You bought a Paris apartment described as 68 square metres in the signed deed. Months later, an architect remeasures and finds 61. Seven square metres have vanished, and at Paris prices that gap can represent more than a year of rental income. French law gives the buyer of a co-ownership lot a specific, powerful remedy for exactly this situation: the loi Carrez (the 1996 statute on private floor area). It is not a general hidden-defects claim and it is not negotiated. When the real private area falls short of the stated area by more than one twentieth, the seller must grant a proportional price reduction, and the buyer has one year from the authentic deed to sue.

This guide explains, for foreign owners and buyers, how the protection works, how the reduction is calculated, which deadlines decide everything, and how to prove the shortfall from abroad. Part I sets out the rule and its two remedies. Part II gives the evidence and procedure playbook, including the Paris practice points that matter most.

Foreign buyers sometimes confuse this sale protection with the rental-area rule they meet as landlords. The loi Boutin (rental habitability measurement statute) governs the living area stated in residential leases and obeys a different definition and a different sanction, enforced through the lease relationship. The two figures for the same apartment routinely differ by several square metres, and neither validates the other. A compliant lease measurement never cures a wrong sale figure, and a correct sale figure never excuses an understated lease area. Buyers who intend to let the property should therefore treat the two measurements as separate files from day one.

I. The stated area binds the seller: scope, calculation and the two remedies

A. Which sales are covered, what counts as private area, and how the reduction is computed

The rule sits in Article 46 of the Act of 10 July 1965 on co-owned buildings, as amended by the statute of 18 December 1996 universally called the loi Carrez (Carrez measurement statute). It applies to every sale of a co-ownership lot or fraction of a lot: any unilateral promise of sale or purchase, and any contract completing or recording the sale, must state the private area of the lot. Three categories escape the duty altogether: cellars, garages and parking spaces, and lots below a small surface threshold set by decree. Everything else sold as a dwelling in a copropriété (co-ownership building) is covered, including resales between private individuals and new-build sales where the lot structure applies.

The area to state is the superficie privative (private floor area), defined by decree as the floor surface of enclosed and covered premises after deducting the surfaces occupied by walls, partitions, steps, stairwells, ducts and door and window recesses. The decree adds a decisive sentence: “Il n’est pas tenu compte des planchers des parties des locaux d’une hauteur inférieure à 1,80 mètre.” Areas with a ceiling height below 1.80 metres simply do not count. That single sentence explains a large share of disputes: mezzanines tucked under the roof, converted attic corners, split-level appendages and storage nooks under stairs are routinely included by sellers and must be removed by a careful surveyor. Balconies, terraces and loggias, which are neither enclosed nor covered in the legal sense, are excluded from the private area as well, however much value a buyer in Paris, Nice or Bordeaux attaches to outdoor space. A foreign buyer comparing the Carrez figure with a foreign notion of gross internal area must therefore reset expectations: the French figure is deliberately narrower than what many Anglo-Saxon measurements include.

When the deed states an area, two outcomes are possible. If the real area is larger than stated, the excess gives rise to no price supplement: the seller cannot come back for more money. If the real area is smaller, the statute provides: “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.” (Article 46) Where the area falls short by more than one twentieth, the seller bears a price reduction proportional to the missing measurement. The threshold is strict. A shortfall of exactly 5 percent does not qualify; anything above does, with no need to prove fault, fraud or intent. The computation is then mechanical: divide the missing area by the stated area and apply that ratio to the price. Take a Paris example at 12,000 euros per square metre: a flat sold for 816,000 euros on the basis of 68 square metres, remeasured at 61 square metres, is short by 7 square metres, or about 10.3 percent. The reduction equals 7 divided by 68 times 816,000, which is 84,000 euros. In the capital, where per-metre prices are the highest in France, even a two-metre shortfall on a small studio converts into tens of thousands of euros, which is why this remedy matters far more in Paris and the inner suburbs than anywhere else. For buyers assisted by counsel experienced in real estate litigation in Paris, the first reflex after any doubt is therefore a counter-measurement, not a letter of complaint.

The asymmetry of the statute deserves emphasis because sellers frequently misread it. An overstatement punishes the seller through the proportional reduction, but an understatement never rewards the seller: the buyer who objectively received more metres than the deed states owes nothing extra and cannot be sued for the difference. The price agreed is a lump sum for the lot as described, adjustable downward only. Estate agents sometimes suggest an amicable rebalancing in the seller’s favour after a remeasurement; the law gives that suggestion no footing, and a buyer who pays a supplement out of goodwill cannot later be compelled to have done so.

B. Two actions, two deadlines: nullity for a missing statement and a one-year price claim

Article 46 organises two distinct actions and they must never be confused. The first targets the complete absence of any area statement in the deed. The statute says: “La nullité de l’acte peut être invoquée sur le fondement de l’absence de toute mention de superficie.” (Article 46) The buyer, and symmetrically the beneficiary of a sale promise or the promisor of a purchase promise, may seek annulment, but only within one month of the authentic deed recording the sale. That one-month window is extremely short, and the authentic deed itself normally purges the defect: signing the notarial deed that does mention the area extinguishes the right to pursue nullity of the earlier agreement for lack of the statement. Foreign buyers should understand the logic. The promise stage is where the buyer is protected against signing blind; once the acte authentique (notarial deed of sale) is signed before the notaire (public officer conveyancer) with the figure in it, the law considers the buyer informed.

The Cour de cassation polices that purge strictly. In a published ruling of 22 November 2018, the Third Civil Chamber held that where the preliminary agreement omits the private area, “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”, meaning only signing the authentic deed that mentions the area extinguishes the nullity action. The sellers in that case argued that the buyers had signed the surveyor’s measurement certificate marked seen and acknowledged, forming one inseparable contract with the preliminary agreement. The Court quashed the appeal judgment: a signed certificate cannot substitute for the authentic deed. For a foreign buyer, the practical lesson is sharp. Signing any measurement certificate at the agency or forwarding it by email does not waive anything; only the notarial deed counts, and a missing statement discovered before that deed is signed is still fully actionable within the month that follows it.

The second action, the workhorse of this field, is the price-reduction claim for a shortfall exceeding one twentieth. The statute fixes its deadline in equally severe terms: “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.” (Article 46) The buyer must sue within one year of the authentic deed, on pain of forfeiture. This is a délai de forclusion (time bar extinguishing the right), not a flexible limitation period: courts apply it rigorously, and negotiations, complaints to the agent or requests for an amicable discount do not stop it running. Only a formal step suffices, and the Cour de cassation has confirmed that an application to the urgent-applications judge for a court-ordered measurement interrupts it. In its ruling of 12 November 2015, the Third Civil Chamber held that “le délai d’un an prévu par l’article 46 de la loi du 10 juillet 1965 pour engager l’action en diminution du prix de vente avait été interrompu par l’assignation en référé expertise”, so the one-year period had been interrupted by the writ seeking a court-appointed expert. Filing for a référé-expertise (urgent court-ordered expert assessment) within the year therefore both secures the evidence and saves the deadline, a double effect that structures the entire strategy developed in Part II. The general principle now codified in Article 2241 of the Civil Code confirms the mechanism: “La demande en justice, même en référé, interrompt le délai de prescription ainsi que le délai de forclusion.” Even an urgent application interrupts time bars.

A further defence worth defusing early is the argument from the purchase price itself. Sellers occasionally contend that the price already reflected the smaller area because the buyer negotiated hard, so no reduction is due. Courts reject that reasoning: the reduction is proportional to the measurement gap applied to the agreed price, whatever the bargaining history, because the statute compares square metres, not value for money. Evidence of a hard negotiation is therefore irrelevant to liability, though it may colour settlement discussions. Conversely, buyers should not inflate the claim by adding notaire fees, agency commission or renovation costs to the base: the ratio applies to the sale price, and ancillary losses belong, if anywhere, to a separate fault-based claim against the person who produced the wrong certificate.

II. Proving the shortfall and litigating it: the foreign buyer’s procedure manual

A. Measuring, documenting and freezing the evidence before the year expires

A Carrez claim stands or falls on measurement, and the measurement must follow the legal definition, not a commercial one. The buyer who suspects a shortfall should commission an independent counter-measurement from a géomètre-expert (licensed surveyor) or a qualified measurement technician working strictly to the decree: enclosed and covered rooms only, walls and recesses deducted, anything under 1.80 metres excluded, balconies and terraces left out. The resulting report should detail room by room, show the height measurements, and state the method, because the seller will invariably produce the original vendor’s certificate and the court will compare methodologies. A report that merely announces a total without showing deductions carries little weight against a reasoned one.

Three recurring traps deserve attention because they generate most of the shortfalls foreign buyers encounter. First, rooms under sloping roofs: charming attic bedrooms in Haussmann top floors or Montmartre studios often include large bands below 1.80 metres that the seller’s certificate counted in full. Second, converted verandas, enclosed loggias and kitchen extensions whose enclosure or roofing does not meet the closed-and-covered test, or whose height fails the threshold. Third, internal reconfigurations where the seller counted demolished partitions’ former surfaces or included a cellar or parking area in the headline figure even though those annexes are outside the private area entirely. Each of these is invisible on a listing portal and obvious to a surveyor with a laser and the decree in hand, which is why a pre-deadline counter-measurement routinely pays for itself many times over.

Once the counter-measurement confirms a shortfall above one twentieth, the buyer should move on two tracks at once. On the evidence track, apply to the president of the judicial court for a référé-expertise under Article 145 of the Code of Civil Procedure, which provides: “S’il existe un motif légitime de conserver ou d’établir avant tout procès la preuve de faits dont pourrait dépendre la solution d’un litige, les mesures d’instruction légalement admissibles peuvent être ordonnées à la demande de tout intéressé, sur requête ou en référé.” A legitimate reason to preserve or establish facts before trial suffices, and a disputed measurement after a property sale is its textbook case. The court-appointed expert measures independently, both parties attend, and the resulting report normally settles the technical debate; very few Carrez cases survive an adverse court-expertise report to a full trial on the facts. On the deadline track, that same writ interrupts the one-year forfeiture period, as the 2015 ruling confirms, so the buyer who files within the year keeps the substantive claim alive even if the expert’s operations run past the anniversary of the deed. The sequence matters: measure privately first to confirm the claim is real, then file for the court expertise well before month twelve, then quantify the reduction from the expert’s figure and sue for it.

The seller’s predictable defences should be anticipated in the file. The seller may argue the buyer knew the real area and accepted it, invoking confirmation of a voidable act. The Civil Code answers in Article 1182 that voluntary performance confirms only where it is knowing: “L’exécution volontaire du contrat, en connaissance de la cause de nullité, vaut confirmation.” Mere signature of a certificate marked seen does not prove knowledge of the defect, as the 2018 ruling demonstrates, and paying the price without knowing the shortfall confirms nothing. The seller may also seek to pass the loss to the surveyor who produced the original certificate or to the estate agent, through third-party warranty claims; that is the seller’s litigation, not the buyer’s, and it does not suspend the buyer’s one-year deadline against the seller. Finally, the seller may dispute the buyer’s methodology room by room, which is precisely why the court-appointed expert, rather than a second private certificate, should be the centrepiece of the evidence.

Document preservation runs alongside measurement. The buyer should keep the listing particulars, the preliminary agreement with its annexes, the surveyor’s certificate attached to the deed, all correspondence with the agent about surface, and the completion file from the notaire. Screenshots of portals showing the advertised area matter because online advertisements disappear; a contemporaneous record that the seller marketed 68 square metres while the deed repeated the figure closes off the argument that the buyer never relied on it. Where the purchase was financed, the bank’s valuation report occasionally contains its own measurement, which can serve as a useful cross-check, though it never replaces a decree-compliant survey.

B. Litigating from abroad and the Paris and Ile-de-France specifics

Non-resident buyers face no nationality or residence barrier to bringing a Carrez claim: the action belongs to the purchaser as purchaser, and French courts routinely hear cases brought by British, American, Middle Eastern and Asian owners of Paris property. The practical difficulties are representation, presence and timing. A buyer living abroad grants a power of attorney, increasingly signed remotely: the notarial profession now routinely establishes distance proxies with electronic consent and signature, and the same remote-signing facilities serve litigation mandates. Hearings on the merits do not require the client’s physical presence where counsel represents the party, and the référé (urgent applications) timetable, measured in weeks rather than months, rewards buyers who instruct counsel early instead of negotiating by email until month eleven.

Jurisdiction follows the property. For a Paris apartment, the competent court is the Paris judicial court, whose property chamber handles a heavy volume of measurement disputes and applies the case law described above without surprise. Paris specifics amplify both stakes and proof issues. Prices per square metre among the highest in Europe mean the proportional reduction routinely reaches 50,000 to 150,000 euros on family apartments, which justifies expert costs that might seem disproportionate elsewhere. The housing stock concentrates the classic risk profiles: subdivided Haussmann floors where rooms were recombined without remeasurement, top-floor chambres de service (former maid’s rooms) aggregated into studios with sloped ceilings, and bourgeois apartments whose listed area silently absorbed loggias glazed decades ago. In the inner suburbs, post-war co-ownership blocks generate a different pattern: original developer measurements reused across successive resales, each reproducing the same error until a buyer finally commissions a fresh survey. Across the Paris region, co-ownership documents held by the syndic (managing agent) sometimes include old area schedules that contradict the deed; obtaining them early through the notaire’s completion file or directly from the managing agent can corroborate the claim before any expert is appointed.

Costs and recovery follow the ordinary rules of French civil litigation and should be budgeted from the start: the buyer’s surveyor fees, the court expert’s deposit advanced by the claimant, counsel’s fees, and the possibility of recovering part of these costs against the losing seller under the court’s costs order. The reduction itself is a money judgment against the seller, enforceable against a seller still in France through the usual enforcement channels; where the seller has moved abroad, European or treaty enforcement mechanisms may be needed, which counsel should assess before filing rather than after winning. One final Paris practice point: never let the file sleep between the private counter-measurement and the court filing. The one-year forfeiture runs from the authentic deed, not from discovery of the shortfall, so a buyer who discovers the error in month ten has weeks, not months, to file the référé writ. The buyers who recover are not those with the largest shortfalls but those who diary the deed anniversary on the day they sign it. Readers dealing with a suspected mismeasurement in the capital can have the file reviewed within that timetable through counsel practising French real estate law for international clients in Paris, before the deadline decides the case for them.

Conclusion

The loi Carrez gives the buyer of a French co-ownership lot a remedy of rare mechanical clarity: state the private area, and if reality falls short by more than one twentieth, reduce the price proportionally. Around that simplicity the law builds two unforgiving deadlines. A missing statement supports annulment within one month of the notarial deed, and only the authentic deed mentioning the area purges the defect, never a signed certificate. A wrong statement supports a proportional reduction within one year of the deed, on pain of forfeiture, but an urgent application for a court-appointed measurement interrupts that year while freezing the proof. For foreign buyers, the method is therefore fixed: commission an independent counter-measurement to the decree’s definition at the first doubt, file for a court expertise well before the anniversary of the deed, compute the reduction room by room, and litigate where the property sits, with Paris stakes justifying Paris diligence. Measured early and filed in time, a shortfall of a few square metres becomes what the statute intended it to be: money back, not a lesson learned.