How much does house extension cost in the UK?

Adding more space to your home is an exciting idea. Maybe your kitchen feels too small, your children need their bedrooms, or you want a room to work from home. A house extension can make your home feel brand new without moving.

But before you grab your toolbox or call a builder, you need to know how much a house extension costs. This guide explains it all in a simple and friendly way. You’ll learn what a house extension is, how much it can cost, and if it’s worth doing.

What is a house extension?

A house extension is when you build something new onto your home to make it bigger. It’s like giving your house a little extra room to grow—just like when you outgrow your clothes and need something larger.

Instead of buying a bigger house, which can be very expensive, many homeowners choose to stay where they are and build more space. That way, they can enjoy their neighbourhood, keep their same school and friends, and still have a more comfortable home.

There are lots of different kinds of extensions. Here are the most common ones:

Single-storey extension

This is when you add a new room or make a room bigger on the ground floor. For example, many people add a large kitchen-diner at the back of the house, or a playroom where children can have their own space. You can also build a bathroom, utility room, or home office.

Double-storey extension

This adds new rooms both upstairs and downstairs. It's a clever way to get more space because you're building on the same patch of ground. For example, you could add a bigger kitchen downstairs and a new bedroom and bathroom upstairs.

Side return extension

This uses the narrow space down the side of a house. In some homes, this area is just a dark alley or path. With a side return extension, it becomes part of your home. You can create a bigger kitchen or open up space for a dining area.

Rear extension

This is built at the back of your house, going out into your garden. It’s great if you have outdoor space that you’re not using much. Many people create big, open kitchens or family rooms this way, often with big glass doors leading into the garden.

Loft conversion

This turns your attic, which might just be full of boxes, into a brand-new bedroom or office. It’s one of the easiest ways to extend because you’re using space that already exists.

Each type of extension comes with different costs, building times, and planning rules. Some are easier to do than others, but they all help your house feel bigger and better suited to your needs.

How much does house extension cost in the UK?

Now let’s talk about the big question—money. How much does it cost to build an extension in the UK?

There’s no single answer because every house and every family is different. But builders usually give prices based on the size of the space you're building, using something called “price per square metre.”

What does “per square metre” mean?

Imagine a square that’s one metre wide and one metre long—about the size of a small table. That’s one square metre. If you’re building a room that’s five metres by four metres, that’s 20 square metres.

Now here’s what that might cost:

  • A basic extension (simple materials, small project): £1,800 to £2,300 per square metre
  • A mid-range extension (good quality, popular finishes): £2,300 to £2,800 per square metre
  • A high-end extension (luxury kitchen, glass walls, fancy details): £2,800 to £3,500+ per square metre

So, a 20 square metre extension could cost:

  • Basic: £36,000 to £46,000
  • Mid-range: £46,000 to £56,000
  • High-end: £56,000 to £70,000+

And that’s just the building part. There are other costs too:

Extra costs to remember:

  • Architect fees: These are the people who design the extension. They usually charge 5% to 10% of the total cost, but for smaller jobs, they may use fixed fee packages. It starts from around £1,500–£3,500, especially for standard designs or permitted development schemes.
  • Planning permission: This might cost a few hundred pounds, plus the time it takes to get approved.
  • Materials and finish: A fancy kitchen or big sliding glass doors will cost more than basic walls and windows.
  • VAT: Most builders charge 20% VAT, which can add up.

Also, where you live matters. If you’re in London or the South East, prices are usually higher. In the North or in rural areas, costs might be lower.

Is a house extension worth it?

Before you build anything, it’s a good idea to stop and ask, “Is it worth it?” A house extension can be a big project. It takes time, money, and patience. But for many homeowners, the result is worth it.

Here are some reasons why:

It gives you more space

Maybe your family has grown—more children, more toys, or maybe a grandparent has moved in. A house extension gives everyone more breathing room. You could build a quiet study room, a bright new bathroom, or a lovely place to eat meals together.

You don’t have to move house

Moving to a new house can be stressful. You have to pack all your things, you may need to change schools, and get used to new neighbours. But if you love where you live, a house extension means you can stay in your home while making it work better for your life.

It can make your home more valuable

When you build more space, your house could be worth more money. That’s great if you plan to sell it later. For example, an extra bedroom or a bigger kitchen can attract more buyers and increase the selling price.

Some estate agents say an extension could add 10–20% to the value of your home. To learn more, read our guide: Which home improvements can add value to your home?

But it’s not always perfect. There are some things to think about before you go ahead:

It can be noisy and messy

Building work means people will be coming in and out of your home. There will be tools, ladders, dust, and noise. Some families choose to stay somewhere else during the building, while others live through it—but it can feel stressful.

It costs a lot of money

Even a small extension can cost tens of thousands of pounds. And sometimes the price goes up if builders find problems or if plans change. You need to plan your budget carefully. To learn more, read our guide: How can I plan a successful home renovation on a budget?

You might need permission

Not all extensions are allowed straight away. You might need planning permission from your local council, especially if your home is old, listed, or in a special area. Getting permission can take time and cost extra.

Conclusion

A house extension can be one of the best ways to make your home feel bigger, better, and more comfortable. It gives you more room for your family to grow, work, and play—all without leaving your street or school. Whether you need a new kitchen, an extra bedroom, or a space for toys and games, building an extension can help you stay in the home you love.

But it’s not something to rush into. House extensions cost a lot of money, and the building process can take time. Before you start, make sure you know what kind of extension you want, how much it will cost, and how you plan to pay for it. Don’t forget to check if you need planning permission and always talk to professionals like architects or builders.

At Central Trust, we offer flexible home improvement loans from £3,000 to £250,000. Whether you need a small update or a major project, we can help you transform your home. Call us free 0800 980 6273, or complete our enquiry form, and we will call you back at a convenient time.

 

THINK CAREFULLY BEFORE SECURING OTHER DEBTS AGAINST YOUR HOME. IF YOU DO NOT KEEP UP REPAYMENTS ON A MORTGAGE OR ANY OTHER DEBT SECURED ON YOUR HOME, THE LENDER MAY REPOSSESS IT.