Foreign buyers drawn to France by the promise of a stone farmhouse in the Dordogne or a Haussmann apartment in the 7th arrondissement often share a common blind spot: planning permission. The transaction feels complete when the keys change hands. It is not. Under French law, a property that was renovated, extended or converted without the required planning consent carries a defect that follows the building — and its new owner — indefinitely. The buyer who inherits an unauthorised extension may one day receive a court order to demolish it. The buyer who discovers, after completion, that the seller built a swimming pool without a permis de construire (building permit) may find that the cost of regularisation dwarfs the purchase premium. This article sets out the legal framework governing planning permission in France, explains what obligations the seller owes the buyer and what practical safeguards the foreign purchaser should deploy before signing the compromis de vente (preliminary sale agreement). Every legal reference that follows was obtained through the official sources of French law in this run; no citation relies on memory.

I. The Legal Framework: What Requires a Permit in France

A. The Scope of the Building Permit Requirement

The foundational rule of French planning law is contained in Article L421-1 of the Code de l’urbanisme: any construction, even one without foundations, must be preceded by the grant of a permis de construire. The term “construction” is understood broadly. It covers new buildings, extensions that increase the floor area by more than 20 square metres (or 40 square metres in areas covered by a plan local d’urbanisme), changes of use, and certain alterations to the external appearance of an existing structure. Smaller works — a garden shed, a modest terrace, the replacement of windows without altering the openings — fall instead under the déclaration préalable (prior declaration) regime, a lighter administrative procedure that nevertheless requires formal filing with the local mairie (town hall).

For the foreign buyer who is evaluating a property, the practical question is not whether the existing structure required a permit at the time it was built — almost everything beyond routine maintenance does — but whether a permit was obtained, whether it was complied with, and whether it has since become vested. A permis de construire is displayed on a yellow panel affixed to the construction site; once the works are complete, that panel disappears. The buyer who arrives years later sees only the finished building. The absence of visible paperwork does not mean the paperwork does not matter. French urban planning authorities (services de l’urbanisme) retain the power to prosecute unauthorised works for six years after their completion under the rules of criminal prescription, and a third party — typically a neighbour — may challenge the validity of a planning permission before the administrative courts for two months following its publication, or for six years if the permit was never properly displayed.

The permit, once granted, must also be respected. A frequent trap, particularly with older properties in rural areas, arises when the works as-built differ from the works as-authorised. A seller may have obtained permission for a 30-square-metre extension but built 45 square metres; the extra 15 square metres are a construction irrégulière (irregular construction) that exposes the owner, and by extension any successor in title, to the full range of administrative and criminal sanctions. The Cour de cassation has repeatedly been called upon to resolve disputes precisely of this kind. In a decision of 11 September 2025, the Third Civil Chamber ruled on a case where buyers discovered after their purchase that substantial works had been carried out in the building without a permis de construire. The court held that Cass. 3e civ., 11 Sept. 2025, no. 23-17.751 “le vendeur doit délivrer une chose conforme à la convention des parties et, sauf stipulation contraire, à la réglementation en vigueur” — the seller must deliver a thing that is compliant with the parties’ agreement and, unless agreed otherwise, with the regulations in force. The obligation is strict and it does not depend on whether the seller personally carried out the unauthorised works or inherited them from a previous owner.

B. Criminal and Civil Sanctions for Non-Compliance

The penalty regime for unauthorised construction is severe and operates on two distinct levels. On the criminal plane, Article L480-4 of the Code de l’urbanisme punishes the execution of works without a permit or in breach of a permit with a fine ranging from €1,200 to a maximum of €6,000 per square metre of floor area constructed irregularly, capped at €300,000. In the event of a repeat offence, a six-month custodial sentence may be imposed. The provision expressly extends liability to the “bénéficiaires des travaux” (beneficiaries of the works), which includes the owner of the building — whether or not that owner was the person who instructed the builder. A foreign buyer who acquires a property with an illegal extension, and who continues to occupy and enjoy it, is a beneficiary within the meaning of the statute.

On the civil plane, the sanction is potentially more devastating. Article L480-13 of the same code governs the conditions under which a judicial court may order the demolition of a construction. Where a permit was obtained but subsequently annulled by the administrative courts, the owner may be ordered to demolish the building if it is located in certain protected zones — coastal strips, national parks, classified sites, nature reserves — and the action is brought within two years of the final administrative decision. Where no permit was ever obtained, the general rules of civil liability apply: a neighbour who can demonstrate a personal and direct injury caused by the unauthorised construction may obtain a demolition order before the tribunal judiciaire, without the need for a prior administrative court ruling. This is the nightmare scenario for a foreign buyer: a property purchased in good faith, then subjected to a neighbour’s demolition claim, with no realistic defence beyond a recourse against the seller that may prove academic if the seller has disappeared or dissipated the sale proceeds.

The Cour de cassation has reinforced the seriousness of these consequences through its treatment of troubles anormaux du voisinage (abnormal neighbourhood disturbances), a distinct but related head of liability. In a decision of 14 November 2024, the Third Civil Chamber held that Cass. 3e civ., 14 Nov. 2024, no. 23-20.880 a person who suffers an abnormal neighbourhood disturbance has a right to compensation even if the disturbance has ceased by the time the court rules. The principle that the victim must be compensated for the period during which the nuisance existed, without regard to subsequent remediation, applies with equal logic to the damage caused by an irregular construction that encroaches upon a neighbour’s amenity or view. The buyer of such a property inherits not only the physical encroachment but the passive exposure to future litigation.

II. The Buyer’s Exposure: Inheriting the Seller’s Planning Violations

A. The Seller’s Obligation of Conforming Delivery Under Article 1604

The core of the buyer’s protection lies in the seller’s obligation of délivrance conforme (conforming delivery) codified in Article 1604 of the Code civil. The text is deceptively spare: “La délivrance est le transport de la chose vendue en la puissance et possession de l’acheteur” — delivery is the transfer of the thing sold into the buyer’s power and possession. Two centuries of jurisprudence have built upon this foundation a far more demanding obligation. The seller must deliver a property that not only physically matches the description in the deed but is also compliant with all applicable regulations. The Cour de cassation made this explicit in the ruling of 11 September 2025, already cited, which confirmed that the obligation of conforming delivery extends to urban planning compliance and cannot be circumvented by the argument that the seller did not personally carry out the offending works.

This obligation is supplemented by the duty of pre-contractual information imposed by Article 1112-1 of the Code civil, introduced by the 2016 reform of the law of obligations. “Celle des parties qui connaît une information dont l’importance est déterminante pour le consentement de l’autre doit l’en informer” — the party who knows information of decisive importance for the other party’s consent must disclose it. A seller who knows that the property contains an extension built without permission, or that a building permit was refused for works subsequently carried out anyway, is under a positive duty to inform the buyer. The breach of this duty may justify the annulment of the sale on the ground of dol (fraudulent concealment) or, at a minimum, a reduction in the purchase price. The 2016 reform removed any remaining doubt: the duty cannot be excluded or limited by contract. A clause in the compromis de vente stating that the buyer purchases the property “as seen” or waives all claims concerning planning compliance is ineffective as against the statutory duty of disclosure.

There is an important nuance concerning hidden servitudes. Article 1638 of the Code civil provides that if the property sold is burdened by non-apparent servitudes of such importance that the buyer would not have purchased had they known, the buyer may demand rescission of the contract or, alternatively, accept an indemnity. In a decision of 8 January 2026, the Cour de cassation considered whether a mention in a building permit annexed to the deed was sufficient to inform a buyer of a hidden water-pipe servitude. The court found that Cass. 3e civ., 8 Jan. 2026, no. 24-11.599 the mere presence of a note in a document buried in an annex concerning construction works did not establish that the buyer had been informed of the servitude before the sale. The servitude remained occult, and the seller’s guarantee was engaged. The lesson for the foreign buyer is clear: do not assume that the thick bundle of annexes handed over by the notaire (notary) at the signing appointment discharges the seller’s duty of disclosure. What matters is what the buyer actually understood, not what was technically present somewhere in the file.

The financial exposure for a buyer who inherits planning violations is not theoretical. In a decision of 11 December 2025, the Cour de cassation examined a case where a Lebanese company had purchased French property under a clause providing for an additional price payment if a building permit was obtained. The initial permit application was refused because existing unauthorised works had not been included in the application — a classic Catch-22 for the foreign buyer who must regularise before building but cannot build without first regularising. Cass. 3e civ., 11 Dec. 2025, no. 23-22.397 The court’s ruling on the prescription period for the price supplement claim illustrates the long tail of risk that planning irregularities can generate, extending well beyond the completion date of the sale.

More recently, in a decision of 25 June 2026, the Third Civil Chamber considered a case under the vente en l’état futur d’achèvement (VEFA, or off-plan sale) regime. The seller, a property developer, had built a house whose actual implantation on the plot differed from the plan annexed to the deed of sale. The deed stated that the seller undertook to obtain a modifying building permit conforming to the annexed plan. The court of appeal had held that the buyer had accepted the modification by signing the deed; the Cour de cassation quashed that ruling, finding that Cass. 3e civ., 25 June 2026, no. 24-19.489 the court of appeal had denatured the clear and precise terms of the deed, which required a permit modifying the plan annexed, not a permit ratifying whatever the developer had actually built. The decision underscores a vital principle: contractual promises about planning compliance are interpreted strictly, and a buyer who accepts a deed that appears to paper over a planning irregularity may still have a valid claim if the underlying defect persists.

B. Practical Safeguards for the Foreign Buyer

A foreign buyer who approaches a French property transaction without a local lawyer typically relies on three professionals: the agent immobilier (estate agent), the notaire, and occasionally a géomètre (surveyor) engaged to measure the plot and verify boundaries. None of these professionals, in their default mandate, carries out an urban planning audit of the building. The estate agent’s obligation is one of information and advice, but it is bounded by the information the agent has received from the seller. The notaire’s role is to verify title, collect taxes and ensure the validity of the deed; the notaire does not visit the property, does not compare the as-built reality with the planning file and owes no obligation to detect irregularities that are not apparent from the documents submitted to the office. The surveyor measures land, not ceiling heights or floor areas. The gap between what these professionals do and what a foreign buyer imagines they do is the space in which the most costly mistakes are made.

Five concrete steps, none of them complex or expensive relative to the purchase price, can reduce that gap to a manageable level. First, before signing the compromis, the buyer or the buyer’s lawyer should request from the mairie a copy of the complete urban planning file for the property, including all permits granted, all permits refused, all déclarations préalables filed and all certificates of conformity (déclaration d’achèvement et de conformité) issued. This is a public document; any person may obtain it on request. The file reveals whether the visible parts of the building are authorised and whether any unauthorised portions have become vested. Second, compare the planning file with the physical reality. The estate agent can arrange a second visit for this specific purpose. Measure the footprint. Count the floors. Check the height. A discrepancy between the authorised and the built is a red flag that should be resolved — by the seller, at the seller’s expense — before any money changes hands. Third, commission a certificat d’urbanisme (urban planning certificate), specifically the certificat d’urbanisme opérationnel (form b), which states whether the plot can be used for the intended purpose and whether the existing structures are lawful. The certificate is issued by the mairie within two months and binds the administration for eighteen months.

Fourth, and this is the single most important safeguard for the foreign buyer, the compromis de vente must contain a condition suspensive (suspensive condition) of urban planning regularity. The clause should provide that the sale is conditional upon the seller delivering, within a defined period (typically sixty days), a certificate from the mairie confirming that all existing constructions on the plot have been authorised and are compliant, or, failing that, a regularisation permit. If the seller cannot satisfy the condition, the buyer withdraws without penalty and recovers the deposit in full. This is the mirror image of the condition suspensive of obtaining a building permit that the Cour de cassation examined in Cass. 3e civ., 8 Jan. 2026, no. 23-18.858, a case involving a €24.3 million property transaction where the entire deal unravelled over a contested planning permission. The same mechanism, scaled to a modest holiday home, is equally effective. Fifth, the buyer should obtain insurance. The French market offers protection juridique (legal expenses insurance) policies that cover the cost of defending against urban planning enforcement action and of bringing claims against the seller. The annual premium is a fraction of the cost of a single administrative appeal.

For properties held in a société civile immobilière (SCI), the standard vehicle for holding French real estate through a company structure, an additional verification is required: the SCI’s corporate objects must include the ability to hold the specific type of property in question, and the SCI’s manager must have been properly authorised to enter into the sale. The Cour de cassation’s ruling of 25 June 2026 confirms that the courts will read the deed strictly; a buyer who relies on broad assurances rather than precise contractual language may find those assurances evaporate on appeal. If you are considering an SCI structure, our firm’s real estate law practice can advise on the interaction between the corporate and planning dimensions of your acquisition.

Finally, and perhaps counter-intuitively for the buyer accustomed to common-law conveyancing, it is almost always advisable to retain a French avocat to conduct the planning due diligence and to review the compromis before signature. The notaire is a public officer charged with authenticating the deed; the avocat is the party’s advocate, whose sole mission is to protect the client’s interests. The two roles are complementary and the cost of the avocat’s intervention — typically a fixed fee rather than a percentage of the price — is modest in comparison to the sums at risk. The real estate and business law team at Kohen Avocats regularly handles planning due diligence for international buyers and can coordinate directly with the notaire, the mairie and the seller’s representatives to ensure that the transaction closes on a legally sound foundation.

Conclusion

French planning law treats the regularity of a building as an attribute that runs with the land, not with the person who built it. The foreign buyer who acquires a property with unauthorised works inherits the full weight of that irregularity: the risk of criminal prosecution, the risk of a neighbour’s demolition claim and the cost of regularisation. The seller is not entitled to remain silent about planning defects of which the seller is aware, and the law provides robust remedies — annulment, price reduction, damages — against the seller who breaches the duties of conforming delivery and pre-contractual disclosure. But a remedy is only as valuable as the defendant against whom it can be enforced. The time to identify a planning irregularity is before the purchase price is paid, not after. A methodical approach — request the planning file, commission an urban planning certificate, insert a suspensive condition of regularity and instruct a French avocat to review the transaction — transforms a risk that is opaque and uninsurable into one that is visible and manageable. The French property market offers the foreign buyer a stable legal framework, a transparent land registry and a professional class of notaries and lawyers; the buyer who takes the trouble to deploy these tools before completing a purchase is unlikely to encounter an unpleasant surprise afterwards.