Illegal Construction: Even Without Planning Permission, Works Are Subject to the Town Planning Code

Imagine: you own a flat in Borgo, near Bastia, and you decide to convert a large cellar into a rental studio. You think it's a simple interior fitting, without consequence. Yet, without knowing it, you could be in breach of the law. What you may not have known is that even if the room was originally built without planning permission, any conversion works remain subject to town planning rules. This is what the Court of Cassation reminded us in a judgment of 15 April 2008 (n° 07-84.150).

This decision, unknown to the general public, has concrete repercussions for any owner who touches an existing building, even if irregular. Whether you are a landlord, buyer or co-owner, you should know that the administration can prosecute you for lack of planning permission, even if you did not erect the walls. But what exactly does this change? Let's decipher this case law and its practical consequences together.

In this article, I will tell you the story behind this decision, explain the judges' reasoning, and give you concrete advice to avoid pitfalls. As a lawyer specialising in property law, I have seen cases where owners found themselves before the criminal court for works they thought were harmless. Do not let ignorance cost you dearly.

The Facts: A Story Like Any Other

Mr X, a property developer, had bought a building in Bastia. In this building, there were storage rooms that had been built without planning permission, probably by a previous owner. Mr X decided to convert these storage rooms into flats, to resell or rent them. For this, he undertook works: partitioning, installation of sanitary facilities, electricity, etc. He did not apply for any planning permission, believing that the storage rooms already existed and that he was merely refurbishing them.

The problem is that converting storage rooms into dwellings changes the use of the premises and increases the number of dwellings, which requires planning permission. The municipality of Bastia became aware of this and drew up a report of the offence. Mr X was prosecuted before the criminal court for building without permission.

Before the judges, Mr X pleaded good faith: he had not built the storage rooms, they were already there, and he was merely fitting them out. But the Court of Cassation rejected this argument. It held that works carried out on an existing building, even if illegally erected, are subject to the requirements of the Town Planning Code. In other words, the original irregularity of the building does not exempt the current owner from complying with town planning rules when carrying out works. Mr X was therefore convicted of the offence of building without permission.

What is striking in this case is that the developer had bought the building with full knowledge of the facts: the deed of sale may have mentioned the irregularity, or he should have checked it. undefined, I have come across cases where buyers discover after the event that their property includes illegal areas. Caution is therefore required.

The Reasoning of the Court — Explained

The Court of Cassation relied on the articles of the Town Planning Code relating to planning permission (in particular Article L. 421-1, now codified in Article L. 421-1 of the Town Planning Code: "Constructions, even those without foundations, must be preceded by a planning permission"). The reasoning is simple: town planning rules apply to all works, whether they relate to a regular building or not. Previous illegality cannot be invoked as an excuse for not complying with the law.

The judges also considered that converting storage rooms into dwellings constitutes a change of use (from storage to dwelling) and a creation of floor area, which requires planning permission. It does not matter that the walls are already standing: what matters is the modification of use and the urban planning impact (increase in the number of dwellings, parking, etc.).

However, note that this decision does not concern simple maintenance or repair works. If you re-roof or repaint a façade, you do not need permission. But as soon as you modify the structure, use or external appearance, the rules apply. In short, the Court wanted to prevent illegal buildings from becoming "no-go zones" where anything is allowed.

This solution has been consistent since 2008. It has been confirmed by other judgments, particularly in matters of change of use. What few people know is that the administration can also require the demolition of illegal works, even on an existing irregular building. The risk is therefore twofold: criminal (fine, imprisonment) and administrative (restoration).

What This Changes for You — Practically

If you are the owner of a property with outbuildings (cellar, garage, storage room) that you wish to convert into a dwelling, you must imperatively check the original planning permission and, if the works are subject to authorisation, apply for it. In Bastia, for example, the town hall is particularly vigilant about conversions of garages into studios, common in the old centre. An owner who carries out such works without permission risks a fine of up to €300,000 and a prison sentence (Article L. 480-4 of the Town Planning Code).

For buyers, be vigilant: if you buy a property with non-compliant areas (for example, a conservatory without permission or a converted basement), you may be required to regularise or demolish. Before buying, ask the seller to provide all planning permissions and, if in doubt, consult a lawyer. A notary is not always able to detect these irregularities.

For co-owners, be careful with common parts converted into dwellings. If a co-owner has carried out works without authorisation on a common part (for example, a bicycle storage room turned into a studio), the management company can take action to stop the breach. In a co-ownership in Borgo, I saw a case where an owner had converted a cellar into a dwelling without permission: the town hall ordered demolition, and the co-owner had to reimburse the costs to the co-ownership.

If you are a tenant, you are not directly concerned, but you can report suspicious works carried out by your landlord to the town hall. In the event of a dispute, know that your lease may be cancelled if the dwelling is illegal (for example, if it has no permission).

Four Tips to Avoid This Type of Dispute

• Before any works, ask the town planning department of your town hall. Even for a simple fitting, an operational town planning certificate will tell you if permission is needed. It is free and legally covers you.
• Consult a lawyer specialising in property law before buying a property with outbuildings. A thorough survey may reveal hidden irregularities. In Bastia, the cost of a consultation (around €150) is negligible compared to the cost of demolition.
• If you inherit a property with illegal constructions, regularise them quickly. You can apply for retrospective planning permission if the construction complies with the Local Town Planning Plan (PLU). Otherwise, you will have to demolish.
• Never carry out works without permission on an existing building, even if it is old. The administration has a limitation period of 6 years to act (Article L. 480-17 of the Town Planning Code), but it can also prosecute you criminally within 3 years of the completion of the works.

Further Details: Related Case Law and Developments

The 2008 decision is part of a consistent line. As early as 2001, the Court of Cassation had ruled that "works to convert a room into a dwelling constitute a construction subject to planning permission" (Crim., 13 June 2001, n° 00-86.406). More recently, it extended this logic to changes of use without works (Crim., 12 January 2016, n° 15-81.851).

The trend is therefore towards firmness: judges no longer tolerate ignorance of the rule. Town halls, especially in high-demand areas like Bastia, are increasingly active in combating clandestine dwellings. With the ALUR law of 2014, the powers of mayors have been strengthened to penalise and stop illegal works.

For the future, we can expect case law to become even stricter, particularly in matters of limitation periods and penalties. If you have an irregular property, it is urgent to regularise it. The cost of retrospective planning permission is much lower than that of legal proceedings.

Frequently Asked Questions

1. Can I convert my garage into a studio without permission? No, if the garage is an existing building, even if illegal, the change of use requires planning permission. You risk a fine and an obligation to restore the premises.
2. What if I have already carried out works without permission? Consult a lawyer to assess the limitation period. If less than 6 years, apply for retrospective planning permission. If refused, prepare to demolish.
3. What are the time limits for the administration to act? The criminal action is time-barred after 3 years from the completion of the works. The administrative action (demolition) is time-barred after 6 years.
4. Must the seller inform me of illegal constructions? Yes, he must inform you of any irregularity. If he does not, you can claim a reduction in price or cancel the sale for latent defect.
5. Is retrospective planning permission always granted? No, it depends on compliance with the PLU. If the construction is in a flood zone or without parking, the town hall may refuse.

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