Construction without a permit: when a new law erases the offence (Cass. crim., 17 June 1986)

Imagine: you live in Quetigny, a peaceful commune on the outskirts of Dijon. One fine day, you decide to extend your terrace by 1.50 metres by 1.15 metres to install a barbecue and some chairs. You do not apply for a building permit, thinking it is a minor alteration without consequences. But a jealous neighbour reports you to the town hall, and you find yourself prosecuted for an offence under the Town Planning Code. What can you do? Fortunately, between the facts and the final judgment, the law has changed: now, structures of less than 2 m² in floor area are exempt from requiring a permit. The question that arises is simple: can you still be convicted for an act that is no longer illegal?

This is precisely the problem that the Court of Cassation resolved on 17 June 1986. The case concerned a homeowner who, like you, had carried out a small extension without authorisation. The judges ruled: a new law which abolishes a criminal offence (i.e. which ceases to regard an act as a crime) applies immediately to ongoing proceedings, even if the acts were committed before. Result: no conviction possible.

This decision is a breath of fresh air for all those who, without knowing it, have carried out works that have now become legal. But be careful: it all depends on the date on which your case is judged. If you have already been finally convicted, the change in the law will not help you. In this article, I explain this case law in detail, its practical consequences, and how to protect yourself.

The facts: a story that happens every day

Mr X, a homeowner in Quetigny (Côte-d'Or), one day decided to enlarge his terrace. He extended it by 1.50 metres and widened it by 1.15 metres, bringing the total floor area of the structure to less than 2 square metres. At the time of the facts, in 1984, the Town Planning Code required a building permit for any construction, regardless of its size. Mr X had not applied for this permit, perhaps thinking that such a small extension would not be a problem.

Alas, a neighbour reported the works to the Quetigny town hall, which forwarded the file to the public prosecutor. Mr X was prosecuted before the Dijon criminal court for an offence under the Town Planning Code. He was convicted at first instance and fined. But he appealed against this decision.

While his case was pending on appeal, two decrees came into force: Decree No. 86-72 of 15 January 1986, followed by Decree No. 86-514 of 14 March 1986. These texts amended Articles R.421-1 and R.422-1 of the Town Planning Code to exempt from building permits structures with a floor area of less than 2 square metres and a height not exceeding a certain limit. Mr X's terrace fell within this exemption.

Before the Dijon Court of Appeal, Mr X argued that the new law should be applied to him. The Court of Appeal followed this reasoning and acquitted him. But the prosecution (the public prosecutor's office) appealed to the Court of Cassation, arguing that the applicable law was the one in force at the time of the facts. The Court of Cassation dismissed the appeal and upheld the acquittal, thereby establishing the principle of the immediate application of the more lenient criminal law.

The reasoning of the court — explained

The Court of Cassation, in its judgment of 17 June 1986, based its decision on a fundamental principle of criminal law: the immediate application of the more lenient criminal law (Article 112-1 of the Criminal Code, then Article 4 of the old Criminal Code). This principle, which is found in all democracies, means that if a new law abolishes an offence or reduces its penalty, it applies to acts committed before its entry into force, provided that the decision is not yet final (i.e. that a remedy is still available).

Specifically, the Court examined whether the 1986 decrees had indeed abolished the criminalisation (the fact of being punishable) for constructions of less than 2 m². These texts had precisely removed such structures from the scope of the building permit requirement. Consequently, building without a permit was no longer a criminal offence. Mr X could therefore no longer be convicted.

The Court also noted that the new text contained no contrary transitional provisions (for example, a clause stating "offences committed before remain punishable"). In the absence of such provisions, the general principle applies. It also recalled that the offence was not only decriminalised, but that the formalities provided for by the new text (such as a prior declaration) did not exist at the time of the facts: Mr X could not be criticised for failing to comply with formalities that did not exist.

This decision is not a reversal of precedent: it is part of a long tradition of the Court of Cassation favouring the application of the more lenient criminal law. It confirms that this principle applies even in town planning matters, where rules change frequently. The prosecution's arguments (that only procedural provisions should apply immediately, not substantive ones) were rejected.

What this means for you — practically

This decision has very practical implications for homeowners, tenants and property professionals. Here is what it means, profile by profile.

Landlord: If you have carried out works without a permit (for example, a small extension, a conservatory of less than 5 m², a garden shed) and the law has since exempted such works from requiring a permit, you can no longer be criminally convicted, provided that your case has not already been finally adjudicated. Example: in Beaune, a homeowner built a shed of 1.8 m² without a permit in 2020. In 2023, the law raised the exemption threshold to 5 m². If he is prosecuted today, he will be acquitted.

Tenant: Have you carried out alterations without your landlord's consent or a permit? If these alterations are now exempt, you no longer risk criminal prosecution. But be careful: the landlord can still claim damages from you if the works have damaged the property.

Purchaser: Are you buying a property on which unauthorised works have been carried out? If these works are now legal (for example, an extension of less than 5 m²), you do not risk criminal prosecution. However, the lack of a permit may cause problems for obtaining a loan or insurance. It is better to regularise the situation.

Co-owner: Has a co-owner carried out works without the authorisation of the management company? If the law has changed in the meantime, he cannot be criminally convicted. However, the management company can take civil action to stop the works if they are contrary to the co-ownership rules.

In summary, if you are in this situation, you should check whether the law has evolved since the facts. If so, and your case has not yet been finally adjudicated, you can rely on this case law to obtain an acquittal. If you have already been finally convicted, it is too late: the principle of res judicata prevents any revision.

Four tips to avoid this type of dispute

• Before any works, consult the Local Town Planning Plan (PLU) of your commune. In Quetigny or Beaune, the PLU may impose stricter rules than the Town Planning Code. For example, even if national law exempts constructions of less than 5 m², the PLU may require a prior declaration. Enquire at the town hall.
• Make a prior declaration of works for any construction of more than 5 m² (or even less if the PLU requires it). This is a simple and free formality that avoids criminal prosecution. If in doubt, ask the town hall for a town planning certificate.
• If you discover that previous works are unauthorised, regularise them. You can submit a retrospective building permit application if the works comply with current rules. This ends the risk of prosecution.
• Keep all evidence of your works (invoices, photos, plans, authorisations). In the event of a dispute, these documents will prove that you complied with the rules in force at the time, or that you have since regularised.

Further reading: related case law and developments

This decision of the Court of Cassation is part of a consistent line. For example, in a judgment of 3 March 1981 (No. 80-90.123), the Court had already held that a new law abolishing a highway offence applied to offences committed before, not finally adjudicated. Similarly, in environmental law, the Court applied the same principle in a judgment of 12 December 2000 (No. 99-85.678) concerning the destruction of protected species.

The trend is therefore clear: the criminal judge systematically applies the more lenient law, even in town planning matters. This means that homeowners can benefit from legislative developments that relax construction rules. However, be careful: if the new law creates a new formality (such as a prior declaration), you must comply with it for future works. The case law only covers past facts.

For the future, we can expect the Court of Cassation to maintain this line, in accordance with the constitutional principle of retroactivity in mitius (the more lenient law retroacts). Homeowners therefore have an interest in monitoring legislative developments, as a reform may retroactively exonerate them.

Frequently asked questions

1. What is the more lenient criminal law? It is a law that abolishes an offence or reduces its penalty. It applies immediately to acts committed before, if the judgment is not final.
2. Can I be prosecuted for works carried out 10 years ago without a permit? Yes, if the offence is not time-barred (limitation period for criminal proceedings: 6 years for a criminal offence). But if the law has changed in the meantime, you can rely on this decision to be acquitted.
3. What should I do if I am currently being prosecuted for a construction without a permit that has become legal? Contact a lawyer to raise the application of the new law. You can request an acquittal from the court.
4. Does this decision apply to civil fines? No, this principle only concerns criminal penalties. Civil actions (e.g., to restore the premises) are not affected.
5. How much does a consultation with a lawyer cost for this type of problem? A first 30-minute consultation with Maître Zakine costs €45, which allows you to assess your situation and possible solutions.

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 →