How much does an extension cost in 2026?

How much does an extension of 12 or 24 m² cost?

These figures are market indications for a rear extension to a terraced or end-of-terrace house, delivered with plastered walls, a screed floor and connected electrics. They include VAT. An overview of the price per square metre for each size can be found under extension costs per m².

• Small, 2.5 by 3 metres: roughly €26,000 to €37,000
• Average, 3 by 4 metres: roughly €35,000 to €50,000
• Generous, 4 by 6 metres: roughly €60,000 to €90,000
• A sliding door, roof lantern and kitchen usually come on top

What is and is not included in the price of an extension?

A complete price usually covers the foundations, the concrete floor, the walls, the insulated roof, the window and door frames, the opening in the rear wall with a steel beam, and the finishing of walls and ceiling. The structural engineer and the drawings are often part of the total, although they are sometimes quoted separately.

What is often not included: the kitchen, floor finishes such as tiles or vinyl, painting, lighting and the municipal fees. So when comparing quotes, always ask what is and is not included. Tips for this are in choosing a contractor and comparing quotes.

• Usually included: foundations, floor, walls, roof and frames
• Sometimes separate: engineer, drawings and permit application
• Hardly ever included: kitchen, floor finishes and painting
• Municipal fees usually come on top of the building price

Which factors make an extension more or less expensive?

The largest items are the foundations and the connection to the existing house. In West-Friesland and much of Noord-Holland the ground is often soft, so driven piles or screw piles are regularly needed. You can read more about this under the foundations of an extension.

Glass matters too. A wide sliding door or a roof lantern brings in plenty of daylight, but costs more than a solid wall with a window.

• Type of foundation: shallow, driven piles or screw piles
• How much glass, sliding door or roof lantern you want
• Roof shape: flat roof or sloping roof with tiles
• Level of finish and installations such as underfloor heating
• Access to the building site

How do you get from an indication to a fixed price?

An indication helps you see whether your plan fits your budget. You only get a fixed price once the drawing, the structure and the finish are known. At Bouwbedrijf R. Vlieland the budget comes first: in the first conversation we look at what you want and what fits. If you wish, we also take care of the drawings and the permit.

One dedicated project manager runs the work from start to finish, so you have a single point of contact. Take a look at the extension in Zaandam or read more about having an extension built. Would you like to know what it costs for you? After a no-obligation conversation you will receive a tailored quote.

Frequently asked questions