Article

Leaking Drain Stack in a Shared Building: Who Pays?

10 August 2026

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Leaking Drain Stack: the Management Company Can’t Dodge Responsibility

Does your plumber refuse to open the duct housing your leaking drain stack? Does the management company pass the buck, claiming it’s a private matter? That’s a legal mistake. The vertical stack serving the floors falls under common property pursuant to Article 3 of the Decree of 17 March 1967, even if it only serves a single unit. The stakes are high: who funds the diagnostic and repair work depends on precisely identifying the leak’s location (common section vs. private branch after the connection point).

The Legal Framework: Article 3 (1967 Decree) and Article 30 of the Co-ownership Bylaws

Article 3 of the Decree of 17 March 1967: Ducts and Vertical Stacks = Common Property

The text leaves no room for doubt: “Ducts and vertical stacks serving one or more sections of the building are, by way of exception to the provisions of this article, considered common property.” This classification does not depend on how many units the stack serves. However, the private branch begins after the connection to the stack. The boundary between the shared duct and private property is legally critical.

Article 30 §2: Emergencies Allow Protective Works Without a General Meeting

A leak that seeps into the floors below or threatens the structure is an emergency. The management company does not need to call a general meeting to order protective works: “Emergency works are those necessary to address an imminent danger threatening the safety of occupants or the preservation of the building.” Diagnostic work falls under this provision.

How Cassini Settles the Question: Three Evidence-Gathering Methods

1. Dye or Smoke Testing

Injecting a liquid or gas into the stack to trace the exact path of the water. Moderate cost (€300-500), immediate results. Pinpoints the faulty common section.

2. Endoscopic Camera Inspection

Visual inspection inside the pipework (diameter, cracks, fittings). Reveals the exact source without any demolition. Budget: €500-800. Provides photographic documentation of liability.

3. Complementary Non-Destructive Investigation

Moisture readings, thermal imaging, and acoustic listening devices to detect hidden leaks. Together, these form the expert report that identifies the exact faulty section – this is the document that unblocks the management company and the insurers.

Maintenance Obligations

The co-ownership association is responsible for maintaining and keeping common property in good condition (Article 10 of the Law of 10 July 1965). A leak on a shared stack cannot be blamed on the owner of the unit above unless there’s proof of a faulty act (aggressive unclogging, overload, alteration) that occurred within their private section. In cases of simple wear or a lack of maintenance on the stack: the cost falls on the co-ownership association and its liability insurance.

Procedure: How to Break the Deadlock

1. Written request to the management company with photos and a moisture report. 15-day deadline.
2. Formal notice if there’s no response.
3. Call in an outside expert (Cassini or another recognised firm) for a non-destructive diagnostic.
4. Send the report to the management company and its insurer.
5. If the management company refuses to act: refer the matter to the civil court (expedited procedure for emergencies).

FAQ

Can the plumber refuse to open the duct?

Not if the management company orders it. However, an individual owner cannot force a plumber to open a duct without authorisation. Plumbers fear liability in case of hidden damage. A prior expert inspection (camera) removes that doubt.

Can I do the repair work myself and ask the management company for reimbursement?

Very risky. The management company could challenge the quality of the work. Only a repair carried out by a professional, ordered by the association, generates an undisputed right to reimbursement.

What if the leak comes from the private branch above my duct?

Then it’s the owner of the unit above who pays, not the management company. Hence the importance of the expert report: it identifies the exact location (common or private) of the leak.

How much does an emergency Cassini expert assessment cost?

A full diagnostic (dye test + camera + report): €800-1,200, depending on access and complexity. A negligible investment compared to repair work (€5,000-15,000) and long-term damage.

Conclusion

A leak on a drain stack is never solely the private owner’s problem. Article 3 of the Decree of 17 March 1967 makes it clear: it’s common property, meaning collective responsibility and funding by the association. Non-destructive diagnostics (dye testing, endoscopic camera) are the tools that unlock the situation and force the management company to act. At Cassini, we cover the 06, 83 and 13 areas and concentrate on this type of expert assessment: we offer a fast response, an indisputable report, and a solution without destructive work. Contact us before the damage gets worse.

Cassini Expertise – Areas 06, 83 & 13
Phone: 04 22 46 06 04
Email: contact@cassini-expertise.fr