What are the extension costs per m²?

What are the extension costs per m² for each size?

The price per square metre is a handy way to compare plans, but only if you know what it covers. The figures below are indications for a complete rear extension with a flat roof, a standard set of doors and a finish ready for wallpaper. Including VAT, 2026 price level.

If you want to see the total amount and everything else involved, read how much an extension costs.

• 7.5 m² (2.5 by 3 m): roughly €3,500 to €5,000 per m²
• 12 m² (3 by 4 m): roughly €2,900 to €4,200 per m²
• 18 m² (3 by 6 m): roughly €2,700 to €3,900 per m²
• 24 m² (4 by 6 m): roughly €2,500 to €3,750 per m²

Why does a small extension cost more per m²?

A good part of the costs does not depend on the number of square metres. The rear wall has to be opened, a steel beam goes in, the site has to be set up and the structural engineer works out the foundations and the beam. Those items are almost as high for 7 m² as for 20 m².

Together, allow roughly €12,000 to €20,000 for these fixed costs. Spread over a small extension, that adds a lot per square metre; spread over a large one, it fades away. Do keep the maximum depth for building without a permit in mind.

• Opening in the rear wall with a steel beam
• Structural engineer and drawings
• Site set-up, scaffolding and removal of rubble
• Connecting roof, walls and installations to the house

What does and does not count in the price per m²?

Never simply compare two prices per m². One provider prices only the shell, meaning wind and watertight with frames, another an extension that is ready for flooring and painting. The shell is roughly 60 to 70 percent of the total.

Design choices shift the price per m² considerably. An extension with a roof lantern or a wide sliding door costs more than a solid wall, but makes the room behind it a lot lighter.

• External or internal size, which easily makes a 10 percent gap
• Shell only or finished ready for wallpaper
• With or without foundations on piles
• With or without underfloor heating and electrics

How do you get the most out of every square metre?

Look not only at the price per m², but also at what an extra metre gives you. An extension 3 metres deep often leaves a kitchen just too tight for an island, while 4 metres does give you room. With an extension for a kitchen-diner that extra metre is often the best use of the budget.

In the first conversation, Bouwbedrijf R. Vlieland thinks along with you about size, layout and budget, so you can see which option gives you the most. One example is the extension to a terraced house in Zaandam. A tailored quote follows, with one dedicated project manager from design to handover.

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