Mandatory structural checks for old buildings

Several French cities have introduced mandatory structural diagnoses for older collective housing buildings to prevent potential collapses. This measure follows past incidents, such as building collapses in Marseille in 2018 and Lille in 2022, which highlighted risks from the degradation of aging structures.

Legal basis for the requirement

The mandatory structural diagnosis, known as DSO, was established by the "Degraded Housing" law of April 9, 2024, and regulated by a decree of August 12, 2025. The goal is to identify vulnerabilities that could threaten a building's stability, such as cracks, sagging floors, and weakened load-bearing walls.

Scope of the requirement

The requirement applies to collective housing buildings over 15 years old in areas designated by local municipalities. The diagnosis must be renewed at least every 10 years to monitor deterioration and allow for timely interventions. Several cities, including Marseille, Lille, Honfleur, Saint-Denis, and Annecy, have already adopted this measure, though not all areas within these cities are affected.

Specific areas targeted in cities

In Marseille, four neighborhoods have been targeted since a resolution in December 2025: Noailles, Belle de Mai, Hoche-Versailles-Pelletan, and La Cabucelle-Les Crottes. In Lille, several streets and sections of the Grand'Place are affected. In Honfleur, the Sainte-Catherine island has been targeted since October 2025. In Saint-Denis, 245 collective buildings are affected based on their age and characteristics. In Annecy, the measure was adopted in February 2026, focusing on the old town's buildings.

Implementation and deadlines

Cities inform building owners through registered letters or official notices. The diagnosis must be submitted within 18 months. If weaknesses are found, additional work or examinations may be required. Existing multi-year work plans (PPPT) can sometimes replace the DSO, provided they meet regulatory standards.

Costs and procedures

The cost of the diagnosis varies depending on the building's size, complexity, and the investigations needed. It is typically shared among co-owners or borne by a sole owner. The procedure includes analyzing existing documents, inspecting the building, and submitting a report on detected anomalies and safety risks.

Consequences of non-compliance

If the diagnosis is not completed within the 18-month deadline, the city can request it. If no response is received within a month, the city may carry out the diagnosis at the owner's expense. If a building is deemed dangerous, the mayor can initiate safety procedures, including urgent repairs or temporary evacuations. Other cities, such as Bordeaux, Lyon, and Paris, are considering similar measures. Property owners can check if their building is affected by consulting their municipality and the local urban planning plan (PLU).