House Extension Cost

Trying to find out how much a house extension costs?

In this guide, we breakdown extension prices for all the different types, including rear, lean-to, side, side return, wrap-around, porches, garages and even conservatories.

To give you an idea, the average extension cost is typically anywhere around £40,000.

Whether you're after a single or double storey extension, finding out how much it will cost has never been easier.

By providing the cost of an extension per square metre we've made it simple for any homeowner to calculate how much their extension will cost them.

Are you in need of a quote?

Then look no further! We have a wide range of local builders ready to offer you a free quote!

For all cost information, carry on reading below...

How Much Is An Extension?

When it comes to building an extension to the final cost will depend on a wide range of choices you make. The most important of those choices is the size and type of extension you choose to build. This is then followed by the level of finish you want.

For a basic finish, with just the bare essentials built, you are looking at costs of £900 - £1.700 per m². To upgrade to a high-quality finish, with top range and bespoke choices throughout the cost will be in the range of £1,750 - £2,200 per m².

You can lower your cost per meter square by building over more floors. The more floors you build, the cheaper the extra space is per m². This is because a large percentage of the costs go towards building the foundations for the new space.

The average cost of an extension is around £40,000.

House Extension Prices

The major cost factors that will affect the price of your house extension are the type of extension you choose, how big the extension will be, and the quality of the finish.

Type of Extension

The type of extension you chose will come with different costs to construct. To allow you to make a comparison, the following is the cost per m2 for different types of extension assuming a good quality finish throughout.

Quality of Finish

The quality of the finish will have a large impact on the final price per square meter of your home. These show you the variation based on a single storey extension

Labour Costs and Timescales

The total costs for labour will vary a great deal depending on the exact nature of the work that you have completed. The following is a rough idea of costs and timescale.

Timescale and Labour Cost Based on Type of Extension

Cost Per Hour of Different Tradesmen

Supply Only Costs

In most cases, it is best to let your tradespeople source the majority of the materials for a project like an extension. If there are any problems and items, need to be returned, it is much easier for a tradesperson to do so than for a member of the public.

However, to help you get a feel for the costs involved here are the costs of the materials you would need to fit out your extension once it is built.

Flooring Costs

Heating Costs

Window Costs

Door Costs

Kitchen Costs

Bathroom Costs

Tile Costs

Lighting Costs

Kitchen Appliances

Additional Costs

When you are drawing up the budget for your project, there are a lot of costs you need to keep in mind. Some of the most common additional costs are listed here.

Exterior House Painting

If you home has a painted exterior already then you should consider getting the whole house painted as part of your building work. Otherwise, you will end up with parts of your home being a different colour. The average cost to paint the exterior of a home is £850.

Garden Waste

When you clear space for your new extension, this may generate a lot of garden waste. You will need to dispose of this garden waste. The average cost for this is £150.

House Rewire

When you get an extension built, your whole house will be inspected to make sure it meets building regulations. In some older homes, this can mean that the wiring and electrics need some updating. The lowest cost case is when you just need to replace the consumer box. This costs on average £500. If there are problems with the wiring, then it can cost £4,000 on average to rewire a home.

New Boiler

You should check if your current boiler will be able to support the additional load your extension will add. It might be necessary to get a new boiler while you are having work done. The average cost is £1,500 - £2,500. This includes supply and installation costs.

Removing Drains

The location of your drain may cause a problem when you build your extension. If you are not sure of their location and state, it can be worth getting a drain survey completed. The cost of a survey is around £250. If it identifies a need to move a drain this will add £200 -£1,300 to your total build costs.

Underfloor Heating

Underfloor heating is an energy-efficient way to heat your home. When you build an extension is provides an excellent opportunity to lay the pipework. The average cost to lay new underfloor heating during building work is £800.

Site Survey

A site survey can be a good place to start with a large project like this. It will alert you to any possible problems that might arise down the line. If you know about issues early on, you can plan for them. Reacting when they are found can be a costly policy. A site survey should cost £600 - £1,400.

Insurance

If you move out while the building work is done, you will need to get additional insurance for your home. You need to get a bundle that includes public liability insurance, employer’s liability insurance and construction. A reasonable price for this is £500 - £800.

Skip Hire

A skip is a necessary part of having building work done on your home. This is especially true during an extension. This is because there is a lot of rubble created when the walls are broken through. Skip hire may not be included in your contractor's quote. In which case you should add £250 - £450 to your budget.

Kitchen Added

Adding a new kitchen to your extension will have a big impact on your costs. The quality and type of appliances you choose can add an extra £3,000 - £10,000.

Bathroom Added

Adding a new bathroom will increase the cost of your extension. It will add between £2,000 – £6,000 to your final price.

Adding a Toilet

Adding a toilet with a single basin is a cheap way to increase the number of bathrooms in your home. The average cost for a basic bathroom is £100 - £200.

Adding a Utility room

Utility rooms are very hand in a home with many occupants. To add one into your extension costs on average £3,500 - £7,000 this includes the costs for the extra plumbing, a sink and the appliances.

Planning Permission

If you need to apply for planning permission, you need to include £206 to your budget for the application.

Building Regulations

The costs for building regulations will vary depending on your local council. You will need to pay to submit the paperwork and for site inspections. The paperwork costs are usually around £100. The costs for site visits usually come out at £200 - £400.

Architect Fees

An architect is usually not necessary. However, despite there being a cost for one, most homeowners who use an architect find that their final costs are lower. This Is because there are fewer changes made during the process. A full set of plans also reduced the opportunities for miscommunication.

An architect will usually charge 7 – 15% of the cost of the work. If you simply require planning drawing this will cost £2,500 - £3,000.

Structural Engineer

To be structurally sound, it may be necessary to have a steel beam embedded into the wall. To calculate the size of the beam, you will need a structural engineer.

They will charge you based on the complexity of the work you need completing. You can expect to pay £400 - £4,000.

Cost Factors of Building a House Extension

Building an extension is a big project. There are a lot of different factors that can influence how much your extension will cost.

Type of Extension

The type of extension you chose impacts the cost of the extension because it decides how big the job will be. It is the combination of a few other factors. Such as if you are having a kitchen and how much floor space you will be creating.

Size of Extension

The more floor space that will be created when you build your extension, the higher the costs will be. However, it is important to be aware that the cost per square meter drops, the more floors you have.

So, to get the same floor space, it is more cost-effective to get a double storey extension or even a double storey extension with a loft space conversion.

Quality of Extension

The quality of the finish will have a huge impact on your final costs. Your cheapest option is to go with a basic finish. This means only getting the bare essentials, nothing fancy.

A mid-range finish would include a few bespoke items or high-end finishes. If you decide to push the boat out and get everything top of the line and ultra-modern, then you can end up paying 2 to 3 time the total cost of a basic finish.

Location of Property

If you live in the London area, you will find that you are likely going to be paying a premium. You may also find your costs are higher if you live in a remote or hard to access location.

What's Involved in Building a House Extension?

Regardless of the type of extension, you will be getting there is an order in which the work will be completed. The size of the job often only changes how long each step will take.

Planning

Possibly the most important stage is planning your project. This may involve getting an architect to make a drawing. If you need planning permission, you need to apply for it in good time before you expect to begin work.

Once all the plans have been approved, and the contractor lined up, it is time to prepare the site. This may involve clearing the space for the extension. Materials for the building work will be delivered to the site in preparation for the work. A skip may also be placed on-site during this time

Groundworks

The foundations will be dug. And reinforcements will be installed. Any pipework and drainage will be laid or moved as needed. Then the concrete footing will be poured and levelled. There will be at least one building control visit, possibly two during this process.

Superstructure

This is all about making sure that the structure will be sound and resistant to damp. The brickwork will be completed up to the level of the damp proof course. Concrete lintels will be installed as needed.

The builders will fit the insulation at this point as well. The flooring will then be poured. There will be another building control inspection during this stage of work.

External Walls

The external block and brickwork will be completed next. This includes tying the new walls to the old ones. The lintels and frames for the doors and windows will be fitted as the brickwork goes up. The cavity wall insulation will also be fitted before the walls are finished.

Internal Walls

All of the internal walls and divisions will be built next.

Roof structure

The carpenters will build the structure to support the roof. If there are to be any roof windows or dormers, these will be framed during this process.

Roof Covering

The coverings for the roof are installed. The battens and membrane go on first. The roof tile is laid next. Once the main tiles are on the roof, the valley and ridge tiles, along with the flashing, are fitted. The fascias, soffits and verges are completed as the last step.

Windows and Doors

Any external rendering will be completed at the same time as the windows and doors are fitted. Guttering and drainpipes will also be completed during this time.

First Fix

Once the extension is weatherproof, the first fix will happen. This is the carpentry, plumbing and electrics that underpins the extension.

Breaking Through

The dirtiest part of the project is next. The wall between the extension and the rest of the house will come down. If any steel girders need to be installed, this is when they will go in. In this case, there will be another building control inspection.

Plastering

The internal insulation will go in. Then the plasterboard will go up. The walls will then be skimmed ready for decorating.

Second Fix

The second fix of plumbing and electrics will go in. This means that the sockets and switches go in, as well as the lights. Any taps and plumbing connections will also be completed. Flooring will be laid. Once this is done, any kitchen work will be fitted. There will usually be a final building control inspection during or after this stage in the project.

Snagging

Once the work is done, you will need to spend some time in the extension to find any problems that may need to be addressed. This might be leaks, ill hanging doors or heating problems.

Can I Build a House Extension Myself?

Even for the most experienced DIYer, a house extension is not a DIY job. There are aspects of the job that should only be undertaken by qualified professionals. One example of this is the electrics.

All electrics in the extension must meet building regulations. This means that the work should be carried out by a Part P qualified electrician.

If you want to keep your budget for the project low by completing some of the work, yourself there are parts of the job that can be DIYed. Which tasks you choose to complete will depend on your confidence and skill level.

The most DIY accessible jobs are finishing jobs. Things like fitting tiles, laying flooring, decorating. Installing a kitchen is doable but is often a more than one-person job.

If you intend to complete some parts of the work yourself, you should make sure to speak to your lead contractor about your plans. You will need to liaise with them about when you will be completing tasks. This will allow them to plan the tradespeople around your timings.

It can be a good idea to speak to lead contractors about your plans to complete some of the work yourself while you are getting a quote. Some will be more open to the idea than others.

Types of House Extension

Once you've decided that you want to get an extension built on your house, the next step is to decide, what sort of extension you want.

Lean-To Extension Cost (Rear or Side)

A lean-to extension typically adds a single room to the back of the building. The roof is most often pitched, which is the reason for the name. A lean-to extension is a good choice if you only require a small extension. The cost of an extension like this is usually between £25,000 - £40,000.

Pros

• ✔ Offers flexibility
• ✔ Easily add a single extra room

Cons

• ✖ Size is limited by garden space

Side Return Extension Cost

Some homes have alleyways that run down one side of them. You often find these in Victorian terraces. Most homeowners use them to store their bins. In this extension, the alleyway is used to extend the ground floor of the home. Because this is a small job, the cost of extension is comparatively low. The average cost is £15,000 - £25,000.

Pros

• ✔ Quick and cheap option
• ✔ No garden space sacrificed

Cons

• ✖ Only adds a limited amount of extra space
• ✖ Only an option for some homes

Kitchen Extension Extension Cost

One of the most common uses for an extension in the kitchen. This can involve extending and remodelling the existing kitchen. The cost of a kitchen remodel varies largely based on the quality of the fittings and appliances chosen for the kitchen. The costs range between £25,000 - £100,000.

Pros

• ✔ Good opportunity to create an open plan kitchen and dining room
• ✔ Can rearrange the kitchen to suit your needs

Cons

• ✖ Can be the most expensive type of extension

Wrap Around Extension Cost

A wrap around extension is when you extend to both the rear and the side of your home at the same time. This creates a lot of extra space in your home. It is ideal for creating large open plan living spaces. The average extension cost is £40,000 - £100,000.

Pros

• ✔ Creates lots of space
• ✔ Flexibility of design

Cons

• ✖ Expensive

Single-Storey Extension Cost

Single storey extensions are extensions that only expand your ground floor space. Their roofs can be completely separate from the main roof of your home. The cost of a single storey extension is £15,000 - £100,000 depending on which type of extension you choose.

Pros

• ✔ More roofing options
• ✔ Quicker to build

Cons

• ✖ Higher cost per meter square

Double-Storey Extension Cost

Lean-to and wrap around extensions can be built as two storey extensions. If you want to go even further, you can also get the loft spaces also made into liveable spaces. The average cost of a double storey extension is £40,000 - £50,000 for a lean-to extension and £60,000 - £150,000 for a wrap around.

Pros

• ✔ Lowest cost per m²
• ✔ Creates more space for the amount of garden sacrificed

Cons

• ✖ Can be very expensive

Building Regulations and Planning Permission for a House Extension

Building regulations will apply to any substantial work you have done on your home. Planning permission is not always needed. Permitted development allows you to do a lot of work on your home without applying for permission

Building Regulations

Building regulations aim to ensure that all homes are built up to a suitable standard. This means that when you get an extension done, building regulations will be applied to the whole of your home. Not just the new extension.

You should be aware of this as it can add a lot of costs. Small changes can be needed, like the addition of fire doors throughout your home. However, much larger renovations can be needed like the rewiring of the whole house.

To get the work approved as meeting building regulations, you need to complete some paperwork and then pass inspections. The whole process usually costs between £50 - £100. As the homeowner, you are responsible for ensuring that the work is completed following building regulations.

In most cases, your lead contractor will ensure it is done. You should make sure it is clear who is taking responsibility for doing this at an early stage.

Do You Need Planning Permission?

Many extensions do not need planning permission. The following are the limits of what you can have done without getting planning permission.

• Single storey extension can extend up to 4m on a detached property and 3m on any other type of property
• The maximum height is 4m
• The new building work should be completed using similar materials to the rest of the home
• A maximum of half the garden space can be used
• A side extension can be no more than half the width of the original home

Anything beyond these limits may be subject to planning permission. You can use the government’s planning portal to check. Another option is to speak to your local council. Most have a planning department. These offer consultations to advise you about the need for planning permission. There is usually a cost of around £50 - £150.

If you live in a national park or a conservation area, then you should be aware that these limits may be much smaller.

Applying for Planning Permission

Applications for planning permission can be made either online through the planning portal or directly with your local council.

If you are unsure about completing the application yourself, then you could speak to your architect or designer. Many of them are familiar with the process and can submit applications on your behalf.

Every application costs £206. The documents required vary between local councils so you will need to check what yours asks for. Many councils provide a support service for applications. For a fee, they can help you to file the necessary paperwork.

After the application is submitted there is an average of an eight-week wait. This time allows anyone to file a complaint about the planned work. It's best to speak to your neighbours in advance of this. It reduced the likelihood of them filling a grievance.

You will either be granted permission or informed of the reason for rejection. If your application is rejected, you can make changes to your plans and reapply.

Benefits of a House Extension

There are many reasons why people invest in an extension. Some of the most common ones are listed below.

No Need to Move Home

As your family grows it your existing home can begin to feel crowded. To make your home liveable, you might face the possibility of moving home. However, if you are attached to your home, and the location, an alternative is to extend the property instead. Adding an extension can allow you so stay in a property that you love.

More Room

The most obvious benefit of an extension is the added space. With an extension, space is added to the floors of your home where you already spend most of your time. By extending the existing living areas, you are not creating a tall and thin home, which can be undesirable for some.

Update House

Adding an extension is a big opportunity to change the layout of your home. It can allow you to create an open living area. Many extensions involve an update to the kitchen. This can make your home feel like new.

Increase House Value

Adding an extension to your home will add to the value of it. The more space you add, the more value you will add. Typically, you can expect to increase your home value by around £2,000 per m².

In London where space is at a premium, an extension can add as much as £4,000 per m².

Where Can I Put a House Extension?

You can put an extension on your home onto any side where there is space. The back of the house is the most common choice. This is because most homes have space to the rear of the property, and it is easy to create a feeling of flow into your home.

Extension to the side of a property is possible as long as you are not joined to another home. A wraparound extension is a combination of both a side and rear extension.

Front extensions are possible but are quite rare. Most homes do not have large amounts of space at the front and adding an extension to the front can be complicated. It changes the look of the building, so getting planning permission can be difficult or impossible depending on your location.

Alternatives to a House Extension

If you are looking to add space to your home or increase the property value, there are other options.

Conservatory Cost

Traditionally conservatories are a mix of brickwork and glass. The glass is panes are similar in size to large windows, and the brickwork usually rises about 1m in height. The average cost of a conservatory is £15,000.

Pros

• ✔ Quick and Easy to Build
• ✔ Cost-Effective

Cons

• ✖ Not considered a liveable space, so do not add as much value as an extension
• ✖ Can be hot in summer and cold in winter

Summer House Cost

A summer house is a separate building in your garden. The price varies depending on the quality of the construction. To have a space that could act as a bedroom or sitting room all year round costs on average £12,000.

Pros

• ✔ Can add as much as 5% to the value of your home
• ✔ Less disruption to home life

Cons

• ✖ Can be expensive to make a liveable space
• ✖ Considered a luxury addition

Orangery Cost

Orangeries are the forebears of conservatories. They are made with more brickwork than a conservatory. The roof to an orangery is usually flat with a glass lantern window. The average cost of an Orangery is £22,000.

Pros

• ✔ Offers more light than an extension
• ✔ Provides more space than a conservatory

Cons

• ✖ Flat roofs can be difficult to maintain
• ✖ Can be more expensive per square meter than other options

Glass Room Cost

Glass rooms are made almost entirely from glass. It is like a conservatory; only the glass continues all the way to the ground; there is no brickwork. The large glass panels create a modern finish. The costs for this are £15,000 - £70,000.

Pros

• ✔ Clear views over your garden and surrounding area
• ✔ Bespoke systems

Cons

• ✖ Expensive to buy and install the glass
• ✖ Expensive to heat

Prefab extension Cost

It is possible to create your extension off-site, and then just install it by using cranes to lift the pieces into place. The average cost for this is £2,000 per m².

Pros

• ✔ Quick and easy installation
• ✔ Minimal disruption for you and your neighbours

Cons

• ✖ Need access space for a large crane
• ✖ Limited options

Loft Conversion Cost

A loft conversion is often the most cost-effective way to add space to your home. The amount of space you gain will depend on your existing loft and the type of conversion you choose. The average cost is £40,000. A very basic loft conversion can cost as little as £15,000.

Pros

• ✔ Cheapest cost per m² gained
• ✔ No loss of outdoor space

Cons

• ✖ Available space depends on the style of roof
• ✖ Can be expensive to make more awkward spaces useable

Cost of Removing a House Extension

If there is already an extension on your home, but you are not happy with it then you have two options. You can either replace the existing extension, or you can remove it.

Removing an extension can be a big job, depending on the type and how it is integrated into your home. If the roof of the extension is joined to the main house, then you will need the services of a roofer to fix the main roof when you are done.

To remove an extension will cost between £3,000 - £5,000 for a single storey extension. For a double storey extension, the costs can be as much as £10,000.

This will cover the costs of bringing down the old extension and removing the rubble. You will then need to consider what you want to do with the open wall.

Hiring House Extension Contractors

When you are hiring contractors to build your home extension, you have a choice to make. You can choose one contractor to be your project manager, in which case they will be responsible for finding and vetting the rest of the workers on site.

The other option is to act as the project manager yourself. In which case, you will need to consider the credentials of all the workers you hire. Even though you pay a contractor more to run the project, it can work out as a cheaper option. Especially if you don't have experience of running a building project.

Here are some of the key things to look for in a contractor who will also be acting as your project manager.

• Expect to see examples of previously completed work.
• They should be happy to give you details of previous clients so you can speak to them yourself.
• They should be able to give you a breakdown of the costs. Do not expect this on the day. To give an accurate quote will take time.
• A good indicator is that they take notes on the project as you are talking, or just after.
• Check that they will take responsibility for arranging the building control visits.
• Membership in a traded association is not a guarantee of quality, but it is a good indicator that they take pride in their work.

FAQs

Sources

https://www.which.co.uk/reviews/conservatories/article/conservatories-and-orangeries/conservatory-prices
https://www.planningportal.co.uk/info/200130/common_projects/17/extensions
https://www.homebuilding.co.uk/extension-beginners-guide/
https://www.self-build.co.uk/prefabricated-extensions/
https://www.realhomes.com/advice/qa-update-or-replace-a-dated-extension
https://www.simplyextend.co.uk/planning/types-of-extension/
https://www.leaders.co.uk/advice/how-much-value-does-summerhouse-or-garden-building-add