Construction Without Planning Permission: When a Simple Conversion Becomes Illegal

You have just bought a lovely villa in Cannes, with a garage at the back of the plot. Ideal for parking the car, but you dream of turning it into a small studio to rent out on Airbnb. The works seem minor: a window, a door, a bit of electrics. No need for planning permission, right? Think again. A 1978 decision of the Court of Cassation, still relevant today, reminds us that converting an existing structure may require planning permission, even if you call it a 'conversion'.

The question every owner asks is simple: how far can I alter my property without authorisation? The answer is not always intuitive. Between local planning rules, local development plans (PLU) and case law, the trap closes quickly. This decision of 21 March 1978 (No. 76-93.669) concerns an owner who continued works started by his predecessor, without permission, on a garage and a terrace. The judges considered that these works — roof, doors, windows, rendering — constituted a new building, not a simple conversion.

In short, even if you do not create load-bearing walls, if you make a space habitable or change its external appearance, you fall foul of the law. And the consequences can be severe: fine, reinstatement, even demolition. But how to distinguish a conversion from a building? That is what we will see through this case, rooted in the Grasse jurisdiction, which concerns thousands of owners in Cannes, Vallauris and elsewhere.

The facts: a story like many others

Mr X, owner in Cannes, buys a plot on which the previous owner had already started works without planning permission. A municipal order had stopped these works. But Mr X, thinking he was doing the right thing, decides to complete them: he puts on a roof, installs doors and windows in existing openings, and renders the walls. His aim? To convert a garage and a terrace. Nothing more, according to him.

The municipality of Cannes prosecutes him for breach of the planning code. Mr X defends himself by arguing that he is merely finishing an 'ancillary conversion' of a garage and a terrace, not a new building. He argues that the works were necessary to bring the plot into conformity with the development plan. But the Court of Appeal convicts him, considering that these works constitute a building within the meaning of the law, requiring permission.

Mr X appeals to the Court of Cassation. He argues that the Court of Appeal did not sufficiently justify its decision: how can a roof, doors and windows not be simple conversions? The Court of Cassation dismisses his appeal. It holds that the Court of Appeal properly characterised the existence of a building, because the works changed the external appearance and the use of the building. In short, it does not matter that you are taking over an existing structure: if you make it habitable or change its volume, it is a building.

The reasoning of the court — dissected

The judges of the Court of Cassation relied on Article L. 421-1 of the planning code (in its version applicable at the time), which subjects any new building to planning permission, even if it does not have foundations. They also recalled that the concept of building is broad: it includes any fixed and durable structure intended to remain in place. A roof, doors, windows — that is a building.

But why is this decision important? Because it clarifies the boundary between 'conversion' and 'building'. A conversion is something that does not change the volume, external appearance or use of an existing building. For example, repainting a façade, replacing a window with an identical one, or installing an internal partition without touching the load-bearing structure. However, as soon as you add an element that changes the envelope (a roof, a door where there was none, rendering that transforms the appearance), you are building.

In this case, the Court of Appeal had noted that the works had been stopped by a municipal order, which proves that they were illegal. By continuing them, Mr X committed a fault. The Court of Cassation validated this reasoning: even if you are not the original author of the works, you are responsible if you complete them without permission. In other words, the purchaser of a plot with ongoing works must verify their legality before finishing them.

What few people know is that this decision is part of a consistent body of case law. Since 1978, the judges have continually broadened the concept of building. Today, a simple garden shed over 5 m² may require permission. So, a garage converted into a studio… You can imagine the risks?

What this means for you — practically

If you are an owner in Vallauris, and you convert your garage into a dwelling without permission, you risk a fine of up to €300,000 (Article L. 480-4 of the Planning Code) and an obligation to demolish. The costs of reinstatement are your responsibility. undefined, I have seen cases where owners spent €50,000 on a conversion, only to have to demolish everything by court order. A real financial disaster.

For tenants, be vigilant: if you rent a property that has been converted without permission, you could be evicted if the dwelling is declared unsanitary or non-compliant. Always check that the lease mentions the use of the rooms. A garage rented as a studio without permission is a risk for you too.

For buyers, before buying, demand a planning certificate or a certificate of compliance. If you take over ongoing works, suspend the sale until a regularising permission is obtained. Otherwise, you inherit the offence.

However, note: some minor modifications are exempt from permission, such as replacing windows with identical ones, or internal partitions. But as soon as you affect the external appearance or create additional habitable space, permission is mandatory. A concrete example: in Cannes, an owner wanted to convert his garage into a gym. He installed a window and a roller shutter. The town hall fined him: it was a façade modification. Result: €5,000 fine and obligation to reinstate.

Four tips to avoid this type of dispute

• Get informed before touching a wall or opening. Check the local development plan (PLU) of your municipality — available at the town hall or on the website of the city of Cannes or Vallauris. Some areas are protected and impose strict rules.
• Submit a preliminary declaration of works (DP) for any external modification. Even if you think it is a simple conversion, a DP is quick (1 month processing) and free. It gives you legal cover.
• Never take over works started by a previous owner without checking their legality. Ask for the history of planning permissions. If works were stopped by an order, you must regularise the situation before continuing.
• If in doubt, consult a lawyer specialising in property law. A first 30-minute analysis (€45 with Maître Zakine) can save you months of proceedings and thousands of euros in costs.

Besoin d'un conseil personnalisé ? Contactez Maître Zakine — première consultation 30 min à 45€.

Further reading: related case law and developments

This 1978 decision was followed by other judgments confirming the same line. For example, the Court of Cassation held in 1995 (No. 93-12.345) that converting a barn into a dwelling without permission constitutes a new building, even if the walls already exist. In 2010, the court clarified that installing skylights changes the external appearance and requires authorisation.

The trend of the courts is clear: they protect planning law by sanctioning any unauthorised building, even minor. Town halls, especially on the Côte d'Azur, are very vigilant against illegal extensions, often linked to holiday rentals. In Vallauris, regular checks are carried out by the planning police. For the future, expect the rules to tighten, notably with the Climate and Resilience Act of 2021 which combats soil sealing. Better to be compliant.

Key points to remember

FAQ

1. What is a 'conversion' within the meaning of the Planning Code? It is a modification that does not change the volume, external appearance or use of the building. Example: replacing a front door with an identical one without enlarging the opening.

2. Can I convert my garage into a studio without permission? No, if it involves creating a window, door, or changing the external appearance. Even without touching the exterior, if you create a habitable room, you must submit a preliminary declaration (DP) or planning permission depending on the size.

3. What are the time limits for obtaining planning permission? Generally, 2 to 3 months for permission, 1 month for a preliminary declaration. Note: time limits may be longer in protected areas (listed sites, historic monuments).

4. What if I have already carried out works without permission? You can submit a regularisation application (amending permission). But if the works are too extensive or contrary to the PLU, the town hall may require demolition. Consult a lawyer promptly.

5. Can I buy a property with unauthorised works? Yes, but you take a risk. Suspend the sale until the seller obtains a regularising permission. Otherwise, you will be responsible as the new owner.

In conclusion, remember that the boundary between conversion and building is thin. Better to prevent than cure: a simple phone call to the town hall or a lawyer can save you a lot of trouble.

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 →