Roof extension costs: what does an extra storey on your house cost?

How much does a roof extension on a terraced house cost?

A roof extension replaces the pitched roof with a full storey with straight walls, or raises the existing roof. You gain a complete floor without giving up any garden. That often makes a roof extension better value per m² than a ground-floor extension with its own foundations, but the structure needs more engineering work.

The range is wide. A simple prefab roof extension with standard frames sits at the bottom, a traditionally built storey with lots of glass, new stairs and a bathroom at the top. Also read the trade-off between an extension or a roof extension.

• Prefab roof extension, about 25 m²: roughly €50,000 to €70,000
• Traditionally built, about 30 m²: roughly €65,000 to €90,000
• Bathroom on the new storey: allow €12,000 to €25,000 extra
• New or extended stairs: roughly €3,000 to €8,000

What do roof extension costs consist of?

The largest item is the roof extension itself: floor, walls, roof, insulation and frames. On top of that there are items that are often forgotten. The structural engineer has to check whether the existing walls and foundations can carry the extra weight. Sometimes a steel frame or extra reinforcement is needed.

There are also costs for demolishing the old roof, moving the boiler or the ventilation, scaffolding and sometimes a crane with traffic measures. And the fees, because a roof extension almost always needs a permit. See roof extension permit.

• Structural engineering work and any reinforcement
• Demolition and removal of the existing roof
• Moving the boiler, ventilation and pipework
• Scaffolding, a crane and possibly an exemption for the street
• Fees for the environmental permit

Prefab or traditional: what is the difference in price?

With a prefab roof extension the elements are made in a workshop and installed in a short time. The house is therefore only open for a short while, which is a big advantage in changeable weather. The price difference with a traditional build is often limited, but the time on site is shorter.

Building traditionally in timber or masonry is more flexible with unusual dimensions, older buildings or when the roof extension has to match the style of the street. Prefab and modular building also fit well with sustainable building, with less waste on site.

How do you keep the costs of a roof extension under control?

Start with the structure and the permit, because they determine what is possible. A roof extension is rarely decided overnight: allow a few months of preparation with drawings, structural engineering work and the application. Bouwbedrijf R. Vlieland can take care of the whole process, from drawings and permit to construction, with one dedicated project manager.

You can see an example of a timber roof extension in the roof terrace with a roof extension in Amsterdam. Read more about the options under roof extension and roof terrace. Would you like to know what it costs for you? In a no-obligation conversation we look at your house, followed by a tailored quote.

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