Real Estate

What’s the cost of building an extension in 2021?

Extensions can be a difficult subject. It can be difficult to get an understanding of all the rules, regulations, and costs. That’s why it’s a good idea to get a good idea on extension costs before you dive in.

So, how much is an extension?

As with most things, the cost of building an extension varies depending on what you want. The smaller or less complex extensions are cheaper, two storey extension cost, single storey extension cost – all of these will differ.

Where you live plays an important factor too. If you live anywhere near Cities, it’s likely your extension will cost more.

But that does not mean there aren’t general guidelines or rules. Below is some rough numbers for each kind of extension that can help give you a general idea.


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Single storey extension

If it all depends, how much does a single storey extension cost?

In 2019, an estimate for the cost of a single storey extension is anywhere between £1,450 and £1,850 per m2.

In London, this could be anywhere between £1,800 and £2,500+ per m2. These prices are for a quality extension. Basic quality would cost less and premium would be more.

If you were looking for a 5m x 5m extension. The cost of an extension might be around £30,000. In London, maybe even up to £60,000+.

If we add upto 20% for professional fees for the architect, planning application, building regulations, structural engineer and so on the cost goes up.

And let’s not forget about VAT.

All in all, a single storey extension could cost £35,000 at the lower end. £70,000 in London.

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Two storey extension

What about two-story extensions, then?

If both storeys are roughly the same size, a generally-accepted rule is to add 50% extra to the build cost of a single storey extension.

£40,000 + 50% = £65,500

Add 20% for professional fees

Again, London will more likely be pricier.

To get a general overview of your specific needs, plug your numbers into a house extension cost calculator.

Bungalow Extension

You now know the cost of a house extension, but what if you live in a bungalow? What would extension prices be then?

Well, bungalows are on the same level, bungalow extension costs are similar to single storey costs.

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Things to think about

You should get 3-5 quotes for any extension to your home. That way you can get a feel for what the market rate is, as well as see who you get on with the most or feel is most capable of the job. After all, they are going to be around for a while!

But don’t confuse an estimate with a quote. Usually, when builders, surveyors, architects and so on first visit a property they’ll give you an estimate. This is a good starting point but it can differ from an actual quote.

You’ll receive an actual quote in writing usually after everyone has gone away and done some thorough calculations. This is your quote and is what the project should cost.

It’s also worth making sure you have someone else with you when you get quotes. It can be helpful having another opinion on price, timeframes, and personalities. And you’ll also feel less pressured to make a decision there and then if you have someone else you trust with you.

To round it all up

The average cost per m2 for an extension outside of London is between £1,300-£1,700.

In London, the average cost per m2 is around £1,600-£2,200+.

For two-storey extensions, add 50% to the cost of a single-storey extension.

If you want to add a bathroom or kitchen, add £3,000-£12,000.

Don’t forget about windows, finishings, fixtures, or trees! Make sure you include these in your planning and cost estimates. If you don’t, you could be in for a surprise when the final bill comes.

Get 3-5 quotes and ideally have someone else with you when you get them.

Planning a house extension is a big job that can seem daunting, especially with so many things to think about. It’s best to start with figuring out the cost. Once you’ve got a rough idea of how much your extension will cost, you can move forward with everything else.

There are other places to start, of course. But the best place to start will always be with a general cost calculation.

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