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Last updated on March 6th, 2024

How much does it cost to build a double storey extension?

Building a double storey extension is a practical solution to increase the floor space in your home. Whether you want to increase the size of current rooms, add new rooms, increase the value of your home, or alter the layout of existing rooms, there are lots of options.

Instead of adding two single floor extensions separately, choosing to extend two storeys simultaneously means you will save money in the long run, plus reduce project time and any disruption.

Are you looking for other extension types? Then take a look at our in-depth house extension cost guide.

How much does a double storey extension cost?

To find the cost of planning and building a double storey extension, we spoke to the online estimators at My Build Estimate – a professional estimating company monitored by the Royal Institute of Chartered Surveyors (RICS).

This guide features the estimated two-storey extension cost examples they provided.

Type of extensionCost + VAT
(Range low - high)
Average cost
Standard quality double storey extension per sqm£1,650 - £2,150£1,900
Good quality double storey extension per sqm£1,830 - £2,350£2,090
Excellent quality double storey extension per sqm£2,150 - £3,000£2,575
Extension planning drawings cost£500 - £1500£950
Foundations based on 60m2 double storey (30m2 per floor)£6,000
Framing based on 60m2 double storey (30m2 per floor)£36,000
Roofing based on 60m2 double storey (30m2 per floor)£14,000
Surveyors fees£500 - £2,000£1,250
Party wall agreement£500 - £1000£750

Our costs are ballpark averages – get a local tradesperson to quote now

The average per sqm price of a double storey extension is £1,783.33.

The average timescale of a double storey extension is 8 – 14 weeks.

All prices used throughout this guide are based on standard construction, foundations, framing and roofing costs. Be mindful that these costs exclude internal fixtures and fittings, and the price for these will depend on the room’s purpose.

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How do double storey extensions compare to single storey extensions?

If you are hoping to eventually extend both the ground and first floor of your home, it is a wise decision to tackle both at the same time. As you are already paying for a roof and the foundations of your new extension, this cost will not change when choosing to extend two storeys instead of one.

Then there is the time difference; double storey extensions do not take double the time of single ones. It is also worth noting that the overall cost of a two-storey extension vs a one-storey extension is an average increase of 50% – 70%, a significant reduction compared to completing both floor extensions separately.

Types of double storey extensions

Where you locate the extension on your home will play a key role in how much you get out of it. Choose poorly, and you may achieve disappointing results with obstructed views, reduced privacy, light reduction through your and your neighbours’ windows and reduced garden access.

Location of extensionCost + VAT
(Range low - high)
Average cost
Double storey side extension cost (5m x 4m)£66,000£100,000
Double storey front extension cost (5m x 4m)£66,000£100,000
Double storey wraparound extension cost (5m x 4m)£66,000£100,000

The location of your extension may impact the cost due to the ease or difficulty of site access. Your chosen roof design could also impact the cost.

Rear of home

While the most popular, these extensions can drastically reduce your garden space, so they are more viable for homes with extensive gardens.

Front of home

Less common than rear extensions, front extensions completely alter the look of your home and must comply with strict regulations.

Side of home

Double storey side extensions are less popular than rear extensions but perfect for detached or semi-detached homes. They have little impact on garden space and home appearance.

On average, a two-storey side extension costs £66,000 for a 5m x 4m extension.


There is excellent extra space potential when working with wraparound extensions (typically made up of side and rear extensions); however, they also can be very costly and time-consuming.

Interior construction work on double storey extension

Double storey extension cost calculator

To calculate the cost of your double storey extension, there are many variables to consider. Planning a budget is one of the essential steps for any significant home improvement project.

When building a double storey extension, here are some of the most common elements that you’ll need to factor in your cost calculator.

Architect and surveyor fees

Whilst not a legal requirement, an architect can optimise the construction of your extension and can cost £800 – £2,500. Surveyors can ensure that your planned project is safe to build, and they cost on average £1,250.


The larger your new extension, the higher the cost due to the extra materials needed and the effort to complete the increased floor space.


The quality of materials used and work done will affect the overall two-storey extension price.


Whether you require your new extension to be plastered or painted will incur an additional cost.


Foundations and groundworks are essential and vary from project to project. Therefore, depending on your current situation, this price can vary.


Due to health and safety requirements, safe working at height regulations must be followed, and in most cases, this will mean scaffolding will be required. This scaffolding cost should be included in your budget, especially when building a two-storey extension.


It is essential to inform your home insurance company of any structural changes to your home, which may affect your premium cost. If you do not have an up-to-date policy, you may not be covered for any accidents or damage.


The location of your home in the country plus the site of your new extension on your house will alter the cost of your two-storey extension.


Bathrooms and kitchens must have the correct drainage added to ensure waste is properly dealt with. Due to the extra work, this will increase the overall cost.


Essential for any extension, even just for small power points, electrics must be fitted and inspected by a qualified electrician at an added cost.

Purpose of the room

Be mindful that adding a new kitchen or bathroom is more costly than a bedroom due to electrics, plumbing, and the room’s finish. The addition of a kitchen or bathroom may add £7,000 – £10,000 to the job.

Function of extensionCost + VAT
(Range low - high)
Average cost
Bathroom cost (additional cost)£2,500 - £11,000£6,750
Kitchen cost (additional cost)£10,000 - £25,000£15,000

Windows and doors

Choosing to add windows and doors to your new extension can increase light and improve access. Extra enhancements and a higher quality of a product can vastly increase the overall cost of your two-storey extension.


Adding stairs to a new extension can be very important to allow ease of access. Depending on the solution you opt for and the complexity of the stair installation, you can expect to add an additional £2,750 to your build cost.  For more information, please read our new staircase cost guide.

Openings to outdoors

Any doors that allow access to the outside of the home must be secure and adequately insulated, likely affecting the cost.

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Does a double storey extension need planning permission?

You must ensure that any new extension meets legal and structural regulations. Several requirements will affect double storey extension planning permission being granted (or not), such as:

  • Double storey extensions aren’t permitted if you live in any of the following areas:
    • a National Park or Conservation Area
    • an Area of Outstanding Natural Beauty
    • a World Heritage Site
  • Extensions (that includes your planned extension and any previous extensions you’ve had built) can’t take up more than half the total area of land around the original house.
  • The eaves and ridge height of the extension can’t be higher than your existing house structure. If your extension will sit within two metres of a boundary, then the maximum height for the eaves is three metres.
  • Double storey extensions can’t be more than three metres deeper than your existing house or within seven metres of the opposing boundary.
  • Where possible, the roof pitch of the extension should match your existing house as best it can.
  • The materials you use for the exterior of your extension should match the existing building as much as possible.
  • Balconies and verandas are not permitted on a double storey extension.

If you have any doubts about the plans for your extension and any of the double storey extension planning permission restrictions, contact your local planning office.

Planning permission cost

It is always worth getting early advice to confirm if planning permission is required, and you should check with your local authority—costs are typically around £200.

Party wall agreement cost

Before adding an extension, it may be essential to draw up a party wall agreement which costs roughly £750 per neighbour.

Survey costs

These are critical to ensure your extension is built in a safe and structurally sound way. Your tradesperson will be able to help decide on the appropriate surveys for you. For example, if you have a tree survey, this will cost approximately £200.

Double storey extension hourly rates

Specific costs of your double storey extension, like the architect or surveyor fee, planning permissions, etc., are fixed, but here are the hourly rates you can expect from:

BuildersBuilder hourly rates vary based on the type of builder they are, but in general, you can expect to pay around £35 per hour.

Unskilled labour: £100 per day

Plumbers: A plumber’s hourly rate is between £30 – £50 per hour.

Electricians: You will pay around £45 per hour to an electrician.

The hourly rates will vary according to the size of the company as well as the location. Areas in and around London and the South East tend to be more expensive, while rates are lower the further north you go.

Double storey extension quotes

When you look for double storey extension quotes, you want tradespeople you can trust. And, no one can be better than people who your neighbours have used and can recommend. That’s the most significant advantage of using local tradespeople. That is why we make it easy for you to get your quotes from local builders. Fill in our ‘request a quote‘ with information about your job and we’ll send this to builders near you.

We always recommend that you compare quotes from at least three tradespeople before you pick one so that you can get the best price. You can also check out their reviews to see how well they satisfied other customers and ask them for samples of similar work that they may have done previously.

Double storey extension building regulations

As with any construction project, you’ll need to ensure that all of the work on your double storey extension is compliant with current UK Building Regulations. In some cases, you’ll need to get prior approval before starting any work on the extension.

It’s essential to make sure the tradespeople working on your extension fully comply with Building Regulations. If they don’t, they can be prosecuted and, if your home doesn’t comply with double storey extension building regulations, you could have problems when you come to sell it in the future.

Scaffolding around two storey extension

How long will a double storey extension take?

While two-storey extensions do not require double the time necessary for single storey extensions, the time taken will be significant and largely depends on the above factors. The effort is fundamentally focused on two stages:

  • Preparing and planning: Architect designs, any drawings, obtaining planning permission, structural planning etc. – This can be from 2 weeks to several months depending on any legalities and issues that arise.
  • Construction: 8 – 14 weeks dependent on the size of the extension and any of the other essential factors listed above.

Can I build a double storey extension myself?

Building an extension is not an easy and quick job. It isn’t easy to work with heavy materials, especially at the heights required for this job.

Aside from the arduous construction process, not finishing the job to a high standard opens you up to endless difficulties down the line. These include water damage from moisture seeping into the home, electrical and plumbing issues, danger to yourself and others living in the house from collapse and unstable foundations, not to mention the legalities and regulations that you may have broken. This can lead to your insurance provider not covering your home, and you may face legal issues. As such, we would strongly recommend hiring a professional.

Use our free search feature to find a local, reputable tradesperson in your area and get a personalised quote for a double storey extension cost.

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Key takeaways

  • Extensions can be added to the rear, side or front of your home or even wrap around the side and back of the house.
  • There are a large number of factors such as size and location that affect your two-storey extension price.
  • Adding a two-storey extension does not cost twice the amount of a single storey extension.
  • There are several legal regulations when extending your home that must be complied with.
  • It is dangerous and extremely difficult to add a two-storey extension yourself.

We check the reviews on Checkatrade are from real people, and that trades meet our high standards.

Working with professional estimators, we collate cost estimates for the common home improvement and repair jobs in the UK.

All the costs are estimates only. For accurate costs for your particular requirements, you are encouraged to reach out to professional tradespeople to receive a quote for your job.

Our estimators are Chartered Members (MRICS) of the Royal Institution of Chartered Surveyors and Members of the Chartered Institute of Building (MCIOB). See full disclaimer.

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