How Much Does an Extension Cost?

The average house extension cost is around £15,000 to £125,000. However, these prices may vary depending on the type of extension you choose, as there are various options including single-storey extensions which cost around £21,000 to £100,000.

This type of extension is normally used for small additions such as a bathroom or adding on space to a kitchen or living room. While a double extension which ranges from £42,000 to £200,000 features two floors, that can help you expand the space both downstairs and upstairs.

There are also more specific extensions such as kitchen extensions which range from £10,000 to £60,000 and bathroom extensions for £6000 to £30,000. You can also enhance the front of your home with a porch extension that is typically built around your front door and is typically priced at £1500 to £7000.

The location of your extension will also determine the price, with options such as rear extensions which cost around £15,000 to £80,000 and are located at the back of a property and are normally added to homes with a large garden space.

If you have room at the side of your home, you may want to opt for a side extension for £20,000 to £120,000 or even a side return extension which is usually a small space on the side of your home that can be utilised to expand rooms in your home. A side return extension costs around £9000 to £28,800. For properties with more exterior space, you can choose a wrap-around extension for £40,000 to £180,000 which covers two or more sides of the home.

Another popular option is a prefab extension, which is a pre-constructed building which is built in a factory then shipped and installed quickly by a professional team of tradesmen. This normally costs around £18,000 to £65,000.

House Extension Prices

To help you understand, the costs of adding an extension onto your home, take a look at the following price breakdown for different types of home extensions.

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 £1400 to £2000.

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

Size (m²) Basic Average Premium
Small (15m²) £21,000 £26,000 £30,000
Medium (25m²) £35,000 £43,000 £50,000
Large (50m²) £70,000 £85,000 £100,000

Double-Storey Extension Cost

A double-storey extension is built across two floors of a property, which enables you to increase the space and add on multiple rooms. The cost of an extension with two floors is around £1400 to £2000 per square metre.

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

Size (m²) Basic Average Premium
Small (30m²) £42,000 £51,000 £80,000
Medium (60m²) £84,000 £102,000 £120,000
Large (100m²) £140,000 £170,000 £200,000

Rear Extension Cost

A rear extension is installed at the back of a property where there is a large garden area. The home extension cost is around £1000 to £1600 per square metre.

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

Size (m²) Basic Average Premium
Small (15m²) £15,000 £21,000 £24,000
Medium (25m²) £25,000 £35,000 £40,000
Large (50m²) £50,000 £70,000 £80,000

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. Side extensions tend to cost around £1000 to £2000 per m².

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

Size (m²) Basic Average Premium
Small (20m²) £20,000 £30,000 £40,000
Medium (40m²) £40,000 £60,000 £80,000
Large (60m²) £60,000 £90,000 £120,000

Side-return Extension Cost

Properties with a small amount of space at the side of their home which is used to store bins, bikes and more may benefit from a side return extension. The price of extension per square metre is around £1500 to £2400.

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

Size (m²) Basic Average Premium
Small (6m²) £9000 £12,000 £14,400
Medium (9m²) £13,500 £18,000 £21,600
Large (12m²) £18,000 £24,000 £28,800

Kitchen Extension Cost

If you want to build a larger kitchen in your home, the best option is to add on a kitchen extension which would cost the same as a single-storey extension at £1400 to £2000 per square metre plus £200 to £1000 per m² for the actual kitchen installation itself.

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

Size (m²) Basic Average Premium
Small kitchen extension (6m²) 9,600 £13,800 £18,000
Medium kitchen extension (9m²) 14,400 £20,700 £27,000
Large kitchen extension (18m²) £28,800 £41,400 £54,000
Small kitchen suite (6m²) £1200 £3600 £6000
Medium-sized kitchen suite (9m²) £1800 £5400 £9000
Large kitchen suite (18m²) £3600 £11,800 £18,000

Bathroom Extension Cost

A bathroom extension is ideal if you only have one bathroom in your property or you want a bigger bathroom. The cost of house extension installation with a bathroom is based on single-storey extension prices which range from £1400 to £2000 per m² along with the bathroom installation price which is around £500 to £1000 per square metre.

The following table details the costs of installing different-sized bathroom extensions with varying qualities:

Size (m²) Basic Average Premium
Small bathroom extension (3m²) £5700 £7400 £9000
Medium bathroom extension (6m²) £11,400 £14,700 £18,000
Large bathroom extension (9m²) £17,100 £22,100 £27,000
Small bathroom suite (3m²) £1500 £2300 £3000
Medium-sized bathroom suite (6m²) £3000 £4500 £6000
Large bathroom suite (9m²) £4500 £6800 £9000

Porch Extension Cost

A porch extension is a great way to enhance the entrance of your home. Porch extensions tend to cost around £500 to £800 per m².

The following table displays the prices for uPVC, wood, aluminium and brick porch extensions:

Size (m²) uPVC Wood Aluminium Brick
Small porch extension (3m²) £2400 £1500 £2300 £2300
Medium porch extension (6m²) £4800 £3000 £4500 £4500
Large porch extension (9m²) £7200 £4500 £6800 £6800

Prefab Extension Cost

If you have a low budget in mind, then a prefab extension may be your best option, as it will save on labour costs due to its being prefabricated before installation. The average cost is around £1200 to £1700 per square metre.

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

Size (m²) Basic Average Premium
Small prefab extension (15m²) £18,000 £21,800 £25,500
Medium prefab extension (25m²) £30,000 £36,300 £42,500
Large prefab extension (35m²) £42,000 £50,800 £59,500

Wrap-around Extension Cost

A wrap-around extension is one of the largest extension types which is normally attached to the rear and side of the home. The average cost per square metre is around £2000 to £3000.

The table shows the prices of different-sized wrap-around extensions on a basic, average and premium budgets:

Size (m²) Basic Average Premium
Small wrap-around extension (20m²) £40,000 £50,000 £60,000
Medium wrap-around extension (40m²) £80,000 £100,000 £120,000
Large wrap-around extension (60m²) £120,000 £150,000 £180,000

What are the Additional Costs of An Extension?

The cost of building an extension including the following additional costs:

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 £18 to £30 per hour.

Extensive Extension Groundwork Costs

Before building an extension, it is important that the ground is fully prepared, as 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 to £50 per cubic metre.

Another extensive type of groundwork is installing drainage where necessary. 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 around £700 to £1000 or more.

Extension Planning Permission Costs

Before building an extension, it is important that your plans align with planning permission regulations to avoid paying around £200 for an application. To avoid incurring extra costs, you need to make sure that your extension meets the following criteria:

  • The extension must not cover over half the property’s land.
  • They 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 home.
  • 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. 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 which are 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 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 is normally made up of concrete. The soil used should also 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 does 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?

If you are planning a DIY extension or wish to purchase the supplies yourself, then you will need to consider the following supply costs:

Supply description Average supply cost
Skirting Board £2 to £8 per m²
Plasterboard £3 to £16 per m²
Wood Flooring £35 to £90 per m²
Laminate Flooring £7 to £26 per m²
Wall Tiles £9 to £45 per m²
Floor Tiles £12 to £50 per m²
Paint £3 to £20 per litre
Plug Socket £2 to £120 per socket
Light Switches £1 to £200 per switch
Radiators £14 to £400
Underfloor Heating £60 to £100 per m²
Internal Doors £70 to £500
External Doors £35 to £900
Windows £100 to £320
Door Handles £3 to £220
Light Fittings £2 to £80 per light

Tradesmen Costs an Extension

When calculating the final cost of your house extension you will also need to consider the labour costs of the different tradesmen who will be working on the new extension, including

Extension Builder Cost

Builders have one of the most important jobs when constructing an extension, as they are 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 to £260 per day or £10 to £15 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 tend to charge around £200 to £400 per day for full bathroom installations or £30 to £60 an hour to plumb a sink.

Extension Electrician Cost

To ensure your extension is fitted out with lighting and electrical appliances, you will need to hire a professional electrician to ensure everything is compliant and working properly. The average hourly for an electrician is typically around £30 to £60 per hour or £170 to £340 a day.

Extension Plasterer Cost

To prepare your walls and ensure any paint or wallpaper lasts, you will need to hire an expert plasterer. You should expect to pay £150 to £220 per day for a tradesman to plaster your new extension. They may only charge an hourly fee between £10 and £20 to re-plaster walls.

Extension Painter and Decorator Cost

Once the plastering is complete, you will need to bring in a painter and decorator to paint or wallpaper your internal and external walls. The average tradesman will charge around £15 to £40 per hour to paint one or more walls. For multiple rooms, you should expect to pay £100 to £300 a day.

Extension Carpenter Cost

If installing a new extension, you should hire a professional carpenter to help with the construction and installation of the new extension. For a full day’s work, you should expect to pay around £160 to £240 per day. You may also want to hire them for smaller jobs such as fitting a new door frame, which is normally priced at £20 to £40 an hour.

Extension Kitchen Fitter Cost

For a new kitchen extension, you should consider employing a kitchen fitter who will be able to install your kitchen cabinets and worktops. For a small kitchen, you should expect to pay an hourly fee of £10 to £20, while a large kitchen may be subject to a day rate of between£120 to £200.

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 £8 to £20 an hour, or £100 to £200 per day for a full set of windows on a double-storey extension.

Extension Labourer Cost

Another important tradesman 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 to £160 a day or £7 to £15 per hour.

Extension Bricklayer Cost

To ensure your extension is built properly, you will need to hire an experienced bricklayer who knows what they are doing. Bricklayers tend to charge around £130 to £180 a day for a large extension or £12 to £20 per hour for a porch extension.

How Long Does It Take to Build an Extension?

Building an extension can be quite time-consuming, so it is important that you understand the timeframe of the type of extension you choose. To help you choose the right extension, here is a breakdown of the different durations for each extension type.

Extension type Duration
Single-storey extension 2 to 3 months
Double-storey extension 4 to 6 months
Side extension 2 to 3 months
Side return extension 1 to 2 months
Rear extension 2 to 4 months
Wrap-around extension 4 to 6 months
Kitchen extension 2 to 6 months
Bathroom extension 2 to 4 months
Prefab extension 8 to 10 weeks
Porch extension 3 to 14 days

How Much Does Each Stage of an Extension Cost?

There are various stages involved in building an extension, which all have their own individual costs that you need to consider.

Building Regulations & Design

The first step involved when building in extension is ensuring that your extension design is compliant with current building regulation and planning permission. If your current plans do not adhere to the conditions, then 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 with the help of an architect who will charge around £18 to £30 per hour. Their main job is to draw up plans for the structure which include the dimensions and the aesthetic of the extension, making sure they adhere to the regulations.

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 may involve excavation which can range from £30 to £50 per cubic metre, so the overall preparation will depend on the size of the land you are working on.

You may also have to remove pipework and install new drainage which tends to around £700 to £10,000. This will ensure that your extension is protected against flood and damage, while also ensuring water flow is running and is connected to the main property if need be.

Once all the groundwork is complete, the foundations can then be set to provide a stable framework for the installation of the extension. Installing foundations can be time consuming and normally cost around £100 to £130 per cubic metre.

Building the Outer Shell

Once everything Is prepped and the foundations are in place, the outer frame and walls which can be built using timber, brick, block and tile materials. The average price of an extension outer shell is around £800 to £900 per square metre for professionals to install a weatherproof extension shell.

Fixtures and Fittings

The finishing touches of the extension include installing furniture, such as kitchen cabinets and worktops which will cost around £1000 to £7000. For a bathroom extension, you should expect to pay around £1400 to £6000 for brand new bathroom fixtures.

At this stage, your windows and doors will also be installed, which costs around £400 to £600 per window, while door installation is typically priced at £40 to £90 per door. It also includes fitting indoor and outdoor light fixtures, which normally amounts to £60 to £1000, if fitted by a professional electrician.

How Much Does an Extension Roof Cost?

One of the most important elements of a house extension is the roof. There are various roof types to choose from including:

Duo-pitched Extension Roof

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 £3000 to £4500.

Flat Extension Roof

A flat roof is type of roof that is almost completely flat except for a slight slope which allows for drainage. A flat extension's roof typically cost around £1200 to £2000.

Catslide Extension Roof

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 around £1000 to £1500 per square metre.

Mono-pitch Extension Roof

A mono-pitch roof or a lean-to roof is a single-sloped roof that is one of the most affordable roof solutions. The installation price for a mono-pitch extension roof is normally around £2000 to £3200.

Hipped Extension Roof

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 £4000 to £4500.

Cost of Removing an Extension

If you’ve moved into a new property with an existing extension you may want to have it removed if you want more garden space, or the extension is old and damaged. To ensure the extension is removed properly, you should consider hiring professionals, which will cost around £500 to £3000 to demolish, along with the waste removal which is typically priced at £70 to £300.

FAQs

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

A: If building a double-storey extension, it should be built no closer than seven metres from the boundary. For any other type of extension that is within two metres of the boundary cannot exceed more than three metres of the existing property’s eaves.

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

A: Adding an extension onto your home can result in a return of investment up 23% for an additional bedroom and en-suite, 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 meets permitted development. If you’re planning to build a single-storey rear extension, then this should not exceed a depth of 3 to 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.realhomes.com/advice/side-return-extensions-planning-designing-and-budgeting-tips/
  2. https://www.self-build.co.uk/extension-cost-guide/
  3. https://www.houseup.co.uk/news/double-storey-extension-guide/
  4. https://www.realhomes.com/advice/single-storey-extensions-costing-planning-and-designing-your-single-storey-extension
  5. https://architectureforlondon.com/news/permitted-development-for-house-extensions/
  6. https://www.designingbuildings.co.uk/wiki/Flat_roof
  7. https://www.thespruce.com/how-long-to-remodel-small-bathroom-1821360/
  8. https://divinedesignbuild.com/blog/how-long-it-takes-for-a-new-kitchen-build/
  9. https://architectureforlondon.com/news/basement-extension-costs-in-london/
  10. https://resi.co.uk/advice/cost-and-planning/how-much-do-architects-charge/
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.