Calculating the cost of your extension.

Extensions can vary greatly in shape, size and therefore budget. Whether you are planning a simple pitched roof extension or a larger project, costs can start to add up very quickly.

It's not just the size of your extension. Where you live can also dictate price. In some areas the qualified tradespeople you need could cost less than £100 a day or more than twice this. Knowing the day rate of local tradespeople can be useful research prior to securing extension quotes.

Below are different ways to create costings for your conversion based on the permitted development of 3 to 4 metres in the UK. In England until 30th May 2016 if you secure approval from your Local Authority you may be extend your home by twice this length.

Estimates by size

Most builders can give you an idea of what your extension will cost per square foot or metre. For example, a basic single storey extension would typically cost around £1,000 per square metre but it could be up to £1,600 or more for a premium two storey extension.

So a 3 x 5 metre extension would cost £15,000 and up to £50,000 for a two storey, more premium extension. These costs are just to create a room, they would not typically include the cost of a kitchen or bathroom.

This average cost should cover design through to decorating of standard rooms, but it is worth having a 10-15% contingency to cover unexpected costs.

Individual estimates for an extension

Securing individual quotes for an extension may mean you can save money, but it may cost you time as most projects will require you to be on-site pretty much full time to project manage the build.

To cover you for errors and unforeseen mistakes during the build, consider taking out an insurance to cover your extension or speaking to your own insurance company to check you are covered as this can help give you peace of mind.

extensions budgets

Full estimates

There are companies who will carry out the whole extension project for you and give you a quote for all the costs, including project management.

Check their quotes as they may be higher than using individual tradespeople but it will relieve you of the day to day hassle of managing the project, which may be worthwhile if you have to work full time.

An independent quote for the full costs of a loft conversion can be secured through on-line estimation companies such as Estimators Online

Before you accept a quote:

  • Make sure it is clear who will be responsible for securing building regulations sign off including electrics, gas, structural, drainage and general building control certificates.
  • Understand if additional work is required for the sign off, who is responsible for the extra costs.
  • Ensure you have a contract which protects you
  • Check the tradespeople have the required insurance.
  • Make sure you have a contingency of 10-15% to cover unknown costs.