1641 of the Civil Code, and the action it creates must be brought within two years of 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. » That is the first paragraph of Article 1648 of the Civil Code. Pleading the wrong ground wastes the year you have. If your complaint is square metres, plead Article 46.
B. What counts as private area, and what is left out
The figure in your deed is not the number on the estate agent’s floor plan, and certainly not the carpet area a foreign listing might advertise. It is a legal construct defined by the decree of 17 March 1967 taken under the 1965 Law. Article 4-1 of that decree provides that the private area is the floor area of enclosed and covered premises, after deducting the surfaces taken up by walls, partitions, steps and stairwells, ducts, and door and window reveals. Then comes the sentence that eliminates half of all Paris disputes before they start: « Il n’est pas tenu compte des planchers des parties des locaux d’une hauteur inférieure à 1,80 mètre. » No account is taken of floor sections under a ceiling height of 1.80 metres. The official text was read on the Légifrance page of Article 4-1 of the Decree of 17 March 1967.
In practice, that single rule decides the fate of mezzanines, converted attics, chambres de service (maids’ rooms) under the eaves and any mansarded bedroom where the slope eats into headroom. Only the portion of the floor with at least 1.80 metres of height counts. A mansard room of 14 square metres on the ground may lawfully yield only 10 square metres of Carrez area, and that is not an error: it is the definition. Before alleging a shortfall, ask your surveyor to show the height line on the plan. Many foreign buyers discover that the supposed missing metres were never legally there.
The second filter is Article 4-2 of the same decree: « Les lots ou fractions de lots d’une superficie inférieure à 8 mètres carrés ne sont pas pris en compte pour le calcul de la superficie mentionnée à l’article 4-1. » Lots or fractions of lots under 8 square metres are disregarded, as stated on the Légifrance page of Article 4-2 of the Decree of 17 March 1967. Combined with Article 46 itself, which excludes cellars, garages and parking spaces from the guarantee altogether, this means the box in the basement, the cave (cellar) and the parking slot never enter the count, even if the agent’s listing rolled them into a flattering total. Where the cellar or parking space forms a separate lot in the co-ownership schedule, it is outside the guarantee by definition.
The subtlest point, and the one that most often surprises even French sellers, concerns balconies, terraces and loggias. The Cour de cassation settled the question on 28 January 2019 in substance in a ruling buyers still cite: where enclosed private loggias form part of the lot sold and are closed and habitable at the date of the sale, they must be included in the private area, even though each loggia measured under 8 square metres. The Third Civil Chamber reasoned that the trial judges, having sovereignly found the two private loggias closed and habitable at the sale date, had rightly concluded that the loggias had to be taken into account, in the Court’s words, « en a déduit à bon droit que ces loggias devaient être prises en compte pour le calcul de la superficie des parties privatives vendues ». Read the full ruling on the official site of the Cour de cassation, 3rd Civil Chamber, 28 January 2015, No. 13-26.035. The lesson is twofold. First, the 8-square-metre exclusion targets small separate lots and fractions, not individual rooms inside the dwelling: a closed, habitable loggia integrated into the flat counts in full. Second, the physical state at the date of the sale is decisive. An open balcony does not count; the same balcony, glazed and heated and used as a study at the sale date, does. For Paris buyers, where glazed loggias and enclosed former balconies are common in post-war blocks from the 15th arrondissement to Levallois, the question is never the label on the plan but the clos, couvert and habitable condition on the day the deed was signed.
Apply this as a checklist before you allege anything. Reconcile the deed figure with the co-ownership schedule (état descriptif de division): separate cellar and parking lots are out. Deduct wall thicknesses and reveals, which the surveyor does but the architect’s refit plan may not. Draw the 1.80-metre height line under every slope. Verify whether any glazed extension was closed and habitable at the sale date. Only the residue, compared against the deed figure with more than 5% missing, is a claim.
II. Claiming the reduction within the one-year deadline
The Carrez action is a sprinter’s race, and foreign owners lose it more often on procedure than on substance. The statute allows exactly one year, counted from the final notarial deed, and Paris judges enforce both the deadline and the standard of proof without indulgence, as two recent Paris decisions show. The good news is that the path is entirely mapped: act inside the year, prove the shortfall with court-grade evidence, and sue the seller.
A. One year from the authentic deed, and the nullity trap before it
The final paragraph of Article 46 of the Law of 10 July 1965 states the deadline without ambiguity: « L’action en diminution du prix doit être intentée par l’acquéreur dans un délai d’un an à compter de l’acte authentique constatant la réalisation de la vente, à peine de déchéance. » The price-reduction action must be brought by the buyer within one year of the authentic deed recording the sale, on pain of forfeiture. Three features of that sentence deserve emphasis, because each contradicts a natural assumption.
First, the starting point is the signing of the acte authentique before the notaire (public notary who authenticates French conveyances), and the same sentence attaches the penalty of déchéance (forfeiture): once the year expires, the right is extinguished, not merely time-barred in a way a judge might soften. Diarise twelve months from the signing date, not from the handover of keys, the first tax bill or the architect’s visit. Second, the plaintiff is the buyer alone, and the defendant is the seller: the notaire who recorded a wrong figure and the agent who advertised it are not the debtors of this action, whatever their separate professional liability. Third, the remedy inside that year is reduction only. You cannot use this action to unwind the sale; resolution belongs to other grounds such as a hidden defect or fraud, with their own conditions.
The Paris judgment of 9 April 2026 illustrates the deadline in motion. The authentic deed was signed on 5 December 2023 and the buyer’s writ was served on 22 November 2024, just inside the year, so the court declared the action admissible before examining the merits. Many foreign owners discover the shortfall during renovation works in the second year and assume the clock started at discovery. It did not. Commission an independent check of the area in the first months after completion, especially if you bought off-plan measurements you never verified, a mansarded top floor or a flat with a glazed extension.
Alongside the reduction action sits the nullity action for a deed that states no area at all, and the Cour de cassation polices the boundary strictly. On 22 November 2018 the Third Civil Chamber quashed a Paris appeal ruling that had allowed sellers to cure a missing area mention by a contractual workaround: an undated measurement certificate initialled « pris connaissance » (acknowledged) by the buyers alongside the sellers’ signatures, treated as an addendum forming one contract with the preliminary agreement. The statute allows no such cure: « 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 précédé, fondée sur l’absence de mention de cette superficie. » Only the signature of the authentic deed of sale stating the private area extinguishes the right to bring or continue a nullity action against the earlier contract for lack of that mention, as Article 46 of the Law of 10 July 1965 provides; the Court of Cassation applied exactly that exclusivity when it set aside the Paris reasoning. Read the full ruling at the Cour de cassation, 3rd Civil Chamber, 22 November 2018, No. 17-23.366. No initialled certificate, no addendum, no handshake regularisation can substitute for the authentic deed. Concretely, check both documents: if the compromis de vente (preliminary sale agreement) omits the area but the final deed states one, the nullity action dies with the signing; if even the final deed omits it, the nullity action survives the sale. And where the deed states an area that later proves short, you are in reduction territory with your one year, not in nullity territory.
Paris practitioners add one refinement worth knowing. The one-year forfeiture governs the filing of the claim, so a protective writ issued in time preserves the right even if the measurement debate then takes months. The Paris buyer of April 2026 filed within weeks of his second certificate and still lost, but on evidence, not on time. File first, perfect the proof second, and never let the anniversary of the signing pass while negotiating amicably with the seller.
B. Proving the shortfall the Paris way
This is where Carrez claims are won and lost, and the Paris courts have just given foreign buyers a masterclass in what not to do. Return to the 9 April 2026 judgment of the Paris judicial court, 8th chamber, 2nd section (RG 24/14368). The buyer had two certificates: 15 square metres from the seller’s surveyor annexed to the December 2023 deed, and 13 square metres from a surveyor he commissioned himself in March 2024. A 2-square-metre gap on 15 stated metres is a 13% shortfall, far above the twentieth threshold, and the arithmetic pointed to 17,720 euros of reduction. The court rejected everything. Its reason states the governing evidence rule: a private area certificate commissioned and produced by the claimant alone cannot by itself prove the alleged shortfall. A private area certificate commissioned by one party cannot, on its own, prove the alleged shortfall. The court recalled the settled principle, derived from a 2012 mixed-chamber ruling of the Cour de cassation and confirmed in Carrez litigation by the Aix-en-Provence Court of Appeal on 11 February 2026, that a judge cannot rest exclusively on a non-judicial expert report ordered by one side, outside the procedural safeguards of a court-appointed appraisal. Comparing the two certificates, the judges noted that the rooms had not even been measured on the same layout: the first certificate merged the kitchen into the living room while the second split out a separate entrance-kitchen, so the second document proved disagreement between surveyors, not error in the first. The buyer produced no other technical evidence, and the claim failed in full, costs included.
The operating lesson is blunt: a counter-measurement bought from a second diagnostiqueur (certified property surveyor) is the beginning of the file, never the file. What persuades a Paris judge is a expertise judiciaire (court-appointed expert appraisal), ordered within proceedings brought inside the one-year deadline, conducted adversarially with both surveyors’ methods tested on site. Structure your dispute accordingly. First, send the seller a formal demand (mise en demeure) by bailiff, attaching your second certificate and offering a joint re-measurement. Second, if the seller refuses or the joint exercise confirms nothing, file the reduction action before the year expires and ask the court to appoint an independent surveyor. Third, freeze the layout: do no renovation works between the two measurements, because any alteration destroys comparability and hands the seller its best defence.
That last warning is not theoretical. On 19 February 2025 the Paris Court of Appeal (Pôle 4, Chamber 8, RG 22/10396) rejected a buyer’s claim against the surveying firm that had measured his flat, holding that on the evidence produced nothing established any error by the firm in drawing up its Carrez measurement. The buyer’s own works had removed a bedroom to enlarge the open-plan living room between the visits, the two surveyors had measured different layouts, and the buyer produced no plans, invoices or insulation details to isolate the effect of his works. The court confirmed the dismissal and added 4,000 euros of costs against him. Two holdings emerge for foreign owners. Against the seller, the reduction action succeeds or fails on court-grade proof of the shortfall, regardless of which surveyor the seller used. Against the surveyor or agent directly, you must prove a personal fault, such as a measurement error untainted by later works, plus your loss and causation: a mere gap between two certificates proves neither.
Since a 2000s reform of the implementing decree, the notaire must, on the very day the authentic deed is signed, hand each party against signature a copy of the signed deed or a certificate reproducing the clause stating the private area, together with a copy of the provisions of Article 46 itself where they are not reproduced in full. That rule is Article 4-3 of the Decree of 17 March 1967: keep that handover paper with the deed, because it proves exactly which figure you were told you were buying.
Paris and Île-de-France specifics sharpen every step. Territorial jurisdiction for the reduction action lies with the judicial court of the property’s location, so a Paris flat means the Paris judicial court, whose eighth chamber handles this litigation routinely. Paris price levels make even modest gaps litigable: one and a half missing metres at Paris prices funds an expert appraisal and a full proceeding, which is why sellers settle credible, well-evidenced files. Conversely, the same price levels make judges exacting about proof, as the two Paris rulings show. Practical points for the Paris file: keep the preliminary contract, the final deed and both survey certificates together; photograph the layout before any works, including ceiling heights under slopes with a visible tape; instruct a certified surveyor carrying professional liability insurance, since an uncertified opinion has little weight; and if the flat has a glazed loggia, a veranda or a converted maid’s room, document its closed and habitable state at the purchase date with dated photographs, because that state decides inclusion under the 2015 case law. For further reading on how Paris property disputes are handled locally, see the overview of real estate law assistance in Paris for English-speaking owners, and the analysis of preliminary-contract pitfalls in the firm’s Paris real estate practice.
One final Paris lesson from the April 2026 judgment: the buyer also sought a refund of the supposedly overpaid notaire fees, and the court dismissed that head of claim with the rest. The reduction action reprices the property between seller and buyer; it does not rewrite the registration duties already collected or manufacture a fee refund. Price your claim on the property price alone, and treat any tax or duty consequence as a separate question for your adviser rather than as part of the court demand.
Conclusion
The loi Carrez is one of the most buyer-friendly devices in French property law: a stated area in every deed, a one-way 5% tolerance that can only benefit the buyer, and a strictly proportional refund of the overpaid price. The Cour de cassation has kept the device coherent, counting closed and habitable loggias in the area while refusing any contractual shortcut around the authentic deed’s area statement. But the Paris courts of 2025 and 2026 attach two non-negotiable conditions that foreign owners must internalise. The action must be filed within one year of the authentic deed, a forfeiture deadline that discovery of the shortfall does not move. And the shortfall must be proved with court-grade evidence, because a second private certificate alone will not carry the claim, especially after renovation works have blurred the comparison. Measure early, freeze the layout, demand jointly, file inside the year and ask the court for an independent expert: that sequence converts a good substantive right into money recovered.