House extensions: should I get one and how much do they cost?

You want a new home – but you don’t want to move. The answer? Improve or extend the home you’ve got.

When space is tight or your décor’s looking tired, you may be tempted to move house. But if your current location still suits you, an extension may be a far lower-cost option.

Here’s how to decide whether to go down the home improvement route, and how to make sure it delivers what you need.

Should I move or extend my house?

If it’s space you’re after, getting some more room (or extra rooms) is often possible with an extension or even just a shuffle around of the internal walls.

Extending can also be more cost-effective than upsizing to a bigger home.

Home improvements often pay for themselves by adding to the value of your home when you come to sell, so in many cases you’re not ‘spending’ money so much as putting it into a long-term investment.

You’ll also avoid the costs and fees associated with moving.

Some things (e.g. location, parking, garden size, quiet neighbours) can only be obtained by moving.

Make a list of your priorities and then see which ones can be achieved in your current property.

If you’re still stuck with a long list of unsolved issues, then maybe you do need to move. 

How do I find out if I can extend my home?

The first question to ask is, ‘Can I legally extend?’

Many properties come with permitted development rights, which mean you don’t need planning permission for certain extensions.

Assessing these rights will help you decide what home improvements are possible.

Bear in mind that work done by previous owners can affect your property’s rights, so consult your local authority and obtain a Building Notice before starting any work.

If you can’t extend using your permitted development rights, you’ll need to apply for planning permission through the Government Planning portal.

Your neighbours can comment on the plans, but the final decision is up to your local authority.

It helps to find out about their policies in advance, and for a fee you can get pre-application advice.

Your home improvement plans might also be restricted by external factors, like the placement of sewers, protected trees and conservation restrictions.

You may need Building Regulations approval to check the work is structurally sound – again, ask your local authority. 

Do I need an architect to plan my extension?

You’re not required by law to use an architect for home extensions, but for major building work this kind of expert help can be very useful.

An architect can help you make the most of your space and create more adventurous designs, as well as suggesting ideas and possibilities that never occurred to you.

The value they end up adding may more than compensate for their fee – and you’ll end up with a truly quality extension. 

What extension will be best for my home?

From a value perspective, it’s most economical to create extra space within the existing walls. Examples of this are loft and garage conversions.

Loft conversions cost around £20,000 and can be a relatively easy way of adding a bedroom and bathroom.

You can also convert an adjoined garage into an extra reception room or even (in some cases) a downstairs bedroom with an en suite, for only around £10,000.

Other popular home improvements include knocking together kitchens and dining areas to create open-plan kitchen-diners.

These typically cost between £1,260 and £1,680 per square metre without the fixtures and fittings. 

Which extensions add the most value to a home?

Some kinds of extension add more value than others. According to the National Association of Estate Agents, the best value improvements are as follows:

Beware of using up too much garden, as reducing your outside space can bring the value down and cancel out some of the benefits.

Merely enlarging existing rooms is probably the least effective way to add value, but that doesn’t mean it’s not a good idea if more space is what you want.

With the increased prevalance on working from home, a garden office can be a good way to add value to your property, for instance.

Another thing to bear in mind is that some streets have a natural ‘ceiling price’, beyond which it’s hard to raise the value of your house.

Do some research to find out what your street’s highest prices are, and beware of carrying out major work if it might take you over that ceiling.

You might find it hard to sell a half-million pound home in a street of houses half the price. 

How much does it cost to extend a house?

According to latest 2023 figures, building an extension is likely to cost around £1,500-£2,250/m² of new internal space (excluding VAT).

Other factors that can impact the cost of your extension project are:

• The ground conditions and foundation type required
• How many storeys you want to build
• The size and shape of your extension
• The quality of the build
• The amount of glazing you'd like
• Specialist features you may want, like air conditioning, smart home technology etc 

What do I need to bear in mind when planning a house extension?

You don’t want to fall out with any neighbours over your extension, so think about how it will affect them.

Will any new windows make their property (or yours) less private. Will roof lights disturb them?

Will you need access to the site through their land, and if so do you need an arrangement? Will any adjoining walls increase the level of noise?

You should also think about whether your existing property could be adversely affected.

Extensions can make it more difficult to get natural light into the main house.

Also hire a plumber to assess whether your boiler can cope with the extra space it needs to serve. 

How long do house extensions take?

Building a house extension involves everything from laying the foundation to installing roofing, which is why the whole process can take between 8 to 16 weeks.

A major decision to make is whether to vacate during construction.

While pricey, temporarily renting elsewhere avoids the hassles of living on-site amid dust, debris, scaffolding, utility disruptions, and contractors traversing your home for access.

Before kicking off your project, have an open discussion with builders to set realistic expectations about the daily disruptions, noise, parking limitations, and other inconveniences intrinsic to major renovations.

Knowing what to anticipate will help you prepare both logistically and mentally for this intensive, yet rewarding, home improvement journey. 

How can I make sure my extension is successful?

You should ensure your extension is:

• Legal
• In line with your needs
• Affordable
• Good value (i.e. adding to property price)
• Insured
• Not intrusive or disruptive to neighbours
• Well managed
• Carried out by trusted contractors

Use the Planning Portal website to get the necessary permission and make sure your builders stick to it.

You will also need to get site insurance before knocking anything down, because your existing buildings insurance is unlikely to cover your property while it is undergoing work.

Plan well ahead, and don’t skimp on advice.

It may be cheaper than moving, but you’re still spending a lot of money on your biggest asset, so keep those experts close.