Permit for a house extension in Belgium: what you need, what it costs and how long it takes
Short answer: An extension attached to your house needs an environmental permit in Flanders since 1 March 2026: the notification route for attached additions was abolished. In Brussels a permit with an architect is almost always required; in Wallonia it depends on the type and size. Flemish authorities decide within 60 days (simplified) or 105-120 days (ordinary procedure), and file fees vary by municipality.
Prices in this article are indicative Belgian market ranges, not Alpha Services Benelux's price list. Your fixed price is in the quote.
Permit, notification or exempt: what applies to an extension?
An extension that enlarges your home's building volume normally needs a permit. Exemptions mainly cover work that leaves the volume unchanged, such as interior alterations.
In Flanders, some home extensions used to fall under a simple notification until 28 February 2026. According to the official guide of the Department of Environment, building additions attached to the main dwelling is no longer a notification matter since 1 March 2026 and is back under the permit requirement. Exempt work includes interior renovations (without change of use and with the same number of dwellings) and facade and roof work that does not change the physical volume or worsen energy performance.
An exemption is never a free pass: it does not apply if the work conflicts with a zoning plan, an allotment or an urban planning regulation.
What applies in each region?
Rules differ by region, and your municipality also has a say. The table gives the broad picture; always check your own situation with the municipality.
| Region | Permit or notification | Architect | Official source |
|---|---|---|---|
| Flanders | Environmental permit (notification for attached additions abolished on 1 March 2026) | In principle required for permit-bound work | omgeving.vlaanderen.be |
| Brussels | Planning permit; extension or veranda is listed among work requiring an architect | Yes, apart from exceptions in the CoBAT | homegrade.brussels, urban.brussels |
| Wallonia | Permit (CoDT); a table of small permits provides exemptions and simplified files | 1939 law with exceptions in art. R.IV.1-1 CoDT; form annexe 4 (with) or annexe 6 (without) | territoire.wallonie.be |
In Wallonia, the list in art. R.IV.1-1 CoDT (column 3) determines which works can be filed without an architect (form annexe 6). For a habitable extension, plan on hiring an architect and have this confirmed by your municipality.
Size and distance rules in general terms
Exemptions and simplified files almost always depend on a combination of floor area, height and distance to the plot boundary. For an extension attached to the house, those exemptions no longer apply in Flanders.
- Area: in Flanders, freestanding outbuildings can be exempt under strict conditions, but that does not cover an extension against the house.
- Distance: position relative to boundaries and neighbouring buildings is checked against the zoning plan, the allotment and the Civil Code (views and windows).
- Number: the number of outbuildings or volumes already on the plot may also count; ask your municipality.
- Local rules: a zoning plan, allotment or municipal bylaw can be stricter than the regional rule.
If in doubt, ask the municipal planning department for a preliminary opinion.
When is an architect mandatory?
Every project that needs a permit requires an architect, apart from the exceptions each region lists. This follows from article 4 of the law of 20 February 1939.
For an extension, preparing the permit application is therefore architect work. In Brussels an extension or veranda is expressly among the works requiring an architect. In Wallonia a small file can be submitted without one (annexe 6); for a habitable extension, plan on an architect, as noted above.
New in Flanders: since 5 September 2026 an architect is also needed for permit-exempt interior alterations that affect stability. This is relevant if you open a load-bearing wall inside the house without an extension; for an extension that work is part of the permit application anyway.
What do the permit and the architect cost?
Municipal file fees range from tens to a few hundred euros; the architect's fee is the main cost. The figures below are examples from official or published sources.
| Item | Amount or range | Source |
|---|---|---|
| File fee Landen (Flanders) | 75 euros without, 100 euros with mandatory architect | City of Landen |
| File fee Edegem (Flanders) | 350 euros simplified with architect, 650 euros ordinary procedure | Edegem local authority |
| File fee City of Brussels | 380 euros with architect, 190 euros without | City of Brussels |
| Sketch or basic design for an extension | 1,000-2,500 euros incl. VAT | Homedeal (03/2026) |
| Full commission for an extension with supervision | 8,000-18,000 euros incl. VAT (Homedeal table) | Homedeal (03/2026) |
| Fee as % of the works | 8-12 % | Homedeal |
| Renovation: example percentages from an architect's office | about 12 % and 18 % (basic or full commission) | VRT NWS (example given by the NAV chair, 12/2025) |
Sources partly disagree because architect fees are freely negotiated. Other passages in the same Homedeal article give 6,000-10,000 or 6,000-12,000 euros for a full commission. The VRT article itself says there are no fixed rates and that a smaller budget means a higher percentage. Ask for a written scope: plans, filing, supervision, tendering.
How long does it take?
Flanders decides within 60 days (simplified procedure) or 105-120 days (ordinary procedure); Brussels timelines are longer. Add the architect's preparation time and the completeness check.
| Region | Period | Source |
|---|---|---|
| Flanders, simplified procedure | 60 days | VLAIO |
| Flanders, ordinary procedure | 105 days, 120 with a permit committee | VLAIO |
| Brussels, decision by the municipal college (art. 156 §2 CoBAT) | 75 days; 90 days with involvement of the delegated official or special publicity measures; 160 days with both (+30 days if the period falls in the summer holidays) | urban.brussels |
| Wallonia | roughly 30 to 115 days depending on procedure | Airplan (trade media) |
A granted permit is only the start: you still need to choose a contractor and schedule the build. Expect several months of paperwork before work begins; for the building stage, see also our interior renovation page.
Comparing quotes and avoiding surprises
Have the permit approved before the final order and ask for fixed prices based on the approved plans. That way you compare quotes on the same basis.
- Agree who submits the file and who pays the file fee and any planning charges.
- Ask for the stability study, EPB declaration and utility connections to be listed separately.
- Request a written quote after a site visit; a market range on a blog is never a fixed price.
- Check that the work stays within what was permitted; deviations lead to regularisation and sometimes fines.
- Check the official portals (vlaanderen.be, homegrade.brussels, wallonie.be) for premiums; do not assume an extension itself qualifies.
Alpha Services Benelux has been active since 2014 and works with its own team in Brussels, Flanders and Wallonia. Renovation is by appointment; after a site visit you receive a fixed written quote. See the renovation page or estimate your budget first with the renovation calculator.
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
Do I need a permit for a house extension in Belgium?
In Flanders yes: since 1 March 2026 the notification route for attached additions is gone and an environmental permit is required. In Brussels a planning permit with an architect is the rule. In Wallonia it depends on the type of work; the list in art. R.IV.1-1 CoDT determines which works can go without an architect.
Is an architect mandatory for an extension?
In principle yes for all permit-bound work (law of 20 February 1939). Exceptions are set per region, for example small files in Wallonia via annexe 6. For a habitable extension, plan on hiring an architect and have this confirmed by your municipality.
How much does a permit for an extension cost?
File fees vary by municipality. Examples from the sources: 75-100 euros in Landen, 350-650 euros in Edegem (simplified with architect, resp. ordinary procedure) and 190-380 euros in the City of Brussels. The architect's fee comes on top.
How much does an architect cost for an extension?
Homedeal quotes 1,000-2,500 euros for a sketch and 8,000-18,000 euros incl. VAT for a full commission with supervision (Homedeal table), or 8-12 % of the works. The NAV chair, quoted by VRT NWS, gives about 12 % (basic) and 18 % (full commission) as an example for renovation. Fees are freely negotiated.
How long does an extension permit take?
In Flanders 60 days (simplified) or 105-120 days (ordinary) after a complete file. In Brussels a private extension is usually decided by the municipal college: 75 days, 90 days with the delegated official or special publicity measures, and 160 days with both (+30 days if the period falls in the summer holidays).
Is there a grant for a house extension?
Do not assume so. Check the conditions on the official portals: vlaanderen.be/mijn-verbouwpremie, homegrade.brussels and energie.wallonie.be, before signing a quote.
Sources
- Hulpgids inzake de vergunningsplicht, vrijstelling en melding — Departement Omgeving, Vlaanderen
- Wijzigingen vrijstellingenbesluit, meldingsbesluit en besluit limitatieve lijst — Departement Omgeving, Vlaanderen
- De omgevingsvergunning — VLAIO (Vlaamse overheid)
- Travaux dispensés de permis d'urbanisme ou d'architecte (biens non classés) — Homegrade (Brussels Gewest)
- Délais de traitement du dossier (permis d'urbanisme) — urban.brussels (Brussels Gewest)
- Aanvraag tot stedenbouwkundige vergunning indienen / berekening administratieve kosten — Stad Brussel
- Omgevingsvergunning - Stad Landen — Stad Landen
- Omgevingsvergunning - Lokaal bestuur Edegem — Lokaal bestuur Edegem
- Formulaires - SPW Territoire — SPW Territoire (Wallonie)
- Wat kost een architect? 2026 prijzenoverzicht — Homedeal (25/03/2026)
- Wanneer heb je een architect nodig en hoeveel kost dat? — VRT NWS (04/12/2025)
- Travaux sans permis d'urbanisme et dispensés d'un architecte en Wallonie — Airplan (vakmedia)