How Much Does a House Extension Cost?

by Jason Lyons

Building an extension is one of the most common ways for homeowners to create more space without the hassle of having to move.

There’s also the added benefit of the potential increase in the property value.

However, it can be difficult to get to grips with the kinds of costs you can expect to face. So how much does a hose extension cost?

The average cost of a house extension in the UK breaks down to between £1,100 – £1,400 per square metre.

So a medium-sized extension of 20m² will cost between £22,000 and £28,000

However, the cost of your individual project might be higher or lower, depending on the size and type of extension as well as the quality of material, fixtures, fittings etc.

House Extension Cost Calculator

The following calculations show how much you can roughly expect to pay depending on the size and quality of your extension.

Small (15m²)£12k – £16k£16k – £21k£21k – £30k
Medium (24m²)£19k – £26k£26k – £34k£34k – £48k
Large (48m²)£38k – £52k£52k – £67k£67k – £100k

Important Note

These costs are for the essential parts of an extension build. So the construction of the foundations, building of walls, sub-floor, plasterboarding, installing the basic provisions for plumbing and electrics etc.

They don’t include, the installation of new kitchens, bathrooms, fixtures and fittings or decorating.

Plus, they’re subject to VAT calculated at 20%.

It’s also worth noting that where you live in the country will impact the cost. For example, a single story extension in London will be considerably more expensive than it would be in Hull.

The Different Types of Extension and How They Affect the Cost

While the best way to get a roughly work out the cost of a house extension is by the cost per square meter, different types of extension will have an impact on the final cost.

Ground Floor Rear Extension

These are very popular as they build into the garden space.

Costs will depend on how integrated you want your rear extension to be with your existing home. Different configurations will have different structural implications.

You also need to consider doors, windows and access.

Ground Floor Side Return

Also known as a side infill, these types of extensions make use of dead spaces at the side of a property taken up by a passageway.

These are common a common feature of Victorian and period terraces. They’re a good alternative to a rear extension as don’t give up any garden space.

The cost considerations for a side extension are very similar to those of a rear extension.

Ground Floor Wrap Around