An extension can present an alternative to selling up and moving home when homeowners feel that their property is no longer large enough for their needs

Building an extension offers a number of excellent benefits for homeowners. It creates more living space that can be used in a variety of ways, and it boosts the value of the property too. An extension can present an alternative to selling up and moving home when homeowners feel that their property is no longer large enough for their needs. 

It's often a more affordable way to gain more living space when compared to moving home. However, if you're thinking about building an extension, knowing how much it could cost will help you to make your decision.

There are many factors that can affect the price of building an extension for your property. The type and size of the extension will make a difference, and you need to consider various costs ranging from labour and materials to taxes. 

Even your location will affect how much you are likely to pay for a new extension. To start budgeting for an extension, use this in-depth guide to understand the factors that you should be taking into account.

Timber clad extension with connecting glass walkwayTimber clad extension with connecting glass walkwayTimber clad extension with connecting glass walkwayTimber clad extension with connecting glass walkway

An extension to your property really increases the value and saleability

Type of Extension

The type of extension that you want to build is one of the key factors affecting how much it would cost. You might be thinking about a conservatory, a single-storey extension or a two-storey extension. Perhaps you're considering extending a bungalow or you want to make use of an attic or cellar to maximise your space.

Conservatories

A conservatory might not be suitable for use as a bedroom, but it's a great space to have available on a sunny day

A conservatory offers one type of extension that many people decide will be most valuable to their home. It's usually a more affordable option compared to a full extension, although a conservatory has both benefits and drawbacks in comparison. 

It provides a specific type of living space, best used as a space for relaxing and socialising, such as a dining room or lounge. A conservatory might not be suitable for use as a bedroom, but it's a great space to have available on a sunny day.

The cost of a conservatory can vary greatly, depending on the size, style, roof type and a number of other factors. Some people also choose to combine a traditional conservatory with an extension. To create an orangery or perhaps a kitchen extension that can save money compared to a single-storey extension.

A small conservatory could cost as little as £5,000 or £6,000 or it could cost as much as £20,000 or more. According to Evis Build, a low-E glazing conservatory with a lean-to roof costs an average of £9,000, while a fancier design with a gable or hipped Edwardian roof could cost around £11,000.

Single-Storey Extensions

Professional fees and VAT are just two of the other costs you might need to consider

If you're looking for a full extension, a single-storey extension is a top choice for many people. You can extend an existing space or add a further room to your home, and you don't need to consider the technicalities of adding a second storey. 

Your single-storey extension is probably going to be a rear or side extension for your home. The cost of a single-storey extension could reach around £35,000 or in London up to £45,000 or even more.

The cost of your extension can be calculated per metre, but there are also other expenses to consider outside of the build itself. Professional fees and VAT are just two of the other costs you might need to consider. If you want to extend your bungalow, you're likely to be looking at prices that match any other single-storey extension.

Two-storey Extensions

Getting planning permission for a two-storey extension can take longer and be more difficult

If you're considering a two-storey extension, you might assume that you need to double to cost of a single-storey extension, but that probably won't be the case. As a general rule, adding about 50% of the cost of a single-storey extension can demonstrate how much it might cost add another storey. 

The cost of important elements such as the foundational structures is shared between the storeys, so you get a lower cost per metre. There are some things that will cost more, however, such as fees for architects and other professionals. You are planning to build a larger space, so it's naturally going to have a higher price tag.

A two-storey extension could cost from £55,000 to over £70,000, depending on the size and your location. In London and the surrounding regions, you could be paying closer to £80,000 on average. Getting planning permission for a two-storey extension can take longer and be more difficult, and this complication can push up your costs too.

Home extension interior with roof lights and brick wallHome extension interior with roof lights and brick wallHome extension interior with roof lights and brick wallHome extension interior with roof lights and brick wall

Have you thought about how you will use your home extension?

Basement Extensions

Not every home is suitable for a basement extension, and seeking planning permission can sometimes be tricky.

Some people consider the idea of a basement extension, which is a very different way to add space to your home. While it's another type of extension, it's one where you need to dig down, rather than simply building onto your property. 

A basement extension will cost you significantly more than other types of extension, with costs per metre starting at around £3,000. In London, a basement extension could cost between £5,000 and £6,000 per square metre.

Not every home is suitable for a basement extension, and seeking planning permission can sometimes be tricky. If it's something that you want to do, finding the right architect is important. Which could mean paying more to have someone who knows what they're doing? 

There are difficulties and expenses that your builder will face with a basement extension too, which wouldn't be necessary to deal with when building a standard extension.

Extension Purpose

It's easy to choose more affordable options if you need to, with the amount of choice that you have available.

The purpose of an extension is also important to consider. This is because you will need to consider factors such as wiring and plumbing, windows and ventilation, as well as other elements of your build. 

If you want to build a bathroom extension or a kitchen extension. You will need to take these things into account, more than if you wanted to add an extra bedroom to your home.

The fixtures and fittings that you choose for bathrooms and kitchens will play a large role in how much it costs, which gives you plenty of control over your budget. It's easy to choose more affordable options if you need to, with the amount of choice that you have available.

When you need to install plumbing, you need to consider the additional time that will be required and the planning aspect of it too. While some plumbing elements could be installed with DIY, paying for professional help is definitely worth it if you want to ensure good quality. 

You could be adding around £5,000 to the cost of your extension for a bathroom and around £10,000 for a kitchen.

Key Factors Affecting Cost

Anyone who has seen an episode of Grand Designs knows that it's not exactly easy to just decide to take control of these things yourself

As well as the type of extension, there are other factors that will affect the cost of your project. As you're sure to aware if you live in London or the surrounding counties. You're likely to be paying more for any work that you want to be carried out on your home. It's something that can be difficult to get around, although getting quotes from different places can help you to keep your costs down.

Renovating a staircase is always the most inexpensive option for the home as changing out the balustrading or replacing treads and risers is a good solution. DIY renovation kits can be as cheap as £250 to £300, but this is for a basic kit. If you choose to use glass or heavy metals as your material, the cost will soon climb.

The size of your extension is, of course, going to affect how much you will pay too. It's important to consider how much space you have available. Whether you will need to clear any space (for example, by removing trees), and whether you want to use all of the space that you might have. Think about what you're looking for from your extension and how big you really need it to be.

While some factors that affect the cost of your extension are obvious, others might not be. For example, the soil type you're dealing with will affect the installation of new foundations. The soil type can influence the choice of a foundation system, which will affect just how much it will cost to get the extension of your construction started.

Something else to consider is glazing. If you want to install a conservatory or perhaps have floor-to-ceiling windows on one wall, this will affect the total cost of your extension. You need to consider the type of glazing and the quality too.

Of course, how you choose to build your extension will also make a difference. You can find various ways to save money, from DIY construction to managing the project yourself. Anyone who has seen an episode of Grand Designs knows that it's not exactly easy to just decide to take control of these things yourself. 

Unless you have any particular expertise or you're capable of dedicating yourself to learning something new very quickly. It's often much more cost-effective to leave things to the professionals who know what they're doing.

Expenses Breakdown

Having an understanding of all of the costs that go into building an extension will help you to budget and get a grip on the numbers. In addition to the cost of construction, you will have planning fees, the cost of hiring an architect, other professional fees, insurance and VAT.

Construction Costs

Construction costs include a range of different elements that make up your extension. Some of the expenses are:

  • Commencement

  • Foundations

  • Oversite and slabbing

  • Brickwork shell

  • Roof structure

  • Roof covering

  • Internal preparing

  • Electrics and plumbing

In addition to the expenses for getting the main structure in place. There can then be plenty to do to create the interiors. From plastering to decorating, it's important to think about the whole space and what it will take to make it completely liveable.

Planning Fees

If your extension falls within the rules, you will only need to pay £103 for a lawful development certificate

Not many of your expenses are fixed when you build an extension. But there is a standard planning fee so you know exactly how much you will have to pay. The standard fee is £206 to alter or add to one existing property. 

You might pay even less if you don't need planning permission. Which you might not if your extension is within your permitted development rights.

This might apply if you're building a conservatory or single-storey extension to the side or rear of your house that meets other conditions. Such as being within a certain size and using similar building materials as the rest of the house.

If your extension falls within the rules, you will only need to pay £103 for a lawful development certificate. It's not essential to have one, but it can help to prevent problems and will be useful if you ever decide to sell your property.

Small extension being built onto a bungalowSmall extension being built onto a bungalowSmall extension being built onto a bungalowSmall extension being built onto a bungalow

Even small extensions add valuable floor space to the smallest of homes

Architect

An architect is essential if you want someone to help you realise your idea for an extension. You might have some thoughts about what you want it to look like. But it's an architect who can design something, create technical drawings and show you digital images of what it could really look like when it's built. 

You can find different rates for architects that can be affected by various things. It's worth looking at some architects that you like the look of. Checking if they have any packages and getting some quotes from several places to see how much you could be paying. 

You can discover some architects who specialise in designing extensions or you might choose based on design style, location or other factors.

Other Professional Fees

Your architect might not be the only expert you need to consult when planning and constructing your extension. Not everyone will need to consult with additional services, but you might need the help of someone like a structural engineer, who can assess the foundations of your property. 

Your architect can often help you if they think you might need help from other services. They can refer you to the professionals that you need and perhaps make recommendations based on your budget.

VAT

Don't forget about 20% VAT when you're calculating the cost of your extension

Don't forget about 20% VAT when you're calculating the cost of your extension. Most home extensions will be subject to VAT on labour and materials. You might not have to pay VAT for labour if you use a contractor who isn't VAT registered, but you will still need to pay it on materials. 

Sometimes, your extension project could be eligible for VAT relief. Such as if you are adding an extension to a property that has been empty for more than two years. However, most homeowners will find that they do have to pay the tax.

Insurance

A new insurance policy might be necessary while you're carrying out the construction of your extension. Before beginning construction, check with your home insurance provider to see if they will cover you while construction is ongoing. 

Some insurance providers won't, so you will need to take out a separate insurance policy to protect you while your extension is being built.

It shouldn't cost too much to take out insurance if you need it. And it could save you a lot of money if anything does happen and you need your insurance provider to step in. It's better to be safe than sorry.

Creating a Budget

Creating a budget for your extension will help you to avoid overspending. And have a clear idea of how much you want to spend on different elements of building your extension. Start by considering the type of extension you want to build and the average prices to get a ballpark figure for how much it will cost to build. 

You can then add on the additional expenses, such as your architect and any fees. The cost of materials and contractors will make up a large part of your budget, with VAT accounting for a further 20%.

When you create a budget, you can itemise where your money is going and prioritise based on what's most important. If you want to save money, you can find plenty of ways to do it while ensuring you still get a great quality extension. 

You might decide to take the DIY route for some things, keep a low budget for your interiors. Or make other choices to focus your budget in the most important places.

Collect quotes and estimates from contractors and professional services so that you have a good idea of the local market. And what you could be expected to pay for some of the important elements of your extension.

Construction process of extending your homeConstruction process of extending your homeConstruction process of extending your homeConstruction process of extending your home

Break your properties current mould and extend out into new space

Planning Your Extension

If you are planning on building or digging foundations within 3m of the property boundary, party wall or party wall structure. You need to make sure that the work complies with the Party Wall Act

When you're planning an extension, you should first consider some things before going ahead with your project. For example, if you are planning on building or digging foundations within 3m of the property boundary, party wall or party wall structure. You need to make sure that the work complies with the Party Wall Act. 

Practical issues, such as how contractors are going to have access to the site while they're working are essential to consider. It's also a good idea to think about issues such as whether your boiler will be able to handle heating. And other hot water demands from the new space.

Paying For Your Extension

When you're budgeting for your extension, it's also smart to think about how you're going to pay for it. Perhaps you have already made up your mind about how you're funding it, but if not, you can consider a few different options. Some people might be lucky enough to have savings that would cover the cost of an extension.

Other options include using a credit card, taking out a personal loan or using your home for a secured loan or to remortgage. It's important to consider affordability and how much money you need if you're thinking about borrowing money. 

Completing a monthly budget factoring in your expected repayments will help you to work out whether you will be able to afford to repay anything that you borrow.

Finding The Right Architect And Contractors

Remember that choosing the cheapest builder isn't always the best way to go. It's worth paying a little more if it means you're going to get better results and service.

Finding the right people to design and build your extension for you is obviously extremely important. You need to consider the cost, but you also need to choose people who understand what you want and can deliver the extension you've been dreaming of.

When you're looking for an architect or designer, the first thing you will probably want to do is take a look at some examples of their previous work. Being able to view their portfolio of past projects to see if they can offer something you would like is essential. And most architects will have one on their website. 

Speaking to past clients can be useful too. Take a look at what services architects offer and their process for designing your extension.

Choosing a good builder means finding someone who can complete your project efficiently. You should be able to get along with them because you're going to be seeing them a lot while your extension is being built. References and recommendations can help you to find someone reliable and affordable. 

Remember that choosing the cheapest builder isn't always the best way to go. It's worth paying a little more if it means you're going to get better results and service.

Building Your Extension

If you want to add to your home, try to create a budget before you get started with your project to plan how much you want to spend.

You have a number of options for building your extension, depending on how much help you want. It's possible to take at least a partial DIY approach, whether that means doing some of the labour yourself or managing the project yourself.

You can DIY around a third of the work while getting help for anything that you're not capable of doing yourself. This means sourcing the materials that you need directly. Which can give you more control but might mean you can't get the good deals a contractor might be able to secure for you.

If you manage the project yourself, you can hire individual tradespeople and purchase the materials that you need yourself. You won't have to do much DIY and you can save money, but need to dedicate more of your time to managing the build.

If you use a contractor, you have two options. The contractor can handle everything for you so that you don't have to get involved to a particularly high level. Or the main contractor could complete the work to a weathertight stage, with subcontractors completing the rest.

The cost of your extension is affected by a wide range of factors. If you want to add to your home, try to create a budget before you get started with your project to plan how much you want to spend.