Georgian House reduced No Text

Chartered Surveyor


Chequers Cottage, Lower Road

West Farleigh, Kent ME15 0PE

Tel.  07908 641668

Email. [email protected]


Kirk-Brown Limited



Although a budget figure of £1,000.00 per m2 of additional floor area created is often quoted, but this can vary significantly either way depending upon the exact nature of the scheme. We have listed some of the main factors that can affect home extension costs but obviously there may be others in some circumstances.




There are some regional differences between the costs of building work, with London being one of the most expensive areas. Other variables which can affect the price are the accessibility of the site, clearly if all the materials need to be unloaded the carried by hand along a narrow alleyway this will be reflected in the price. Likewise if machinery cannot be used for excavation works the cost will rise.


Size and Shape


Generally two storey extensions are more cost effective per meter squared than a single storey extension as there is usually every little in the costs of the foundations or roof between the two options. Simple rectangles or squares also tend to have a lower cost than more complex shapes. In addition an extension which utilises more of the walls of the existing property will have a lower cost. Extensions over 100m2 may be subject to a Community Infrastructure Levy.

Work to the existing Property.


Most extensions will involve some works to the existing property, whether it is the replacement of an existing external door for an internal one or the removal of an entire wall. Other costs are likely to include the extension of the heating, plumbing and electrical systems, some of which may result in wholesale replacement if isn't suitable to cope with the additional load.




The choice of materials is bewildering, both for internal and external finishes and likewise they come with a range of price tags. For example bricks start at around £450.00 per 1,000 for new bricks, but can rise to £1,200 per 1,000 for second hand stocks. As a guide there are 58 bricks/m2 of cavity wall. Internal finishes present similar choices, white glazed tiles may be £7.00/m2 compared to £190.00/m2 for some types of resin based tiles.


The choice of accommodation within the extension also has a bearing upon the overall cost, unsurprisingly kitchens and bathrooms are considerably more costly than dining rooms or bedrooms.




VAT is charged at the standard rate on the majority if domestic extensions. There are a few exceptions including if the works are part of a Disabilities Facilities Grant or if the works are part of a conversion to a property which has not been used a dwelling in the past. For more detailed explanation of the VAT rules please consult the VAT Notice 708, 'Buildings and construction' published by HMRC.

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