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Extension Cost Calculator

With the extension cost calculator you can get a quick, free, rough estimate of at least some of the costs involved in building extra room(s) for your house.

By entering information about the extensions external size, roof type, number of storeys and the UK location, an estimate of the building cost can be found. The location of the build is needed, as costs vary across the country and the price is weighted according to this information.

Calculator - Extension cost

Tell us about the job

Use external dimensions for length & width. A wall thickness of 30cm will be deducted to calculate the internal floor area.

Excludes VAT. Assumes the work is carried out by an experienced contractor with good access.
We do not store your email address.

With the extension cost calculator you can get a quick, free, rough estimate of at least some of the costs involved in building extra room(s) for your house.

By entering information about the extensions external size, roof type, number of storeys and the UK location, an estimate of the building cost can be found. The location of the build is needed, as costs vary across the country and the price is weighted according to this information.

About the Extension Price Calculator

house extension diagram 5

The extension cost calculator above produces approximate costs of various sizes and types of side and rear extensions with either a pitched or flat roof.

The data is based upon input from a quantity surveyor on real UK home extensions ranging in size from 3x3m to 5x8m. Extensions outside of these sizes are likely to be less accurate.

Price allows for a finished and plastered extension made of block and brick with a standard concrete floor. We’ve allowed for one UPVC door and window, electrical work and one radiator extension from an existing central heating system. Basic decoration has also been included.

Once you’ve determined the sizes and cost you can then calculate the added value of the build, this again is determined regionally to provide you a clear idea of what you can expect your house price to increase by following the build.

These extension costs exclude:

  • VAT
  • kitchen/bathroom equipment
  • Floor coverings
  • external works such as drainage, paths and drives
  • removal of any obstructions such as sheds and greenhouses.

It should be remembered that the extension building costs displayed are indicative only and quotations should be obtained from reputable contractors.

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