Construction without Planning Permission: When a Mistake of Law is Not Enough to Avoid Penalty

Imagine: you are the owner of a property in Annemasse, with a lovely plot of land overlooking the Salève. You decide to build a small garden shed, nothing major. A neighbour tells you it is not regulated. So you go ahead. A few months later, the planning department issues you with an infringement notice: construction without planning permission. You plead mistake of law, the famous excuse 'I didn't know'. But is that enough? Not necessarily, as shown by a judgment of the Court of Cassation of 12 September 2006.

This decision, rendered under number 05-83.235, answers a question every owner asks: can I be prosecuted if I made a good faith mistake about the regulations? The Court of Cassation, the highest French court, ruled: to be exonerated, it is not enough to plead ignorance of the law. You must also demonstrate that the mistake was unavoidable and that you legitimately believed you had authorisation.

But concretely, how do you prove that? And above all, what are the risks if you build without permission in the French Genevois region? Let us analyse this judgment and its practical consequences.

The Facts: An Everyday Story

Mr. Bernard A. is the owner of a plot in Annemasse. Without applying for planning permission, he erects a structure on his land. The problem: the local land-use plan (POS) prohibits this type of construction in that location. The mayor prosecutes him for two offences: construction without planning permission (Article L.421-1 of the French Town Planning Code) and non-compliance with the POS.

Before the criminal court, Mr. A. is convicted. But he appeals. The Court of Appeal of Chambéry (which has jurisdiction over Annecy) acquits him outright. The reason: he allegedly made a mistake of law within the meaning of Article 122-3 of the French Criminal Code. In other words, he sincerely believed he did not need planning permission. Perhaps he was badly advised by a neighbour, or misinterpreted a planning document. In any case, the appeal judges believed him.

But the civil parties (probably the municipality or neighbours) are not satisfied with this acquittal. They appeal to the Court of Cassation. The Court of Cassation quashes the appeal judgment. It considers that the judges did not justify their decision: they did not show that Mr. A.'s mistake was unavoidable, nor that he legitimately believed he held valid authorisation. In short, the Court of Appeal acquitted without checking the strict conditions for mistake of law.

What few people know is that the Court of Cassation also recalled an important point: in case of doubt about a planning offence, the judge should stay proceedings if the construction is capable of being regularised by a modified planning permission. But that was not the case here.

The Reasoning of the Court — Analysed

The legal basis of this case is twofold: on the one hand, Articles L.480-4 et seq. of the French Town Planning Code (which penalise construction without permission), and on the other, Article 122-3 of the French Criminal Code (which excuses mistake of law).

Article 122-3 provides: 'A person is not criminally liable if they prove that, by a mistake of law which they were unable to avoid, they legitimately believed they could lawfully perform the act.' Translation: to be exonerated, you must prove two things: 1) that you made a mistake about the rule of law, and 2) that the mistake was unavoidable (you could not have known, despite all reasonable precautions).

In our case, the Court of Appeal merely noted that Mr. A. had made a mistake. But it did not check whether the mistake was unavoidable. For example, had he consulted a lawyer? Had he applied for a planning certificate from the town hall? Had he checked the POS? None of this was reported. The Court of Cassation therefore held that the Court of Appeal had not given a legal basis to its decision.

In other words, the mere assertion 'I didn't know' is not enough. You must demonstrate that you did everything possible to ascertain the rule, and despite that, you were mistaken. This is a heavy burden of proof. undefined, I have come across cases where owners had consulted an architect, but the architect was wrong. In that case, the mistake might be considered unavoidable. But if you relied solely on a neighbour's opinion or a hunch, the courts will not accept it.

However, note: this decision does not create a new principle. It merely recalls the strict conditions for mistake of law. The Court of Cassation here confirms its earlier case law, such as the judgment of 23 March 1999 (Bull. crim. no. 57).

What This Means for You — Practically

Whether you are an owner, landlord or buyer, this decision has direct consequences.

If you are an owner and considering work: never rely on a mere verbal opinion. Before building, apply for planning permission or make a prior declaration at the town hall. If you are unsure about the legality of your project, consult a professional (architect, lawyer). Mistake of law is a defence only if you have taken all reasonable precautions. Example: in Saint-Julien-en-Genevois, an owner built an extension without permission because his neighbour told him it was allowed. The court fined him €5,000 and ordered demolition. The mistake was not accepted because he had not checked with the town hall.

If you are a tenant: you may be at risk if you carry out work without the owner's consent and without permission. But generally, the owner is responsible. However, note: if you are the one who carried out the work, you can be prosecuted.

If you are a buyer: before purchasing a property, check that all constructions comply with planning permissions. If the seller built without permission, you could inherit the problems. Apply for a planning certificate and a certificate of no prosecution.

The penalties are severe: a fine of up to €120,000 (Article L.480-4 of the French Town Planning Code), demolition of the construction, and restoration of the site. And you cannot obtain a regularisation permit if the construction is prohibited by the Local Town Planning Plan (PLU).

Four Tips to Avoid This Type of Dispute

• Consult the PLU of your municipality before any project. Go to the town hall or check the website. Verify zoning, height rules, ground coverage, etc. In Annemasse, the PLU is available online.
• Obtain a planning certificate. This official document tells you whether your land is buildable and what rules apply. It is free and valid for 18 months.
• Never rely on an unofficial opinion. A neighbour, estate agent or tradesman can be wrong. Only a document signed by the town hall is authoritative.
• If in doubt, consult a lawyer specialised in planning law. A 30-minute consultation (€45 with Maître Zakine) can save you months of proceedings and thousands of euros in work.

Further Reading: Related Case Law and Developments

The Court of Cassation has issued several decisions on mistake of law in planning matters. For example, in a judgment of 8 June 2005 (no. 04-85.233), it held that mistake of law could not be invoked by a construction professional who should have known the regulations. Since then, the trend is to reserve this excuse for private individuals who are not experts, but only if they have taken precautions.

In 2018, the ELAN law increased penalties for construction without permission, with fines of up to €300,000 for legal entities. Courts are becoming increasingly strict. Mistake of law is therefore a defence that is increasingly difficult to establish.

In the future, expect judges to require tangible evidence of verification steps. The digitisation of PLUs makes consultation easier, so unavoidable mistakes will become rarer.

Key Points to Remember

• Mistake of law is not an automatic excuse. You must prove it was unavoidable (consultation with a professional, application for a planning certificate, etc.).
• Building without permission exposes you to a fine and demolition. Amounts can reach €120,000.
• Always check the PLU before starting work. It is free and easy.
• If in dispute, do not plead ignorance of the law alone. Get a lawyer to assist you.
• Regularisation is only possible if the construction is permissible. Otherwise, demolition is inevitable.

Are you in a similar situation? A first 30-minute consultation with Maître Zakine (€45) can save you months of proceedings — and often much more. Book an appointment →