Party Wall: When Your Neighbour Builds Without Your Consent

Imagine you own a beautiful villa in Cannes, with a garden overlooking the Mediterranean. You share a party wall (a wall common to two properties) with your neighbour. One morning, you discover that they have built a lean-to (a small annex building) that leans against this wall, without having asked for your opinion. Your first reaction? Demand immediate demolition! But is it really that simple?

I encounter this situation regularly in my practice, whether in Grasse, Le Cannet, or the residential neighbourhoods of Cannes. Owners are often convinced that any unauthorised construction on a party wall must automatically be demolished. Yet, the justice system does not always work that way.

The decision of the Court of Cassation of 16 June 2004 provides a nuanced answer to this thorny question. It reminds us that the lower court judges (the magistrates of the first instance courts and the courts of appeal) have a sovereign power of assessment to decide whether to order demolition or not. In other words, it all depends on the specific circumstances of each case. But what exactly does this change for you, as an owner, tenant, or real estate professional?

The Facts: A Story as Common as Any

Ms. Martin (fictitious name), owner of a house in Le Cannet, shares a party wall with her neighbour, Ms. Dubois. One fine day, Ms. Dubois decides to build a small garden shed that leans against this common wall. She does not ask for Ms. Martin's authorisation, perhaps thinking it does not directly concern her.

Ms. Martin discovers the works and is outraged. She considers that this construction infringes her property rights over the party wall. In her view, her neighbour cannot use the wall to support a structure without her express consent. She then initiates legal proceedings to obtain the demolition of the shed.

The first instance court, seized at first instance (first level of jurisdiction), rules in favour of Ms. Martin and orders the destruction of the structure. But Ms. Dubois appeals this decision. The court of appeal (second level of jurisdiction) examines the case and adopts a different position. It notes that the shed only leans against the party wall for a length of 90 centimetres, and that the works have not affected the wall's strength. It therefore dismisses Ms. Martin's claim for demolition.

Ms. Martin, dissatisfied, appeals to the Court of Cassation (appeal to the Court of Cassation, which checks whether the law has been correctly applied). She criticises the court of appeal for refusing demolition when her consent had not been obtained. This is where the Court of Cassation intervenes with its decision of 16 June 2004.

The Court's Reasoning — Analysed

The Court of Cassation rejects Ms. Martin's appeal. It recalls a fundamental principle: the lower court judges assess sovereignly whether there is cause to order the demolition of a structure built against a party wall without the other neighbour's consent. In plain terms, they have full freedom to examine the facts and decide, on a case-by-case basis, whether destruction is justified.

The legal basis for this approach lies in Articles 653 and 654 of the Civil Code, which govern party walls. Article 653 states that "any co-owner may build against a party wall, and place beams or joists within the entire thickness of the wall, within fifty-four millimetres." But beware: this right is regulated. Article 654 specifies that if the works harm the wall's strength or make it more costly to maintain, the neighbour may demand the removal of the structure or compensation.

In this case, the court of appeal found, after technical expertise, that Ms. Dubois's construction had not affected the party wall's strength. It also noted that the support was limited (90 cm) and that a counter-wall (a supporting wall) had been built. These elements allowed it to conclude that there was no cause to order demolition, despite the absence of prior consent.

What few people know is that the Court of Cassation does not re-examine the facts. It merely checks whether the lower court judges correctly applied the law. Here, it validates their reasoning: provided the structure does not cause damage to the wall's strength, demolition is not automatic. This confirms prior case law (the body of judicial decisions), which favours a pragmatic rather than systematic approach.

What This Means for You — Practically

If you are a landlord (who lets a property) in Cannes, this decision changes your strategy. Imagine your tenant reports that a neighbour has built a conservatory on your party wall. Previously, you might have demanded outright demolition. Now, you must first check whether the structure harms the wall's strength. How to react? Have an assessment carried out by an architect or a surveyor (cost: €500 to €1,500 depending on complexity) to evaluate the impacts. If no damage is found, an action for demolition is unlikely to succeed. You might instead negotiate compensation or an amicable agreement.

For tenants, the situation is indirect. You are not the owner of the wall, but you suffer the consequences. If neighbouring works worry you, report them immediately to the owner or the estate agency. Keep evidence (photos, emails) and insist on a verification. undefined, I have handled cases where tenants had to temporarily leave a property due to issues related to poorly executed party wall constructions.

Purchasers (buyers) must be vigilant. Before buying a house with a party wall in Le Cannet, have a notary or a land surveyor check if any structures lean against it. A latent disagreement with the neighbour may resurface after the sale. Including a clause in the deed of sale to cover this risk can be wise.

Finally, for co-owners, this decision also applies to party walls between private lots. The managing agent must be alerted to any suspicious construction. Timeframes? Legal proceedings can last 1 to 3 years, with legal and expert fees often exceeding €3,000. It is better to prioritise mediation (assisted negotiation) from the outset.

Four Tips to Avoid This Type of Dispute

• Always request your neighbour's written consent before building against a party wall. A simple email or registered letter with acknowledgment of receipt suffices, but a notarial deed is safer. This avoids misunderstandings and secures your works.
• Have a preliminary technical assessment carried out by a professional (architect, engineer). They will evaluate the impact on the wall's strength and may propose technical solutions (such as a counter-wall) to minimise risks. Average cost: €300 to €800.
• Consult the co-ownership regulations or easements if you are in a co-ownership. Some documents impose specific rules on party walls. A check before works can avoid action by the managing agent.
• In case of disagreement, propose property mediation before initiating legal proceedings. In the Grasse jurisdiction, accredited mediators can help you find a compromise (e.g., compensation, modification of plans) within a few weeks, at a cost much lower than a lawsuit.

Deep Dive: Related Case Law and Developments

This decision fits into a jurisprudential trend dating back several years. For example, in a Court of Cassation ruling of 7 March 2001 (No. 98-21.302), the judges had already refused demolition of a construction built against a party wall, on the grounds that it caused no damage. Conversely, in a decision of 12 January 1999 (No. 96-18.745), demolition had been ordered because the works had weakened the wall.

The current trend in the courts is clear: they favour proportionality. If the structure is minor and safe, they avoid demolition, which is a radical and costly measure. They often prefer to award damages (financial compensation) or impose consolidation works. For the future, this means that owners increasingly need to prove concrete damage to succeed. Simple arguments of principle (“it's my wall”) are no longer enough.

In Practice: What to Do

Here is a numbered checklist to guide you:

1. If you discover a construction on your party wall without your consent: take photos, note the dates, and immediately contact your neighbour in writing to request an explanation.
2. If dialogue fails: consult a lawyer specialising in property law to assess your chances of success. An initial consultation (€45 with me) can direct you towards technical expertise or mediation.
3. Before undertaking works yourself: obtain your neighbour's written consent and have the wall's strength checked by an expert. This will protect you in case of future dispute.
4. In case of legal proceedings: prepare for long delays (1-3 years) and costs (expertise, lawyer). Weigh the cost/benefit: sometimes, negotiated compensation is more advantageous than uncertain demolition.

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