Published 2026-10-15 · Updated 2026-10-15 · Alpha Services Benelux

Dry rot (mérule) in Belgium: how to spot it, treat it, what it costs and who pays

Short answer: Treating dry rot (Serpula lacrymans, 'mérule' in French, 'huiszwam' in Dutch) in Belgium costs from a few thousand euros for a localised spot (€3,500-6,000) to €15,000-70,000 for a whole roof frame; one room is €5,000-12,000, after a diagnosis of €175-450. Hidden-defect rules apply on a sale; insurance usually only steps in if the moisture came from a covered event.

Prices in this article are indicative Belgian market ranges, not Alpha Services Benelux's price list. Your fixed price is in the quote.

How to recognise dry rot in a Belgian home

Dry rot shows as white, cotton-like threads, wood that cracks into cubes and a strong musty smell. It often hides behind walls, under floors, in cellars or in the roof, so a professional diagnosis is needed to confirm it.

• White or greyish threads running through wood and masonry.
• Brown or rust-coloured spore layers edged with white.
• Crumbling timber, paint blistering on wood, sagging floors or loose beam ends.
• A strong musty smell in a closed or rarely used space.

Dry rot needs moisture: sources cite wood moisture of 20 to 40 %, a temperature around 18-20 °C and little light. The cause is almost always a leak, condensation, poor ventilation or rising damp. The spores can irritate the airways. Do not confuse it with saltpetre, a crystalline mineral deposit. For moisture causes, see our article on treating damp walls.

What dry rot treatment costs in Belgium in 2026

Prices vary widely: a diagnosis costs roughly €175-450, a room €5,000-12,000 and a whole roof frame €15,000-70,000. This depends on the extent, accessibility and how much timber must be replaced.

One source gives an average of €2,500-3,500 for early treatment and €6,000-10,000 at a later stage. The €70,000 ceiling comes from a single source; most cite €60,000. Some prices exclude labour.

Sources differ (€50-150 versus €80-200 per m²); we give the wider range, which depends on finish level and the amount of repair work.

What drives the price

The price depends mainly on how far the rot has spread and how hard it is to reach. A localised patch in a cellar is a different job from an infested roof.

• Extent: square metres of timber and wall, one beam or a whole floor.
• Accessibility: working in a roof frame or behind finishes costs more.
• Demolition and rebuilding: affected timber must be replaced, plus repair of plaster, floor or roof.
• Moisture cause: as long as the leak or condensation remains, the rot returns. That budget comes on top.
• Finish level: what you restore after remediation and how you finish it.

How a specialist treats dry rot

A specialist deals with the cause first and then the affected material, not just what is visible. Have the extent assessed by a professional; shop-bought products often leave spores behind.

1. Inspection and moisture measurement, ideally with a lab analysis confirming Serpula lacrymans.
2. Eliminating the moisture source (leak, condensation, rising damp).
3. Removing and replacing affected timber and plaster, beyond the visible area.
4. Treating timber and masonry. Fungicides do not work if the wood is destroyed or unreachable; it must then be replaced.
5. Restoration and follow-up of moisture levels.

Bleach and ammonia are advised against because they may encourage growth. For repair work after remediation, see our renovation page.

Buying or selling: who pays when dry rot turns up

On a sale, hidden-defect rules apply: the buyer can ask to cancel the sale or for a price reduction, whether or not the seller knew about the defect. An exoneration clause often changes this, except where the defect was deliberately concealed.

• Around 95 % of private-to-private contracts reportedly contain a clause releasing the seller from the hidden-defect warranty.
• A professional seller (such as a developer) cannot rely on it against a consumer.
• The clause fails if the defect was deliberately hidden, for example by panelling in front of a damp wall.
• The buyer must prove the defect existed before the sale and, in bad-faith cases, that the seller knew about it.
• The maximum period is ten years after the sale, but you must act quickly once you discover it: notify the seller in writing and commission an expert report. Without prompt action, a court may treat the defect as accepted.

Photograph the damage, keep all sale documents and get help from a notary or lawyer. When buying, having a diagnosis done before signing is a sensible step.

Insurance: when is dry rot covered?

Dry rot as such is rarely covered; cover is mainly possible when it results from an insured event, such as a leak or water damage. Sources do not fully agree, so check your policy.

• Insurers typically ask for identification of the fungus (Serpula lacrymans), proof it appeared during the policy period and work by a specialist firm.
• Common grounds for refusal: lack of maintenance, chronic moisture or a presumption that the problem is long-standing.
• A refusal is not always final; an expert can help build the claim.

Photograph and date the damage before changing anything, and declare the claim within the contract's deadlines. Depending on the policy, legal-expenses cover may pay part of the expert's fees.

Obligations, financial help and comparing quotes

The sources we reviewed mention no specific legal duty to report dry rot; general sale law and good faith still apply. If in doubt, ask your notary or municipality.

Also check the official regional portals for any support: wallonie.be, vlaanderen.be/mijn-verbouwpremie and, in Brussels, Homegrade.

• Ask for a detailed quote that separates area, method, timber to replace and restoration.
• Ask whether a lab analysis is included, as insurers often require it.
• Check that the quote tackles the moisture cause, not just what is visible.
• Compare at least two quotes and check whether labour is included. More tips: comparing contractor quotes.

For the restoration work (walls, floors, finishes), Alpha Services Benelux works with its own team, active since 2014, with a fixed written quote after a site visit; see the renovation page or the renovation calculator. The prices on this page are market ranges, not the company's price list.

Frequently asked questions

How much does dry rot treatment cost per m² in Belgium?

Sources give a wide range of roughly €50 to €200 per m² for curative treatment. Removing affected timber (€60-120 per m²) and fixing the moisture cause come on top. The total depends on extent and finish level.

Must I declare dry rot when selling my house?

The sources we reviewed cite no specific duty to declare it. However, the seller remains liable for hidden defects, and an exoneration clause does not protect against deliberate concealment. If you know about it, state it in the deed.

Does my home insurance cover dry rot?

Rarely directly. Cover is possible if the rot results from an insured event, such as a leak, with lab identification and treatment by a specialist firm. Chronic moisture is often excluded. Check your policy.

Can I cancel a purchase if I find dry rot?

Possibly: the buyer can ask to cancel or for a price reduction, but an exoneration clause complicates this unless the seller deliberately hid the defect. The maximum period is ten years, but you must act quickly. Consult a notary or lawyer.

How fast does dry rot grow?

Sources cite up to roughly 10-12 cm per week in favourable conditions: wood moisture of 20-40 %, 18-20 °C and little light. That is why a quick assessment by a specialist matters.

Sources

1. Traitements Mérule : comment s'en débarrasser, et à quel prix ? — Bobex (Belgique)
2. Traitement de la Mérule : zoom sur les traitements et leurs prix — Guide-renovation.be (Belgique)
3. 2025 Coût d'un traitement contre la mérule — Tafsquare Belgique
4. Huiszwam herkennen, bestrijden & voorkomen — Meesterklusser (België)
5. Huiszwam: oorzaken, herkennen en bestrijding — Vochtbestrijding Snel (België)
6. Huiszwam? Advies gevolgen & bestrijding 2026 — Bouwadviseur.be (België)
7. Huiszwam bestrijden: prijzen, inspectie door experts & advies — Vochtbestrijding-gids.be (Bobex, België)
8. La mérule, des infiltrations d'eau cachées derrière des lambris... Que se passe-t-il si on trouve des vices cachés dans une maison en Belgique ? — L'Avenir (interview Benoît Kohl, ULiège)
9. L'indemnisation des dommages de la mérule en Belgique — EAB Expert (bureau d'expertise, 2021)
10. Mérule : comment être indemnisé par l'assurance — Expert Bel (bureau d'expertise, 08/2026)