Roof insulation: cost per m² in Belgium in 2026
Short answer: Roof insulation in Belgium costs roughly €20 to €115 per m², installed and excluding VAT (Renergo). Attic floor: €20–50, pitched roof from inside: €25–55, sarking: €40–100 and flat roof from outside: €45–115. Other guides quote €100–200 or more for sarking including a new roof covering. For R = 5 you need about 11 to 24 cm of insulation, depending on the material.
Prices in this article are indicative Belgian market ranges, not Alpha Services Benelux's price list. Your fixed price is in the quote.
Roof insulation price per m² by method
The method drives most of the price: attic floors and insulation between the rafters come at the lower end, while sarking and flat roofs insulated from outside cost more. The guides do not use the same VAT basis or finish level, so read the column headings.
| Method | Renergo (excl. VAT) | Devis-Wallonie (excl. VAT) | Isolation-info (incl. VAT) |
|---|---|---|---|
| Attic floor / unheated attic | €20–50 | €20–55 (blown-in) | €20–40 |
| Pitched roof from inside | €25–55 | €25–70 | €40–90 (between rafters) |
| Sarking (from outside) | €40–100 | €100–200 | €80–150 (insulation only); €120–300 with new roof covering |
| Flat roof | €25–40 (inside); €45–115 (outside, warm roof) | €60–140 | €60–160 (cold, warm or inverted) |
Across all methods, Renergo's overall spread is €20 to €115 per m². For sarking the guides differ widely because the highest figures usually include a completely new roof covering, so the exact price depends on the finish level.
Pitched roof: from inside, sarking or attic
From inside, insulation goes between or under the rafters without touching the roof covering; sarking sits on top of the rafters and therefore means work on the roof itself.
From inside
This is the usual choice when the roof covering is still in good condition. Interior finishing (plasterboard, plastering, painting) adds €25–45 per m² according to prijs-dakisolatie.be.
Sarking
Rigid PIR or PUR boards with an integrated underlay go above the rafters, mostly together with a new roof covering (prijs-dakisolatie.be: €80–130 per m²). The upside is that you keep your interior space. Always ask whether the roof covering is in the price.
Attic floor
If the attic is not lived in, insulating the floor is often enough. Prijs-dakisolatie.be quotes €15–25 per m² without a walkable finish and €30–45 with one.
Insulating a flat roof
A flat roof is mostly insulated from outside, above or below the waterproofing layer: €45–115 per m² at Renergo, €60–140 at Devis-Wallonie. From inside it is cheaper (Renergo: €25–40 per m²) but less advisable, as moisture can stay trapped in the build-up.
In a warm roof the insulation sits under the membrane; in an inverted roof it sits on top. Prijs-dakisolatie.be lists €45–80 per m² for a warm roof and €50–90 for an inverted (XPS) roof. Isolation-info is higher (€70–130 and €100–160, VAT included). For the waterproofing itself, see our guide on EPDM vs bitumen.
What thickness for R = 5, and what does the material cost?
For R = 5 you need roughly 11 to 24 cm of insulation: less with PIR/PUR, more with mineral or wood wool. The exact thickness depends on the product's lambda value.
| Material | Isolation-info | prijs-dakisolatie.be | Devis-Wallonie |
|---|---|---|---|
| Mineral wool (glass or rock) | 18–19 cm | 16–22 cm | 20–24 cm |
| PIR/PUR | 12 cm | 11–14 cm | 14–16 cm |
| XPS | 16 cm | – | – |
| Wood fibre / wood wool | 20 cm | 18–24 cm | – |
| Material | Renergo | prijs-dakisolatie.be (pitched roof, inside) |
|---|---|---|
| Glass wool | €25–45 | €20–40 (mineral wool) |
| Rock wool | €30–55 | €20–40 (mineral wool) |
| EPS | €30–55 | – |
| PIR boards | €35–75 | €30–55 (PIR/PUR) |
| Sprayed PUR | €35–70 | €25–45 |
| Wood wool | – | €40–60 |
Renergo works with Rd 4.5 (about 11 cm of PIR to 17 cm of rock wool). The legal minimum in Flanders is, per the same source, only R 0.75, or 3 to 4 cm: legal, but not very effective.
Budget for 100 m² of roof
For 100 m² the total runs from about €2,000 for an attic floor to €30,000 for sarking with a new roof covering. The range is wide because the guides differ in VAT basis and finish.
| Method | Devis-Wallonie (excl. VAT) | Isolation-info (incl. VAT) |
|---|---|---|
| Attic / attic floor | €2,000–5,500 | €2,000–4,000 |
| Pitched roof from inside | €2,500–7,000 | €4,000–9,000 |
| Flat roof | €6,000–14,000 | – |
| Sarking | €10,000–20,000 | €12,000–30,000 |
Devis-Wallonie states its estimates can deviate by about 25 to 35%. Add access, scaffolding and waste removal.
What drives the price of roof insulation?
The price depends mainly on the method, the material, the finish and the condition of the roof. Less visible: the VAT basis of the guide you read and whether the roof covering is included.
- Method: attic floors and between-rafter insulation cost less than sarking or a flat roof.
- Material and thickness: PIR/PUR costs more per m² but is thinner than mineral or wood wool.
- Finish: plasterboard, plastering and painting add €25–45 per m² (prijs-dakisolatie.be).
- Roof covering: with sarking a new covering is often included, which pushes the figures up.
- Access and shape: scaffolding, roof windows and chimneys take extra hours.
- VAT basis: some guides show prices excl. VAT, others incl. VAT.
EPC label and the Flemish renovation obligation
If you buy a home with EPC label E or F in Flanders, Test-Aankoop says you must reach at least label D within six years of purchase and prove it with a new EPC. The obligation applies since 1 January 2023; the deadline was extended from five to six years.
Test-Aankoop names no specific roof-insulation duty, but an uninsulated roof is often one of the biggest gains for your label. Read more in our article on the Flemish EPC renovation obligation. For financial support, check the official regional portals (vlaanderen.be/mijn-verbouwpremie, wallonie.be and, for Brussels, Homegrade).
6% or 21% VAT on roof insulation
VAT is 6% if the home is at least ten years old, mainly used as a private residence and the contractor supplies and installs the materials. The invoice must be addressed to the end consumer, the owner or the tenant. Otherwise 21% applies.
Materials you buy yourself stay at 21% (Renergo, Test-Aankoop). When comparing quotes, check whether an amount is excl. or incl. VAT. More in 6% VAT on renovation.
Comparing roof insulation quotes without surprises
Only compare quotes that show the same method, R-value and VAT basis. Have a professional assess the roof's condition before you decide.
- Ask for the R-value and thickness, not just the brand.
- Check whether roof covering, underlay and vapour barrier are included.
- See whether the interior finish (plasterboard, painting) is in the price.
- Ask whether the amount is excl. or incl. VAT and which rate applies.
- Request a written quote after a site visit, with price per m² and a total.
Alpha Services Benelux, active since 2014, works with its own team and provides a fixed written quote after a site visit. Prices in this guide are market ranges, not a price list. See also our roofing and renovation pages.
Fixed quote after a site visit
Alpha Services Benelux does the work with its own team, active since 2014. VAT BE 0541.320.178.
Request a quoteFrequently asked questions
How much does roof insulation cost per m² in Belgium?
Renergo gives €20 to €115 per m², installed and excl. VAT. By method: attic floor €20–50, pitched roof from inside €25–55, sarking €40–100, flat roof outside €45–115. Other guides are higher, especially for sarking with a new roof covering.
What does sarking cost per m²?
Renergo lists €40–100 per m² excl. VAT, prijs-dakisolatie.be €80–130 and Devis-Wallonie €100–200. Isolation-info gives €80–150 for insulation only and €120–300 incl. VAT with a new roof covering. The gap comes from the finish level.
What thickness do I need for R = 5?
About 11–14 cm of PIR/PUR, 16–24 cm of mineral wool and 18–24 cm of wood wool, depending on the source and lambda value. Isolation-info gives 16 cm for XPS. Always check the R-value on the quote, not just the thickness.
Do I have to insulate my roof with EPC E or F?
In Flanders, with label E or F you must reach label D within six years of purchase and prove it with a new EPC (Test-Aankoop). No specific roof duty is mentioned there, but the roof is often an efficient step.
What VAT applies to roof insulation?
6% if the home is at least ten years old, mainly private use, and the contractor supplies and installs the materials, invoiced to the end consumer (owner or tenant). Materials you buy yourself stay at 21%.
Sources
- Dakisolatie prijs per m², premie en offertes in 2026 — Renergo
- Prix isolation toiture en Belgique (2026) : coût au m², primes et matériaux — Devis-Wallonie.be
- Prijs dakisolatie in België (Update 2026) — prijs-dakisolatie.be
- Isolation toiture : prix au m², primes et méthodes en 2026 — Isolation-info.be
- Renovatieverplichting 2026: wat verandert er in Vlaanderen, Wallonië en Brussel — Test-Aankoop
- Wanneer en hoe krijg je verminderd btw-tarief van 6% voor werken aan je woning? — Test-Aankoop