Published 2026-10-13 · Updated 2026-10-13 · Alpha Services Benelux

Damp walls in Belgium: causes, treatment and prices (2026)

Short answer: In Belgium, injecting a wall against rising damp costs €50–200 per running metre depending on the source; for a terraced house the total is often around €800–1,600. Tanking a cellar typically costs €50–100 per m² (up to €400 in one guide), façade water-repellent treatment €8–15 per m². Always get the cause diagnosed before comparing quotes.

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

What kind of damp do you have? The cause decides the treatment

Damp walls have four possible causes: rising damp, penetrating damp, condensation or a leak. Only rising damp is treated by injection or a cut-in membrane. That is why diagnosis comes before the quote.

• Rising damp (capillary rise): water moves up from the ground into the masonry. Typical signs are marks at the bottom of the wall, peeling paint and salt efflorescence.
• Penetrating damp (infiltration): rainwater gets in through the façade, poor pointing, a roof edge or a leaking gutter. Marks often appear after rain and can sit higher on the wall.
• Condensation: warm, humid indoor air condenses on cold surfaces. Mould in corners, behind furniture and on windows, mostly in poorly ventilated rooms.
• Leak: a leaking pipe or drain can cause similar stains. It must be located and repaired first.

A handheld moisture meter only gives an indication and does not tell these causes apart. Have a professional assess the pattern, the height, the ventilation and the surroundings. Some providers include a moisture measurement with a quote; ask about it.

Rising damp: injection or cut-in membrane, price per running metre

Rising damp is priced per running metre of wall in Belgium, not per m². Injection costs €50–200 per running metre depending on the source, a cut-in membrane €100–200.

Injection means drilling holes in the wall and introducing a water-repellent product. A cut-in membrane places a waterproof barrier in a slot cut into the masonry. The choice depends on the wall, access and the condition of the masonry.

Watch the price basis: some sources quote excluding VAT and labour, others excluding VAT but including labour, and others do not say. Always compare quotes on the same basis.

Penetrating damp and condensation: façade and ventilation

Penetrating damp is dealt with at the façade, condensation through ventilation. A water-repellent façade treatment costs €8–15 per m², a ventilation system €1,000–6,000.

For penetrating damp, a professional first checks pointing, gutters, roof edges and cracks. A water repellent can help on a sound façade, but it does not fix failed pointing or cracks. Anti-damp paint (roughly €15–40 per m²) does not treat the cause either.

For condensation, what matters is air renewal, not the wall. An extractor fan or vent is a cheap first step; a decentralised heat-recovery unit treats a single room, a full system the whole house.

The spread for façade cladding is wide because it runs from a light finish to a complete new façade layer. The higher the finish level, the higher the bill. The price basis differs per source.

Damp cellar: tanking and drainage

Tanking a cellar from the inside typically costs €50–100 per m²; other guides quote up to €150 and even €400 for heavier systems. A complete drainage project costs €3,000–12,000.

Tanking makes the inside of the floor and walls waterproof against pressurised water. Drainage carries the water away and is more invasive, especially with a sump and pump. Whether it is needed depends on water pressure, groundwater level and the condition of the walls.

The total depends on surface area: one source counts €2,000–5,200 for 40 m², another about €4,000–10,000 for an average cellar. The same work can differ a lot between contractors because the scope of the quote is not identical. The price basis (VAT, labour) differs per source.

What drives the price

The price depends mainly on the cause, the extent of the problem and the finishing afterwards. These three explain most of the gap between quotes.

• Cause and method: injection, membrane, façade work, ventilation or tanking have completely different unit prices.
• Length, thickness and access of the wall: thick or double walls and hard-to-reach areas increase labour.
• Finishing: removing old plaster, new plaster, salt-resistant mortar and painting are often added on top of the treatment. The higher the finish level, the higher the bill.
• Water pressure and groundwater: in a cellar these decide whether tanking is enough or drainage and a pump are needed.
• Price basis: excluding or including VAT, with or without labour and finishing.

The figures in this article come from Belgian price guides and are market ranges. They are not fixed rates from Alpha Services Benelux.

How to compare quotes and avoid surprises

Compare quotes only once the cause of the damp is clearly established and all quotes cover the same scope. A low price sometimes covers only the treatment itself.

1. Ask for the cause in writing: rising damp, infiltration, condensation or a leak.
2. Check whether stripping old plaster, new plaster, salt-resistant mortar and a ready-to-paint finish are included.
3. Ask for the unit: per running metre, per m² or a lump sum, and whether labour is included.
4. Check whether the price is excluding or including VAT, and which VAT rate is applied.
5. Ask what happens if an extra problem turns up during the work, such as a defective gutter or pipe.
6. Get at least two or three quotes after a site visit.

Alpha Services Benelux, active since 2014, works with its own team and issues a fixed written quote after a site visit. See our renovation page for our work, or get a first budget indication with the renovation calculator (in Dutch).

VAT 6% or 21% and grants

For damp treatment in a private home older than ten years, VAT can be 6%; otherwise it is 21%. The rate depends on the conditions, not on the technique.

According to the Belgian federal finance service (FOD Financiën), the reduced 6% rate can apply to renovation or repair of a private dwelling more than 10 years old. In practice the invoice goes directly to the end customer and the same contractor supplies and installs the materials; materials you buy yourself stay at 21%. The difference is significant: on work of €5,400 excluding VAT, the total is €5,724 versus €6,534 including VAT, a €810 gap (worked example from Kelderdichting Vlaanderen).

Flanders: damp treatment ("vochtbestrijding") can qualify for the Mijn VerbouwPremie under conditions, including your income category; check your situation with the simulator at vlaanderen.be/mijn-verbouwpremie. Brussels: Renolution premiums no longer exist for recent invoices; ask your municipality about local premiums and get advice from Homegrade (homegrade.brussels). Wallonia: the Primes Habitation ended on 30.09.2026; check energie.wallonie.be for current support (Rénopack/Rénoprêt loans).

Frequently asked questions

How much does it cost to treat rising damp in Belgium?

Injection costs €50–200 per running metre according to Belgian price guides, a cut-in membrane €100–200. For a terraced house the total is typically €800–1,600, finishing not included. Wall thickness, access and price basis change the amount.

How much does cellar tanking cost per m²?

Tanking from the inside typically costs €50–100 per m², though sources quote up to €150 and even €400. A full drainage project costs €3,000–12,000. An average cellar comes to roughly €2,000–10,000.

Does injection fix every damp wall?

No. Injection only helps with genuine rising damp. Penetrating damp needs façade work, condensation needs better ventilation and a leak must be repaired. Have a professional establish the cause first.

What does finishing cost after a damp treatment?

Plaster repair, salt-resistant mortar and a ready-to-paint finish cost roughly €15–40 per m². In a terraced-house scenario, expect €200–450 of finishing on top of an injection. Check whether the quote includes it.

How much does a ventilation system against condensation cost?

An extractor fan or vent costs €10–70 per piece, excluding installation. A decentralised heat-recovery (MVHR) unit for a single room costs €1,000–1,500 per unit according to one source, a complete system €1,000–6,000. The price depends on the type and the number of rooms.

Is VAT 6% or 21% on damp treatment?

6% can apply in a private home older than ten years when invoiced directly to the end customer. Materials you buy yourself stay at 21%. Always check which VAT basis the quote uses.

Sources

1. Opstijgend vocht behandelen: prijs 2026 — Trustlocal.be
2. Quel est le prix des différents traitements humidité ? — Bobex.be
3. Wat kost een kelder waterdicht maken? Prijzen 2026 — Kelderdichting Vlaanderen (prijsbron Aquaproved, 2 oktober 2026)
4. Traitement de l'humidité : méthodes, prix et primes en 2026 — Guide-renovation.be
5. Kelder waterdicht maken - 2026 Prijzenoverzicht — Homedeal.be
6. Wat kost vochtbestrijding in 2026? Prijzen per techniek — De Muurdokter
7. Prijs vochtbestrijding 2026: kosten per methode & besparing — Vochtbestrijding Antwerpen
8. Vochtbestrijding prijs van verschillende technieken — Murenvochtig.be
9. Werken die in aanmerking komen voor Mijn VerbouwPremie — Vlaanderen.be (Vlaamse overheid)
10. Entrepreneurs étrangers (SPF Finances) – taux réduit de 6 % pour rénovation/réparation d'un logement privé de plus de 10 ans — FOD Financiën / SPF Finances (finance.belgium.be)
11. Tijdelijk verlaagd btw-tarief … (FAQ, versie december 2023) — FOD Financiën / SPF Finances (finance.belgium.be)
12. Renolution-premies Brussel afgeschaft: wat nu? — Energyprotect.be
13. Réforme des primes rénovation en Wallonie : le nouveau régime Rénopack / Rénoprêt en vigueur dès le 1er octobre 2026 — Certinergie.be