Cost Of An Extension In 2021







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Our extension cost calculator will provide you with a high level figure to help give you an understanding of the cost of an extension.

Extension cost calculator

What factors impact the cost of an extension?

Our tool allows you to customise based on several factors which will impact the cost of an extension.

Type of renovation 

The labour and build cost will vary depending on whether you care carrying out a garage conversion, loft conversion or a rear extension. 

Similarly a double storey extension isn't necessarily twice the price of a single storey extension as there are a number of factors that make the second floor slightly more economical.

Which rooms the renovation will include

If you are adding a kitchen or bathroom then this will have an impact on the cost of an extension, compared to if you were simply adding a bedroom.

Location in the UK

The location in the UK will have an impact on many of the costs but mainly the labour and build. 

An extension in London and the South East of England will likely cost more than most other parts of the UK.

Overall finish quality

It might be that you would like a high end kitchen or your extension has high end architectural glazing rather than a simple extension. 

The quality of finish should be factored in the early stage. It might be that the budget might not quite stretch as far as you had hoped, so this is an area you may be able to make some savings.

Size of the renovation

Our tool allows you to update based on the size of your project which has a significant impact on the total cost of an extension.

So what makes up the total cost of an extension?

Here is a rough breakdown of the big items which contribute towards the cost of an extension.

Professional fees

The fees can vary depending on the scale of your project, however a broad estimate of 10 - 15% of the total build costs should be used at the initial stages.

Labour and build costs

These are the greatest cost on an extension and will include everything from the labour, materials, skip and scaffolding hire.

The cost is greatly impacted by the type of renovation and also the location.

Product and finishing

Our cost calculator includes an estimate for the products such as bathroom, kitchen, windows, doors, heating, flooring, paint and other finishes.


VAT is often forgotten about when trying to get a high level figure cost of an extension. Our cost calculator applies 20% to ensure it's not missed off.

Contingency fund

We always recommend ensuring you have a contingency of around 10% of the build cost set aside. When you start a renovation there can often be unforeseen 

Published: March 10, 2021

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