How Much Does It Cost to Build a Double Storey Extension?

As your family grows, your home may become too small. Instead of moving home, you may prefer to stay where you are and, instead, invest in a two-storey extension to increase the size of your home. So how much does a double storey extension cost?

The overall cost of a double storey extension will vary depending on the size, the complexity of the job, and your location. The average cost of a double storey extension is around £40,000-£100,000.

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On average, you can expect to pay around £1000-£1750 per square metre, plus additional costs for the installation of fixtures and fittings such as kitchen fixtures or bathroom fixtures. These additional costs will depend on what you plan to do with the extra space.

Doubles Storey Extension Prices

Below is a list of the prices you can expect building a double storey extension. Keep in mind that a small extension is around 30m2, a medium extension is around 60m2, and a large extension is around 100m2.

Job Description Average Cost
Small basic double storey extension £35,000-£45,00
Small average double storey extension £40,000-£50,000
Small deluxe double storey extension £50,000-£60,000
Medium basic double storey extension £60,000-£70,000
Medium average double storey extension £65,000-£75,000
Medium deluxe double storey extension £70,000-£80,000
Large basic double storey extension £85,000-£95,000
Large average double storey extension £90,000-£100,000
Large deluxe double storey extension £100,000+


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What are the Supply Costs of a Double Storey Extension?

There are many different supply costs that come with a double storey extension. Below is a list of the potential double storey extension prices you may need to think about:

Types of Supply Average Cost
Foundations £3000-£10,000
External Brickwork £2000-£5000
Roof Materials £1000-£3000
Bifold/French Doors £1500-£2500
Windows £1500-£3500
Rendering Materials £30-£50 per m2
Internal Decorating Materials £400-£1500
Radiators £400-£3000
Underfloor Heating Materials £1000-£4000
Kitchen Units £3000-£10,000
Kitchen Worktops £20-£500 per m2
Washing Machine £200-£500
Oven £300-£800
Hob £100-£400
Cooker Hood £200-£500
Dishwasher £300-£600
Fridge Freezer £200-£800
Flooring £10-£100 per m2
Wall Décor (Tiles/Wallpaper/Paint) £20-£50 per m2
Windows £200-£600 each
External Door £400-£900
Internal Doors £50-£300 per door
Bathroom Suite £2000-£10,000


What are the Additional Costs of Building a Double Storey Extension?

There are several additional costs that may come up when installing a double storey extension. Below is a list of the main additional costs that may come up with this type of work:

Scaffolding Hire

When installing a double storey extension, you will need to hire scaffolding so that the builders can access all areas of the worksite. Sometimes, the building company may provide the scaffolding for you. However, when they don’t, you’ll need to know how much it costs to hire scaffolding.

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The average cost of having a scaffolding tower erected is around £200-£300. The costs will increase depending on how long you need to hire the scaffolding.

New Roof Installation

When you have a double storey extension installed, you will need to install a roof on top of the new extension. The average cost to install a roof on your new extension is around £1000-£2000, depending on the size of the roof.

New Bathroom Installation

When you get a new double storey extension, you may want to add a bathroom to the extra space. If this is the case, then you can expect to pay around £3000-£6000 to have a new bathroom installed at your home.

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New Kitchen Installation

Similarly, you may also want to add a kitchen to the additional space in your double storey extension. The average cost to install a kitchen at your home is around £6000-£9000, although this will differ for various sizes and finishes.

Tradesmen Costs for a Double Storey Extension

The labour costs of building a double storey extension depend on the size of the extension, the difficulty of the job, and the location of your property.

On average, you can expect to pay around £150-£250 per day for each contractor on the job. Most of the time, the builders will work in a team of around 3-4 people.

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It’s important to note you will need to also pay additional contractors for this type of work. Below is a list of the additional labour costs that may be involved with a double storey extension installation:

Tradesperson Average Cost Per Day
Electrician £125-£300
Plumber £150-£200
Roofer £150-£225
Kitchen fitter £125-£175
Joiner/Carpenter £125-£180
Plasterer £100-£250
Painter/Decorator £150-£200
Floor Fitter £150-£200
Tiler £150-£200


How Long Does It Take to Build a Double Storey Extension?

The build time for double storey extension will depend on various factors, including the efficiency of the contractors, the weather conditions during the build, and the difficulty of the job.

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Below is a list of the timeframes for various double storey extension installation jobs:

  • Small (30m2) double storey extension installation – 8-10 weeks
  • Medium (60m2) double storey extension installation – 10-12 weeks
  • Large (30m2) double storey extension installation – 12-14 weeks

You should also factor in extra time for more complex additions and larger extension sizes. If you need to get planning permission, get work completed by an architect, or gain a party wall agreement, you will need to add on some extra time before the building can start.

Types of Double Storey Extension

There are several types of double storey extensions you can choose from. Below is a list of the different types of double storey extensions for you to consider:

Double Storey Front Extension

A double storey front extension is probably the least common extension type. This is because it has the most impact on the overall look of the property. When you build an extension here, there are stricter building regulations that need to be adhered to.

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Double Storey Side Return Extension

This type of extension is built on the side of the property and doesn’t have any effect on the garden area. This type of extension is only suitable for semi-detached or completely detached properties with enough room at the side for the extension.

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Double Storey Rear Extension

This type of extension extends out of the rear of the property and usually extends out into the garden area. This type of extension is suitable for semi-detached and detached properties. However, it can also work on terraced properties that have enough space at the rear too.

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Double Storey Wrap Around Extension

This type of extension is a mixture of the rear and side extensions. If you are looking to add extra space to your home, a wraparound extension may be the best option. This type of extension can add a lot of space to the home, and is suitable for semi-detached and detached properties.

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Benefits of a Double Storey Extension

There are many benefits to installing a double storey extension at your home. Below is a list of the advantages of this type of work:

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Extra Space

Adding a double-storey extension to your home is a great way to increase space without having to move. With this in mind, there are also additional savings as you don’t need to worry about the expenses of solicitor’s fees, estate agent fees and stamp duty.

Additional Rooms

When you add a double storey extension, it enables you to add additional rooms to your home. You can choose the size and type of room that will suit your needs. Some examples of additional rooms include a guest bedroom, a wet room, an office, a new kitchen, or bathroom.

Also, if you don’t want additional rooms, your double storey extension can be used to make your existing rooms bigger. When it comes to a double storey extension, there are so many options available for you to choose from, and you have the freedom to customise your home the way you want it.

Pro-Rata Costs

Adding a single-storey extension will provide additional space, however, it costs less per metre squared to add an extra level.

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Since you have to build foundations and a roof regardless of whether you are building a one-storey extension or a two-storey extension, your additional storey will only require the internal walls, external finishing and the interior finish.

FAQs

Q: Does a double storey extension add value to a home?

A: The value of your home will increase with an extension, however, there is no way to determine how much it will increase by. The appeal of more living space is a plus for potential buyers. However, the sale price may be affected by the appeal of the neighbourhood and the value of your local properties.

Q: How deep do foundations need to be for a double storey extension?

A: The minimum foundation depth for a double storey extension is 200mm. This will ensure they have the necessary strength to fulfil their purpose.

Q: Do I need to move out while my double storey extension is getting built?

A: If the builders need access to all or most of the rooms in your home, it’s best to move out for a few months. This will not only save your sanity, but it will also help the contractors stick to the timescales for your build. Some contractors will not complete an extension on an occupied home.

Many homeowners opt to live in a caravan in the garden. However, a hotel may be a quieter and more comfortable option. This will work out more expensive in most cases, so it will depend on your budget.

Q: Do I need planning permission for a double storey extension?

This will depend on the size of the extension and where it will be placed on the house. As long as your extension plans are within the permitted development guidelines, you shouldn’t need to worry about planning permission.

If your home is a listed building or if it is located in a conservation area, you will need planning permission for any type of extension. There are some other exceptions that may mean you will need planning permission. Just to be sure, you will need to contact your local authority before the work starts.

Q: What is a Party Wall Act?

A: If you share a boundary wall with a neighbour, you will need to obtain consent from them formally before you can start building your extension. If you don’t, you will need a Party Wall agreement.

If you don’t follow through with the Party Wall Act, then this could mean your neighbours can take civil action against you, which will result in the work on the extension being stopped partway through.

This will delay your extension build and will also increase the costs. Your neighbours will also be able to get compensation and can even force you to remove any of the work that has already been carried out.

Q: How much disruption will a double storey extension cause?

A: Any type of building work can be very disruptive and stressful. If your budget allows for it, then you can avoid the disruptions by moving out of your home while the work is being carried out.

You should also remember to pack away any valuables or anything that may become damaged. If you can’t move out, then the building company will try to minimise the disruption. However, this will result in the work taking much longer.

Sources

  1. https://www.realhomes.com/advice/double-storey-extensions-costing-planning-and-designing-your-two-storey-extension
  2. https://www.houseup.co.uk/news/double storey-extension-guide
  3. https://blog.bdsarchitecture.co.uk/foundation-depth-for-two-storey-extension
Author: Kim J

I have a bachelor's degree in Journalism, which I studied in both the UK and USA. I've been a freelance writer for over eight years and have experience working with many large brands. My experience in writing is over a wide range of different niches, and I've specifically worked in the DIY and trades section for nearly two years. My favourite thing about freelance writing is working wherever I want as I love travelling and discovering new places and cultures.