For many homes, an aanbouw or uitbouw (an extension) at the back is the most far-reaching renovation that can be done without a permit: a kitchen that moves a few metres into the garden, an extra living room behind the existing facade or a utility room against the side wall. The space it adds is immediately noticeable, and precisely for that reason the regulations are strict. If you stay within the fixed dimensions for the achtererfgebied (rear yard area), you do not need to apply for anything from the municipality; if you build half a metre deeper or end up too high, you suddenly find yourself in a permit procedure of two to three months. This article zooms in on the extension. The general overview of permits for renovations can be found in When do you need a permit for a renovation; the dormer has its own article: Fitting a dormer: permit-free or permit required?
Two tests under the Omgevingswet
Since 1 January 2024, the Omgevingswet (Environment and Planning Act) has applied, and with it the question "may I build an extension without a permit?" has been split into two questions. The first concerns the technical building activity: does the structure comply with the technical building rules of the Besluit bouwwerken leefomgeving (Bbl, the Dutch Building Decree) on structure, fire safety, insulation, ventilation and daylight? The second concerns the omgevingsplan activity: does the extension fit into your municipality's omgevingsplan (local zoning plan), which determines where you may build, how large and how high? Each test has its own list of permit-free cases, and only if your extension appears on both lists do you not need to apply for anything.
In practice, the spatial test is the tricky one. In the Bbl and in the omgevingsplan, an extension is a bijbehorend bouwwerk (ancillary building): an extension of the main building or a structure functionally connected to it on the same plot, such as an extension, conservatory, garage or shed. Under the Omgevingswet there are two tracks for ancillary buildings. Both tracks are in the bruidsschat (literally the "dowry"), the set of national rules that automatically landed in every municipality's omgevingsplan when the Omgevingswet was introduced. The first track is article 22.27, under a: a ground-level ancillary building in the rear yard area that is no higher than 5 metres, stays more than 1 metre from publicly accessible areas, has no habitable area on an upper floor and does not get a roof terrace or balcony is permit-free, but only as long as it also fits within the other rules of the omgevingsplan itself, for example on the building envelope and the building percentage. The national list in article 2.29 Bbl (dormer at the back, solar panels, frames in the rear facade, low boundary fences) does not include the extension. The second track is article 22.36, under a: if, in addition to the requirements of article 22.27, you also meet fixed dimensions, you are building in accordance with the omgevingsplan by operation of law. This contains the familiar dimensions from the old Besluit omgevingsrecht (Environmental Law Decree; annex II, article 2, part 3): the extension within 4 metres of the rear facade, the height limits and the building percentages. If you meet those dimensions, you may build even if the omgevingsplan otherwise leaves little room. Note: both tracks are bruidsschat rules, and your municipality may amend them; many municipalities have since done so or are in the process of doing so (the bruidsschat applies until the end of 2031 at the latest). The dimensions below are therefore the national starting points; for your address, the permit check is decisive.
Rear yard area and building area: where may you build
Everything revolves around two concepts. The achtererfgebied (rear yard area) is the part of the plot behind the line that crosses the main building 1 metre behind the front, and from there runs parallel to the adjacent publicly accessible area. In plain words: the back garden and the part of the side garden that is not on the street. With a terraced or mid-terrace house that is clear; with a corner house, the side garden along the street is not rear yard area, so an extension against that side wall does not fall under the permit-free rules. The front yard is never rear yard area; an extension at the front generally requires a permit, however small.
The bebouwingsgebied (building area) determines how much you may build in total. It is the rear yard area plus the ground under the main building, minus the original main building: the home as it was built or permitted on completion. Earlier extensions, an existing garage or a shed therefore count as built-up area, even if a previous owner built them. The maximum works in three tiers:
| Building area | Maximum that may be built on |
|---|---|
| Up to and including 100 m² | 50% of the building area |
| From 100 up to and including 300 m² | 50 m² plus 20% of the part above 100 m² |
| More than 300 m² | 90 m² plus 10% of the part above 300 m², with a maximum of 150 m² |
A worked example: a rear yard of 60 m², plus 40 m² of ground under the main building that does not belong to the original main building, gives a building area of 100 m² and therefore a maximum of 50 m² of ancillary buildings. If there is already a 12 m² shed, 38 m² remains for the extension. Many plans founder not on the depth of the extension, but on this total.
The dimensions: within 4 metres or further from the rear facade
The bruidsschat distinguishes between an ancillary building within 4 metres of the original main building and a structure further away from it. Note the word "original": the 4 metres is measured from the rear facade as it was once built, not from an earlier extension. So if you want to lengthen an existing 2-metre extension, you only have 2 metres left.
- Within 4 metres of the original main building. The extension may be no higher than 5 metres, measured from the adjoining finished ground level, no higher than 0.3 metres above the top of the separating structure with the second storey of the main building (the upper floor), and no higher than the main building. Within this zone, the extension may have a residential function: a kitchen, living room or bedroom on the ground floor. This is the zone in which the classic 3 to 4-metre extension with a flat roof falls.
- More than 4 metres from the original main building. Stricter dimensions and a functional requirement apply here. A structure with a flat roof may be no higher than 3 metres. With a pitched roof, the eaves may be at most 3 metres high, the ridge at most 5 metres and the roof pitch at most 55 degrees, with the maximum building height also depending on the distance to the boundary. In addition, this part must be functionally subordinate to the main building: a storage room, garage, hobby room or utility room, and not a bedroom or extra living room. An exception exists for housing related to mantelzorg (informal care for a family member).
- Distance to public areas. The structure is more than 1 metre from publicly accessible areas (street, square, park, public waterway). The old exception for areas without welstand (aesthetic) requirements no longer exists under the Omgevingswet.
- No roof terrace, balcony or other outdoor space not at ground level on the extension.
- Standing on the ground: an addition on top of an existing extension or a second storey does not fall under this, and a habitable area (living or sleeping space) may only be on the ground floor (article 22.27, under a, 5°).
- No extra dwelling. The number of dwellings may not increase as a result of the extension, except for mantelzorg (article 22.23 bruidsschat).
Two limits that often go wrong. The rule about 0.3 metres above the upper floor means that an extension with a flat roof usually ends just above the ground floor and does not continue up to the bedroom window on the floor above; if you want a higher extension, for example for a high ceiling or a roof lantern that protrudes higher, you need a permit. And if you build at the back right up to the boundary, you may in principle do so under these rules, but you run into neighbour law, about which more below.
For listed buildings and protected townscapes or village views, the permit-free rules do not apply or apply only to a limited extent. On a national, provincial or municipal monument, an extension always requires a permit (articles 22.28 and 22.38 of the bruidsschat). In a nationally protected townscape or village view, the second track with the fixed dimensions lapses entirely (article 22.38 bruidsschat); an ancillary building there is only permit-free via the first track if it stands on the part of the plot directly behind the main building, that part of the plot does not also run along the side of the home and does not face publicly accessible areas, and it also complies with the omgevingsplan itself (article 22.28, third paragraph).
The permit check and the application
The only way to get certainty for your address is the permit check in the Omgevingsloket (the national permit portal) on omgevingswet.overheid.nl. You enter the address and the features of the extension and see, per test, whether a permit or notification is required. Keep the result. Many contractors do the check for you as standard, but as the owner you remain responsible for what is built. If in doubt, for example because the municipality has amended the bruidsschat or because your plot has an unusual shape, request a preliminary consultation or draft application. The municipality will then indicate informally whether the plan is feasible.
If you need a permit, the application goes through the Omgevingsloket with DigiD (the Dutch government login), or you authorise the contractor or draughtsperson. You supply a site plan, floor plans, elevations and cross-sections of the existing and the new situation, with dimensions and materials. The regular procedure applies to an extension: the municipality decides within eight weeks of receiving a complete application and may extend that period once by six weeks. Missing documents suspend the period. After the decision there is an objection period of six weeks in which neighbours can object; building during that period is allowed but at your own risk. The municipality charges leges (administrative fees), the amount of which is set out in your municipality's fee by-law and usually depends on the construction cost.
The technical side: building notification, Wkb and the Bbl requirements
For the technical building activity, article 2.25 Bbl determines when a building with a roof requires a permit: only if it does not stand on the ground, is higher than 5 metres, gets a habitable area on an upper floor, has a roof terrace or balcony, or becomes a main building through the construction itself. An ordinary ground-floor extension up to 5 metres high does not fall under this and is therefore technically permit-free, including the opening in the existing rear facade. A larger or higher extension, or an extension with a bedroom on an upper floor or a roof terrace, technically requires a permit. For homes, the intention under the Wet kwaliteitsborging voor het bouwen (Wkb, the Quality Assurance for Building Act) is ultimately a building notification in consequence class 1, at least four weeks before the start, with an independent quality assurer who checks the work. For renovations, including an extension, that system is not yet in force, however, and no date has been set (the Bbl expressly excludes renovation in article 2.17); as long as that is the case, you apply to the municipality for an omgevingsvergunning (environmental permit) for the technical building activity for such an extension. What the Wkb changes for you as a client, including the contractor's extended liability and the consumer file, is explained in Quality Assurance Act (Wkb): what it means for your renovation.
Permit-free means that nobody checks in advance, not that the rules do not apply. The Bbl applies in full and the municipality can enforce afterwards. The most important requirements for an extension:
- Structural safety and foundation. An extension needs its own foundation, matched to the subsoil. On sand, a shallow foundation (strip footings or a slab) is often sufficient; on clay or peat, and where the main building is on piles, a foundation on piles or screw piles is usual to prevent uneven settlement. A structural engineer calculates the foundation, the lintels or steel beams in the opening to the existing home and the roof; that calculation is also required with a permit application. An expansion joint between old and new prevents cracks.
- Insulation. The new-build values apply to new separating structures of an extension: a thermal resistance of at least 4.7 m²·K/W for the facade, 6.3 m²·K/W for the roof and 3.7 m²·K/W for the floor, and for windows and doors a thermal transmittance of at most 2.2 W/m²·K per component and on average at most 1.65 W/m²·K (article 5.20, third paragraph, Bbl, which refers to the new-build articles 4.152 and 4.153). Ask the contractor to include the Rc-values in the quote.
- Daylight. A new habitable room must get enough daylight; a deep extension can also take away daylight from the existing room. For new builds, the Bbl requires at least 10% of the floor area as equivalent daylight area per habitable area and 0.5 m² per habitable room (article 4.147); windows within 2 metres of the boundary do not count. A roof lantern or large garden doors solve this, but take the effect on the existing space into account.
- Ventilation. A new habitable room needs an air supply of at least 0.9 dm³/s per m² of floor area, with a minimum of 7 dm³/s per habitable room (article 4.122 Bbl); a kitchen in the extension also needs an extraction point. Connect the extension to the existing ventilation system or give it its own grilles and extraction.
- Fire safety. With a terraced house, the extension may not weaken the fire-resistant separation from the neighbours. An extension that runs up to the boundary needs a fire-resistant wall on that side if the neighbours (could) also build there.
- Water drainage. The roof of the extension must be arranged so that no water runs onto the neighbours' plot, a rule that is also part of neighbour law (article 5:52 of the Dutch Civil Code). Your own rainwater drainage to your own sewer or garden is therefore not optional.
Neighbours, the boundary and the VvE
An extension almost always affects the neighbours: less light, a wall on the boundary, a window looking into their garden. Neighbour law in Book 5 of the Dutch Civil Code sets the limits. Article 5:50 of the Civil Code prohibits windows or other wall openings with a view of the neighbours' plot within 2 metres of the boundary, unless the neighbours give permission. A side window in an extension that runs up to the boundary is therefore not allowed without that consent; fixed and opaque windows are allowed (article 5:51 of the Civil Code). Article 5:37 of the Civil Code prohibits unlawful nuisance, including taking away light or air. An extension that stays within the permit-free dimensions is rarely judged to be unlawful nuisance, but it remains a case-by-case assessment; a 4-metre-high extension right next to the neighbours' kitchen window may turn out differently.
If you build up to the boundary, the question is who owns the wall. A party wall that stands exactly on the boundary is mandelig (jointly owned, article 5:62 of the Civil Code). Both neighbours may build against a jointly owned wall and have beams bear on it up to half its thickness, as long as the wall is not adversely affected (article 5:67 of the Civil Code). If the neighbours' wall stands entirely on their land, for example the side wall of their earlier extension, that wall is theirs and you may not build against it or connect to it without permission; you then build your own wall next to it, with a small cavity or an expansion joint. If you temporarily need their garden for the work, for scaffolding or to do the bricklaying, the neighbours must allow this after proper notice, against compensation for any damage (the so-called ladderrecht or ladder right, article 5:56 of the Civil Code). Establish the boundary in advance; if in doubt, the Kadaster (Land Registry) can mark out the boundary. How to have the conversation with the neighbours is explained in Renovating and the neighbours.
If you live in a ground-floor apartment with your own garden, an extension is a change to common parts (facade, foundation and often the land itself). You need permission from the owners' meeting and often an amendment to the deed of division. Arrange that before you have drawings made.
Who does what, and how long does it take
An extension is almost always a project involving several tradespeople, and usually one party that keeps the overview is the best choice. A contractor coordinates the sequence, arranges the subcontractors and is your point of contact for extra work and handover. An architect or building draughtsperson makes the drawings for the permit check or the application and for construction; a structural engineer calculates the foundation, opening and roof. The bricklayer builds the facades and the cavity, fits lintels and neatly joins the new brickwork to the existing, often in the same brick and pointing. The carpenter makes the roof structure, fits frames and garden doors and takes care of the interior boxing and trim. In addition, there is a roofer for the flat roof, a plumber for rainwater drainage and possibly heating, an electrician for the circuits and a plasterer for the walls. With a prefab timber-frame extension, a large part of the structure comes from the factory, which shortens the construction time.
For a permit-free extension, allow a few weeks to two months of preparation for drawings, structural calculation, quotes and planning, and four to eight weeks of construction time for an average extension, depending on the foundation, the weather and the finishing. If a permit is required, add the eight-week procedure, a possible six-week extension and the objection period, so you can quickly be looking at three to five months before the first spade goes into the ground. A comparison with other jobs can be found in How long does a renovation take.
Checklist for the quote
- Permit and drawings: who does the permit check or the application, who supplies the drawings and the structural calculation, and are the costs of these included?
- Foundation: which subsoil is the foundation based on, has a soil investigation (cone penetration test) been carried out and what happens if the ground turns out to be different?
- Insulation values: the Rc-values of floor, facade and roof and the U-value of the glass, in black and white.
- Connection to the home: opening, steel beam or lintel, expansion joint, connection of roof and facade to the existing building, and who demolishes and removes the existing rear facade.
- Installations: rainwater drainage, heating (radiator, underfloor heating or connection to the existing system), electrics and ventilation.
- Finishing: plastering, floor, ceiling, painting: what is included and what will you do yourself?
- Schedule and guarantee: start and end date, provisional sums, extra work arrangements and the guarantee on structure and watertightness. How to compare quotes side by side is explained in Comparing quotes.
Common mistakes
- Building without a permit check. "The neighbours have an extension like that too" says nothing about your situation: their building area, their original rear facade and their year of construction differ. If you build without a check and it turns out afterwards that you have built too large, you risk a building stop, an order subject to a penalty payment and, in the extreme case, demolition at your own expense.
- Deviating from the drawing. Half a metre deeper or a roof that ends just above the upper floor makes a permit-free extension subject to a permit. The same applies to a granted permit: deviating from the permitted drawing is building without a permit.
- Not informing the neighbours. Objections arise from surprise, not from the structure. Show the drawing, discuss the boundary, the wall and the window, and record agreements on working hours and damage.
- Forgetting existing buildings. An old shed or an earlier extension counts towards the building area, even if it has been there for decades.
- No structural engineer. An opening in the rear facade or a foundation on soft ground is no guesswork. Without a calculation, you run the risk of cracks, subsidence and an extension that does not comply with the Bbl.
In summary: an extension at the back is permit-free if it stands in the rear yard area, stays within the bruidsschat dimensions and the total built-up area on your plot does not exceed the permitted percentage; within 4 metres of the original rear facade it may be 5 metres high and have a residential function, beyond that lower and only subordinate. Permit-free is not rule-free: the Bbl, neighbour law and the VvE (owners' association) continue to apply. Do the permit check, have a structural engineer do the calculations, inform the neighbours and put the work in the hands of a contractor, bricklayer and carpenter who know the dimensions. On VerbouwPro you post your extension as a job free of charge, and tradespeople from your region respond.