House Extension Cost in Amsterdam: 2026 Prices

A finished rear extension (uitbouw) of 10 to 20 m² costs about €45,000 to €65,000 in the Netherlands in 2026, according to Trustoo (August 2026). Homedeal (July 2026) puts the average at €2,200 to €3,800 per m². In Amsterdam and Amstelveen the ground decides a large part of the bill: on soft clay and peat an extension almost always stands on piles. Below: prices per size and per finish, the foundation, permits and the city's fees, extra storeys, VAT and how to budget.

Extension prices per m² in 2026

Small extensions cost the most per m², because the foundation, the connection to the house and the glazing are needed whatever the size.

Homedeal's worked example for a 15 m² extension with a standard finish comes to about €51,150, once the foundation, windows and doors, underfloor heating, the permit, electrics and 10% for the unexpected are added to the base price. A 20 m² extension costs €40,000-€60,000 with a standard finish and €70,000 or more in luxury.

The foundation: piles in Amsterdam and Amstelveen

Homedeal puts it simply: in the west of the country, on peat and clay, piles are required. In the old channel of the IJ, which runs under part of Amsterdam, the city's map shows soft clay and silt down to as deep as 30 metres below sea level (NAP). A new part of the house therefore stands on piles that reach the firm sand, otherwise it settles and tears away from the old house. Trustoo calls a pile foundation "almost always necessary".

Next to neighbouring houses, vibration-free screw piles are the usual choice, because driving piles shakes the ground and the buildings around it.

Permits and Amsterdam's fees

Many single-storey rear extensions need no permit. The national rules allow it when the extension stands in the back garden, more than 1 m from public space, no higher than 5 m, with living space only on the ground floor and no roof terrace. Within 4 m of the original rear facade it may rise up to 30 cm above the level of the first floor; deeper than 4 m the extension may only serve a secondary use, such as storage. Listed buildings always need a permit, and in a protected cityscape only an extension at the back that does not face public space can be permit-free. Read more in permit or no permit.

When a permit is needed, the municipality decides within 8 weeks and can extend that once by up to 6 weeks (IPLO). Cost sites estimate the permit at €500-€2,000, but Amsterdam's real fees depend on the building costs without VAT:

Add the drawings: an architect costs €1,000-€3,000 according to Homedeal and €3,500-€5,000 according to Trustoo, which notes that an architect is often required for projects that need a permit. A structural calculation costs €500-€2,000 (Offerteadviseur).

Side extensions and extra storeys

• Side extension (aanbouw): €2,200-€3,500 per m², or €37,500-€45,000 for 15 m² (Homedeal). At the front, or on a side that faces the street, it always needs a permit.
• Extra storey on a flat roof (opbouw): €1,600-€2,000 per m² according to Trustoo, about €1,500 on average according to Offerteadviseur, but €3,000-€4,000 according to Rekenmachinepro. An extra storey adds building volume, so it always needs a permit.

How long an extension takes

From the quote to handover Trustoo counts two to six months on average, including about six to eight weeks for the permit. A masonry shell takes at least six to ten weeks; a prefab shell is placed in three to five working days.

VAT on an extension: 21%

Building an extension is taxed at 21%. The 9% rate applies only to insulating, painting, plastering and wallpapering in homes older than two years (Belastingdienst). Some cost sites mention 9% on labour for extensions; that is not what the Belastingdienst says.

How to budget an extension

• Start from the price per m² for your size, not the national average: a 9 m² extension costs more per m² than a 25 m² one.
• Count the foundation separately and ask whether piles are included in the quote.
• Ask whether the glazing, the floor and the kitchen in the new room are in the quote.
• Keep 10% for the unexpected, as Homedeal does in its example.
• Check the permit question for your address first. A permit adds the fees, the drawings and about two months, sometimes more.

Thinking about an extension? See how we build them on our house extensions page, or ask for a free visit and a written quote.