In short
Mérule (dry rot) is a fungus that destroys the timber of damp, poorly ventilated houses (ministère de la Transition écologique (Ministry for Ecological Transition), page updated on 10 April 2026). Where outbreaks are identified in one or more municipalities, an arrêté préfectoral (prefectoral order), available for consultation at the préfecture, defines the zones where a dry rot risk is present (CCH (Construction and Housing Code), art. L131-3). In these zones, the sale of all or part of a built property comes with information on the presence of a dry rot risk, included in the dossier de diagnostic technique (technical survey file) attached to the promesse (preliminary sale contract) or, failing that, to the deed of sale (art. L126-25 and L271-4). Everywhere in France, an occupier who learns that dry rot is present must report it to the town hall; if there is no occupier, the owner must do so, and for the common parts of a copropriété (building in co-ownership), the syndicat des copropriétaires (owners’ association) (art. L126-5).
What is dry rot?
Dry rot attacks timber, roof frames and woodwork. It most often lurks behind wall linings, which explains why it is detected late (ministère de la Transition écologique). Its growth is generally caused by damp:
- poor maintenance of the building;
- water damage;
- design errors during renovation: impermeable renders, blocked ventilation, doors without enough clearance at the bottom, failure to respect the building’s original balance.
Its spores are present throughout the country: only suitable humidity and temperature conditions guarantee that it will not develop. The ministry explains that, unlike termites, dry rot carries no risk of infestation, but a risk of spreading step by step from an initial outbreak. Hence the mainly local importance of reporting. A public guide, “Preventing and combating dry rot in housing” (our translation), can be downloaded from the ministry.
Zones defined by prefectoral order
The information scheme was created by the loi Alur (Alur Act) of 24 March 2014, on the model of the termite scheme. It works at two levels: town halls are informed of the presence of dry rot by occupiers, and the buyer is informed before the purchase (ministère de la Transition écologique).
| Step | Rule |
|---|---|
| Outbreaks identified | Prefectoral order made on the proposal of, or after consulting, the municipal councils concerned (CCH, art. L131-3) |
| Content | Definition of the zones where a dry rot risk is present |
| Consultation | At the préfecture (art. L131-3); préfecture website (service-public.gouv.fr) |
| National map | Kept by Cerema, updated with each new order |
Consulting the municipal councils makes it possible to take account of reports made to town halls (ministère de la Transition écologique). The Cerema map shows whether a municipality or département is covered by an order when you zoom in on the département; it covers mainland France.
Sale: informing the buyer
The principle. When all or part of a built property located in a zone defined by order is sold, information on the presence of a dry rot risk is provided (CCH, art. L126-25). It forms part of the technical survey file (DDT) provided by the seller (art. L271-4, I, 9°), attached to the promesse de vente (preliminary sale contract) or, failing that, to the acte authentique (final deed of sale). Service-public.gouv.fr sums it up as follows: the promesse or the deed must state whether there is a risk of dry rot in the building.
What sets it apart from other surveys. Article L271-4 lists the documents whose absence at signing prevents the seller from being released from the garantie des vices cachés (warranty against hidden defects) (lead, asbestos, termites, gas, electricity, sewerage): the dry rot information is not among them. Nor is it among the documents whose absence allows the sale to be rescinded. The texts consulted set no period of validity for it. For a defect discovered after the purchase, the general rules apply: see our guide on vices cachés (hidden defects).
Outside the zones. The information obligation applies only to zones defined by order. The risk is nevertheless not zero elsewhere, since spores are present throughout the country (ministère de la Transition écologique). The full list of the file is in our guide to diagnostics obligatoires (mandatory surveys).
Reporting to the town hall
As soon as they become aware that dry rot is present in a built property, the occupier reports it to the town hall (CCH, art. L126-5):
- if there is no occupier, the duty to report falls on the owner;
- for the common parts of a building in co-ownership, it falls on the syndicat des copropriétaires.
Article L126-5 does not limit this obligation to the defined zones. Reports made to town halls are then taken into account when the municipal councils are consulted before a prefectoral order (ministère de la Transition écologique).
Dry rot and termites: the differences
| Dry rot | Termites | |
|---|---|---|
| Nature | Wood-destroying fungus | Wood-eating insects |
| Zoning | Zones where a risk is present, by prefectoral order | Zones infested or likely to become so in the short term, by prefectoral order |
| Sale document | Information on the presence of a risk (L271-4, 9°) | Termite survey, valid for 6 months |
| Missing at signing | Not listed among the cases that remove the release from the hidden defects warranty | The seller cannot be released from the hidden defects warranty |
| Failure to report to the town hall | No specific fine in article R184-8 | 3rd-class contravention (minor offence) (art. R184-8) |
Sources: CCH, art. L131-3, L271-4 and R184-8; ministère de la Transition écologique. The termite survey is covered in detail in our guide amiante, plomb, termites (asbestos, lead, termites).
FAQ
How can I find out whether a municipality is in a dry rot risk zone?
Consult the préfecture website or contact the préfecture (service-public.gouv.fr); Cerema also publishes a national map of orders, updated with each new order.
Does the seller have to carry out a dry rot survey?
In a zone defined by order, they provide information on the presence of a dry rot risk, included in the technical survey file (CCH, art. L126-25 and L271-4).
Who must report dry rot to the town hall?
The occupier; failing that, the owner; for the common parts of a building in co-ownership, the syndicat des copropriétaires (CCH, art. L126-5).
Does the reporting duty apply only in risk zones?
No. Article L126-5 does not limit it to the defined zones: it applies as soon as the occupier becomes aware that dry rot is present.
Why does dry rot appear?
Mainly because of damp: poor maintenance, water damage or poorly designed renovation, with blocked ventilation for example (ministère de la Transition écologique).
Which professional to consult
The diagnostiqueur (property surveyor) puts together the technical survey file, which includes the dry rot information in the zones concerned. The notaire (notary) checks that this information is attached to the promesse or the deed. The agent immobilier (estate agent) can check, as soon as the property is put up for sale, whether the municipality is covered by a prefectoral order.
Find a professional
One professional per trade and per area, selected and scored out of 100 from public data, with a verifiable title. The trade, its official register and the professionals selected (pages in French):
The property surveyor (diagnostics) selected in the largest cities
| City | Professional | Area | Score /100 | Status |
|---|---|---|---|---|
| Paris | Expertise & Diagnostic | Paris, 15e arrondissement | 79 | Selected |
| Marseille | ADK Diag 13 | Marseille, 1er arrondissement | 87 | Selected |
| Toulouse | MCP Diagnostic & Ingénierie | Toulouse | 90 | Selected |
| Nice | NiceDiagnostic | Nice | 74 | Selected |
| Lyon | Qualitech Expertises Immobilières | Lyon, 3e arrondissement | 82 | Selected |
| Montpellier | DIMO Diagnostic | Montpellier | 82 | Selected |
| Bordeaux | Aquitaine Diagnostic Immobilier | Bordeaux | 74 | Selected |
| Lille | JBM Expertise | Lille | 78 | Selected |
| Rennes | SHD Diagnostics | Rennes | 70 | Selected |
| Toulon | DIADEX | Toulon | 81 | Selected |
The 10 cities with the most sales (DVF 2025) where a property surveyor (diagnostics) is selected; in a city with several areas, the best-scoring profile. "Verified": title read at the register by Payotte; "Selected": title declared, verifiable on the profile.
Related guides
Sources
- Ministère de la Transition écologique — Termites, insectes xylophages et champignons lignivores (mis à jour le 10 avril 2026) (checked 12 October 2026)
- Service-public.gouv.fr — Quels sont les diagnostics immobiliers à fournir en cas de vente d'un logement ? (vérifié le 7 mars 2025) (checked 12 October 2026)
- Cerema — Cartographie nationale des termites et des mérules (checked 12 October 2026)
- Légifrance — Code de la construction et de l'habitation, article L131-3 (arrêtés préfectoraux termites et mérule) (checked 12 October 2026)
- Légifrance — Code de la construction et de l'habitation, article L126-5 (déclaration en mairie) (checked 12 October 2026)
- Légifrance — Code de la construction et de l'habitation, article L126-25 (information en cas de vente) (checked 12 October 2026)
- Légifrance — Code de la construction et de l'habitation, article L271-4 (dossier de diagnostic technique, version en vigueur depuis le 11 avril 2024) (checked 12 October 2026)
- Légifrance — Code de la construction et de l'habitation, article R184-8 (sanctions, termites) (checked 12 October 2026)
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