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'How much would extending my home truly cost me?'

Johannes van Graan Johannes van Graan
Ground Floor Extension, Drury Rd Classic style houses by London Building Renovation Classic
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Planning a guest bedroom? How about extending that terrace or spacing up your kitchen and/or dining area? Unless you’re living in a dream world, that extension you’re thinking of will cost some money – but the question then becomes, how much money?

What does a typical extension cost these days? What if it extends to your top floor as well, or you feel like splurging on some high-end materials like stone tiles? 

To give you a rough idea of what an extension in the UK costs these days (and to help you plan out a strategy and budget), scroll down…

1. A basic single-storey extension

Ground Floor Extension, Drury Rd Classic style houses by London Building Renovation Classic
London Building Renovation

Ground Floor Extension, Drury Rd

London Building Renovation

£1,200 – £1,500 per m² is a relatively acceptable estimate for a house extension cost today. This also reflects price increases over the last few years. But in London and some parts of the South East, these figures could rise up to about £1,500 – 2,000 per m².

For an ordinary 4 x 5m extension, the building costs at the lowest end of these estimates would be roughly £24,000. Add on 10-15% for professional fees (architect, planning application, building registration, structural engineer) + VAT, and that single-storey extension could be somewhere around £32,000.

2. A double-storey extension

The Cube, Winchester Modern houses by Adam Knibb Architects Modern
Adam Knibb Architects

The Cube, Winchester

Adam Knibb Architects

Going with the same footprint, we can now add 50% extra to the build cost of a single-storey extension. Therefore, £24,000 +50% = £36,000. 

Add on 10-15% for professional fees (architect, planning application, etc.) + VAT, and that double-storey extension leads up to around £48,000. 

Please note that these figures would apply to a typical, uncomplicated extension in most parts of the UK. However, should additional features (like the ones mentioned below) apply, you can of course expect those numbers to increase.

3. Including a kitchen or bathroom

Bright, clean, contemporary Modern kitchen by homify Modern

Bright, clean, contemporary


Add approximately £5,000 for a bathroom. Home renovation costs may be more or (if you are very thrifty or up-to-date with your networking) slightly less depending on your sanitary ware and finishes.

For a lower mid-range kitchen with appliances, you can expect to add roughly £10,000 (again, this will differ depending on your tastes and specifications).

4. Finishes and fittings

Pebbles Modern bathroom by Pixers Modern



Of course one wants some additional beauty touches like modest finishes, fittings, electrics and lighting. Think simple painted walls, carpet floors or possibly engineered oak.

Higher-end finishes like tiles, fitted joinery, etc. will definitely make those costs rise, as will glazing. Sliding or folding doors are also a popular addition to extensions at the moment.

5. What about complex site constraints?

Existing 1900s Family Home in Hindhead, Surrey: modern  by ArchitectureLIVE, Modern

Existing 1900s Family Home in Hindhead, Surrey


Your builder must include additional costs in their quote to you should any of the following apply: 

• Your soil type and ground conditions present more costly construction methods / techniques.

 • Limited access to the site.

• Existing structure (are you removing any structural walls?). 

• Are you fiddling with any piping, drainage, or gas meters?

6. Location, location, location

Your address plays a bigger role than you might think, because you can definitely expect to pay a bit more if you’re located in the South East, and much more if you’re living in London.

7. Materials and construction techniques

Also take into account the type/quality of construction materials involved, as well as the type of construction your property is undergoing.

8. Managing or reducing your project costs

Modern Garden Room Modern conservatory by homify Modern

Modern Garden Room


• Get it right from the start by consulting a professional architect. They can help you realise the main ambitions for your extension while helping you control your costs. They will also give you recommendations to ensure that you get the most out of your budget.  

• Get at least between 3 – 5 quotes from recommended builders (your architect can help compile a tender list for you). This will give you a firm idea of the costs before any work is started.  

• To prevent any nasty surprises down the line, your architect can also help you with your building contract. In addition, they can inspect the builder’s work to ensure it’s being carried out according to the agreed design and specifications.

For some inspiration, we firmly recommend: 18 modern extensions that enhance old British homes.

Planning an extension? Tell us all about it, below...
Whitton Drive by GK Architects Ltd Modern

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