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Cost of Single Storey Extension (UK)

By Sam

Last updated 12th August 2024 - Reading time: 29 mins

At a Glance

The average cost of building a single storey extension in the UK is £35,000.
Single storey extensions take around 12 weeks to complete.

In this single storey extension price guide, you'll find the following:

A breakdown of how much it costs for different types of single storey extensions in the UK - including wraparound, side, rear, and kitchens.
Estimates about how long single storey extension projects take to complete and what's involved from start to finish.
Details about the specific prices of materials that you'll need for a single storey house extension.
How to find and hire a builder to add an extension to your home.

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This price guide includes everything you need to know. This includes the cost per square metre, average costs of different types of single storey extensions, and much more.

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Average Cost of a Single Storey Extension:

Depending on the complexity of the job, it usually takes: 12 weeks

£35,000

What's the Cost of a Single Storey Extension in the UK?
Single Storey Extensions Costs By Type
Extension Labour Costs and Timescales
Single Storey Extension Material Prices
Additional Single Storey Extension Costs
Cost Factors of Building a Single Storey Extension
Do I Need to Hire an Architect for a Single Storey Extension?
Single Storey Extension Roof Costs
Building Regulations for Single Storey Extensions
Planning Permission for Single Storey Extension
What's Involved in a Single Storey Extension?
Can I Build a Single Storey Extension Myself?
Benefits of a Single Storey Extension
Will Building a Single Storey Extension Increase My Home Value?
Single Storey Extension Alternatives
Single Storey Extension Removal Cost
Checklist: Hiring a Single Storey Extension Builder
Sources

What's the Cost of a Single Storey Extension in the UK?

The cost of a single storey extension will largely depend on the size of the extension and the quality of materials you want to go with.

The average cost of a single storey extension per square metre (m²) in the UK is between £1,000 - £2,200.

A small, basic single-storey extension can cost as little as £15,000. This would be a typical price for a 15m² single-storey side extension with the most basic materials you can get.

What about a large single storey extension?

The cost of a large, high-quality single storey extension could cost up to £100,000. This is what you should expect to be quoted for a 50m² single storey wraparound extension.

Let's talk about average costs...

The average cost of a single-storey extension is around £35,000. This would give you a good-sized rear or side extension with basic materials and include the cost of a kitchen (which is the most common use for a single-storey extension).

Single Storey Extension Prices

With all costs included, the quality of the finish is one of the most significant factors affecting the single storey extension cost.

This table highlights how the price range differs between an extension that uses basic, good, or high-end materials.

Quality of Finish	Average Cost (20m²)	Cost Per m²
Basic	£27,000	£1,000 - £1,700
Good	£36,000	£1,700 - £1,900
High	£41,000	£1,900 - £2,200

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But what can you expect the single storey extension cost to be for different-sized conversions?

We've collected together what you should expect in the table below.

Size of Single Storey Extension	Average Cost	Average Cost Range
20m² (Small)	£32,000	£20,000 - £44,000
30m² (Medium)	£48,000	£30,000 - £66,000
50m² (Large)	£80,000	£50,000 - £110,000

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Single Storey Extensions Costs By Type

There are four main types of single storey extensions that homeowners in the UK typically have.

In this section, we've covered the average prices quoted for each of these - as well as the pros and cons of each option.

Single Storey Side Extension Cost

A side return extension uses the alleyways that run down the sides of some houses. Many Victorian houses have these little alleyways, which are often used to store bins.

The average single storey side extension cost in the UK is between £15,000 - £25,000.

Pros

✔ Quick to complete
✔ Doesn’t use garden space

Cons

✖ Only creates a small amount of extra living space
✖ Not an option for all houses

Single Storey Rear Extension Cost

Rear extensions are usually just a single room-sized extension to the rear of a property, so they are a popular choice if you only want a small extension. They're also commonly referred to as lean-to extensions, as the roof is typically pitched (hence the name it has).

The average single storey rear extension cost in the UK is between £25,000 - £40,000.

Pros

✔ Lots of flexibility
✔ Easy way to add a single room

Cons

✖ Not the cheapest option

Single Storey Wraparound Extension Cost

A wraparound extension is the combination of a rear and side extension. This is the style that homeowners tend to go with when they want to add a large amount of space to the ground floor of their property.

The average single storey wraparound extension cost in the UK is between £40,000 - £100,000.

Pros

✔ Creates a lot of extra living space
✔ Provides a lot of options

Cons

✖ Can be much more expensive

Single Storey Kitchen Extension Cost

The most common use for a single storey extension in the UK is to expand and remodel the kitchen. They're used to increase the working area in a kitchen, but are also frequently designed to open up more dining and living space.

The average kitchen extension cost in the UK is £30,000, but the price can extend well beyond this depending on the size of the extension and the quality of the materials used.

Pros

✔ Can get a kitchen to suit your needs perfectly
✔ Facilitates open-plan kitchen and dining rooms

Cons

✖ Can be expensive to replace a kitchen

Other Types of Single Storey Extensions

Side, rear, wraparound, and kitchen single storey extensions are the most popular way of performing ground-level extensions.

However, there are three other options which you could explore:

Timber Frame Extensions. An alternative to using a traditional extension, it's favoured by some people as the prefabricated frames make it quicker and easier to complete the extension. The average single storey timber frame extension cost is £27,000.
Flat Pack Extensions: This involves using a collection of prefabricated flat pack materials to assemble a house extension. You can complete a flat pack extension quicker, but there is more limited customisation available. The average single storey flat pack extension cost is £25,000.
Flat Roof Extension: A type of extension where the roof is almost completely flat, which tends to cost less than a traditional extension. However, it requires regular maintenance to prevent issues from developing. The average single storey flat roof extension cost is £28,000.

Extension Labour Costs and Timescales

The labour costs and time scales will vary greatly depending on the exact work you need to have done in your extension.

The following sections should give you a rough estimate of typical costs and timescales involved.

Timescale and Labour Cost Based on Type of Extension

Type of Extension	Duration	Average Labour Costs
Lean-to Rear	11 – 13 weeks	£25,000 - £40,000
Side Return	9 – 12 weeks	£15,000 - £25,000
Wrap Around	10 – 14 weeks	£40,000 - £100,000
Kitchen	10 – 14 weeks	£25,000 - £100,000

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Cost Per Hour of Different Tradesmen

Tradesman	Average cost per hour
Builder	£20 - £35
Tiler	£20 - £40
Plumber	£35 - £45
Electrician	£50 - £120
Plasterer	£30 - £50
Decorator	£20 - £50
Joiner	£35 - £45
Roofer	£30 - £40
Kitchen Fitter	£20 - £30

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Whenever you get work done on your home, there are things that you need - or problems that arise - that need to be taken into account. This is especially true if you need to have a building control inspection.

In this section, we cover some of the extra costs of a single storey extension that you might not have considered.

Skip Hire Cost

Rubble and waste are created when you have an extension added to your home. The easiest way to dispose of this is by hiring a skip.

The average cost of a skip hire is between £250 - £450. Keep in mind that you may require multiple skips, which will increase the amount of money you need to put aside just the handle waste removal.

New Boiler Cost

If you are adding plumbing as part of an extension - like for a bathroom or a kitchen - then you might need to update your boiler. If your current boiler is working at full capacity, this is your only option.

The average cost of a new boiler is between £1,500 - £2,500.

House Rewire & Consumer Unit Replacement Cost

When you get an extension built, you will be adding to your existing electrical systems. This can bring to light issues with your current setup that might have not previously been known. In the most extreme case, you may need a full house rewire.

The average cost to rewire a house in the UK is around £4,000. A more common issue is needing to update your consumer box. This is a smaller job, with consumer unit replacement prices being around £500.

Removing Drains Cost

If your existing drains are in the way of an extension you're planning, then you'll need to move them to a new location.

To check if this is required, you'll need to have a drain survey carried out. Drain survey prices are typically around £250. If your drains do need to be relocated, then you can expect it to cost between £200 - £1,300.

Underfloor Heating Cost

The benefit of underfloor heating is that it distributes heat evenly throughout a room and can be installed under almost any type of flooring (including wood, tiles, and carpets).

One of the main downsides of installing underfloor heating is that it typically requires disruption to the flooring that's already in place (increasing the cost). But when creating new areas of your home with a single storey extension, this isn't an issue - so it's the perfect time to consider adding it to your home.

The average cost of underfloor heating varies depending on the area it's being fit under. However, it typically costs around £800 for average-sized rooms in the UK.

Site Survey Cost

Before getting any major work done, it's advisable to have a site survey completed. This involves having a surveyor take a closer look at your property to identify any issues that already exist - or might arise during work.

The average cost of a house survey is between £600 - £1,400, varying depending on the size of your home. Although it's tempting to skip this to lower the total project cost, it can save money in the long run.

Architect Cost

It's not a legal requirement to hire an architect to plan the design of a single storey extension in the UK, but many people find hiring one helpful to keep the project on task.

Architect prices are between 8% - 15% of the total cost of the extension you're looking to have.

Planning Application & Building Regulation Costs

It currently costs £258 to apply for planning permission as a homeowner in the UK.

To get your extension certified as meeting building regulations, you will need to complete paperwork and have site visits. These costs vary from £500 - £1,000, depending on where you live and the scope of the work.

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Cost Factors of Building a Single Storey Extension

There are a few factors to bear in mind when you are setting a budget for a single storey extension.

The two main factors that affect the cost of a single storey extension are the size and the finish. But there are other factors that it is worth keeping in mind when you are making your plans.

Size of the Extension

The single biggest factor that will impact the cost of a single storey extension is the size of it. The bigger the extension is, the more you will end up paying.

If the area inside the extension is simple, with no internal walls, this will slightly lower the cost of a single storey extension per m². But even with this in mind, larger single storey extensions will require you to set aside more money.

Quality of Fixtures and Fitting

The next biggest factor impacting the cost of a single storey extension is the quality of the finish. Choosing high-end options can lead to the final price being more than double what it would be when choosing more basic-level materials.

Type of Extension

The type of extension you choose will go a long way towards dictating how large your extension will be.

Side return extensions create the smallest extra living space, so they tend to be the cheapest type of single storey extension. On the other hand, a wraparound kitchen extension will create the most space and likely include the most costly fittings and fixtures, so will be a more costly option.

Groundworks Required

If digging the foundations and laying the footing for your single storey extension proves to be difficult, then the cost will increase. This might be the case if the ground is hard to work with. Debris in the ground can also raise the costs.

Do I Need to Hire an Architect for a Single Storey Extension?

An architect is not necessary for most single-storey extensions. Most experienced builders will also be happy to work without one.

But if you have unusual plans or specific needs, it can be a good idea to hire an architect.

If you have a set of plans to follow, it means that there is a pre-agreed vision for what the final look of your extension will be. This could save money in the long run, as it will reduce any issues that can arise from miscommunication and the number of last-minute changes you make.

Single Storey Extension Roof Costs

When you get a single storey extension, you have a few main roofing options to consider. What option you decide to go with will depend on the aesthetic you want and your budget.

Pitched Roof Cost

A pitched roof allows water to run off and will fit in with the look and feel of the rest of your home. You'll have a range of pitches to choose from, and Velux windows can be incorporated if you want to maximise the amount of light entering your property.

The average cost of a pitched roof is between £9,000 - £15,000.

Pros

✔ Loft space can be used for storage
✔ Long-lasting

Cons

✖ Not cheap

Flat Roof Cost

A flat roof is an affordable and easy-to-install option, which makes them popular choices for single storey extensions.

The average cost of a flat roof is between £5,000 - £8,000.

Pros

✔ Affordable
✔ Easy to install

Cons

✖ Lifespan limited to 10 - 15 years
✖ Can fail

Glazed Roof Cost

Glazed roofs are a popular choice for side extensions. They are priced per panel of glass at £1,000. If you have a large area of roof, this could easily add up to £10,000 or more.

Pros

✔ Natural light
✔ Striking design feature

Cons

✖ Expensive
✖ Poor insulation

Green Roof Cost

Green roofs are quite recognisable, as they have plants - usually turf or shrubs - growing on top of them.

They are an environmentally sound option and also provide excellent insulation.

The average cost of a green roof is £100 - £140 per m². For an average single storey extension, this is around £6,500 - £9,000.

Pros

✔ Excellent insulation
✔ Makes a statement
✔ Environmentally friendly

Cons

✖ Expensive to install

Building Regulations for Single Storey Extensions

Building regulations apply to any building work done on a home that makes major changes - like a single storey extension.

Building regulations ensure that the building materials and techniques used by everyone involved are safe and meet a minimum standard.

To get approval from building control, you will need to complete some paperwork and pass a couple of inspections. When they inspect your home, they will look at the whole house - not just the extension. This does mean you may have to update other things in your house (like fire doors and consumer units).

The costs cover the paperwork and site visits. You will pay between £50 - £100 in total. Most contractors will manage the process for you. However, you should make sure it is clear who is responsible for this. Ultimately, the homeowner is responsible for getting it done.

Planning Permission for Single Storey Extension

Before you start any major work on your home, you should check if you need planning permission.

Recent changes do mean that a lot more building work is allowed without the need for planning permission - so, in most cases, you probably won't need it.

Do You Need Planning Permission?

A lot of extensions will be covered under permitted development regulations. The following list identifies the maximum you can do before you need to apply for planning permission:

A single storey extension on a detached property can extend 4 metres to the rear. The limit for all other houses is 3 metres.
The maximum height is 4 metres.
Any extension should be of the same or similar material as the existing property.
You can use no more than half the garden space for the extension.
A side extension can be no more than half the width of the original home

If your planned extension goes beyond these limits, you may need planning permission. Most councils offer a consultation service that will help you identify if you need to apply for planning permission. There is usually a cost of £50 - £150 for this.

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

Applying for Planning Permission

If you need planning permission, you can apply through your local council's website or through the Online Planning Portal. You can make the application yourself, or you can ask your architect or designer to do it for you.

In the UK, applying for planning permission currently costs £258 - but these fees are increasing every year.

You will need to check what documents your local council requires for a submission. Most local councils offer a support service for a small fee, which usually involves a meeting with a council employee. They can guide you through what you need and any potential problems.

Once your application is submitted, you will receive confirmation of the application. It'll then take around 8 weeks for you to get a response. During this time, anyone can lodge objections to your plans. This is why it's a good idea to speak to your neighbours about your plans before you even submit a planning application, as it can prevent issues from cropping up later.

If your application is rejected, you can see the reasons why. You can then amend your plans and reapply.

What's Involved in a Single Storey Extension?

Many factors need to be coordinated when building an extension.

Problems with scheduling or weather might cause small delays, which can then have knock-on effects that throw the whole plan off by weeks.

The following is an outline for a good-sized single storey extension where everything goes to plan:

Weeks 1 - 2

The first two weeks are used to prepare the building site. The footings will be dug, and the foundations poured. Any drain work will be completed at this time.

Weeks 3 - 4

At this point, the all-important damp proof course and the concrete base for the flooring will be installed. Some drain work may be finished during this time.

Week 5

The external walls will be built. If you have a cavity wall, the insulation will go in as the walls are built. The new walls will be joined to the old as they go up.

Weeks 6 - 7

The internal walls will be constructed, and the cavity wall insulation will be finished. Whatever roof you have chosen, the structure for it will be built now. Any roof windows will be framed at this point. Once the roof membrane is secured, your roofing of choice will be installed.

Week 8

The external doors and windows will be fitted. This will make the new extension watertight, allowing internal work to proceed.

Week 9

The first fit will happen. This is basic plumbing and electrics. Some internal carpentry may also be possible at this point.

Week 10

The extension will be joined to the existing house. This involved breaking through the old external wall.

Week 11

The plaster will be applied to the walls. It must be given time to dry before work proceeds.

Week 12

All the exciting things happen now. The second fit will happen. The electric and plumbing, bathrooms and kitchen, and final trim are fitted - and you can also lay the flooring.

Can I Build a Single Storey Extension Myself?

There are a lot of different skills required to build an extension. Unless you are a professional builder, then you are unlikely to be able to complete the whole job on your own. Even then, you will likely need to hire an electrician or plumber to deal with some of the more specialised jobs.

If you want to bring down the cost of your single storey extension, then you can take-on the jobs you feel confident about. More straightforward tasks including laying flooring, hanging internal doors, and decorating are work you could take responsibility for to reduce the total cost.

If you plan to take on any part of the work, you need to communicate this clearly to whoever is managing the project (usually the lead contractor). This person needs to schedule when all of the work is done, so they will have to plan other work around you.

Benefits of a Single Storey Extension

There are several reasons to consider adding an extension to your home.

This section highlights some of the main benefits.

More Storage Space

Storage space in a home is always a good thing.

Building an extension gives you the opportunity to add storage that perfectly suits your needs. You can ensure you have the perfect space for anything that is currently cluttering up your living spaces.

Extra Living Space

An extension provides you with more space to spread out in your home. For growing families, this can relieve issues and make home life more enjoyable.

Modernise Your Home

Adding an extension is an opportunity to change the look and feel of your home. You could rearrange the floor plan and align it with your needs and wants. Especially if you have an older property, adding a single storey extension is an excellent way to update the space and make it more modern.

Higher Property Value

We cover this more in the next section, but the bottom line is this:

If you add more space to your home, the property tends to usually be worth more if you decide to sell it. However, the approximate amount that an extension adds to your property depends on a few things - such as the square metres added, the quality of the materials, and your location in the UK.

Will Building a Single Storey Extension Increase My Home Value?

Any work you do on your home to increase the liveable space will usually increase its market value.

With a single storey extension, you are trading a part of the outdoor space that your property has for more indoor space. In terms of the value that's added to your home, it's often worth the trade-off as long as you maintain a reasonable outdoor space.

Recent data from Nationwide highlights that extensions can add around 5% to the value of a home for every 10% of extra floor space they add.

Assuming a floor space of 150m² in a detached home that costs £425,000, this means that the addition of a single storey extension that increases floor space by 10% (15m²) could add around £21,000 to the market value of the property in this example.

Single Storey Extension Alternatives

If you're looking to increase the amount of floor space in your home, a single storey extension is not the only option you have.

In this section, we go through a few other options you might want to consider.

Prefab Extension Cost

Prefab extensions (also known now as modular extensions) involve buying sections that are all manufactured elsewhere (i.e. prefabricated). These sections are then assembled and moved into position on your property using cranes.

One of the main advantages of a prefab extension is that it requires significantly less time to complete. However, a modular extension cannot be customised as much as a normal single storey extension.

The average cost of a prefab extension in the UK is around £2,000 per m².

Pros

✔ Minimal disruption
✔ Quick installation

Cons

✖ Limited options
✖ High cost per m²

Conservatory Cost

A conservatory is traditionally a mix of glass and brickwork. When it comes to selling your home, it's not considered a liveable indoor space. This means that is adds significantly less value to your home than some kind of extension. There are also limits on the services you can put in a conservatory.

The average conservatory cost in the UK is around £15,000. However, there are lower-cost conservatory designs that are more affordable. For instance, the average cost of a lean-to conservatory in the UK is around £8,250.

Pros

✔ Quick and easy to build
✔ Affordable options

Cons

✖ Hard to moderate the temperature
✖ Less practical than a single storey extension

Glass Room Cost

Glass rooms are like conservatories - but without the brickwork. The glass panels also tend to be larger, giving them a more modern look.

The average cost of a glass room in the UK is between £15,000 - £70,000.

Pros

✔ Uninterrupted views
✔ Modern finish
✔ Bespoke

Cons

✖ Expensive to build
✖ Expensive to heat

Orangery Cost

Before conservatories, there were orangeries. The main difference is that an orangery is mainly made of fully insulated bricks. Traditionally, the roof is flat and has a raised glass lantern window to allow in light.

The average cost of an orangery in the UK is about £22,000.

Pros

✔ Provides more space than a conservatory
✔ Provides more light than a traditional extension

Cons

✖ More expensive than a conservatory
✖ The flat roof can require maintenance

Loft Conversion Cost

Loft conversions involve turning your loft space into a habitable area. They're frequently used to add bedrooms, bathrooms, and offices to a home. The main advantage of a loft conversion over a single storey extension is that it doesn't sacrifice your outdoor space (i.e. the garden).

The average cost of a loft conversion in the UK is around £40,000. However, a small basic loft conversion that converts about 13m² worth of space (one room) will usually cost between £19,500 - £29,250.

Pros

✔ No need to sacrifice outdoor space
✔ Provides a good return on investment

Cons

✖ Not an option for all homes
✖ Requires sacrificing some internal space for a staircase
✖ Can be expensive to make a usable space

Single Storey Extension Removal Cost

If your home already has an extension, but you are not happy with it, then you have two options:

You can work with what you have and renovate the existing house extension.
Take down the extension that already exists and start fresh.

The average cost to demolish an old extension is between £3,000 - £5,000 in the UK. However, this will depend on the type of rooms that you're looking to demolish - with kitchens and bathrooms costing a bit more to remove than offices, living spaces, and bedrooms.

Consider that you'll also need to plan what you want to replace the old extension with ahead of doing any demolition work. Otherwise, you'll just be left with a hole in your house.

Checklist: Hiring a Single Storey Extension Builder

The contractor you hire for the extension will also likely handle all the project management. This is an important role, as many people need to be coordinated to keep things rolling along.

If you get the wrong person in charge? The whole project will be more expensive and time-consuming than it needs to be.

Here are some things to look out for:

They should be able to show you examples of previous work they have completed.
They should be happy to let you speak to previous clients who've had single storey extensions.
They should be able to give you a breakdown of the expected costs of a single storey extension. Don't expect this the first time you meet them though! They'll need to go away and calculate all the relevant prices to give you an accurate quote.
A good sign is a contractor who takes notes when you discuss what you want from your home extension. It means that things are less likely to get forgotten about.
Check who is responsible for organising building control visits. Most contractors will do this on your behalf, but make sure it's clearly agreed - as this is ultimately the homowners responsibility.
Check if they are members of a trade association like the Federation of Master Builders. This is not a guarantee of quality, but nevertheless a good sign.

FAQs

What is a single storey extension?

Single storey extensions are the most popular type of house extension in the UK.

They're favoured by many as they're more straightforward than multi-storey extensions, which tends to make them more affordable options to create more space in your home. You often won't need to go through the planning permission process either, as many of these types of extensions fall under Permitted Development Rights.

Single storey extensions involve extending outwards from the rear or side of a property. This allows homeowners to add more rooms (e.g. a dedicated office or another bedroom) to their properties or extend the ones they have (e.g. a larger kitchen or living room).

How close to property boundaries can you build a single storey extension?

Under Permitted Development Rights, or if you have obtained planning permission, you can usually build a single storey extension up to 50mm from the boundary that you share with someone else.

Alternatively, you can negotiate a Party Wall Agreement with the party you share the boundary with. If they don't object, you could build right up to the boundary of your property.

It's recommended to always start by talking to your neighbours to identify and resolve any potential issues they might have with a single storey extension that you're considering building.

What is the cost of a single storey extension per square metre (m²)?

In the UK, single-storey extension prices per square metre (m²) range between £1,000 - £ 2,200. Where you land in this cost range depends on the size of the conversion (larger conversions can be more cost-efficient per m²), the type and quality of materials you use, and where you're located in the UK (southern regions have more demand for builders).

Where can you get single storey extension ideas?

There are lots of interesting home extension ideas from which you can draw inspiration to create the perfect space for you and your family.

There are plenty of home design magazines and self-build websites that are brimming with directions you could take, but YouTube and social media websites are particularly valuable places where you can find a vast variation of what real people have done with home extensions.

It can also be rewarding to speak with people that you know who have built a single storey extension.