Planning a house extension is a big job that can seem daunting, especially with so many things to think about.
There are so many decisions to make before you even start building your extension, and so many rules and regulations to follow. That’s why it’s a good idea to get a proper handle on extension costs before you dive in.
In this guide, we’ll discuss:
If you want to extend your home and add to your living space, but aren’t quite sure where to begin, keep reading to find out everything you need to know.
Extension costs vary widely depending on factors such as the size and how you intend to use it. Smaller, less complex extensions tend to be the most affordable.
The table below shows the estimated cost of building a single-storey extension, either on a budget or using luxury materials:
|Budget or Mid-range Extension Cost
|Luxury Extension Cost
|Small Single-storey Extension (20 sqm)
|£30,000 to £44,000
|£46,000 to £50,000
|8 to 10 weeks
|Medium Single-storey Extension (30 sqm)
|£45,000 to £66,000
|£69,000 to £75,000
|10 to 12 weeks
|Large Single-storey Extension (50 sqm)
|£75,000 to £90,000
|£110,000 to £125,000
|12 to 16 weeks
On average, building a single-storey extension costs anywhere from £1,500 to £2,500 per square metre. If you’re working according to a small or mid-range budget, you should allow between £1,500 and £2,200 per square metre for your extension (excluding VAT).
If your budget is more flexible, you should expect to pay upwards of £2,300 per square metre to build a luxury single-storey extension (not including VAT).
These estimates include the cost of building the shell of the extension, but they exclude the cost of any fittings, fixtures, and finishes since these depend on how you plan to use your extension, and your personal preferences. In addition, these prices exclude VAT as not all builders are VAT-registered.
If you’re planning a small single-storey extension measuring approximately 20 square metres, you can expect to pay anywhere from £30,000 to £44,000 for a basic or mid-range extension or between £46,000 and £50,000 for a luxury extension (excluding VAT).
For homeowners planning a medium-sized single-storey extension measuring roughly 30 square metres—the typical extension size for Victorian terraces—you should anticipate costs between £45,000 and £66,000 for a budget or mid-range extension (without VAT). For a bespoke extension of this size, prices start at around £69,000 and can rise to £75,000 or more.
Finally, if you own a detached property and would like to extend it further by adding a large 50 square metre extension, you should expect to pay from £75,000 to £90,000 for a basic or mid-range structure or between £110,000 and £125,000 (or more) for a stunning luxury extension (not including VAT).
Most extensions can be completed in a period of two to four months, unless the site of your extension requires extensive preparation and groundworks, or the design of your extension is quite unique.
For a small single-storey extension, you should allow between 8 and 10 weeks to complete the build. Medium-sized extensions normally take between 10 and 12 weeks to complete, whilst building and finishing a large single-storey extension can take between 12 and 16 weeks.
To learn more about what affects the cost of building an extension, as well as how much you can expect to pay for other types of extensions such as double-storey extensions, side return extensions, glass extensions, and flat pack extensions, keep reading below.
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If you really want to extend your living space and make the most of your property, you may want to consider a double-storey extension.
The table below shows the estimated cost of building a double-storey extension, working either to a small, mid-range, or luxury budget:
|Budget or Mid-Range Extension Cost
|Luxury Extension Cost
|Small Two-storey Extension (40 sqm)
|£66,000 to £96,800
|£101,200 to £110,000
|12 to 16 weeks
|Medium Two-storey Extension (60 sqm)
|£99,000 to £145,200
|£151,800 to £165,000
|16 to 20 weeks
|Large Two-storey Extension (100 sqm)
|£165,000 to £242,000
|£253,000 to £275,000
|20 to 24 weeks
Building a single-storey extension and a double-storey extension costs almost the same per square metre. Unless you’ve chosen a truly bespoke design, the footprint of a single-storey extension—including the foundations and roof—is likely to be the same as the footprint for a two-storey extension.
On average, you can expect to pay approximately £1,650 to £2,420 per square metre for a double-storey extension done on a small or mid-range budget (excluding VAT). If you have the budget for a luxury extension completed to the highest standards, you should expect costs in the range of £2,530 and £2,750 per square metre (not including VAT).
That said, the total cost of adding a double-storey extension to your home is quite a bit higher overall. This is because the total area of the extension is larger, requiring more raw materials such as bricks, blocks, timber, or steel beams. In addition, larger extensions take longer to build and therefore total labour costs are higher.
This means that the cost of a small double-storey extension measuring approximately 40 square metres can cost anywhere from £66,000 to £96,800 if you have a small or mid-range budget, or from £101,200 to £110,000 if your budget is bigger.
For a medium-sized double-storey extension measuring roughly 60 square metres, the costs vary between £99,000 and £145,200 for homeowners on a budget or from £151,800 to £165,000 if your budget can stretch further.
Finally, for a large extension measuring 100 square metres, you should expect to pay between £165,000 and £242,000 if you’re trying to keep costs down or anywhere from £253,000 to £275,000 or more for a truly grand extension completed to the highest standards.
The cost of building a single- or double-storey extension can vary significantly depending on a broad range of factors.
Below, we offer a more detailed look at what affects the cost of building your extension—including not only the size and height of extension you choose, but also design and planning fees, groundworks, your choice of fittings, fixtures, and finishes, as well as your location.
Finally, we briefly discuss how adding an extension can impact your home insurance premiums.
As we saw in the two pricing tables above, the size of your extension and the number of storeys you want has a considerable impact on the cost of building the shell of your extension.
The style of extension you choose can also have a significant impact on cost. In addition to the traditional bricks-and-mortar extensions seen around the country, there are other styles to consider, including:
Although garage conversions aren’t an extension in the traditional sense, they can be an affordable option for anyone seeking a practical solution and a way to maximise the use of space in their home.
The cost of converting a garage into a more useable space can be anywhere from £5,000 to £61,800. The cost depends on the size of your garage, whether it’s integrated, detached, or detached, and the standard of construction you can afford.
The overall cost of a garage conversion also depends on whether you want to remove the original garage doors, whether you want to add windows and doors, as well as the cost of making the garage more habitable by adding insulation, electrics, and plumbing, as well as fittings and finishes.
For more information about garage conversions, visit our dedicated page.
Kitchen and Bathroom Extensions
Things get a bit more complicated when you start thinking about kitchen and bathroom extensions.
Planning permission needs to account for plumbing, and then the plumbing actually needs to be installed. To ensure your extension is safe and stands the test of time, it’s a good idea to get this done properly.
For a bathroom, you’ll need to add about £5,000 to the cost of building your extension’s shell. However, these costs can vary depending on the bathroom suite and finishes you choose.
A kitchen will cost you more than a bathroom, adding on around £10,000 to your fee for a low- to mid-range kitchen.
In addition to the costs of building the shell of your extension, you’ll need to consider the cost of any fittings.
If you’re building a 20-square metre kitchen extension, you should allow an extra £2,600 to £6,200 on top of the building costs if you’re on a strict budget (including labour, but excluding appliances).
If your budget is higher, you could pay anywhere from £5,600 to £12,000 on top of the cost of the extension (including labour, but excluding appliances).
Bathroom extensions tend to be smaller. The average costs of fitting a new bathroom suite range from £2,750 to £7,000 for a high specification finish.
Flat Roof Extensions
Flat roof extensions are an increasingly popular style of extension since they tend to be more affordable than pitched roof extensions.
Flat roof extensions cost anywhere between £30,000 and £75,000, whereas the cost of a pitched roof extension starts at around £40,000 and can increase up to £80,000.
The cost of adding a flat roof extension depends in part on the size and shape of the extension you want to build, as well as your choice of roofing material. Common choices for roofs include felt, rubber, fibreglass, and lead.
More information about flat roof extension is available in our guide.
Conservatories are a common feature in many UK homes, and conservatory extensions are becoming increasingly attractive as many homeowners want to make better use of their conservatories throughout the year.
Conservatory extensions tend to be used as multifunctional spaces, not just as an additional garden room. Depending on your needs and budget, a conservatory extension can become an extra lounge or even a fully fitted kitchen.
Building a lean-to conservatory with a budget kitchen and appliances costs approximately £15,000 to £17,625 depending on the fittings and fixtures you choose.
If you have more space, an Edwardian conservatory with an affordable kitchen and appliances could cost between £16,500 and £20,250.
As with so many construction projects, the cost of a conservatory extension depends on the style and size of conservatory you choose, as well as the roofing material (such as uPVC, glass, or polycarbonate) and how much plumbing, heating, and electrics you require.
For further details on conservatory extensions, please visit our comprehensive guide.
Whilst traditionally designed as a single-storey home, bungalow extensions are becoming increasingly common as homeowners seek to increase the amount of living space.
The cost of a bungalow extension ranges from as little as £25,000 to as much as £125,000 (not including VAT).
The range of prices reflects differences in the size and style of bungalow extension you choose. For example, you can add a 20 square metre roof extension to your bungalow for between £25,000 and £45,000. Conversely, a large 45 square metre wraparound extension starts at £65,000 and can increase to £125,000 or more.
In addition, you’ll need to budget for all the usual additional costs, such as design and planning fees, groundworks, fittings and finishes, and rubbish clearance among others.
For more information about bungalow extensions, please visit our detailed guide.
Flat Pack or Prefabricated Extensions
Flat pack or prefab extensions are growing in popularity because they are generally much more affordable and quicker to build than traditional extensions.
This style of extension costs anywhere from £19,950 to £43,750 depending on the size you prefer and whether you choose a prefab extension built off-site or a flat pack extension that must be assembled on your property.
Other fators that can influence the cost of flat pack and prefab extensions include your choice of building materials, such as uPVC, timber, or metal, as well as the cost of adding structural beams to support the opening between your existing home and the extension.
Click here to read our informational guide to flat pack and prefab extension costs that covers everything you need to know about this extension style.
Side Return Extensions
Side return extensions can help you make the most of your property without making your garden smaller. Depending on how much glazing you include, this extension style can feel more private than a conservatory or traditional extension.
Like most other types of extensions, side return extensions may require the advice of an architect or structural engineer, and you’ll need to decide how you want to finish your extension in order to budget for the appropriate fittings and fixtures.
To learn more about the cost of side return extensions, visit our guide.
Unless your extension is classified as permitted development, you will almost certainly need to apply for planning permission before moving forward with your extension.
The cost of applying for planning permission ranges from £462 in England in Wales to £600 in Scotland and £868 in Northern Ireland.
If your extension is approved, you’ll need to apply for building regs approval to ensure that the quality of construction meets current government regulations. The cost of applying for building regs approval varies by local authority, so you’ll need to contact your council for futher details.
As part of your planning application, you may want to consider hiring an architect, a surveyor, or a structural engineer to help you develop a sensible design and plan for your dream extension.
The cost of hiring an architect can vary depending on how they charge their fees, and the reason you’re hiring them. Some architects will charge an hourly rate, whilst others have fixed fees for services such as conducting a site survey or preparing drawings for planning applications and building regs approval.
If you want to hire an architect to oversee the construction of your extension, most architects charge anywhere from 7 to 12 per cent of the total build cost. Their fees work on a sliding scale, so they charge a higher percentage for small budget projects, and a lower percentage for high budget builds.
To learn more about how much architects charge, visit our complete guide here.
Depending on your exact needs, you could consider hiring a structural engineer instead of an architect. Whereas architects are experts in both building design and structure, structural engineers mainly focus on the structure and stability of a building.
However, they can also help you in the planning process by conducting a site survey and preparing drawings and calculations to support your application.
Structural engineers typically charge a flat fee for this type of service, ranging from £700 to £2,200 for a property extension. Our comprehensive guide offers more insight into what structural engineers do, and how much they charge.
The groundwork, such as digging a foundation, improving drainage, or underpinning will all play into your final cost.
If you’re looking to build upon an area of uneven terrain, expect your prices to be higher than if you were building onto something existing and flat.
Trees can sometimes be even trickier than the extension itself. Many trees are protected by Tree Preservation Orders (TPOs), so make sure you take any tree into account when you are requesting planning permission.
If you remove or alter a tree without the correct permission, you could end up in big trouble.
Do not forget to factor in additional costs for your site. If you have a complex site, you’ll need to ask your builder to factor in any extra costs.
For this, issues may include:
Windows and doors can be pricey and easily increase the cost of even a modest extension.
Choosing larger windows, triple glazing, or bi-fold doors can further increase your costs.
If you want to bring light but keep costs down, ask your builder whether a small bit of bespoke glazing could work in combination with standard-sized windows and doors.
As briefly mentioned above with kitchen and bathroom extensions, it’s all the little extras that can sometimes add up and lead to a hefty bill.
If you’re happy with simply painted walls, carpet or engineered wood floors, and standard lighting and electronics then your costs will be relatively low.
More luxurious touches such as bespoke flooring or tiling and fitted joinery can add a unique look to your extension but also increase the costs.
An unfortunately inescapable fact is that your location will dictate your price – living in London will ramp up your project costs considerably.
Also, remember that if you don’t have off-road parking available at your home or site, you will be expected to pay a parking permit for your contractors over the duration of their stay.
Whilst many homeowners know that an extension can increase the value of their home, not everyone realises just how this can impact the cost of home insurance.
Given that an extension represents a major change to the structure and value of your home, you should inform your home insurance provider of the building work.
Your insurer may then need to adjust your cover to reflect these changes and the difference in the value of your home. This could lead to a permanent increase in your monthly or annual premiums.
However, since home insurance is so important (and is usually a requirement to obtain a mortgage), it’s absolutely vital to inform your provider as soon as possible to ensure your investment is properly protected.
Comparing quotes is a great way to potentially reduce the cost of your home’s extension. HouseholdQuotes can help you get quotes from multiple builders near you, so that you can find someone that suits your budget.
Click the button below to get started:
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You can see how costs can spiral when getting an extension added to your home, so it’s important to also know the ways in which you can bring those costs down.
The devil is in the details—so plan ahead to avoid any costly last-minute changes. If you have your architect drawings complete and finalised, it can be expensive to have them changed, so make sure you really assess things at each stage of the sign-off process to make changes when it’s most easy to do so.
Similarly, if you know you want to use your extension for a certain purpose – like as a kitchen or a bathroom – it’s important everyone knows this beforehand so that certain considerations can be taken into account when building to ensure electricity, gas and water can be accessed in the space.
Don’t cut costs when it comes to the structure. Hire a surveyor and structural engineer or architect to draw up plans – you can look to save on fitting costs if you’re on a tight budget, but you shouldn’t try to scrimp on the structural integrity of your extension.
Permitting this is within your allowable home development, it might be more cost-effective to undertake a conversion over an extension when looking to add space to your home. Basements, lofts and garages are all perfect spaces to do this – so make sure you explore your options before going down one route.
Where possible, it’s best to avoid the need to move gas, electric or water pipes. If you’re planning a kitchen extension, it’s best to do it as sympathetically as possible, and have your fittings put in place where they make the most sense for your existing pipework.
Take advantage of online marketplaces, or choose off-the-shelf products from high street retailers over bespoke options. This will help you to save considerably on your fixtures and fittings. Similarly, you can buy ahead during sales or percentage-off periods at shops, which will also save you money in the long-run.
The steps will differ depending on the scope of your extension, but you can expect some, if not all, of the below to be involved when adding an extension to your home.
Firstly, you need to obtain Building Regulations or Planning Permission (if required), while also checking your leasehold agreement (if applicable) to make sure you can do what you want to do.
You can then enlist an architect to draw up plans, considering your intended use (kitchen, bathroom, study).
Make sure you consult your insurance provider to let them know of the planned work ahead of it beginning and obtain parking permits if required for your contractors to ensure they have easy access to your property.
Before work begins you may need to clear the space and excavate if necessary, including the removal of trees (if not held under TPOs or in protected areas).
Once all these elements have been completed, building work can begin.
It can feel overwhelming trying to decide whether or not undertaking such a big building project is actually the right move for you. We’ve listed the advantages and disadvantages of home extensions in the table below to help you come to the right decision.
|Home extensions can add value to your home
|They are expensive to complete
|It is more affordable than moving house
|Home extensions can be stressful projects to undertake
|There is huge scope for creativity and personalisation
|You may not be able to get exactly what you want
One of the key advantages to home extensions is that they can add value to your home. Most home extensions increase the sale value of your property, meaning that if you do end up selling the house it will make you more money.
In most cases undertaking a home extension is more affordable than moving house. Instead of searching for the right property and dealing with the stress of moving, you can simply extend the house to fit your specification.
This also means that the scope for creativity and personalisation of the property is endless. You can have your dream home without having to move neighbourhoods.
Whilst a home extension may be more affordable than moving house, they are still expensive to complete and will involve huge costs depending on what work you choose to have done. Budgeting is absolutely vital for home extensions so that you don’t end up spending thousands more than you wanted to.
Another disadvantage is that home extensions can be stressful projects to undertake that are time-consuming and involve a lot of planning and you may not get exactly what you wanted (depending on building regs and planning permission approval).
Finding the right builder can be challenging. At HouseholdQuotes, we can connect you to builders in your area.
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When seeking out a contractor for your work, you should look to get three to five quotes for any extension to your home. That way you can get a feel for what the market rate is, as well as see who you get on with the most or feel is most capable of the job.
It’s important you don’t confuse an estimate with a quote. It’s fairly common for tradespeople, surveyors, and architects to offer an estimate the first time they visit your property. This estimate is a good starting point, but if you think they might be a good fit for the job, be sure to ask for a detailed quote so you can get a more precise idea of the costs.
It’s also worth making sure you have someone else with you when you get quotes. It can be helpful to have another opinion on price, timeframes, and personalities. What’s more, asking a family member or trusted friend to join you might help you feel less pressured to make a commitment on the spot.
When looking for contractors, you can ask your friends and relatives – even neighbours – if they’d had work done recently of a similar type and whether or not they’d recommend their professional to you.
This can help you in your search by speeding up the process if someone you trust has used someone who can do exactly what you need doing in your home.
Depending on the type of work you’re having done, you may need different types of tradespeople involved in your project. Builders, plumbers, electricians, heating engineers, painters and decorators – they all come with their own skill sets and their own pricing strategies.
It’s good to note that small vs large contractors will offer very different prices. Where possible, opt for the smaller companies as they won’t have large overheads to recoup with their pricing, and will generally cost you less than the bigger national companies.
First things first, a written quote is an essential part of any job. You should never accept a verbal agreement as your binding terms when undertaking any work, let alone an expensive home renovation.
With a written quote, you have something firm to refer to if needs be, simply stating what is and isn’t included in your quote, as well as for what fee and under what time frames.
Just like with a job interview, it’s good to find out your contractor’s experience, and whether or not they’ve built something like the structure you’re wanting for your home extension. Even if you have a brilliant verbatim recommendation from a friend or neighbour, if the contractor isn’t familiar with what you want, they mightn’t be the best fit for you.
Similarly, anyone can write something that sounds good on a website – but the proof is in the finished project. Asking for photos or videos of the contractor’s past work can further help to ensure you’re getting exactly what you want from your trader.
You should finally always double-check your professional has insurance to cover both themselves and you in the event of any trouble while constructing. This will also help you sidestep any cowboy traders, as they likely won’t bother with insurance and will get tetchy if you ask to see proof of it.
If the answer to your lack of space at home lies in an extension, here’s our final checklist to make sure you’ve considered everything before embarking on your project.
Use HouseholdQuotes to find local builders and potentially save money on your home extension.
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You can read more detailed advice on the Planning Portal website.
If an extension is a step too far for you right now, there are alternative ways of adding some extra square footage into your property.
Instead of adding space outside, you can venture into the basement with a cellar conversion, or upwards with a loft conversion. If you have a garage that is more of a dumping ground than it is somewhere to store a vehicle, then turning that space into a useful room may be an option, too.
For something quite a lot like an extension, but not quite with the same level of commitment, you can opt for a conservatory or a lean-to, instead.
In short – yes. According to the insurer Hiscox, adding a bedroom could add up to 11.8% to the value of your home.
Adding a kitchen or dining room extension could increase the value of your home by up to 10.8%, while adding a bathroom could increase the value by up to 5.7% (all figures based on the average UK home value of £226,071 as priced in 2017).
If you’re planning to extend your home and live close to or are attached to your neighbour’s properties, then it’s likely that you will need to notify them of your plans. They then might request additional information from you which could take more time and could also increase your costs.
Your best bet is to keep your neighbours as informed as you can, as early on in the process as you can. Whilst they can’t stop from you building an extension, they do have the right to be aware of what you’re planning and request further information or action if they want to.
This is a common rule used by planning offices and is assessed on both plan and elevation. An extension should not exceed a line taken at 45 degrees from the centre of the nearest ground floor window of a habitable room in an adjoining property.
If a proposed extension breaks this rule, it could be deemed unacceptable and not receive the permissions required to build.
Comparing Quotes Could Save You Up To 40%:
For years, the Household Quotes Team has been the trusted partner for homeowners and tenants throughout the UK, ensuring they never overpay for essential home improvements. Whether it’s a malfunctioning boiler or the need for new windows, we believe that everyone should have access to affordable home maintenance. Our goal is to make it easier for you to keep your home nice without breaking the bank.