Sold everywhere:

How Much Does An Extension Cost?

  • Free Cash Offer
  • No Hidden Fees
  • Sell In Your Own Timeframe

Home improvements are quite often something that appear high up on our to-do list, but some take more priority than others. An extension is often seen as a bit of a luxury expense, the outlay being more expensive than say, tiling your bathroom! An extension, though, gives you plenty of options, it can increase your property value, and it can even allow you to investigate the potential of renting a room out. It could also be useful for a new addition to the family.

How much does an extension cost though? And how much can it change the answer to the question, “How much is my house worth?”

Due to the type of extensions you can add to your house, the prices can vary significantly.  Smaller projects can cost upwards of £10,000 but a larger piece of work could set you back £300,000.

House extension ideas

You may be weighing up the options for which type of extension works best for you. It largely depends on the property type you have. So, before you develop grand ideas only to find it is not possible, look at the list below for the most common types you could add to your property.

  • Single-storey extension
  • Multi-storey extension
  • Semi-detached extension
  • Basement extension

Single-storey house extensions

A single-storey house extension is often seen as the easiest to build and is used as a space for an additional back bedroom, a playroom, or a relaxing area to view your garden. For a build itself, the costs associated with a single storey house extension can get cheaper per square metre the bigger you build.

When looking to build a single-storey extension you are most likely to look at adding these to the side or back of the building.

What is a full extension?

A full extension means that rather than just the shell of the building, your extension is complete once finished, aside from any decorations you wish to add to the room. This means all windows, doors, flooring and internal walls will be part of the finished project.

A 20m2 full extension could cost between £25-£50,000 and a 50m2 could cost £62,500-£112,500.

Shell extension cost

Shell extensions typically cost £800 per m2 to £1,600 per m2. A shell extension is often used when converting a building. It refers mostly to external changes, meaning the walls, roof and foundations. Shell extensions are popular with people that like to do all internal work themselves. Shell extensions tend to be preferable for those that may look to complete the job in stages and when funds allow.

Most shell extensions involve a change of property use or function. A conversion commonly seen that would involve a shell extension is developing an office building into residential apartments. For this reason shell conversions can be challenging and require a vast amount work modifying structure, layout, and systems to facilitate the change of use. Planning permission is often required from local authorities, as well as different permits and following building regulations. 

Double storey extension cost

A two-storey extension is a popular addition to a house and contrary to popular belief, won’t cost twice the amount of a single storey. With the foundations and roof already added, it is simply a cost of walls, floor joists and interior fixtures. To save money it is often advisable to save up and do both storeys at once rather than do one at a time. An expected cost of a standard two storey extension is between £75,000-£135,000

Semi-detached house extension

Semi-detached property extensions are among the most common type of house extension. One thing to be particularly aware of is whether a party wall agreement will be needed. The costs for this can add significantly more to your overall building project costs. Depending on the type of extension you are going for will determine the cost. Expect to pay from £1,200 up to £3,000. This could be more though, so it is always advisable to consult a surveyor for guidance. In total, the cost for completing such an extension is similar to the single or two-storey options.

Terrace house extension

With space more limited, the options for an extension here are restricted to the rear. They can cost up to £60,000 but can be as cheap as £15,000.

Side return extension cost

Most side return extensions cost between £30,000 and £65,000. Things can get more expensive when you choose a glass side return extension, with the average cost per m2 around £3,000 alone. 

Side return extensions are popular with those who live in terraced homes, particuarly those which are Edwardian or Victorian. More often than not these properties have a small strip of land down one side which is often used for storage or access to the garden. These alleys are used in side return extensions to add more living space and can be two storey to add extra bedroom or bathroom space upstairs too. The extension can be designed to blend in with the existing structure of the house for a seamless look. 

Kitchen extension cost

The average cost of a kitchen extension in the UK ranges from £30,000 to £50,000. However, size and materials can see this price higher or lower. Below are some factors which can affect the cost of a kitchen extension in detail: 

  • Size – The larger the extension the higher the price. Whether you’re adding on a small section for a utility room or a full-scale extension the size will have the primary affect on cost. 
  • Materials – The quality and type of materials used on countertops and floors can impact the cost of your kitchen extension. Natural stone and real wood are more expensive materials when compared to laminate and plywood. 
  • Features – White goods, lighting, amenities, flooring, and other kitchen elements can affect the price of your extension.

Don’t forget, other fees such as planning permission and building regulations may be need to worked into your budget too.

Basement extension

A basement extension is the most expensive form of extension and allow you to increase the value of your house where additional space is limited. If you can’t extend up, sideways or backwards, the only other way is down. The costs of the extension itself may match those of the other types. However significant additional costs are added due to the fact that pipes and roots must be moved as well as the groundwork required to create the space. This means the total cost for the extension can be more than £100,000.

How long will an extension take?

Depending on the size of the project will determine how long it will take. Add to this the ever-changeable British weather and you could see the full job take anything from 3-6 months.

Is it better to extend up or out?

Sometimes you may be limited due to the property location, house type or party wall disagreements. If you are open to all options though, both have their benefits. By moving up, you do not encroach on any of your outdoor space, and you potentially create a room with a view-very appealing to tenants or prospective future buyers.

If you extend out, you lose some green space, but you do create something visually spectacular. The amount of square footage added to your house can do wonders for the value and allow you to create a very marketable open plan room.

Do I need planning permission for an extension?

A new rule has come into force for 2022 and has made it easier for people to extend their properties. If you are building within your permitted development rights, then you do NOT need planning permission.  However, there are several situations when you will need permission granted. If you are unsure if you are within your permitted development rights, you can speak to the local planning department for further guidance.

Will an extension add value to my house?

Whilst an expensive project, the returns on this investment can be huge. It will depend on the type of room you choose to add but as an example, a double bedroom could see you benefit with a 12% increase on your house value.

Have you recently built an extension and are looking to cash in on your property development project? With online estate agent SOLD.CO.UK we can sell your house for free meaning that there are no expensive costs to factor into your property plans. Or maybe building an extension isn’t for you but finding a new property with one is, either way contact us today to learn more about how the team at SOLD can get you moving. Get an instant valuation today.

Featured articles

How to Battle Against Rising Damp
Does a Security System Add Value to Your Home?
How Much Value Does a Garden Add to Your House?

Please enter your details below and a member of our team will be in touch to discuss a free valuation for your home.

"*" indicates required fields


Section Break


Section Break

This field is for validation purposes and should be left unchanged.

By submitting your details, you agree that we may keep this information safely. Our Privacy Policy has further details