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  • Karenna Wilford

How much does an extension cost to build?

Updated: Jan 31

The cost of an extension will depend on many factors, the size of the extension being an obvious one. The overall square meterage and whether it is a single or two storey extension. The current approximate budget cost in the South East for a single storey extension is £2,600 per square metre and £2,200 per square metre for a two storey extension.


The actual building cost will depend on the type and quality of materials used externally and internally. The type of extension is another factor, where it is located in relation to the existing building, and the location and accessibility to the site. 


It is important to decide on what your building budget is and to subtract VAT from your overall figure. We also recommend having a 10% contingency fund to cover any unforeseen problems such as finding rot in the existing timber structure. You may have some building skills yourself which will help bring the overall cost down.


Karenna Wilford Architects work closely with our clients to design a scheme that is within your budget and can offer guidance on what is possible.

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