Insulation prices in Belgium in 2026: roof and cavity walls

Of all renovation works, insulation is the one that pays for itself: every winter, a poorly insulated house lets a large share of its heat escape through the roof and the walls. The good news is that the two most effective jobs, insulating the roof from the inside and filling the cavity walls, also remain the most affordable. Here are the prices charged in Belgium in 2026, complete worked examples and the support schemes to activate in the three regions.

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. 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.

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 underroof, 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 scenarios 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.

These amounts are before deduction of regional grants, which can lighten the invoice noticeably depending on your situation.

VAT at 6% or 21% and regional grants

First lever: VAT. Insulation works carried out by a contractor in a private dwelling over 10 years old qualify for the reduced 6% rate instead of 21%. The rate applied must appear on the quote.

Second lever: grants. All three regions support insulation, each through its own channel:

• In Brussels, the Renolution grants cover part of the insulation cost, with higher amounts depending on household income. Applications go through the Renolution portal.
• In Wallonia, the Walloon grants support roof and wall insulation, with technical requirements on materials and amounts linked to income category.
• In Flanders, Mijn VerbouwPremie centralises insulation applications, again with amounts that vary with the applicant's profile.

In all three cases, the works must be carried out by a contractor and meet performance criteria. Check the conditions on your region's portal before signing the quote, not after.

Mistakes to avoid

• Insulating without treating damp first. Sealing a moisture problem behind insulation makes it worse. A cluttered cavity, a leaking roof, rising damp: remediate first, insulate second.
• Forgetting ventilation. A well-insulated house becomes airtight. Without proper ventilation, condensation settles in. Insulation and ventilation must be designed together.
• Comparing quotes with different thicknesses. A cheaper quote with a thinner layer is not a bargain, it is discounted insulation. Compare at equal performance.
• Signing before checking grant conditions. Some requirements concern the material, the contractor or the file to submit. One missed detail can cost the entire grant.
• Neglecting airtightness. A badly fitted vapour barrier or sloppy junctions ruin part of the benefit. The quality of installation matters as much as the insulant chosen.

FAQ

Which insulation job offers the best value for money?

Cavity wall injection, at €20 to €30 per m², is often the most profitable first step when the house allows it. The roof from the inside, at €25 to €60 per m², follows closely: heat rises, and an uninsulated roof remains the biggest source of losses.

Can regional grants be combined with the 6% VAT rate?

Yes. The reduced rate applies directly on the contractor's invoice, while regional grants come on top, through an application. Each scheme has its own conditions, to check before the works.

Can you insulate yourself to save money?

Technically possible for some jobs, but you then lose the reduced VAT rate on the labour, access to regional grants, which require a contractor's invoice, and the guarantee on the installation. The maths rarely works out.

Compare quotes before you sign

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