A seaside house can lose all its market value without a single wall cracking. What condemns it is not a disaster in the legal sense, but a slow, mapped, documented process over many years: the retreat of the coastline. This phenomenon, as certain as it may be, does not qualify for compensation. The retreat of the coastline is not covered by the natural disaster compensation regime because it is a predictable and progressive phenomenon. The Climate and Resilience Act requires coastal communes to map the exposure of the coastline for the short term (0-30 years) and long term (30-100 years). As soon as a parcel is included in the exposure mapping, its price collapses because this information becomes mandatory for all actors in the real estate transaction. Submersion and erosion: a legal boundary that almost no one knows. The natural disaster compensation regime, funded by a mandatory surcharge on home insurance contracts, is based on a precise logic: compensating for damages caused by a sudden and unpredictable event. Compensation for marine submersion requires an interministerial decree to declare the area as a natural disaster, and that the damages are a direct consequence occurring during the period defined by the decree. The coastline retreat, however, remains outside this framework. Unlike submersion, it is not covered by the natural disaster compensation regime because it is a predictable and progressive phenomenon, not a sudden event. One does not insure against a certain event. The Le Signal building in Soulac-sur-Mer in Gironde, built 200 meters from the coast in 1967, found itself only a few meters from the ocean after the winter storms of 2013-2014, forcing its 75 co-owners to evacuate urgently in January 2014. The Council of State ruled in 2018 that dune erosion is not among the risks that qualify for compensation from the Barnier fund. The Constitutional Council had already validated this exclusion the same year, excluding property owners threatened by erosion on sandy coasts from the regime applicable to marine submersion. A budget amendment passed in late 2018 unlocked 7 million euros, and a protocol signed in late 2020 between the state, the city of Soulac, and the Médoc Atlantique intercommunal community increased the compensation to 70% of the initial value of the homes. This compromise, funded outside the Barnier fund, is intentionally not setting a legal precedent. According to the Littoral Aquitain Public Interest Group, up to 6,700 homes and businesses could still be swallowed by the ocean in the Nouvelle-Aquitaine region alone. The Climate and Resilience Framework: mapping before it cracks. The Climate and Resilience Act of August 22, 2021, established tools to adapt urban planning and development of coastal communities to the retreat of the coastline. It provides for the establishment by decree of a list of communes whose urban planning actions must be adapted to erosion phenomena. The first decree of April 29, 2022, listed 126 communes. The fourth decree, published on February 13, 2026, brings the list to 371 communes. Sellers and landlords must now inform buyers or tenants. Each listed commune must produce a short-term (0-30 years) and long-term (30-100 years) coastline evolution map. In areas exposed to the 30-year horizon, a restrictive list strictly regulates the permitted works and constructions. Between 30 and 100 years, demolition and restoration obligations apply to certain constructions. Communes also have a right of preemption, automatically acquired in the 30-year zone and optional beyond that. For Le Signal, it was ultimately the city of Soulac and the Médoc Atlantique intercommunal community that became the owners of the building, before initiating its demolition. The project, launched on February 3, 2023, was expected to last three weeks. The price freezes before the cliff even moves. As soon as a parcel is included in the exposure mapping, the information becomes public and is mandatory for all actors in the transaction. The buyer discovers it in the urban planning document, the bank identifies it during the file processing, and the insurer incorporates it into its risk assessment. The price is set before the cliff even recedes an additional meter. Some houses no longer find any buyers. The affected communes have the obligation to include this mapping in their urban planning document and to delineate areas subject to specific land use rules. The approach aims precisely to inform and make the erosion phenomenon visible to the widest audience. Once the parcel is classified, the real estate negotiation changes in nature: the buyer no longer only discusses the condition of the property, but the remaining lifespan before it enters the 30-year zone. The seller, on the other hand, often discovers the news at the same time as his notary. Chalk that breaks, dune that slips: two erosions, one same verdict. The coastline retreat does not follow a uniform pace; it depends on the nature of the coast. On cliff coasts, the retreat occurs in sudden bursts: nothing happens for months or years, then suddenly several thousand cubic meters can fall in seconds. For chalk and Tertiary sedimentary rocks, the average speed is between 0.1 and 1 meter per year, but a single violent episode can cause an entire section of the cliff to collapse. The dune line, however, does not collapse all at once; it migrates. Each storm gnaws at the base of the dune through the jet of the shore, this tongue of water projected onto the tidal flat at the moment of the wave breaking, and the sand retreats inland rather than collapsing in a block. This continuous process has eroded, in Soulac-sur-Mer, the beaches disappearing at a rate of about 2.5 meters per year over the last few decades. A retreat more subtle than a cliff collapse, but just as irreversible for those who own a house on the sand. The large equinox tides at the end of September, with coefficients that sometimes approach the maximum values on the French scale, bring this calendar back to the attention of residents each year. They add nothing to the administrative file of a parcel already classified in the 30-year zone, but they remind that the line between cliff and dune, between sudden and gradual, continues to be redrawn with each major tide.