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How much will an extension cost?

These figures provide a useful "high-level" estimate of the associated costs, however it is worth noting they are only ball-park figures and various factors can affect the price.

Websites such as provide more in depth information if you want to look at cost variations across different typologies and areas in the UK.

In short, constructing an extension is likely to cost around £2,000-£2,500/m² of new internal space (excluding VAT). This takes into account finishes but not items such as kitchen units, worktops, furniture, etc.

There are several things you need to know that can affect your project's costs, including:

  • Location of the project

  • The size and shape of the extension

  • The quality of the build

  • How involved in the project you'll be

  • Whether the extension contains a kitchen or bathroom 

  • Specialist features you may want, like renewables, air conditioning, smart home technology etc.

On top of this you're likely to pay around 10-15% of the construction cost on professional fees for the project. This can include but is not limited to:

  • Consultant fees (Architect, Structural Engineer, M&E Consultant, etc)

  • Planning application fees

  • Building regulation application fees

  • Surveys required for planning permission

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