How much does a house extension cost?

Short on space but don't fancy the upheaval of moving? We weigh up the costs involved in expanding your current property, from a side extension to a double-storey extension

The debate over whether to move or extend has long been food for thought for homeowners who’ve outgrown their properties.

READ MORE: 37 amazing home extension projects

If you're happy with your neighbourhood and find the thought of upping sticks stressful, a house extension may be an easier way to achieve the extra space you need, minus the upheaval.

To make matters easier, the UK's permitted development rights allow homeowners to undertake single-storey extensions, and as of 2020, double-storey extensions, without applying for planning permission. There are exceptions to this, however, if your home is listed or located in a protected area. 

Nevertheless, extensions don't come cheap and recent global events have increased the expense. The ongoing war in Ukraine has led to a 10% increase in the cost of building materials, according to the Construction Leadership Council. 

Extending may still be a more cost-effective option than relocating, especially when moving costs and stamp duty are taken into consideration, but it's important to do the math and weigh up the potential costs involved. 

What does a house extension cost?

According to tradesperson listing site Checkatrade, prices vary enormously, ranging from £7,500 for a garage conversion to £160,000 for a basement extension, with some projects costing even more.

Some of the biggest factors that will determine the cost of your extension include its size, the quality of finish you’re after, and how easy it is to access your property.

Location also plays a big role—builders in London and the southeast typically charge more than builders in other parts of the UK.

It will also cost more if you employ an architect, structural engineer or project manager, although hiring these professionals can also save you from costly mistakes so overall it may prove worthwhile.

Image: Peter Landers / Conibere Phillips Architects

Especially if planning permission is required, you may have to at least hire someone to produce drawings, although this could be an architectural technician rather than an architect if your budget is tight.

You could also opt for a shell-only extension if you’re looking to save money—this is where a builder gets you to the watertight external build stage and you arrange all the internal works yourself.

As a rough guide, Checkatrade suggests the following average costs as a ballpark for some of the most typical home extensions.

Will an extension offer a return on investment?

One of the key considerations if you’re thinking about extending is likely to be whether or not you’ll get your money back when you sell.

Allerton Damp Proofing crunched the numbers last year in a bid to work out which major towns and cities in the UK provided the best returns for those building extensions.

Despite it being one of the priciest places to build in, London topped the table when it came to the profit possible from a 30sqm extension.

The damp proofing company estimated that after accounting for construction costs, Londoners could add an average of almost £100,000 to their property’s value.

Cambridge and Oxford were the next most lucrative places to build extensions, with the full list of the top 10 in the table below.

Average house prices are according to Rightmove and accurate at the time of publishing.

Joe Trivett, damp expert at Allerton Damp Proofing, said: “An extension is a great opportunity to add space to your home, without starting over in a new property. 

“The housing market has been highly competitive recently as people look to upsize, so opting for an extension instead of a move can save you lots of time house hunting, especially if you’re really happy with the location you currently live in.”

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Top image: Da Feng