Extension: rules, permit and costs

When is an extension permit-free?

Under the Environment Act (in force since 1 January 2024), the permit-free scheme for associated structures is set out in the Bbl. The old terms Wabo and Besluit omgevingsrecht (Bor) have been abolished; do not use them any longer with the municipality or your contractor.

For an extension or annex at the rear, the following main criteria for permit-free building apply:

1. Location in the rear garden area The extension must lie entirely within the rear garden area. The rear garden area is the part of your plot that starts 1 metre behind the front facade of the house and does not border publicly accessible land such as a pavement or park. If even part of the extension falls outside the rear garden area, you need a permit.

2. Surface area limit How much you may add depends on the total size of the so-called building area, meaning the rear garden area plus the land already built on with existing extensions. The surface area limits are set out in the Bbl and are tiered: with a smaller building area you may add proportionally more than on a large plot. An absolute maximum applies. Always count existing structures; an existing shed or outbuilding reduces your available space.

3. Height An associated structure may be a maximum of 5 metres high. If the extension is directly against the home, there are additional rules about eave height and roof form that follow from the Bbl. Always have the height calculated if you are in doubt.

4. Use An extension directly against the home may have the same use as the home, i.e. residential. An outbuilding that is more than 4 metres from the home may only have a subordinate use, such as a storage room or hobby space, and may not be fitted out as a bedroom or independent living space.

Always run the permit check These criteria apply to the spatial component (the environment plan activity). However, the Environment Act splits construction into two activities: the environment plan activity and the technical building activity. Requirements also apply to the technical side (structural safety, fire safety), even when the spatial component is permit-free. The only reliable way to know whether your plan is permit-free is the permit check via the Omgevingsloket (omgevingsloket.nl).

When do you need a permit?

There are situations in which an extension is always subject to a permit requirement, even if you are building at the rear:

Corner house or house with a side boundary adjacent to public space If you live on a corner plot, your side garden area borders a public pavement or road. An extension on the side of a corner house is therefore never permit-free, even if it is effectively 'behind' the front door. The location relative to publicly accessible space is decisive.

Front facade or front garden area Any extension to the front facade or in the front garden area (the part in front of and up to 1 metre behind the front facade) always requires a permit. If you want to extend on the side of the home, check precisely whether that location falls within the rear garden area.

Exceeding the area limits If the intended extension exceeds the maximum permitted built area, a permit is required for the excess.

Listed building or protected conservation area If you live in or near a national listed building, a municipal listed building or a protected urban or village conservation area, more stringent rules apply. For a national listed building almost all external building activities require a permit, including small extensions that would be permit-free elsewhere.

Additional rules in the environment plan Your municipality can set stricter rules than the Bbl through the environment plan. Some municipalities impose further restrictions on the height, footprint or design of extensions. Permit-free at national level therefore does not mean the municipality has nothing more to say. The permit check on the Omgevingsloket takes the municipal environment plan into account.

When an environmental permit is required, Tekenpunt handles the complete application including the site plan, floor plans and elevation drawings. The municipality then assesses the plan for spatial fit; where aesthetic review applies (if the municipality has an aesthetic review policy), also for appearance. Tekenpunt gets 90% of applications through the aesthetic review in a single round.

Structure: the steel beam and removing the rear wall

An extension is not simply a matter of adding a wall. The biggest structural intervention in a living room or kitchen extension is removing (part of) the rear wall. In a typical terraced house the rear wall is a load-bearing element: it (partly) supports the upper floor and sometimes the roof structure. When you break through the facade to create a wide opening to the extension, that load-bearing capacity must be transferred.

This is almost always done with a steel HEA or HEB beam (also known as a steel beam or main beam) placed above the opening. The beam rests on two columns or on the brick side walls. The exact dimensions of the beam depend on:

• The width of the opening (span).
• The load of the floor above or the roof resting on it.
• The type of house and the foundation.

De structural calculation determines the required size of the beam and the bearing points. Without a calculation a contractor is not permitted to open up the facade, as you risk cracking, deflection or in the worst case collapse. A structural calculation is required by law, even if the extension is permit-free.

In addition to the beam, there are also choices for the foundation of the extension itself (strip or pad foundation depending on the soil type) and for the roof form (a flat roof with bitumen or EPDM is common for ground-floor extensions). Tekenpunt works together with a KIWA-certified structural engineer who takes care of the calculation.

The drawings that Tekenpunt produces give the contractor all the information he needs: site plan, floor plan before and after, elevation drawings, cross-section and material specifications. This prevents disputes on the building site.

The drawing process at Tekenpunt

Tekenpunt is a draughting firm, not an architect. You work directly with a draughtsman who specialises in residential renovations. The process is as follows:

1. Intake and measurement You send us your wishes (or we discuss them via WhatsApp) and you share the existing dimensions of the house. If you do not have existing drawings, we will arrange a measurement appointment or discuss how you can best provide the measurements yourself.

2. Draft drawings We produce a first set of drawings based on your wishes: existing and new floor plan, elevation drawings and a section. You have the opportunity to provide feedback and make adjustments.

3. Final drawings After processing the feedback, we deliver the final set of construction drawings. The drawings are suitable for:

• Permit-free building (documentation for the contractor).
• The application for a building permit, if required.
• The structural engineer for the bearing points and the beam.

4. Optional add-ons If you also need a structural calculation, we can add it as an add-on. The structural engineer works from our drawings and delivers the calculation that the contractor needs for the steel order.

Delivery time Standard delivery time is approximately 4 weeks. If you are in a hurry, express handling is possible with a delivery time of 1 to 2 weeks. Tekenpunt has been in business since 2016 and has completed more than 800 projects.

Costs: drawing and add-ons

The costs for an extension drawing at Tekenpunt start from €1.195. The base package is included in that starting price: site plan, existing and new floor plan, elevation drawings and section, sufficient for both permit-free situations and a permit application.

In addition, there are a number of add-ons you can include as desired:

When do you need which add-on?

• Building permit: only if your situation is subject to a permit requirement. You'll know for certain after the permit check. Tekenpunt handles the complete application with the municipality.
• Structural calculation: almost always needed for an extension where the rear façade is (partly) opened up for a steel beam. This is a legal requirement even for a permit-free extension.
• 3D visualisation: useful if you want to see what the end result will look like before you start, or if you want to show it to a contractor for a quote.
• Express: choose this if you need a quote or permit application submitted quickly.

The exact price for your project depends on the complexity. Via the quote form on Tekenpunt.nl you will receive a tailored quote, usually within 1 working day.

Common mistakes with extensions

After more than 800 projects, Tekenpunt sees a number of mistakes recurring. Below are the most common ones so that you can avoid them.

Commissioning the structural calculation too late A contractor sometimes starts digging and laying masonry before the structural calculation is ready. If the beam then turns out to be too small, work has to be redone or reinforced. Always have the calculation run alongside or before the start of construction.

Assuming it is permit-free without checking The permit check takes five minutes. Building without a permit when one was in fact required can lead to an enforcement procedure by the municipality with an obligation to demolish the extension at your own expense. It also causes complications when selling your home.

Insufficient internal headroom A flat roof on an extension needs a facade height large enough for the roof build-up (insulation, bitumen or EPDM, possibly a rooflight). Insufficient height means the internal clearance will disappoint or the roof cannot be laid with adequate drainage. Make sure this is thoroughly thought through in the drawing phase.

Forgetting the neighbour rules An extension built right up against the property boundary has consequences for your neighbour. The boundary distances are set out in the Bbl and can be a limiting factor on smaller plots. Discuss plans with your neighbour in good time, even if you formally do not need their permission.

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