A type of fungus known as dry rot, or Serpula lacrymans, can silently damage the wooden structures of homes over many years. This wood-eating fungus thrives in enclosed spaces with abnormally high humidity, and it can spread through walls and masonry to reach other parts of a house. Dry rot begins to grow on wood when the humidity level reaches 20 to 22%, and it flourishes when the humidity climbs to 35%. Early signs of the fungus include a white, felt-like coating on surfaces, a damp or earthy smell in enclosed rooms, and floors that feel hollow when walked on. Under the ALUR law, passed on March 24, 2014, anyone who discovers dry rot in a building must report it to the local town hall. This requirement applies regardless of whether a property is being sold or not. The law aims to help authorities track areas affected by the fungus, which is particularly common in older homes built before 1948. These homes often have ventilation and leakage issues that contribute to high humidity. Even energy-efficient renovations can sometimes worsen the problem if insulation is improperly installed, trapping moisture in wooden structures. Before dry rot visibly damages beams or other wooden structures, it provides subtle warnings. A white, cotton-like felt may appear on wood or masonry, a persistent damp or mushroom-like smell can linger in a room, and a hollow sound underfoot may indicate the presence of the fungus. These signs often precede the appearance of the fungus’s fruiting body, known as the "brown-orange cap," which releases a rust-colored cloud of spores. Eventually, the affected wood can crack into dry, cube-like pieces, a telltale sign of the damage it causes. The ALUR law also mandates that in areas designated as risk zones by prefectural orders, buyers must be informed of dry rot in a property during a sale. Failure to disclose this information can lead to legal challenges. Additionally, if a building in a risk zone is partially or fully demolished, the contaminated wood and materials must be treated or incinerated on-site before disposal. This means that a rotted beam cannot simply be thrown into a regular trash bin. Dry rot is not confined to traditional high-humidity regions like the north and west of France, including Brittany, Hauts-de-France, and Normandy. Recent data shows a 20.4% increase in reported cases between 2024 and 2025, with 3,312 cases recorded across 95 departments. The Puy-de-Dôme region now has the highest number of reported cases, followed by the Loire and Haute-Loire, showing that dry rot is becoming a growing concern in areas previously not considered at risk.