Building permit: watch out for encroachments on public domain (Cass. crim. 1987)

Imagine the scene: you are the owner of a house in Saint-Priest, in the Lyon region. To gain a little more light, you decide to enlarge an existing window to turn it into a French window. Simple works, you think, which do not require a building permit since the area created is less than 20 m². But then your neighbour, the municipality, sues you for lack of a permit. Why? Because your new opening encroaches on the pavement, which is part of the public domain.

This situation, experienced by a resident of the Toulouse region in the 1980s, gave rise to a judgment of the Court of Cassation on 24 November 1987 (No. 86-93.462) which still sets a precedent today. The question was simple: does the exemption from building permits provided for in Article R. 422.2 of the Town Planning Code (now R. 421-2) apply when the works encroach on the public domain? The answer, without appeal, is no.

This decision is essential for any property owner or real estate professional. It concerns you if you are planning even minor works: a conservatory, an awning, an extension, a simple window change. Because encroachment on the public domain (pavement, street, square) changes everything. Let us look at the facts, the judges' reasoning, and what this changes concretely for you, whether you are in Vénissieux, Lyon or elsewhere.

The facts: a story like many that happen every day

Mr X, owner in Saint-Priest, wished to enlarge an opening in his house to turn it into a French window. Seemingly innocuous works: it was not a matter of building an extra room, but simply modifying an existing window. The floor area created was less than the 20 m² threshold which, at the time, exempted from a building permit under Article R. 422.2 of the Town Planning Code.

But there was a catch: the new opening encroached on the public domain. Indeed, the wall of the house was adjacent to the public highway, and by enlarging the opening, Mr X had encroached on the airspace of the pavement. The municipality then sued Mr X for lack of a building permit, and the criminal court of Toulouse fined him 2,000 francs (about 300 euros) and ordered restoration of the premises to their original condition.

Mr X appealed to the Toulouse Court of Appeal, which upheld the conviction on 22 May 1986. He then appealed to the Court of Cassation. Before the Court of Cassation, he argued that the exemption from building permits should apply, since the area created was below the regulatory threshold. But the Court of Cassation dismissed his appeal, holding that the exemption does not apply when the works encroach on the public domain.

This case shows that it is not enough to respect the area thresholds to be exempt from a permit. The location of the works and their impact on the public domain are equally decisive.

The reasoning of the court — dissected

The heart of the dispute was the interpretation of Article R. 422.2 of the Town Planning Code (in its version resulting from Decree No. 86-514 of 14 March 1986). This text listed the constructions and works exempt from building permits. Among them, paragraph (m) referred to works creating a floor area of less than 20 m². Mr X considered that his works fell into this category.

But the Court of Cassation held that this exemption only applies if the works are carried out on the land already supporting the construction, without encroaching on the public domain. Why? Because the public domain is inalienable and imprescriptible: no one can appropriate part of it, even temporarily, without authorisation. Allowing an exemption from a permit for works encroaching on the public domain would circumvent the rules protecting that domain.

The Court relied on the principle that exceptions (such as exemption from a permit) are to be interpreted strictly. Article R. 422.2 did not expressly provide for the case of encroachment on the public domain. Therefore, the judges considered that the exemption could not benefit works which, by their nature, affect the integrity of the public domain. The decision of the Toulouse Court of Appeal was therefore upheld: Mr X had to pay the fine and restore the premises.

This decision is not a reversal of precedent, but a confirmation of a strict reading of the texts. It is part of a logic of protection of the public domain, dear to administrative law. The judges thus reminded that owners cannot rely on exemptions from permits to carry out works that encroach on the public highway, unless they obtain specific authorisation (building permit, permission for road works, etc.).

Note that the Court of Cassation did not question the amount of the fine or the obligation to restore compliance. It simply validated the reasoning of the lower courts.

What this changes for you — concretely

This decision has practical implications for all owners, whether they are occupants, landlords or real estate professionals. Here is what you need to remember:

Owner-occupier: If you plan to modify a window, create a door, install a canopy or awning, first check whether your works encroach on the public domain. For example, in Vénissieux, a simple roof overhang above the pavement may be considered an encroachment. Even if the area created is less than 20 m² (or 5 m² today), you will need a building permit if your works go beyond the boundary of your property.

Landlord: Before authorising works to your tenant, ensure that they do not affect the public domain. An overhanging terrace, an external staircase, an extension… Any encroachment may expose you to a fine and an obligation to demolish. In a recent case in Lyon, a landlord had to pay a €5,000 fine for installing an air conditioning unit on the roof encroaching on the common courtyard, considered as public domain of the co-ownership.

Purchaser: When buying a property, check the planning permissions for any construction or modification. If the seller carried out works without a permit encroaching on the public domain, you could be required to restore compliance. Require guarantees in the deed of sale.

Co-owner: Common parts (courtyards, gardens, roofs) are assimilated to the private domain of the co-ownership, but their use is regulated. An encroachment on a common part without authorisation from the general meeting may be penalised. Case law sometimes extends the reasoning of the 1987 decision to common parts.

In practice, before any works, even minor ones, check with the planning department of your town hall. An operational planning certificate can tell you whether your project requires a permit. The cost of the consultation (a few tens of euros) is negligible compared to the costs of restoration and fines.

Four tips to avoid this type of dispute

• Consult the local town planning plan (PLU) of your municipality: Before any project, check the rules applicable to your plot, in particular distances from public highways (alignment). The PLU is available at the town hall or online.
• Request an operational planning certificate: This official document tells you, for a given piece of land, the applicable planning rules and the feasibility of your project. It is valid for 18 months and costs around €30 to €50.
• Do not rely solely on area thresholds: The exemption from permits for small works does not apply if you encroach on the public domain or if you modify the external appearance of the building in a protected area (listed site, vicinity of a historic monument).
• Use a professional: An architect or a chartered surveyor can help you accurately define the boundaries of your property and check whether your project encroaches on the public domain. This investment (a few hundred euros) will save you much higher costs in the event of a dispute.

Further reading: related case law and developments

The 1987 decision is part of a line of decisions protecting the public domain. For example, the Conseil d'État ruled in 2005 (CE, 18 May 2005, No. 263301) that unauthorised occupation of the public domain by an illegal construction justifies a significant financial penalty. Likewise, the Court of Cassation reaffirmed in 2015 (Civ. 3rd, 10 March 2015, No. 13-25.768) that encroachment on the public domain constitutes a major highway offence, even in the absence of a building permit.

Since 1987, the exemption thresholds have evolved: today, the creation of floor areas of less than 5 m² (or 20 m² in certain zones) are exempt from permits, but the exception remains valid: in case of encroachment on the public domain, a permit is necessary. The courts are increasingly strict: in Lyon and throughout France, town halls are multiplying checks and prosecutions for encroachment. The trend is towards reinforced protection of the public domain, considered as a common good.

This case law could be extended to encroachments on common spaces in co-ownerships, by analogy. Indeed, common parts are the undivided property of all co-owners, and their occupation without authorisation can be assimilated to an encroachment. So remain vigilant.

Frequently asked questions

Can I enlarge a window without a permit if the area created is less than 5 m²?
Yes, if the works do not modify the external appearance in a protected area and do not encroach on the public domain. If your window overlooks the street and the enlargement goes beyond the alignment, a permit is necessary.

What should I do if I have already carried out works encroaching on the public domain?
It is advisable to regularise the situation by applying for a retrospective building permit, if possible. Otherwise, you risk a fine (up to €6,000 per m² encroached) and an obligation to demolish. Consult a specialist lawyer as soon as possible.

What are the time limits for contesting a fine for lack of a permit?
You have a period of 6 years from the completion of the works to be prosecuted criminally. For a highway offence, the period is 1 year. After these periods, you can no longer be penalised, but the town hall can still request restoration.

Does the fact that the works were carried out by the previous owner protect me?
No. As the current owner, you are required to restore compliance if the encroachment persists. However, you can take action against the seller on the grounds of hidden defects or the warranty against eviction, if the encroachment was not mentioned in the deed of sale.

How do I know if my property encroaches on the public domain?
Check your title deed (notarial deed) and the cadastral plan. A chartered surveyor can carry out a precise boundary survey. If in doubt, the planning department of the town hall can advise you.

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