Published 2026-10-27 · Updated 2026-10-27 · Alpha Services Benelux

Wall insulation in Belgium 2026: external (render), cavity or internal – cost per m²

Short answer: External wall insulation with render typically starts around €100 per m² in price guides; the upper end is €130 (Renovatiegevel.be, excl. VAT), €150 (economie-energie.be, excl. VAT) or €180 (Isolation-info.be, incl. 6% VAT), depending on the source. Cavity-wall fill starts around €15–17 per m² and internal insulation around €45 per m². According to economie-energie.be, external work usually takes 1 to 3 weeks; cavity injection is typically done in one day.

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

Cost per m²: external, cavity or internal

Cavity-wall fill costs far less per m² than the other methods, internal insulation sits in the middle, and external insulation costs most but treats the whole envelope. The figures below are Belgian market ranges from price guides, not a company price list. Each range belongs to its own source and has not been merged with the others.

The sources do not all use the same VAT basis. Always ask for a quote that states the VAT rate. For 120 m² of wall, economie-energie.be cites €12,000 to €24,000 (excl. VAT) for external insulation and €2,000 to €3,800 for cavity injection.

What drives the price of insulated render

Finish and the difficulty of the facade weigh more than the insulation material alone. For render on insulation the lower end is close to €100/m² in every source; the upper end differs by source and rises with the finish level.

Isolation-info.be breaks it down by insulant (excl. VAT): EPS €85 to €110 (mineral render) up to €100 to €130 (synthetic render), rock wool €110 to €150, PUR €130 to €160 and wood fibre €140 to €180. Other factors:

• scaffolding or a lift, especially over several storeys;
• condition of the substrate and removal of old plaster;
• number of details (windows, corners, roof edges, plinth);
• grain and colour of the render.

How thick? Insulation and living space

Isolation-info.be gives a standard EPS thickness of 12 to 16 cm; with internal insulation you lose 8 to 15 cm per treated wall, according to economie-energie.be. Bobex says at least 10 cm is often recommended.

Source: Isolation-info.be. The reinforced base coat (4 to 6 mm) and render (3 to 6 mm) add only 1 to 2 cm on top of the insulation according to the same source. A wall thicker than 25 cm often indicates a cavity (economie-energie.be); whether the cavity can be filled should be assessed by a professional.

External insulation keeps interior space intact; Isolation-info.be cites 25 to 40% less heat loss through the facade.

EPC/PEB: what changes after wall insulation

Better-insulated walls generally improve the energy performance, but the label only changes with a new certificate. An EPC (PEB in Brussels and Wallonia) is valid for 10 years; in Brussels a new certificate is to be issued after works that affect energy performance.

• Keep invoices and technical data sheets: without proof an assessor may have to apply a default value.
• The effect on your label depends on what is already insulated (roof, windows, heating). Walls alone are rarely enough.
• To plan the sequence of works, see the Flemish EPC renovation obligation after buying.

We cannot promise a label gain: have it calculated by a certified assessor.

Permit for the facade

Whether you need a permit depends on the region, the thickness, the final look and whether the building is protected. The sources below are practical guides; always confirm with your municipality.

• Wallonia: exemption if the external appearance is kept, the total thickness (insulation plus cladding) is at most 30 cm and colours and materials comply with the applicable rules; otherwise a planning permit. If the facade is on the building line, a road-use authorisation may be needed. Listed or protected buildings may face special rules.
• Brussels: its own rules apply; ask your municipality or check homegrade.brussels.
• Flanders: according to Zonr, an exemption up to 26 cm including finish since 1 March 2026, except for protected or inventoried heritage, projection beyond the building line or plot boundary (neighbour's consent), and local planning rules.

For internal insulation and cavity injection economie-energie.be mentions no permit. See also when a renovation permit is needed.

How long the work takes

Cavity injection generally takes one day, internal insulation a few days and external insulation 1 to 3 weeks. These are economie-energie.be indications for a typical house.

1. Preparation: scaffolding, protecting windows, removing old plaster if needed.
2. Fixing insulation boards with adhesive and anchors.
3. Reinforced base coat; Isolation-info.be stresses full drying before the finish.
4. Primer and render, then detailing around windows and plinth.

Weather, drying time and the number of facades affect the schedule. A good contractor sets out the phasing in writing.

6% VAT and grants

For a dwelling older than 10 years, VAT is 6% if it is for private use and the work is invoiced to you by a contractor. Materials you buy yourself stay at 21%.

Grants differ by region and change often; check the official portal (vlaanderen.be/mijn-verbouwpremie, homegrade.brussels or your municipality, wallonie.be).

Comparing quotes without surprises

Only compare quotes that state the same thickness, insulant and finish. A price of €100 per m² and one of €170 per m² can both be right if the finish or substrate differs.

• Ask for itemisation: insulant and thickness (cm or R-value), plaster and render type, scaffolding, waste removal.
• Check whether the price includes VAT and which rate applies.
• Ask who handles the permit application or municipal notification.
• Have details (sills, corners, plinth) written out.

Alpha Services Benelux is a contractor working with its own team, active since 2014. After a site visit you receive a fixed written quote. See the renovation page or the interior renovation page. Prices on this page are market ranges, not a price list.

Frequently asked questions

How much does external wall insulation with render cost in Belgium?

Price guides start at roughly €100 per m² for render on insulation, installation included. The upper end is €130 (Renovatiegevel.be, excl. VAT), €150 (economie-energie.be, excl. VAT) or €180 (Isolation-info.be, incl. 6% VAT). Across all finishes the range is €80 to €250 per m² (Renovatiegevel.be, excl. VAT). Finish and substrate decide where you land.

How much does cavity wall insulation cost per m²?

Renovatiegevel.be says €15 to €30 per m², economie-energie.be €17 to €32 per m² (excl. VAT, installed). For 120 m², economie-energie.be cites about €2,000 to €3,800. A professional must assess whether your cavity is suitable.

How much does internal wall insulation cost per m²?

Renovatiegevel.be says €45 to €80 per m² and economie-energie.be €45 to €100 per m², depending on the system and thickness. You lose 8 to 15 cm of floor space per treated wall, per economie-energie.be.

Do I need a permit for external wall insulation?

It depends on the region, thickness and protection status. In Flanders, per Zonr, an exemption applies up to 26 cm including finish since 1 March 2026, except for protected heritage. In Wallonia an exemption applies if the look is kept, up to 30 cm in total (insulation plus cladding) and with compliant colours and materials. In Brussels its own rules apply: ask your municipality or check homegrade.brussels. Always confirm with your municipality.

How long does wall insulation take?

According to economie-energie.be: one day for injection, a few days for internal work and 1 to 3 weeks for external insulation. Drying of the base coat and weather can extend the schedule.

Sources

1. Prijs gevelisolatie 2026 — Renovatiegevel.be (Solvari)
2. Isolation des murs : prix au m² par méthode en 2026 — economie-energie.be
3. Isolation des façades extérieures en Belgique : prix au m² (2026) — Bobex
4. Crépi sur isolant : prix au m², pose et primes en Belgique 2026 — Isolation-info.be
5. Buitengevelisolatie: wanneer is een vergunning vereist? — Zonr
6. Isolation de façade par l'extérieur : permis, conditions et primes en Wallonie — Airplan / Wallonie (guide permis)
7. Travaux dispensés de permis d'urbanisme ou d'architecte (biens non classés) — Homegrade (Bruxelles)
8. Le certificat PEB d'un logement en Région bruxelloise — Bruxelles Environnement
9. Rénovation énergétique et nouveau certificat PEB — Droits Quotidiens
10. TVA 6 % rénovation (SPF Finances) — SPF Finances / FOD Financiën