House Extension Cost

How Much Does A House Extension Cost in 2024?

Let's get straight to the point:

The average house extension cost is between £22,500 – £125,000.

This is quite a large price range, as the cost of an extension is dependent on the type of extension you choose to get, how much liveable space it adds, and the quality of the finish.

So let's break this down with some house extension cost examples:

Those based in the London area can expect higher labour costs, which impact the cost of extensions per m².

For instance, a single-storey extension would cost around £22,500 – £125,000. This type of extension is normally used for small additions, such as a bathroom or adding more space to a kitchen or living room.

Now, that's still a huge price range, so let's break it down a bit more.

A small single-storey extension (15m²) has an average price range of £22,500 – £37,500, with the range mainly being affected by the quality of the finish and your location in the UK.

On the other hand, a large single-storey extension (50m²) can cost anywhere from £75,000 – £125,000.

The type of room that you are building and the finish can greatly impact the overall cost of your extension. Making your kitchen bigger or adding a new bathroom will lead to higher house extension costs.

What about the cost of a double storey extension?

Double storey extensions add extra liveable space over two floors — helping you to expand the space in both the downstairs and upstairs of your home. The cost of a double extension ranges from about £45,000 – £245,000.

Nailing down a specific price range for home extensions is challenging.

But stick with us: The rest of this guide will make everything a lot clearer and help you narrow down what you should budget for.

If you're looking to get a more accurate price for a house extension of any type, we can help connect you with builders near you.

House Extension Prices

So, how much does an extension cost in the UK?

House extension costs vary significantly depending on the type of extension you get, the size of the extension, and the quality of the finish.

Let's break it down a little.

Single-Storey Extension Cost

A single-storey extension is a popular house extension and is normally used to enhance the space of a kitchen or living room on the first floor of a property.

The cost of single-storey extension installation is around £1,500 – £2,500 per m².

The table below sets out the single-storey extension cost for different sizes of basic, average, and premium quality builds.

Double Storey Extension Cost

A double storey extension is built across two floors of a property. It allows you to significantly increase the liveable space available in your home with the addition of multiple rooms.

The average double storey extension costs between £1,500 – £2,450 per m².

The following table lays out the costs for different sizes of double-storey extensions with varying quality finishes.

Rear Extension Cost

A rear extension is installed at the back of a property where there is a large garden area.

The cost of a rear extension is around £1500 – £2500 per m².

The table below sets out the prices for different-sized basic, average, and premium rear extensions.

Side Extension Cost

Side extensions are a popular choice for properties with a lot of space on the left or right-hand side of the home.

Typically, side extensions cost around £2,000 – £4,000 per m².

The following table shows the different-sized buildings for basic, average, and premium side extensions.

Side-return Extension Cost

Properties with a small amount of space at the side of their home, which might be currently used to store bins and bikes, may benefit from a side return extension.

The price of a side-return extension is around £2,000 – £4,000 per m².

The table below sets out the different costs of basic, average, and premium side-return extensions.

Kitchen Extension Cost

Want to have a larger kitchen in your home?

Your best option might be to have a kitchen extension.

Kitchen extension costs are about the same as a single-storey extension, at around £1,500 – £2,500 per square metre.

However, you should add an extra £200 – £1,000 per m² to account for the cost of a new kitchen.

The table below sets out the costs for small, medium, and large kitchen extensions for various budgets.

Bathroom Extension Cost

A bathroom extension is ideal if you only have one bathroom in your property or you want to have a bigger bathroom.

The cost of house extension installation with a bathroom is based on single-storey extension prices. This means that it costs about £1,500 – £2,500 per m².

You also need to consider new bathroom installation costs, which are around £300 – £3,000 per m².

The following table outlines the costs of installing different-sized bathroom extensions with varying qualities.

Porch Extension Cost

A porch extension is a great way to enhance the entrance of your home.

Not only can they boost the aesthetic appeal of your property, but they also provide you with extra liveable space (that's especially useful for storage) and can boost the energy efficiency of your home.

The average porch extension costs between £300 – £2,000 per m².

The following table highlights the prices for uPVC, wood, aluminium, and brick porch extensions.

Prefab Extension Cost

On a tight budget?

If you don't have a huge budget, then a prefab extension may be your best option - as it will save on labour costs due to it being prefabricated before installation.

The average cost of a prefab extension is around £1200 – £1700 per m².

The below table sets out the costs for basic, average and premium prefab extensions.

Wrap-around Extension Cost

A wraparound extension is one of the largest extension types, which is normally attached to the rear and side of the home.

The average cost of a wrap-around extension is £2,000 – £4,000 per m².

The table below shows the prices of different-sized wraparound extensions on a basic, average, and premium budget.

What Additional House Extension Costs Should I Budget For?

What other costs might you need to consider when building an extension?

Let's tackle that now.

Extension Architect Costs

You may want to consider hiring an architect to design and plan your new extension, while also making sure that it meets building regulations.

The cost to hire an architect is around £50 – £100 per hour.

Extensive Extension Groundwork Costs

Before building an extension, it is important that the ground is fully prepared.

This will ensure that the extension is installed on a robust foundation, while also preventing issues in the future.

If the existing ground is not level, then it may need to be excavated. This can cost around £30 – £50 per cubic metre.

Another extensive type of groundwork is installing drainage. This may involve removing old pipes and installing new pipework and drains to ensure that your new extension has proper drainage.

The cost to install new drainage is between £550 – £1,800.

Extension Planning Permission Costs

Before building an extension, it is important that your plans align with planning permission regulations. This will help you avoid paying around £200 for an application.

To avoid incurring extra costs, you'll need to make sure that your extension meets the following criteria:

• The extension must not cover over half the property’s land.
• It must not exceed the highest point of the roof on the existing property.
• Extensions within two metres of the property’s edge should not have eaves that exceed a height of three metres.
• The work must not include installing raised platforms, balconies, chimney flues, vent pipes or any work to the roof (including cladding).
• Side extensions must be single-storey and cannot exceed four metres in height from the side elevation.
• Extensions on the side of a property must not exceed more than half the width of the building.
• Single-storey rear extensions must not extend more than four metres beyond the rear wall of a detached property or three metres for any other.
• Double-storey extensions must not extend over four metres from the back wall of the property and must not be within seven metres of a property boundary.
• The roof pitch of a double-storey extension must match the existing house as closely as possible.
• All windows on the top floor of a double-storey extension must be obscure-glazed if located on a side elevation.

Extension Building Regulation Costs

The majority of house extensions do require building regulations approval before they can be constructed.

And what's this cost?

The cost of building regulations approval will vary depending on your local council, as all local authorities charge different amounts for building regulations approval.

There are various elements of an extension that must be signed off by a professional in order to deem the property safe.

This includes:

• Internal and external walls

Some extensions require external walls to be built below ground level to ensure the superstructure (the extension) is supported properly.

The new walls that are built will make up the substructure, which normally includes blocks and mortar or brick. To ensure that the whole structure is protected, it is vital that the substructure is resistant to frost and substrates found in the ground.

• Flooring

To ensure that the flooring installed in your extension meets building regulations, it is important that it has a sound structure to support a significant amount of weight.

It should also be heat and moisture-resistant to insulate, ventilate, and protect the extension flooring from damp, weed growth, and contraction.

• Ventilation

One of the most important elements you need to consider when installing a new extension is ventilation. This will improve the air quality in your home and promote better health.

To ventilate your property, you could simply install windows - especially in rooms with poor ventilation such as a bathroom. You can also install trickle ventilation in all the rooms of your home by applying it to window frames.

• Foundations

Before building an extension, it is important that there are robust foundations in place (which are normally made up of concrete).

The soil used should be able to hold the weight of the foundations and extension structure. It should also be dug deep enough to ensure that movement and contraction do not affect the extension. This is especially important for a double-storey extension, as more soil and foundations are required to support a larger extension.

What are the Supply Costs of an Extension?

Planning a DIY extension? Or do you just want to buy the supplies yourself?

In this case, you'll need to consider the following supply costs:

Tradesmen Costs for an Extension

Here's another important thing.

When calculating the final cost of your house extension, you'll need to consider the labour costs charged by all the different tradespeople who will be working on your house extension.

Let's go through them now.

Extension Builder Cost

Builders have one of the most important jobs when constructing an extension.

They're involved in building the foundations and the actual structure of the extension to ensure it is robust and stable.

The average cost to hire a builder for your house extension is around £130 – £280 per day or £16 – £46 per hour.

Extension Plumber Cost

If building a kitchen or bathroom extension, you will need to hire a qualified plumber to install sinks, toilets, appliances, and more.

Plumbers cost around £200 – £400 per day for full bathroom installations or £30 – £60 an hour to plumb a sink.

Extension Electrician Cost

To get your extension fitted with lighting and electrical appliances, you will first need to hire a professional electrician to ensure everything is compliant and working properly.

The average hourly rate for an electrician is typically around £30 – £60 per hour or £170 – £340 a day.

Extension Plasterer Cost

To prepare your walls and ensure any paint or wallpaper lasts, you will need to hire an expert.

You should expect to pay £150 – £220 per day for a tradesman to plaster your new extension. They may only charge an hourly fee between £10 – £20 to re-plaster walls.

Extension Painter and Decorator Cost

Once the plastering is complete, you will need to bring in a decorator to paint or wallpaper the internal and external walls of your new house extension.

The average tradesperson will charge around £15 – £40 per hour to paint one or more walls.

For multiple rooms, you should expect to pay £100 – £300 a day.

Extension Carpenter Cost

If you're installing a new extension, you should hire a professional carpenter to help with the construction and installation of the new extension.

On average, a carpenter costs around £150 – £250 per day.

You may also want to hire them for smaller jobs - such as fitting a new door frame. In this case, they'll usually charge you an hourly rate of £20 – £40 an hour.

Extension Kitchen Fitter Cost

For a new kitchen extension, you should consider employing a kitchen fitter - who will install your kitchen cabinets and worktops.

For a small kitchen, you should expect to pay an hourly fee of £10 – £20, while a kitchen fitter charges between £120 – £200 per day for a large kitchen.

Extension Window Fitter Cost

Once your extension is built, you should hire a professional window fitter to install fully insulated windows.

For one or two windows, you should expect to pay around £25 – £35 an hour.

For a full set of windows on a double-storey extension, you'll likely be charged between £250 – £350 per day.

Extension Labourer Cost

Another important tradesperson you may need to hire is a labourer - who will assist with the majority of jobs onsite — including building foundations, the extension structure, and more.

The average day rate for a labourer is £100 – £160 a day or £7 – £15 per hour.

Extension Bricklayer Cost

To ensure your extension is built properly, you will need to hire experienced bricklayers who know what they're doing.

Typically, bricklayers charge around £130 – £180 a day for a large extension or £12 – £20 per hour for a porch extension.

How Long Does It Take to Build an Extension?

Building an extension can be quite time-consuming.

Because of this, it's important that you understand the timeframes involved in building the type of extension you want.

Here's a quick breakdown:

How Much Does Each Stage of an Extension Cost?

There are various stages involved in building an extension

Each of these stages has individual costs that you need to know about (and budget for).

Let's dive into them now.

Building Regulations & Design

So, what's first?

You'll need to start by ensuring that your extension design is compliant with current building regulations and planning permission rules.

But what if your current plans do not adhere to the conditions?

In that case, you will need to change your plans or pay around £200 or more to apply for your extension to be approved.

Once approval is obtained, then you can plan your extension in more detail.

For this, you'll need the help of an architect. Their main job is to draw up plans for the structure, which include the dimensions and the aesthetic of the extension, making sure that they adhere to the regulations.

Typically, an architect costs between £50 – £100 per hour.

Foundations and Groundworks

Before any building can begin, it is important that the ground is fully prepared.

This can be a costly process, as it involves excavation. This can cost from £30 – £50 per cubic metre, with the total cost being dependent on the size of the land you're working on.

You may also have to remove pipework and install new drainage. This will ensure that your extension is protected against flood and damage, while also ensuring water flow is running and connected to the main property (if it needs to be). This work tends to cost between £550 – £1,800.

Once all the groundwork is complete?

Only then can the foundations be set to provide a stable framework for the installation of the extension. Installing foundations is a time-consuming component of the project and will normally cost around £100 – £130 per cubic metre.

Building the Outer Shell

Once everything's prepped and the foundations are in place, what's next?

The next stage involves building the outer frames and walls - using timber, bricks, blocks, and tile materials.

The average price of an extension outer shell is around £800 – £1,600 per square metre for professionals to install a weatherproof extension shell.

Fixtures and Fittings

The last stage is all about the finishing touches.

This will include installing furniture (like kitchen cabinets and worktops), which will cost between £5,000 – £19,000.

For a bathroom extension, you should expect to pay around £900 – £27,000 for brand new bathroom fixtures.

At this stage, your windows and doors will also be installed. This costs around £250 – £1,200 per window, while door installation is typically priced at £50 – £120 per door.

You'll also want to fit indoor and outdoor light fixtures at this point, which normally amounts to £60 – £1,000 if fitted by a professional electrician.

How Much Does an Extension Roof Cost?

An important element of a house extension is the roof.

The cost of a new roof varies depending on the type that you choose to get installed.

Pitched roofs are the most popular type of extension roof, as they have good drainage and tend to blend in well with the aesthetic of most UK properties.

Let's take a look at your different options and their relevant costs now.

Duo-Pitched Extension Roof Cost

A duo-pitch roof (or a gabled roof) is a simple roof design which features two slopes which meet at a ridge.

Duo-pitch extension roofs tend to cost around £2,000 – £4,500.

Flat Extension Roof Cost

A flat roof is a type of roof that is almost completely flat except for a slight slope, which allows for drainage.

For smaller house extensions (like a single storey extension), flat roofs are becoming more popular — as they're affordable but also give a property a bit more of a modern look.

An average flat roof extension costs around £1,500 – £3,000.

Catslide Extension Roof Cost

A catslide roof is a type of pitched roof which slopes downwards further on one side than the other.

The average cost of a catslide roof is from around £1,200 per square metre.

Mono-Pitch Extension Roof Cost

A mono-pitch roof or a lean-to roof is a single-sloped roof. This continues to be one of the most affordable roof solutions.

The installation price for a mono-pitch extension roof is normally between £2,000 – £3,200.

Hipped Extension Roof Cost

A hipped roof has four sloped sides, which all have an equal length and meet at a central ridge.

The cost of a hipped extension roof is typically around £1,250 – £7,250.

How Much Does Removing an Extension Cost?

What about if you want to remove an old extension? How much should that cost you?

To ensure the extension is removed properly, you should consider hiring professionals. This will cost around £500 – £3,000.

On top of this, the cost of waste removal will be between £70 – £300.

FAQs

Q: How close to my boundary can I build an extension?

A: If you're planning to build a double-storey extension, it should be no closer than seven metres from the boundary.

For any other type of extension that is within two metres of the boundary, it cannot exceed more than three metres of the existing property’s eaves.

Q: How much does a house extension add to the value of my home?

A: Adding an extension to your home can result in a return on investment of up to 25% for an additional bedroom and bathroom, while a bathroom extension can add up to 6% to the value of the property.

Q: What size extension can you build under permitted development?

A: If you want to save money on obtaining planning permission and building regulations approval, then you will need to build an extension that doesn't exceed permitted development limits.

If you’re planning to build a single-storey rear extension, then this should not exceed a depth of 3 – 4 metres. Other extensions can extend to 6 metres, and detached properties can even extend their home up to 8 metres.

Q: How deep does footing need to be for a single storey extension?

A: Single storey extension foundations must be at least 200mm deep to ensure that the structure is completely secure and robust.

Sources

1. https://www.gov.uk/guidance/when-is-permission-required
2. https://www.planningportal.co.uk/permission/common-projects/extensions/planning-permission
3. https://www.planningportal.co.uk/permission/responsibilities/other-permissions-you-may-require/does-my-project-require-additional-consents
4. https://www.nationwidehousepriceindex.co.uk/reports/dwd
5. https://www.alanheathandsons.co.uk/bathrooms/long-take-install-bathroom/
6. https://www.jtatkinson.co.uk/blog/a-step-by-step-guide-to-adding-an-extension-onto-your-home/
7. https://www.designingbuildings.co.uk/wiki/Flat_roof

Author: Heather B

I am a seasoned copywriter from Liverpool - who after graduating with a BA (Hons) degree in English Media and Cultural Studies - went on to specialise in the creation of business and lifestyle copy for a wide range of industries across the UK and USA.