Specific regulation for Flemish Brabant — not for all of Flanders. The Woonkernen HORIZON+ regulation only concerns the municipalities of Overijse, Tervuren, and Sint-Genesius-Rode, as part of a provincial plan for Vlaams-Brabant. It has been in effect in Overijse since 24 January 2025, and in Tervuren since August 2024.
It is not often that a new urban planning rule affects so many garden owners. Yet, this is exactly what is happening in three municipalities of Flemish Brabant from 2024-2025. The Woonkernen HORIZON+ regulation does not only talk about house construction — it sets very concrete limits on what you can do with your garden, your surroundings, your driveway, your parking, your terrace, and your pool.
What fundamentally changes is the basic logic. Until now, the question was: "Does my construction exceed 40 m²?" From now on, the question is: "What is the total area already built and impermeable on my entire plot, and do I still have room?" This is an important change in perspective — and I already see it creating surprises for clients in Jezus-Eik, Tervuren, or Overijse.
What the regulation exactly covers and why your garden is affected.
The HORIZON+ regulation applies to Overijse (including the villages of Jezus-Eik, Eizer, Tombeek, Terlanen and Maleizen), Tervuren, and Sint-Genesius-Rode. It is the result of provincial work carried out by Vlaams-Brabant in the Zoniënregio — the area south of Brussels, around the Zoniënwoud. It does not apply to the rest of Flanders.
Its central principle: each plot has a maximum quota for built and impermeable surface area. This quota encompasses absolutely everything:
• the house (footprint)
• the garage or carport — whether it is closed (garage) or open (carport). An open carport is considered a "construction" as soon as it exceeds 50 cm above the ground.
• the garden shed (tuinhuis), the pool house
• the swimming pool — in-ground, semi-in-ground, or above-ground
• the terraces, including wooden terraces on posts or decking
• the driveways, paths, walkways
• the parking spaces
• the stabilised gravel, dolomite, grass pavers, porous tiles, synthetic grass — counted as impermeable, even if they "breathe".
A often overlooked point:what the regulation calls "halfverhardingen" (semi-pavings) is explicitly counted in the quota. Gravel, dolomite, grass pavers, synthetic grass, terraces on posts: everything is included. The definition in the text is clear — anything that is not "natural living soil up to 40 cm deep" counts.
Your quota: how many m² do you have left?
The table below, taken directly from Article 3.3 of the regulation, defines the maximum allowed based on the size of your plot. This percentage applies to the entire house + all outdoor facilities.
Plot size Max. allowed Minimum guaranteed
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< 300 m² 60 % —
300 – 500 m² 40 % 180 m²
500 – 1 000 m² 35 % 200 m²
1 000 – 2 000 m² 25 % 350 m²
2 000 – 3 000 m² 20 % 500 m²
3 000 – 4 000 m² 18 % 600 m²
4 000 – 5 333 m² 15 % 720 m²
> 5 333 m² 15 % (absolute ceiling: 800 m²)
The "minimum guaranteed" means that even if the theoretical percentage gives less, you are still entitled to this minimum. For example, a plot of 310 m²: 40 % = 124 m², but the minimum is 180 m² — it is this minimum that applies.
Example in Overijse (Jezus-Eik) — plot of 900 m²:quota = 35 % × 900 = 315 m². Ground floor house: 160 m². Open carport: 20 m². Driveway + 2 parking spaces: 40 m². Terrace: 30 m². Current total: 250 m². Remaining quota: 65 m². The owner wants to add a pool of 35 m² and a garden shed of 15 m² = 50 m². Feasible — there are still 15 m² of margin.
Example in Tervuren — plot of 1 400 m²:quota = 25 % × 1,400 = 350 m². Ground floor house: 180 m². Garage: 30 m². Terrace: 45 m². Driveway + parking: 50 m². Current total: 305 m². Remaining quota: 45 m². The owner wants a pool of 50 m². Impossible without compensation. Solution: remove an old side terrace of 20 m² → quota released = 65 m². The 50 m² pool becomes feasible, with an additional 15 m² margin.
Specific rules by garden zone
The front garden (voortuin) — the most constrained area
The regulation is particularly strict regarding the front garden, as this area is visible from the public road and its vegetation directly contributes to the quality of the neighbourhood.
• Maximum 2 parking spaces allowed in the front garden
• At least half of the front garden must remain green — even if this means there is no space for 2 cars on small plots
• No other construction in the front garden (shelter, carport, etc.)
• Exception for terraced houses (gesloten verband): a bicycle shelter of max. 4 m² and max. 1.5 m in height is tolerated, surrounded by vegetation
• Each front garden must contain at least one shrub or tree (depending on the depth of the garden)
What this means in practice:if you want to concrete over your entire front garden to have 3 cars, that is refused. The regulation imposes a minimum of 50% greenery at the front. And the 2 allowed parking spaces are part of the overall quota — they take up your m² budget.
The side garden (zijtuin) — rules for the placement of outbuildings
It is often here that one wants to place a carport, a shelter or a covered terrace. The rules are as follows:
• On one side of the house: the side strip must remain completely free of any construction along the entire length of the plot — to maintain a visual opening from the street
• On the other side: constructions are allowed from the back of the facade, at least 1 m from the plot boundary (unless written agreement from the neighbour)
• In the green residential areas: a free strip of at least 5 m is required
The back garden — where the pool and garden shed go
This is the most free area, but it remains subject to the overall quota. A few specific rules:
• Garden shed, pool house, pool: allowed at the back, at least 1 m from the side and rear plot boundaries
• Land modifications: limited to the immediate environment of the house and its access. Exceptions are possible for water basins, swimming ponds and pools
• No land modification within 1 m of the plot boundaries — transitions must be sloped (45°), not with retaining walls, unless demonstrated necessity
When the regulation activates on your existing situation
If you already live in one of these municipalities and your situation exceeds the allowed quotas: do not panic. The regulation does not apply retroactively. You can leave what exists in place. But there are specific triggers.
The two situations that trigger the obligation to comply
1.New construction or demolition-reconstruction: the entire project must comply with the maxima from the design stage.
2.Substantial extension: precisely defined in the regulations. It is reached in two cases:
• Case A — area: if the new works (construction + impermeabilisation) exceed a threshold based on the size of the plot. This threshold ranges from 36 m² for small plots (300–500 m²) to 80 m² for large ones (> 5,333 m²). On a plot of 800 m², for example, the threshold is 42 m².
• Case B — built volume: if the total gross floor area (house + annexes) increases by 20% or more compared to the situation at the time of the regulation's entry into force.
In both cases, you will be required to bring the built + impermeabilised area within the permitted limits — for example, by demolishing old outbuildings or replacing hard surfaces with permeable materials.
The intermediate case: works subject to permit only in the garden
If you carry out works subject to a permit in the garden without touching the house — for example, the installation of a swimming pool, significant modifications to the land — the regulation applies progressively: you will not be asked to demolish existing buildings, but you will need to reduce impermeable surfaces in the garden area to move in the right direction.
What this means in practice:Do you want to install a 40 m² swimming pool in Tervuren and your quota has already been exceeded? The permit will be refused or conditioned on compensatory de-paving (removing an old terrace, replacing a concrete driveway with permeable gravel, etc.). It's better to know this before ordering the work.
How to calculate before starting your project
Here is the concrete process, as I apply it with my clients in this area:
1. Find the area of your plot in residential zoning. Note: only the part in residential zone counts — not the parts in green or natural zones. The area is limited to 50 m deep from the public road.
2. Calculate everything that is already built or impermeable: house + garage + terraces + driveways + shelters + pool + gravel. Start from your existing permits, or have it measured.
3. Apply your percentage according to the table. Compare with your current total.
4. Identify your project: how many additional m²? Does it fit within the remaining quota?
5. If you exceed: which areas can you de-pave? Replace an old concrete driveway with uncounted permeable gravel? No — gravel counts too. However, replacing with vegetation does.
Local exception in Overijse: the old vineyard greenhouses
Overijse has a particularity: its historic grape greenhouses. The regulation explicitly states that greenhouses built before 1970 and still used as horticultural greenhouses are not counted in the overall quota. If you have inherited one of these greenhouses on your plot, it does not affect your m² budget.
A landscaping project in Overijse, Tervuren or Sint-Genesius-Rode?
These rules are recent and still not well known. I notice this regularly: clients discover the HORIZON+ constraints at the time of submitting their permit application — sometimes after they have already signed with a contractor. Integrating this calculation from the design phase of the garden helps avoid costly surprises.
I work in this area of southern Brussels and Flemish Brabant, and I can help you calculate the quota, identify the available margins, and design a layout that fits within the permitted limits — while also meeting your desires.
→ Request a garden consultation appointment
Frequently asked questions
Does the gravel in my driveway count as impermeabilisation in Overijse?
Yes. The HORIZON+ regulation explicitly includes semi-pavements in the calculation: gravel, dolomite, grass slabs, synthetic grass, terraces on pedestals (decking). The definition is precise: anything that is not "natural living soil up to 40 cm deep" is counted. The only exception is existing vegetation, even under a tree with bare soil.
How many parking spaces can I create in the front garden?
A maximum of 2 parking spaces in the front garden, in addition to a driveway. And at least half of the front garden must remain green — this rule applies even if it means there is only room for one car on small plots. These spaces are part of the overall quota of m² that are impermeabilised.
Does my swimming pool require a permit in Tervuren or Overijse?
Yes, an in-ground or semi-in-ground pool is subject to an environmental permit. It must also comply with the overall HORIZON+ quota. The act of applying for the permit triggers the verification of the quota. If your existing situation already exceeds the limits, the administration may condition the permit on compensatory de-paving elsewhere on the plot.
I am buying a house in Sint-Genesius-Rode whose terrace exceeds the quotas. What should I do?
You can keep the situation as it is without immediate obligation. The regulation does not apply retroactively to regularly constructed existing structures. The obligation to comply only triggers if you undertake new construction, a substantial extension (from 36–80 m² of new work depending on the size of the plot, or +20% of floor area), or work subject to a permit in the garden. Before any purchase with a development project in mind, check the available quota.
Does this regulation also apply to Hoeilaart or other municipalities?
No. HORIZON+ is a provincial project of Vlaams-Brabant that only concerns three municipalities: Overijse, Tervuren, and Sint-Genesius-Rode. Hoeilaart is part of the HORIZON+ strategic partnership but is not covered by this PRUP. The rest of Flanders only applies the general Flemish exemption decision.