How Much Does It Cost To Build An Extension In 2024?

How Much Does It Cost To Build An Extension In 2024?

Written by  John Davies
Last updated: January 17, 2024

There are a lot of things to consider when looking at adding an extension, including how much it would cost to build an extension. I’ve gone ahead and listed them all below so you can go through them, however, if you’re like me and just want to find out a rough cost, then take a look at the calculator below.

Extension Cost Calculator


Prices Per Square Meter

How Much Does an Extension Cost?

The average cost of an extension is £1600-£2100 per square metre. This estimate should cover the supply and labour cost of the extension’s walls, foundation, plastering, insulation and flooring. It should also cover basic amenities like electrical wiring and plumbing.

On the other hand, it doesn’t include VAT and the cost of painting, furnishing or getting permits for the extension. We excluded these expenses because they are technically “additional costs.” They may also be unnecessary, except for VAT. That’s why most contractors won’t include these additional expenses either. However, you still need to be aware of them when calculating the cost of an extension.

Size of extensionCost of extensionThe average cost of extension
Small (20 square metres)£32,000-£42,000£37,000
Medium (30 square metres)£48,000-£63,000£55,500
Large (50 square metres)£80,000-£105,000£92,500

How Much Does Each Type of Extension Cost?

There are different types of extensions that you can build for your house, and each one of them has a varied price range. The price is determined by the size of the extension and other additions that you may need for the job. The following are some of the common types of extensions and how much it will cost you per square meter.

Bathroom or Kitchen Extension Cost

One of the most significant determiners for the cost of building an extension is where you live. Generally, it will cost you less in the rest of the UK than it would in London and the South East. The total cost of doing construction in these two areas may cost up to 40% more. Note this as it will remain a constant throughout this price guide.

If you want a bigger kitchen or bathroom, you can get it pretty affordably at a total of about £5,000 for a small bathroom with basic finishes. On the higher end, you could spend approximately £8,000 that is if you need fancier tiles, a large bathtub or detailed décor.

The kitchen is a bit costlier because you will need electrical and plumbing work is done. On average, set aside approximately £10,000 minimum for this project and about twice that on the higher side.

Editors Note: Find out how much a new kitchen would increase the value of your home here.

Single Storey/Bungalow Extension Costs

If you have all your plans and permits sorted out, then it will cost you about £1,600 per meter square for basic finishes and affordable labour. On the higher end, a single storey or bungalow extension will set you back approximately £2,300 with excellent finishes. Remember that your choice of material is critical as you need a sturdy building that won’t be a weak link to your home.

Two Storey Extension Costs

Using the price of a single-storey extension, you can come up with a reasonable estimate of how much it will cost you for twice that. However, since you are not precisely doubling everything, you will only add about 50% to the construction of a two-storey extension cost.

So if you add 50% of £1,600, you should expect to pay about £2,400 on the lower end, and approximately £3,450 per square meter for high end finishes in your home. Remember that this is only a base charge; more factors could make the cost higher, including VAT.

two storey extension

Conservatory Cost

This is one of the more straightforward extensions to do since it doesn’t require much. However, the cost of things such as window glazing and type of glass used can make the price shoot up significantly.

Expect to fork out about £850 on the lower end that is assuming you use affordable materials such as UPVC. If you use brick as well as double or triple glazed windows and doors, you may end up paying up to £1500 per square meter.

The great thing about a conservatory extension is you can minimalize the construction and still get a pretty excellent structure. For example, instead of adding three walls, you can do two for something small. Another piece of good news is you won’t require any permits for this type of extension.

Loft Conversion/Extension Cost

When you want to do a loft extension, the first thing that you must do is check with local authorities on the height restrictions for the area. Many of these restrictions were removed, but depending on the location of your home, you will need the confirmation.

The cost of extending your roof for the attic will cost you between £1,300 and £2,500 per meter square. The difference in price depends on the kind of roof that you need and whether you will erect any walls, so ensure when getting a quote, you have a clear plan. You also need to account for windows, Velux windows cost more than ordinary.

Factors Affecting the Cost of Building an Extension

Other than the location of your extension, there are other factors that you must pay attention to so you can have a handle on the full costs of the project. While getting the quote, you should ask about the following and how they affect the overall cost depending on what you want.

Type of Soil

The soil in the location where you want to construct your extension will determine a few things. One it will dictate the construction style that will be used and how long it will take, especially concerning the foundation. A strong foundation is critical to a sturdy house, so it needs careful construction.

The soil can be different from the one under your current house, so don’t be alarmed when this is pointed out. Soil with poor drainage is complicated to work with; hence it may cost you more to fix. Loose earth is also an issue since it may not be strong enough to hold up the house if not well constructed.

Doors/ Windows

You will likely want the same kind of windows and doors as your current house or even an upgrade. In places where you get glazed doors and windows, it will likely cost you more, especially when you need them double and triple glazed. You may need to upgrade from your current option if the extension will probably get hit by stronger wind and snow. As a result, this will significantly impact the overall cost of your house extension.

Restructuring- Walls

Sometimes creating an extension is not straightforward, especially when it is a direct part of the main building. This means you will have to make some changes to the existing house so that it can fit with the new structure coming up. In such a case, you may have to tear down some walls, do steelwork and in some cases bring down part of the roof. Such work can take more time as well as cost more so you can expect that your final quote may be much higher than the figures given above.

To help bring these costs down, you should try as much as possible to reuse, especially for anything that you may have taken from the main house. You should also have a good idea of the materials needed and how to get the same excellent quality at affordable prices. Alternatively, ensure that you get an architect that can come up with a plan that requires minimal changes to the existing house.

Drainage/ Piping/ Gas

This is one area that may be impossible to avoid, and so it is a big consideration regardless of the type of extension that you want to build. The drainage needs to be done correctly; otherwise, it will cause you troubles soon and your insurance may not cover such damages. Ensure that you have a clear plan of what is needed in the new structure, so you know where the connections will be made.

In case you need gas in the extension, you also have to make the changes, and it is always best when a professional does it. This means that you may have to call your gas provider for this; hence it will be an extra charge to consider.

You should also consider if your current central heating would be powerful enough to heat the new space you’re adding. In most cases, it should be fine, but it’s something else to consider.


If your compound is not very big and access is restricted in some way, this will cost you in terms of time. You may have to make different arrangements to ease movement in and out of the construction site. This is something that your contractor or tradesman should be able to identify when doing an initial site visit.

Another thing that may prevent easy access is if there are frequent movements by your family through the construction area. This is why in some cases; you may have to make different arrangements, so you get back home after the construction is completed.


If you have any kind of home insurance, you must check what your provider can cover in terms of the on-going construction and after the structure is completed. One change that you may need is taking a non-negligence policy that is important when you need a way to handle any damages that may come about the new extension. It will cost you about £1,000 yearly and will cover any issues in your property as well as your neighbours as a result of the building activities.

It is essential to inform your insurer well before you start the renovation. If your extension cost is significantly more than £100,000, you may need to take a new renovation policy. This will cost you more so you need to budget accordingly.

How to Save Money When Building Your House Extension

It is easy for the cost of building the house extension to become quite huge if you are not keen on cutting costs when and where you can. If you want to save money, you may have to incur different types of prices, but in the long run, only you can decide what is worth having. The following tips should help you ensure that you save as much as possible on your extension.

Start With a Budget

One of the biggest mistakes that people make is not setting a budget for the project. This is damaging to your finances since it will give you the impression that you can afford any costs that arise from the construction. This can put you in a terrible position and make you spend more than is necessary.

Start with a budget using your estimates and work with it unless it is necessary to add. Included in your budget should be a contingency budget. This also sets a limit of how much you may spend on extras and allows you to be more conscious of decisions that you may make during the construction.

Save on VAT

Usually, you must pay 20% VAT on labour and materials apart from a few situations where you can claim relief. You can claim relief if your building is zero-rated, the construction is a conversion of the current house or any changes that you make to a home that has remained unoccupied for at least two years. Usually, this is about 5% less. If you want to make further savings, using unregistered tradespeople will mean that you don’t have to pay the 20% VAT on labour.

Get Various Estimates

You must balance between getting quality work done, and affordability and the best way to do this is to compare quotes. No matter the type of workers you get for your house extension construction, you can afford to shop around starting with the best recommendations you get from neighbours, friends or family.

Use the estimates and referrals to compare what you expect from them. Remember to ask as many questions as possible, so you have a clear idea of what is on offer. You want people that understand your vision but can work without much supervision.

Start With a Minimalist Design

This doesn’t mean that the construction shouldn’t be fancy or complicated in any way; it means that it can be done without much disruption. For example, if there are any changes to be done to the main structure, they should be minimalistic, and you can get this by getting a good planner.

However, you can also do it yourself with the help of your workmen if you are not too knowledgeable so you can work out the practicability. The design should make the construction process straightforward.

Source the Materials Yourself

Many contractors use this opportunity to inflate the cost, so you must try and get everything that you need yourself. This is why it is essential to get a comprehensive quote when making your comparisons so you can also check the prices and decide what works best.

If you get your materials yourself, you can be sure that there is no wastage and if you buy in bulk, you can get discounts such as free shipping. Also, check your local providers as this will minimize added costs.

Vacate the House

Depending on how complicated the construction will be, it may be best to live elsewhere for the duration of the development. This minimises your interference with the process that may slow down the job hence making it costlier for you. However, make sure to compare any costs that you may incur especially if you have to rent temporarily and find out the best way forward.

Supervise the Construction

Many project managers insist that supervising your construction may ensure that you get a better result and that it may cost you less. You will not have to get someone specifically for that hence saving on costs. It may also teach you a thing or two that may come in handy at a different point as well as ensuring that the construction is done fast. This may also mean that you live at the construction site for easy supervision, put this into consideration.

Get Insured

There are several insurance policies that you may need depending on what you find necessary. It is a good idea to have site insurance not to save on costs during construction. This policy covers everyone, so you don’t have to pay from your pocket in case of accidents. It is still vital even when your construction personnel have their insurance, since their policy may make you liable in case of anything. The site insurance will help to save you unnecessary battles and costs.

This policy also covers your home if you plan to vacate for the time of the construction. It ensures that everything is safe and you don’t have to worry about theft or anything happening on site. Remember also the non-negligence policy, so you and your neighbour are covered even after the construction is over.


What Is the Cheapest Type of Extension?

A single-story extension is the cheapest type of extension. It averages just £1,600 per square metre. At the costliest, you probably won’t have to spend more than £2,300 per square metre. The reasons are simple. The material and labour cost of an extension of this kind is relatively low. The structural design is also relatively simple.

In contrast, a two-story extension is more expensive. The average cost of an extension of this kind is £2,100 per square metre. However, it can reach up to £3,450 per square metre.

Are Conservatories Cheaper Than Extensions?

Yes, conservatories are cheaper than extensions. In fact, they are so much cheaper that you can build a conservatory for as little as £850 per square metre. However, the average cost of an extension is £1,600 to £2,100, while that of an extension is £1,000.

On the high side, you need £1,500 per square metre to build a conservatory. That’s still relatively more affordable than an extension. However, there are limitations to what you can do with a conservatory. For example, you can’t use a conservatory as an additional living space unless you meet building regulations and planning permission.

In contrast, conservatories also have certain advantages over regular extensions. For example, conservatories have better ventilation and natural light. An orangery is your best bet if you want the best of both worlds.

Will I Pay VAT on Extensions?

Yes, you have to pay VAT on extensions. VAT is around 10% to 20% of the total cost of the extension. As stated earlier, some contractors won’t include VAT in their quotes. So, prepare for this. Even better, ask for written quotes.

Will an Extension Add Value to My Home?

Yes, an extension will add value to your home. To be more specific, it will increase the market value of your home by 15% to 20%.

Email newsletter
Tell us about what you want to learn!
We won’t spam you, we promise!