Insulation prices in Belgium: roofs and cavity walls

You feel insulation from the first winter: fewer draughts, rooms that hold their heat, heating that runs for less time. In Belgium, the two most common jobs are also the most affordable. Expect €25 to €60 per m² to insulate a roof from the inside, and €20 to €30 per m² to have cavity walls injected. Below: what moves those prices, three full budgets, and the aid still open now that Wallonia has stopped its per-job grants.

Rates in 2026

• Roof insulation from the inside: €25 to €60 per m².
• Cavity wall insulation by injection: €20 to €30 per m².

For the roof, the bottom of the bracket applies to easily accessible attics insulated with a standard material. The top covers trickier configurations and higher-performing insulants, with or without finishing depending on the quote.

Cavity wall injection remains the fastest insulation job: the pro drills small holes in the facade, injects the insulant into the cavity and seals up. It is often done within a working day, without touching the interior.

Other items exist, such as floor insulation or external wall insulation, but their prices depend too much on the configuration to fit a general bracket. They are priced on quotation. For external wall insulation, our facade renovation price guide gives the ranges published in 2026.

What makes the price vary

• Accessibility. An easy-to-reach attic is insulated quickly. A converted roof where existing finishes must come off takes far more hours.
• The material chosen. Glass wool, PIR, cellulose: each insulant has its price, its required thickness and its behaviour. Our dedicated comparison helps you decide.
• The performance targeted. The further you push the insulation level, the thicker the layer, and with it the material cost and sometimes adjustments to the roof structure.
• The condition of the base. A missing or damaged roofing underlay, a damp cavity or one cluttered with rubble must be dealt with before insulating. A non-negotiable prerequisite.
• The finishing. Insulating a loft stops at the insulant. Insulating a living space involves a vapour barrier, plasterboard and skimming: the budget moves up a category.

Worked examples

Three illustrative examples, built solely with the brackets above:

• Insulating a roof from the inside: around 60 m², so €1,500 to €3,600.
• Injecting the cavity walls of a terraced house: around 100 m² of facade, so €2,000 to €3,000.
• Combined roof and walls project: around 100 m² of roof (€2,500 to €6,000) and 80 m² of cavity walls (€1,600 to €2,400), a total of €4,100 to €8,400.

VAT and aid in 2026

First lever, VAT: insulation work supplied and invoiced by a contractor in a private home over 10 years old qualifies for the reduced 6% rate instead of 21%, if the conditions are met. The rate applied must appear on the quote.

Second lever, the aid, which has changed a lot:

• In Brussels, no Renolution grant can be claimed for work invoiced in 2025 or 2026, as the government has taken no decision. The preferential-rate Ecoreno loan remains open under conditions. See our update on Brussels support.
• In Wallonia, the Prime Habitation ended on 30 September 2026. Since 1 October, Rénopack and Rénoprêt finance insulation within a whole project that gains the home a PEB label, based on an audit less than a year old. Details in our article on the end of the Prime Habitation.
• In Flanders, Mijn VerbouwPremie supports roof, wall and floor insulation, with technical requirements and amounts that depend on the applicant's profile.

In every case, check the conditions before you sign the quote, not after: in Wallonia, for instance, starting work before the credit agreement is signed can put the aid at risk.

Mistakes to avoid

• Insulating without dealing with damp. Locking a damp problem behind insulation makes it worse. Cluttered cavity, roof leak, rising damp: treat first, insulate second.
• Forgetting ventilation. A well-insulated house becomes airtight. Without proper ventilation, condensation sets in. Plan insulation and ventilation together.
• Comparing quotes with different thicknesses. A cheaper quote with less thickness is not a bargain, it is cut-price insulation. Compare at equal performance.
• Signing before checking the aid conditions. Some requirements concern the material, the contractor or the timing. One missed detail can cost the whole aid.
• Neglecting airtightness. A badly fitted vapour barrier or sloppy joints wipe out part of the benefit. Workmanship matters as much as the insulant chosen.

FAQ

Which insulation job offers the best cost-effectiveness?

Cavity wall injection, at €20 to €30 per m², is often the most cost-effective first step when the house allows it. Roof insulation from the inside, at €25 to €60 per m², follows closely: heat rises, and an uninsulated roof is among the biggest sources of loss.

Can regional aid be combined with 6% VAT?

Yes. The reduced rate applies directly on the contractor's invoice, while regional aid (a loan in Wallonia, a grant in Flanders) goes through a separate file. Each scheme has its own conditions, to check before the work.

Can I insulate myself to save money?

For some items you can, but the sums rarely add up. You pay 21% VAT on materials you buy yourself, you give up the workmanship guarantee, and you make access to aid harder, since it usually relies on contractor invoices.

Compare quotes before you sign

Between the accessibility of your roof, the condition of your walls and the material chosen, only a detailed quote can place your project within the bracket. Post your project on Batizzy and compare quotes from insulation companies in your area side by side: find an insulation contractor. To choose your insulant, read our comparison of glass wool, PIR or cellulose, and to pay the right rate, our guide to 6% VAT in Belgium.