Planning is a regional competence: Wallonia, the Brussels Region and Flanders each have their own code, procedures and exemption lists. The underlying principle, however, is common to all three.
The principle: four families of permit-requiring acts
- Building: any new construction, including an extension, a carport, a garden shed above a certain size, a swimming pool.
- Altering: works affecting the load-bearing structure — removing a supporting wall, modifying the roof structure, digging out a cellar, adding a storey.
- Changing the use: turning a shop into a home, a home into offices, a single-family house into several units. This is one of the most frequently overlooked points: splitting a house into two flats requires a permit, even with no works visible from the street.
- Modifying the exterior appearance: replacing window frames with a different model or colour, changing the roofing material, adding cladding, opening a new bay.
In protected areas, near a listed monument or within a heritage perimeter, the usual exemptions fall away and the opinion of additional bodies is required.
What is generally exempt
- Maintenance and like-for-like repairs: replacing tiles with identical ones, repainting a façade in the same shade, replacing a boiler.
- Interior works with no effect on the structure, the use or stability: redoing a kitchen, a bathroom, a lightweight partition.
- Certain small-scale works, whose precise list and maximum dimensions vary between Regions.
« Generally » is not « always »: the only reliable answer comes from the municipality's planning department, consulted before the works. That consultation is free and given in writing.
The architect
An architect is mandatory for most acts requiring a permit, particularly where there is construction or structural modification. Exceptions exist for minor works, defined by Region. An application filed without an architect where one was required is inadmissible.
The real risk: the resale
A planning infringement does not lapse the way people imagine, and it surfaces at the sale. The notary queries the municipality and the Region; the information appears in the deed. An extension never declared, an unauthorised subdivision, window frames replaced without a permit in a protected area: the buyer learns of it before signing.
Consequences range from a simple price negotiation to mandatory prior regularisation, or even a failed sale where the situation cannot be regularised. A property carrying an infringement sells below its market, and the discount almost always exceeds what the permit would have cost.
Before starting works
Three reflexes: request the planning department's written opinion, check what the property's original permit authorised, and keep all authorisations with the property file. Those documents are part of what a buyer will ask for, and their absence weighs on the price.