How Much Does a Two Storey House Extension Cost in the UK?

The average two storey extension cost in the UK ranges between £41,400 and £86,300.

For the most architecturally ambitious projects, it’s not uncommon for a double height extension to cost well above £120,000.

The WhatPrice team has put together the following guide to help you understand the cost of building a double height extension. This includes the necessary, optional and hidden expenses to know about before you go ahead.

Introduction

It’s a well known fact that there is a property shortage in the UK, with house prices also at a premium. So, if you need extra space to accommodate a growing family or even to work remotely, extending rather than moving offers many benefits.

Our research has found that a two storey house extension can add as much as 20% to the value of your property. In particular, adding one or more bedrooms can be extremely lucrative where resale values are concerned.

Overall, a double storey extension is a fantastic way to extend your living space as a family, especially if any rooms currently feel cramped or have an awkward layout. Since this extension type covers two floors, it offers more potential than a standard single storey extension.

What is a double storey extension?

As the name suggests, a double storey extension is when you extend your property over two floors. Typically, this involves adding more space to both the ground floor and the first floor. In doing so, a double storey extension increases both the vertical and horizontal living space in your property.

Why this guide is different: Data-driven and builder-approved

At WhatPrice, our users submit price information for different building projects so that we can create highly informed, data-driven price guides. As a team, we also have direct experience as homeowners, tenants and developers across various building projects.

Use our two storey extension price guide to understand what is the cost of a two storey extension, and how your project scope and location in the UK will influence your quotes.

Who this guide is for (homeowners, developers, self-builders)

Whether you are a homeowner, developer or looking to self-build, you’ll find all of the answers about ‘What is the cost of a two storey extension?’ on this page.

Is a double storey extension right for you?

Simply put, a double height extension is the best option if you want to increase the amount of living space in your home on multiple floors.

For instance, if you want more kitchen and living space downstairs, but also want to add an extra bedroom or bathroom upstairs.

A double height extension is ideal where there is a large plot of land to build on. However, it can also offer a solution when outside space is at a premium, since you will be building up as well as out.

Benefits vs. single storey extensions

A single storey extension is a fantastic way to create extra space for the likes of a kitchen, living room, downstairs bathroom or home office. However, it misses the opportunity to extend small rooms upstairs, let alone add more rooms to maximise the value of your property.

Unlike a single storey extension, a two storey extension will increase your available living space on multiple floors. As a result, you can solve space challenges throughout your home to truly elevate the experience of living in your property.

The potential of a two storey extension is so great that for many families, it can avoid the need to move home rather than outgrow it in the future. For instance, due to a growing family or even to support a multi-generational home.

Added value to your property

As noted above, a two storey extension can add up to 20% to the value of a property. The most value can be gained by adding more bedrooms. Other highly desirable features include an en-suite bathroom, open plan kitchen and a home office.

Ideal home types for extensions

Properties that are detached, semi-detached, end-of-terrace or bungalows are the most suitable for a double height extension. That’s because these property types offer the required plot size and shape, roof structure and access to build an extension.

With these property types, there is also less likely to be problems with planning applications, particularly relating to natural light or privacy issues.

Sometimes, a double storey extension for a mid-terrace home or a flat is still doable. However, this will vary on a case-by-case basis.

How much does a double storey extension cost?

Based on our user submitted prices, we’ve found the average two storey extension cost to range from £1,400 per sq/m to £2,300 per sq/m.

The specification (i.e. good, standard or high spec) is one of the main factors influencing how much an extension costs per square metre.

Example budgets by size (20m², 40m², 60m²)

Double storey extension size	Typical price
20m²	£41,400
40m²	£64,590
60m²	£86,300

Our users have told us how much they paid for a two storey house extension based on the size of the project, as well as their location. This includes areas such as the East Midlands, North West, London, South East and Scotland.

Based on this data, it has revealed that a small 20m² double storey extension can be built for around £41,400. For larger 60m² extensions, the price averages £86,300 across the UK.

London vs. rest of UK: Regional cost differences

In our introduction, we mentioned that double storey property extensions can cost over £120,000. This upper price range applies to high specification or complex extensions.

However, higher prices across the board are also expected if you live in London, where the cost of labour and materials is far greater than the rest of the UK.

Planning an extension? Use our free cost calculator to find the cost of extending your home based on the extension type, extension size and your location.

Types of double storey extensions

When researching how much a two storey house extension costs, it’s important to know the different types of extensions that exist.

Since each type varies in terms of design complexity, it may offer a solution should your initial idea prove too expensive. Also, it’s good to be aware of other options in case you face any planning restrictions.

Rear extension

A rear two storey extension creates additional living space towards the back of your property. Usually, this involves building a larger kitchen area which then flows straight into the garden.

However, by making it a two storey extension, that additional rear living space is also gained upstairs, which can be used for adding an extra bedroom. For grander renovations, the upstairs extension can also transform an existing bedroom into a master suite with its own bathroom and dressing room.

Side extension

Where there is available space at the right or left side of your home, you can use it to build a side extension. In doing so, you’ll immediately make what are often the smallest rooms of the house (i.e. a single bedroom) larger.

A side extension is an ideal solution where space is limited at the back, or likewise, where you want to preserve the garden by avoiding building to the rear.

Wraparound extension

A wraparound extension is also known as a L-shaped extension as it wraps around the rear and side of a house. It is an excellent solution if the downstairs layout of your property currently lacks space, particularly in the kitchen, dining or living areas.

Wraparound two storey extensions can offer some of the most dramatic makeovers. As an alternative idea to adding extra bedrooms upstairs, there is also the option of using the upper floors of a wraparound extension to create vaulted ceilings for the downstairs areas. Doing so can establish an open plan living space.

Over-garage extension

Building on top of your garage is a clever way to gain extra space, particularly if you lack space around the side or rear of your property. For a two storey extension, this could involve adding an extra bedroom above the garage, and also building into the loft to add an additional room.

Semi-detached, detached & terrace considerations

Detached properties are the most suitable property type for two storey extensions. This is due to having the available space to build on, better site access and reduced planning constraints.

It is often still possible to go ahead with a double height extension for a semi-detached property, so long as party wall agreements are put in place.

Terrace properties offer the most challenges for a two storey extension, particularly if the property is a mid-terrace rather than an end-of-terrace. That’s not to say it’s not doable, but there will be more planning restrictions and overall limitations to factor in.

Planning permission & regulations

Before undertaking any building work to your home, it’s essential to check whether any planning permissions are needed. Also, whether you need to comply with any regulations for reasons such as the proximity of neighbouring properties, or because your home is considered of historic significance.

Do you need planning permission?

Two storey extensions don’t require planning permission, so long as they comply with certain stipulations. This is commonly referred to as permitted development rights.

However, if you live in a conservation area then full planning permission is likely to be required for any significant modifications to your property, including a double storey extension.

Permitted development rights explained

As a homeowner, you can do certain types of work on your home without needing planning permission. Such works fall under permitted development rights.

Permitted development rights are quite generous in terms of what is and isn’t allowed. Although, the rules can work differently depending on where you live in the UK.

For two storey extensions in England, permitted development rights include aspects such as:

Where you can build: Permitted development rights include rear two storey extensions, but not side or front elevations.

Maximum depth: You can extend your property a maximum of 3 metres from the rear elevation on a semi-detached, terrace or link-detached house. This increases to 4 metres for a detached house.

Maximum height: The height of a roof ridge and eaves within the extension portion of the property cannot exceed the roof ridge and eaves of the original structure. If any part of the roof will be within 2 metres of your neighbour’s boundary, it cannot exceed 3 metres in height.

Maximum area: Any extension to your home cannot exceed more than 50% of the total land around the house.

These are a brief overview of permitted development rights, but are far from extensive. Furthermore, there can be stricter rules to follow if your home is in a conservation area.

Building regulations you must follow

Most extensions will require approval from building regulations which you can access through your local council’s building control.

There are aspects which will require approval when part of an extension which normally would be permissible, i.e. kitchens, bathrooms, windows and doors.

The regulations fall under Part A-Q. They will relate to things such as:

• Foundations
• Ground floors
• Main walls
• Structural openings
• Upper floors
• Roofs
• Chimney stacks and flues
• Windows and doors
• Internal walls
• Internal joinery
• Services (i.e. electrics and heating)
• Kitchens and bathrooms
• Drainage and rainwater

For the most part, your tradespeople will be responsible for complying with building regulations. However, it’s important to consult your local building control to check any requirements you may be responsible for, including having surveys conducted and work signed off.

Party wall agreements

If you live on a large detached plot, then party wall agreements usually don’t apply. However, you will need to get an agreement in place if you’ll be excavating foundations within 3-6 metres of any neighbouring properties.

The cost of serving a party wall notice ranges between £150 and £250 excluding VAT. However, getting a party wall agreement in place can cost £800 to £3,000.

How to get architect drawings & planning support

If you’ve never worked with an architect before, it can seem like a daunting prospect. However, it’s the job of an architect to help your extension reach its potential, particularly where layout changes are concerned.

An architect can assist throughout the planning process, including helping with issues such as your neighbours right to light, as well as ensuring privacy based on the design choices.

It’s wise to consult an architect early in the project to avoid potential headaches down the line. Similar to other tradespeople, you should research architects in your area. RICS offers a free service to find architects and surveyors who are accredited by them near you.

Detailed cost breakdown

When pricing up your double storey extension cost, there are a few factors which will impact how much you’ll be quoted.

This includes:

• The extension size
• The double storey extension type
• Overall design complexity
• Specification level (i.e. typical vs high end)
• Experience of professionals involved
• Whether you opt for one building firm or hire individual tradespeople
• Your location in the UK

Let’s look at the typical cost ranges for each part of your project in greater detail.

Design & planning

Planning stage	Typical cost
Architect fees for double storey extension planning application only	£2,000 – £3,500
Architect fees for double storey extension to include additional services like building regs, construction drawings and tender works.	£6,000 – £11,000
Structural engineer costs	£1,000 – £10,000
Surveys	£500 – £2,000
Planning submissions	£258 per application and £43 for a follow-up request
£258 per application and £43 for a follow-up request	£800 to £3,000

A two storey extension can be built in a way where planning permission, architect fees and similar planning costs aren’t required.

However, for large or complex projects, the initial planning and permissions required can absorb up 5%-15% of the total budget.

Hiring an architect or structural engineer is a costly investment, with the planning application alone ranging from £2,000 to £3,500. Though, where professional input is warranted, it can offer a fantastic return on your investment.

Construction costs (per trade)

Construction stage	Typical price range	What impacts the cost?
Foundations	£3,000 to £15,000	The type of foundation, with strip foundations being the cheapest and piled foundations being the most expensive.
Ground preparation	£90 – £285 per square metre	The overall condition of the site
Brickwork (per 1,000 bricks)	£650 – £5,000	The quality of the brick (i.e. machine made bricks vs clay facing bricks). The experience of the bricklayer.
Framing	£1,400 – £2,400 per square metre	Complexity of the structure
Roofing	£5,000 – £20,000	Whether replacing only the extension section of the roof or the entire roof. Flat roof (cheaper) vs pitched roofing (more expensive). For pitched roofs, the choice of roof tile.

As you might expect, how ambitious your two storey extension is in terms of its size, scale and design complexity will influence the construction costs. Namely, the materials and labour required.

To keep the price of your two storey extension as low as possible, the design will need to be modest and simple. You will also need to opt for cheaper materials throughout the structure.

But where the aim is to achieve the top level of specification, the costs will naturally increase. This may include aspects such as the use of natural or high-grade materials (i.e. slate roofing or class one bricks).

Consult with your builder about the potential costs, as it may also be the case that you want to save in some areas and invest more financially in others.

Windows, doors & glazing

Window or door type	Typical price range (unit price + installation)	High end/bespoke price range (unit price + installation)
Internal door	£150 – £300	£500 – £1,200
External door	£500 – £2,000	£3,000 – £5,000
Internal window (fixed frame window)	£100 – £250	£300 – £450
External window	£250 – £700	£1,500 – £5,000

Property extensions require additional windows and doors to allow for building access, natural light and ventilation.

It’s possible to buy an internal door from a well known DIY store and have it installed for as little as £150. However, expect to pay far more for designer internal doors made from premium materials such as oak, or those with intricate designs. Likewise, it’s not uncommon for bespoke window shapes or custom front doors to retail for £5,000 per unit.

The good news is that there is plenty of price flexibility here, which isn’t something you will always benefit from elsewhere in your extension project.

The cost of windows and doors for a double storey extension will be impacted by:

The number of windows and doors – This will be influenced by the size and scale of your extension. Optional, but some homeowners choose to replace all of their external windows to match the newer portion of their property.

Window and door size – Large windows or double fronted doors cost more to replace.

Frame material – uPVC windows and doors are usually the cheapest option. Premium materials include timber, composite and aluminium.

Glazing type – Double glazing is standard, but expect to pay more for triple or secondary glazing.

Standard or bespoke shapes – Want to install a circular window or another unusual shape? Expect to pay more than standard window and door shapes.

Need more advice on the cost of new windows and doors in the UK? View our free window replacement price guide.

Labour costs by trade

Trade	Typical day rate
Builder	£250-£500
Scaffolder	£150-£300
General labourer	£150-£360
Electrician	£200-£550
Plumber	£320-£375
Joiner	£180-£300
Plasterer	£200-£400

To build a two storey property extension, a plethora of tradespeople will be required to construct the foundations, build the basic structure and complete all of the internal works.

Some projects also go as far as hiring landscapers to transform the external grounds.

Not all of the trades will be required on site all of the time. Typically, each trade will quote per project rather than per hour. However, the above figures give an idea of how much each tradesperson will cost per day.

Overall, you should expect a large percentage of your total project to cover the costs of labour.

Fittings & finishes

Item	Typical price range	What impacts the price?
Bathroom	£2,000-£25,000	Bathrooms can range from a downstairs toilet and sink to a large luxury suite.
Kitchen	£5,000-£60,000	The number of units, the overall size and the brand of appliances.
Flooring	£25 to £85 per square metre	The type of flooring used.
Lighting	£100 – £600 per light fixture	The type of light fixture and quality of electrics.
Painting	£350 – £1,000 per room	The size of the room and brand of paints used.
Smart home tech	£100 – £15,000	Whether you opt for a basic smart device you can install yourself, or full home automation for your heating, lighting, audio and security systems.
Energy efficiency measures	Variable	nsulating pipes or draught-proofing can be done for a nominal amount, but converting to a heat pump can cost thousands. Seek advice before planning your project.

The level of specification is an area where you have more control over a two storey extension cost.

For homeowners on a tight budget, there are various steps you can skip including adding smart home tech. Likewise, opting for cheaper flooring options like laminate rather than engineered wood or porcelain tiles.

Overall, you can make smart decisions based on what you’re comfortable spending, plus the potential returns you’d be set to gain.

For instance, adding a downstairs toilet is a great addition to any extension and is cost-effective. On the other end of the scale, you could extend your existing bathroom or add a new bathroom upstairs.

View our related price guides:

• How much does a new kitchen cost?
• What is the cost of a new electrical socket?
• Wooden flooring costs
• How much does a new bathroom cost?

Hidden & unexpected costs

Our homes have a unique ability to throw up unexpected surprises, not least when the likes of walls, foundations, roofs and utilities will be disturbed during an extension!

Unfortunately, it’s impossible to predict unexpected costs, including the nature of what they may involve.

For example, according to RICS, if the area around your extension presents access challenges, this can add as much as 15% onto a building project.

Leaving a 10%-20% contingency in your budget can best prepare you for hidden or unexpected costs. Also, ensure you request all building and material prices to be given with VAT included.

Cost-saving tips that don’t sacrifice quality

At WhatPrice, we create our home renovation guides based on our own experiences. This allows us to add hindsight, not least in terms of maximising your budget.

Based on the lessons we’ve learned over the years, we recommend these top tips for keeping your two storey renovation costs in check.

Design efficiently (straight lines save money)

If there’s one thing we’ve all learned from watching countless episodes of Grand Designs over the years, it’s that complex builds are costly. This is not just in a financial sense, but also in terms of the stress for everyone involved.

Using straight lines for the design where possible keeps things simple for your builders and in turn will save your money. A straightforward design can also reduce unnecessary headaches and delays so that you actually enjoy the process of extending your home.

Use off-the-shelf materials

When building a two storey extension, there are endless design decisions to be made. It can be stressful to choose the likes of paint colours, tiles and flooring. However, this is also an area where expenses can get out of hand, especially if you opt for bespoke rather than off-the-shelf materials.

These days, there are lots of retailers both on the high street and online which can supply your building materials and interior finishes. It’s wise to research the materials and costs so that you can strike just the right balance between value for money and quality, depending on the level of specification you are aiming for.

Get quotes from multiple builders

It’s the timeless advice we share on all of our building work price guides, but nothing can replace doing your research, including by getting multiple quotes for your job.

If there’s a huge price difference between quotes, then you should also probe why this is the case. Ultimately, you need to be satisfied with your choice of builder, since a two storey extension is a major undertaking.

Source your own fixtures

A huge part of project management is sourcing all of the materials, including the fixtures. By fixtures, we mean anything which is attached and would cause damage if removed, i.e. a bathroom suite, kitchen cabinets, built-in wardrobes etc.

Sourcing the fixtures yourself can reduce the project management costs, as well as the unit prices especially if you shop around.

For example when adding a kitchen, you can use ex-display retailers. Compared with buying a kitchen through the usual means, this can boast savings of up to 70%.

Build in winter for potential discounts

You may be able to reduce the cost of a two storey extension by opting to build in the winter months. That’s because the demand for building work usually falls during this time.

That said, your project may be subject to weather-related delays which can result in longer completion times.

Financing your extension

Unfortunately, that typical £41,400 to £86,300 double storey extension cost won’t pay for itself!

That’s why an essential part of the planning process is deciding how you’ll pay for the work. You should seek financial advice to find the best options based on your personal circumstances.

Additionally, research the potential profit to be gained based on the ceiling value figures in your local area. This is especially crucial if you plan to sell the property anytime soon and are looking to achieve a decent profit from your investment.

Saving vs. borrowing

Using savings to cover your two storey extension cost offers many advantages. Namely, the need to avoid interest or getting into debt. If you can pay for everything upfront, then this can also reduce project delays.

If you don’t have the money to pay for all of your extension with savings alone, then borrowing is another option. Sometimes, borrowing can also be necessary to cover unexpected costs which arise once the extension is underway.

For some projects, borrowing may make financial sense. This includes to keep the project going, especially where savings alone won’t cover costs and there is a huge profit to be made from continuing. Borrowing may also allow you to lock in cheaper material prices by avoiding inflation.

Best home improvement loans & rates

Lenders, including your own bank, may offer home improvement loans. A benefit of a loan is that you can receive quick access to the cash you need. However, you will always pay more back than you owe on a loan. That’s why you should research interest rates carefully before you go ahead.

Also, your access to a loan including the best interest rates will be dependent on your credit score. It’s a good idea to check your credit score before you apply for a loan so that you’ll know where you stand ahead of time.

Using equity or remortgaging

If you’ve lived in your property for a long time, releasing equity or remortgaging may be an option to consider. That is, once you’ve taken advice and either option makes sense from a financial and practical point of view.

Generally, releasing equity or remortgaging isn’t ideal for smaller home projects. But it can be justified for a two storey extension, especially where there is a significant value increase to be gained on your home.

Grant schemes & energy incentives (e.g. Green Homes Grant – if revived)

If you are disabled, are on a low income or receive certain benefits, you may be eligible for financial help towards home improvement works.

The level of help will vary depending on where you live in the UK, which is why you’ll need to consult with your local council to check. In general, you are more likely to be approved if the works are needed to adapt your home due to a disability, or if you will be improving the energy efficiency of your property.

Also, if you’ve taken out a loan to make home improvements, you may qualify for a government scheme called ‘support for mortgage interest’ (SMI).

Finally, if you don’t qualify for local council or government funding, you may still qualify for one of the various green homes grants. For instance, if you decide to replace a gas boiler with a heat pump, the Boiler Upgrade Scheme (BUS) can give you £7,500 to reduce your total outlay.

Choosing the right builder

Deciding to build a two storey house extension is exciting. But there’s a bit of housekeeping to take care of first to ensure your project is truly in the right hands.

One of the most important parts of the project is choosing the right firm or team or people to build your extension.

Beyond asking them about a double storey extension cost, you ultimately need to base your decision on their skills, experience and reputation.

Vetting tradespeople: What to look for

It will take time to vet tradespeople, especially if you need to get quotes from multiple trades.

Ideally, you should get at least 2-3 quotes. Be prepared for quotes to take up to a couple of weeks to come through, especially if your two storey extension is large or complex.

Questions to ask before hiring

The WhatPrice team recommends writing down some questions to ask your builder when you meet with them to discuss your two storey extension cost.

Some recommended lines of enquiry include:

• How long have you been in business?
• What is your experience of building two storey extensions?
• Can I see some examples of similar projects?
• Are you licensed and fully insured?
• Will you be using subcontractors, and if so, who are they?
• Who will be managing the project day-to-day?
• Do you have a quality control system in place?
• Are you a member of any professional associations?

If there is anything else specific to your property or project, then you should also ask the builders when collecting quotes.

Contracts & insurance essentials

Before undertaking any building work with a contractor, always check that the company is insured. This is essential not just to protect your home, but also yourselves, anyone working on the site and also the general public.

As a minimum, builders should have employers’ liability insurance and public liability insurance.

But responsible builders may have other types of insurance such as:

• Builders risk insurance
• Business interruption insurance
• Business van insurance
• Commercial property and contents insurance
• Contract works insurance
• Professional indemnity insurance
• Tools insurance

Ideally, any insurance held by your builder or contractors would be listed on their website so that you can check this as part of your initial research.

How to avoid cowboy builders

The best way to protect yourself from cowboy builders is to be aware of these top red flags:

• Someone asking for work by knocking on your door (usually to say they’ve ‘noticed a problem’)
• Asking to be paid upfront before any work has started
• Requesting to be paid in cash
• Not providing a written quote
• The company doesn’t have a business address
• A lack of a professional website
• Not Trading Standards approved and not a member of any professional trade associations
• Poor online reviews, or even a lack of reviews

Alongside trusting your gut instinct, you should also take the time to thoroughly research potential builders online. For instance, Googling the builder’s name, company name and location is one of the easiest ways to reveal good or bad signs about a trader.

Post-project snagging & guarantees

It’s one thing when a builder is upbeat when trying to win the job. But what happens when something isn’t quite right during the project or at handover time?

The person responsible for project managing your two storey extension should put together a snagging list. Where any faults need to be rectified, this should be handled by your principal contractor. Make sure you agree on who will be responsible for snags before you sign on the dotted line.

Alternatively, you can hire a surveyor to complete a snagging survey, at a cost of between £300 and £600.

Timeline: From idea to completion

Project stage	Typical timeframe
Architect plans (if required)	4-12 weeks
Planning permission (if required)	8-12 weeks
Quote sourcing and selection	2-4 weeks
Site preparation and groundworks	1-3 weeks
Construction phase	10-12 weeks
Internal decoration	3 weeks
Snagging & completion	1-2 weeks
Post completion (i.e. landscaping)	1-2 weeks

There is no such thing as a fixed timeline for two storey extensions. Though the above gives you an idea of how long each stage will take.

If you are undertaking a very complex two storey installation, more steps and ultimately more time will be involved. So while the typical timeframe is 3 to 8 months, it’s not unheard of for it to take around 12 months to build a large or very complicated double height extension.

Something that can reduce delays is getting any planning permission in place as soon as you can. Or, if your project would be considered a permitted development, you can skip this stage and speed things up.

Also, simplifying the design would reduce timescales as well as costs. So it’s important to consider what you’re comfortable with, especially if your development needs to meet any deadlines.

When to order materials

We know you’re keen to get started with your double storey extension. But it’s always good to check with your contractor about when materials will be ordered, if you will be purchasing anything yourself.

On the one hand, ordering in advance can allow you to take advantage of deals to save money. However, depending on the size and type of goods, this can also create storage challenges.

Overall, it’s wise to research timeframes for any materials you will be responsible for ordering. This will help project delays by ensuring your contractors have everything they need to get to work.

FAQs about two storey extensions

Still have questions about the average two storey extension cost? We’ve answered the top queries below.

For more information on similar topics, take a look at our free building work price guides. Here, you’ll find handy hints on the cost of building an extension along with similar home improvement projects.