How much does a house extension cost per m² in Belgium in 2026?
Short answer: In Belgium in 2026, a house extension typically costs €1,200 to €2,400 per m² excl. VAT in timber frame and €1,400 to €2,800 per m² in masonry, which works out to roughly €18,000 to €112,000 excl. VAT for 15 to 40 m². A fully finished, high-end extension can reach about €3,500 per m² or more. Architect and stability study come on top.
Prices in this article are indicative Belgian market ranges, not Alpha Services Benelux's price list. Your fixed price is in the quote.
Extension cost per m²: Belgian market ranges
In 2026, budget €1,200 to €2,400 per m² excl. VAT for a timber-frame extension and €1,400 to €2,800 per m² for masonry. This is the range on which most comparison sources agree; the final price depends heavily on the finish level. A fully finished, high-end extension can reach about €3,500 per m² excl. VAT or more.
| Type | Range per m² | What the sources say |
|---|---|---|
| Timber frame | €1,200 – 2,400 | Trustup 1,200–2,200; extension-maison-maconnerie.be 1,200–1,900; Housing-service 1,500–2,400 |
| Masonry | €1,400 – 2,800 | Trustup 1,400–2,300; extension-maison-maconnerie.be 1,400–2,200; Housing-service 1,800–2,800 |
| Unfitted vs fully fitted out | approx. €1,900 vs approx. €2,500 (averages, 2025 figures) | Naturhome |
For the higher end, Trustup's overview gives an overall range of €1,200 to €3,500 per m² excl. VAT (steel and glass 2,000–3,500). Waterpas Construction cites €2,500 to €3,500 per m² for a standard finish and an overall range of up to €5,000 per m²; that source does not state whether the amounts include VAT.
These are market ranges, not any company's price list. Many sources are commercial sites, so use them to test quotes, not to replace them.
Budget for a 15, 20, 30 and 40 m² extension
For 15 to 40 m², the rough budget runs from about €18,000 to €112,000 excl. VAT. The table multiplies the ranges above by the floor area; it is our own calculation, not a quote.
| Area | Timber (€1,200–2,400/m²) | Masonry (€1,400–2,800/m²) |
|---|---|---|
| 15 m² | €18,000 – 36,000 | €21,000 – 42,000 |
| 20 m² | €24,000 – 48,000 | €28,000 – 56,000 |
| 30 m² | €36,000 – 72,000 | €42,000 – 84,000 |
| 40 m² | €48,000 – 96,000 | €56,000 – 112,000 |
Small extensions often sit at the top of their range because fixed costs (foundations, opening up the existing wall, connections) are spread over fewer m². A 40 m² extension is usually cheaper per m² than a 15 m² one. For 30 m² with full finishes, one source cites around €70,000.
Timber frame or masonry: what is the difference?
Timber frame is usually a little cheaper and, above all, faster; masonry is heavier and generally costs more. In the sources compared, timber averages a few hundred euros per m² less, but the ranges overlap widely.
- Timber: light structure, lighter foundations, quick build. High-end cladding and large glazing quickly push the price towards masonry.
- Masonry: a heavier technique needing solid foundations; longer build, but a seamless match with an existing brick house.
So the choice depends more on the finish you want, how it joins the existing facade and build time than on a fixed price gap.
What drives the price of an extension
Finish level, ground conditions and floor area drive the price most. One source says finishes can double the initial structural budget.
- Foundations and soil: unstable ground adds €5,000 to €15,000 according to one source; a soil study costs €1,500 to €3,000.
- Architect fees: 7 to 12% of the works for a full mission, 3 to 6% for the permit file only.
- Stability study: €1,000 to €3,000, for instance when opening a load-bearing wall.
- Roof and glazing: a flat roof generally costs less than a pitched one; sliding doors and roof lights weigh heavily.
- Services and fit-out: kitchen, bathroom, electrics, heating.
- Region: Brussels is 10 to 20% higher according to one source.
Also allow roughly 10% for contingencies.
Planning permit and architect for an extension
A habitable extension normally needs a permit in all three Regions, and an architect is then required. Only small, non-habitable annexes may be exempt or need just a notification.
- Wallonia: a heated, habitable extension needs a planning permit even at 15 m²; 30 to 115 days by law, often 3 to 5 months in practice.
- Brussels: an extension changes the volume and needs a permit; about 45 days for a simple file, up to 160 days or more with a public inquiry.
- Flanders: environmental permit, notification (melding) or exemption. Small non-habitable annexes up to 40 m² cumulative, under height and location conditions, may be exempt; a heated living space generally needs a permit. Expect about 60 days (simplified) to 105–120 days.
Local rules and allotment conditions take precedence, so ask your municipality first. For Flanders, see vlaanderen.be/omgevingsvergunning.
VAT: 6% or 21% on an extension
6% VAT can apply if the home is at least 10 years old, is mainly used as a private dwelling and a professional invoices the work. For an extension, the old part must remain more than half of the total floor area after the works.
Materials you buy yourself stay at 21%. On €40,000 of work, the difference between 6% and 21% is €6,000. All prices above exclude VAT, so add 6% or 21%. Details in our 6% VAT guide. An extension is usually not subsidised as such; check Homegrade and your municipality (Brussels), energie.wallonie.be (Wallonia) or vlaanderen.be/mijn-verbouwpremie (Flanders).
Comparing quotes without surprises
Only compare quotes that cover the same thing: same area, finish level and VAT rate. Ask for at least three, as our comparison guide also advises.
- Is the price excl. or incl. VAT?
- Are the architect, stability study and EPB report included?
- What do the foundations cover: soil study, extra depth?
- Closed shell or fully finished (floor, plastering, electrics, heating)?
- Which items are provisional sums, and who pays for extras?
Alpha Services Benelux, active since 2014, works with its own team (not a lead broker) and provides a fixed written quote after a site visit for its renovation work. Start with a rough estimate using the renovation calculator or see the renovation page.
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
What does a house extension cost per m² in Belgium?
In 2026, expect roughly €1,200 to €2,400 per m² excl. VAT for timber frame and €1,400 to €2,800 per m² for masonry. Sources differ and finish level matters most; a fully finished, high-end extension can reach about €3,500 per m² or more. Architect fees and the stability study come on top.
How much does a 15 m² or 30 m² extension cost?
By calculation, 15 m² comes to €18,000 to €42,000 and 30 m² to €36,000 to €84,000 excl. VAT, depending on timber or masonry. One source cites around €70,000 for 30 m² fully finished.
Is a timber-frame extension cheaper than masonry?
Often slightly: timber starts at €1,200 per m² against €1,400 for masonry. The ranges overlap strongly, though, and a high-end finish with lots of glazing quickly erases the advantage. Timber is mainly faster to build.
Do I need a permit and an architect for an extension?
Usually yes: a habitable extension needs a permit in all three Regions, with an architect. Small non-habitable annexes up to 40 m² cumulative may be exempt under conditions. Always check with your municipality.
Can I get 6% VAT on an extension?
Yes, if the home is at least 10 years old, privately used and a professional invoices the work. The old part must make up more than half of the total area after the works. Otherwise 21% applies.
Sources
- Extension de maison en Belgique : permis et prix 2026 — Housing-service.be
- Prix d'une Extension de Maison en Belgique en 2026 : Guide Complet des Coûts — extension-maison-maconnerie.be
- Prix extension maison en Belgique (2026) — Trustup
- Prix pour agrandir sa maison en Belgique : estimation et budget 2026 — Naturhome
- Aanbouw prijs per m2: kosten, voorbeelden en tips — Waterpas Construction
- Wanneer en hoe krijg je verminderd btw-tarief van 6% voor werken aan je woning? — Test-Aankoop
- Heb je een vergunning nodig voor jouw verbouwing? — Test-Aankoop
- Omgevingsvergunning — Vlaanderen.be (Vlaamse overheid)