How Much Does an Extension Cost?

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You may be considering an extension, dreaming about how stunning your house would look with a brand-new kitchen, or a lovely new back porch to spend your summer day read a book on, but you’re wondering how much does an extension cost?

Well, you wouldn’t be thinking about it if you didn’t have a budget. The fact that you’re thinking about a home extension means that you’ve got some money to spare. Investing it back into your home is a great idea, but how much does an extension cost? It depends on many variables:

  • The size
  • The materials being used
  • The type
  • Paperwork
  • Planning permission

It can be a costly affair, so how can you ensure you don’t go bankrupt in the process? 

Don’t forget that the main aim of a renovation is to get the property secure and watertight before you do anything in order to prevent any expensive damage further in the process. Being aware of these things takes professional guidance, which we recommend you seek, but going on the above variables, this is how much an extension will cost you.

Costs and fees involved in a house extension


In the UK, insurance costs are dependent on the property’s postcode risk, rebuild value, and the value of the new building works. Again, this varies, but one can expect to pay anything between £600–£1,200. Insuring your extension is crucial, an expense you simply cannot overlook.

Building regulations

Again, this depends on the extent of your build, ranging anywhere from £80 to well over a few thousand pounds. This fee also depends on the number of visits required during the build for regulation. Our advice is to go through a local contractor who will help you estimate what you’re in for based on past experience.

home extension scafolding


Another fee you need to consider before even starting an extension is a warranty.  It is advised because it covers your build. You can expect to pay anything between £1,000–£5,000 for a 10-year warranty.

A planning application

In the UK, a planning application costs exactly £206. If you’re planning an extension outside England itself, you will need to check with your local municipality, but it wouldn’t be more than that.  

If you are doing your extension through a designer and builder, they will be able to advise on whether your plans will be able to qualify for permission. If you aren’t working with a professional, most local municipalities offer pre-application advice for anywhere between £100–£200.

The actual build

As we mentioned in the beginning, there are so many factors that will influence the cost of your build but adding an extension to your house or building will more than likely drive up the value. So, how much does an extension cost? It depends on the size mostly.

foundations being prepared for a new building

Look, for a 4m x 5m extension you will most likely pay around £30,000 for a basic quality build and anywhere past the £45,000 mark for excellent quality with a beautiful finish. When considering loft conversion extension costs, you need to read this blog

If you are concerned about overlooking anything, check out our ultimate guide, or better yet, get in touch with us for a free, no obligation quote.