House Extension in the Netherlands – Fixed Price, Design to Delivery

A house extension is the fastest way to add real living space without moving: a larger kitchen-diner, an extra bedroom, or a bright home office. Grand Renovation designs and builds extensions across the Netherlands – one team, one fixed price, from the first drawing to the finished room. You pay per completed stage, never ahead of work that hasn’t been checked. And because every project manager and specialist on our team works in English, nothing gets lost in translation. Typical price for a complete extension: from € 45,000, depending on size, foundation and finish.

In short: a house extension in the Netherlands costs on average € 2,200–€ 4,500 per m² in 2026. A 20 m² extension usually lands between € 44,000 and € 70,000. The biggest cost differences come from the foundation, the opening into the existing house, and the level of finish.

What a house extension includes – and what you get from us

An extension is a new space built against your existing home. We handle the entire process, so you deal with one point of contact instead of juggling separate trades:

• Design and 3D concept, matched to your home and the local zoning plan (bestemmingsplan)
• Structural calculation and, where required, the permit application via the Omgevingsloket
• Foundation, shell, roof, façade and the opening into the existing house
• Services: electrics, heating, and water or ventilation where needed
• Insulation to Dutch Building Decree standards and full interior finishing (plastering, flooring, painting)
• Turnkey handover, with a written guarantee

Our own team carries out the plastering, tiling, electrical and carpentry work – no subcontractor guesswork.

Extension, add-on, conservatory – the Dutch terms explained

In the Netherlands you’ll come across several words for “extension.” They affect the design, the permit and the price, so here’s the plain-English version:

• Aanbouw (extension / add-on) – a new room built against the house, functioning as a separate space (extra bedroom, office, utility room). The existing structure stays largely intact.
• Uitbouw (bump-out / knock-through) – an existing room extended outward, with the outer wall opened up into one space (usually the kitchen or living room). This needs a steel support beam and extra connecting work, so it’s typically a little more expensive than an aanbouw.
• Serre (glass extension / conservatory) – mostly glass, for maximum daylight and a seamless link to the garden. Plan for glazing quality and shading.
• Houten aanbouw (timber-frame extension) – lighter and often faster than traditional brickwork, with a strong insulation-to-cost ratio.
• Prefab extension – built in a factory and installed in a few days. The advantage is speed and a predictable price; the cost gap with traditional building has narrowed in recent years.
• Bijgebouw (outbuilding) – a detached structure (shed, garden room, garage) that isn’t attached to the house and falls under different rules.

Not sure which suits your home? At the first visit we advise based on your plot, the zoning plan and your budget.

How much does a house extension cost in 2026?

Cost depends on size, foundation, structure and finish. As a 2026 guideline:

Examples (indicative total price):

• Around 15 m²: € 30,000 – € 45,000
• Around 20 m²: € 44,000 – € 70,000
• A complete extension with Grand Renovation: from € 45,000

What else moves the price:

• Foundation. On soft soil (common in the western Netherlands) piling is needed – add roughly € 2,500 – € 5,000 for foundation piles and the concrete slab.
• Width and depth. Each extra 0.5 m of width shifts the price by about € 1,000; each 0.5 m of depth by about € 1,300, since depth adds more usable floor space.
• Extras. A wide knock-through with a steel beam, a large sliding door, a roof light or underfloor heating are priced separately.
• Region. Labour costs vary – a few percent in the east, noticeably higher in Amsterdam and Utrecht.

Avoid these hidden costs: garden reinstatement, tying into the existing façade, and repairs to the current house are often left out of cheap quotes. Our quote is fixed and itemised – you know exactly where every euro goes before we start.

Permits – what’s allowed without one, and when you need one

Many rear extensions are permit-free, but since the Environment and Planning Act (Omgevingswet, 2024) the rules vary by municipality. The main line:

Often permit-free (rear), provided that:

• the extension is no deeper than 4 metres behind the original rear façade;
• you build on no more than 50% of the rear garden;
• it stays low relative to the ground-floor level.

Usually needs an environmental permit (omgevingsvergunning) when:

• it’s on the side or front of the house;
• it’s larger or taller;
• the property is a monument, in a protected townscape, or the zoning plan differs.

Even when it’s permit-free, a structural calculation is wise, and it pays to tell your neighbours in advance (Dutch neighbour law helps avoid disputes). We always check the zoning plan and run a check via the Omgevingsloket before starting – so you don’t face surprises or an enforcement fine.

Is a house extension permit-free? At the rear, often up to 4 metres deep, if you build on less than 50% of the rear garden. Side and front extensions usually do need an environmental permit. Since the 2024 Omgevingswet, always check the municipal rules via the Omgevingsloket.

Foundation, structure and insulation

An extension is only as good as its foundation and detailing. What we build to:

• Foundation. Depending on the ground, we use strip footings (most common), pad foundations, a slab, or piles/screw piles on soft soil. Across much of the Netherlands a solid foundation isn’t a luxury – it’s a necessity.
• Structure. Traditional brickwork, timber-frame (houtskeletbouw) or steel-frame – the choice drives build time, insulation value and price.
• Insulation (Building Decree). We insulate to at least the legal norms – guide values Rc 4.7 for walls and roof, Rc 3.7 for the floor – combined with HR++ or triple glazing. The result is comfortable, energy-efficient, and kinder to your energy label.
• Roof. A flat roof with EPDM is low-maintenance and pairs well with solar panels or a green roof; a pitched roof or a roof light brings in extra daylight.

How we work – in four steps

• Meet and design – free site visit; we measure up and advise on shape, permit and budget.
• Fixed quote – an itemised, fixed price. No open ends that creep up mid-build.
• Permit and prep – structural calculation, any permit application, and scheduling.
• Build and handover – carried out by our own team, paid per milestone, handed over turnkey with a guarantee.

We can usually start within two weeks of signing.

Why Grand Renovation

• Registered and insured. KvK 94089590 (Grand Renovation Solutions B.V.), a fully insured Dutch company.
• 5.0/5 on Google – verified reviews via Trustindex
• 200+ completed projects across the Netherlands, from apartments to full transformations.
• English-speaking team. Quotes, contracts, progress reports and invoices – all handled in English. No language risk.
• Fixed price, milestone payments – you never pay ahead of verified work.
• 5-year guarantee on structural work and hidden defects, in line with Dutch consumer protection law.

We recently built a modern, turnkey extension in Amsterdam and are expanding our extension work across the Randstad.

Service area

Grand Renovation builds extensions throughout the Netherlands, with most projects in Amsterdam, Rotterdam, Utrecht and The Hague and the surrounding regions. Tight timeline or a hard-to-reach city site? We factor that into the design and planning from the start.

House extension FAQ

How much does a house extension cost per m² in 2026?

Expect on average € 2,200 to € 4,500 per m² in 2026. Shell (casco) is around € 1,800–€ 2,200 per m², a standard finish € 2,500–€ 3,000, and premium bespoke work € 3,200 and up. Price per m² usually drops on larger extensions, as fixed costs are spread over more floor area.

What’s the difference between an aanbouw and an uitbouw?

An aanbouw is built against the house as a separate room; the existing structure stays intact. An uitbouw enlarges an existing room by opening up the outer wall into one space. An uitbouw often needs a steel support beam and extra connecting work, so it’s usually a little more expensive.

Do I need a permit for a house extension in the Netherlands?

A rear extension is often permit-free up to 4 metres deep, if you build on less than 50% of the rear garden. Side and front extensions usually do need an environmental permit. Since the 2024 Omgevingswet the rules vary by municipality – we check this for you before starting.

How long does it take to build an extension?

A traditionally built extension takes on average a few weeks to a couple of months, depending on size and finish. A prefab extension is made in the factory (typically 4–8 weeks) and installed on site in a few days.

Is prefab cheaper than traditional building?

The gap has narrowed. At a standard finish, prefab is on average 0–10% cheaper. The real advantage is the shorter build time and a predictable price, not a much lower final cost.

Does an extension add value to my home?

Usually yes – you’re adding floor area and comfort. How much value depends on build quality, the layout, and demand in your region.

Do you work in English?

Yes. Our entire client-facing team works in English – quotes, contracts, updates and invoices included – so you always know exactly what’s agreed.