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Cost of a Double-Storey Extension

Thinking of having a double-storey extension constructed? In the following guide, we’ll look at the costs of installing a new double story extension based on size and type. We’ll also break down the labour and supply costs separately and explore additional, relevant subjects such as how long this work tends to take and whether you can construct a two-storey extension DIY.

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

The average cost of constructing a 30m2 double-storey extension is £43,000 to £50,000. If you’d prefer a 60m2 extension, you’ll need a budget of about £66,000 to £74,000.

Double storey extension construction

The total cost estimate rises to a range of £88,000 to £101,500 for a 100m2 two-storey extension.

Labour Cost

As for the trade cost in particular, you can expect to pay about £150 to £250 per labourer a day. Considering that an electrician will also be required and possibly a landscaper and plumber, the labour cost can add up quite quickly.

For a 30m2 two-storey extension, the overall labour cost will land around £26,000 to £30,400. Should the extension be 60m2, expect a labour price of £40,000 to £44,000 or for a 100m2 extension, roughly £54,000 to £60,000.

Supply Costs

Let’s now take a look at the double-storey extension prices for materials. There is a vast array of supplies that will be needed to construct a two-storey extension.

In total, they would cost approximately £15,000 to £17,000 for a 30m2 extension or £23,000 to £26,000 for a 60m2 extension. The cost of double-storey extension is around £30,000 to £36,000 in the case of a 100m2 extension.

Waste Removal Costs

The third major cost element is that of waste removal. For a 30m2 extension, this would cost about £2000 to £2700, with the price rising to around £3000 to £4000 for a 60m2 extension or £4000 to £5500 if you want to build an extension that is 100m2 in size.

Cost Factors

There are plenty of ways the cost of building a double-storey extension may vary. For example, beyond the size and type of the extension, the design is also important. Among the most popular double-storey extension designs are side return, wrap around, rear, and front extensions.

Man on the roof of double storey extension

In addition, the type of room beings being extended, the quality of finish, ease of access, the state of the work area, and where you live are also significant cost-factors.

Property location is relevant since labourers charge different rates in different parts of the UK.

Double-Storey Extension Cost

Size of Extension Labour Cost Supply Cost Waste Removal Total Cost
30m2 £26,000 to £30,400 £15,000 to £17,000 £2000 to £2700 £43,000 to £50,000
60m2 £40,000 to £44,000 £23,000 to £26,000 £3000 to £4000 £66,000 to £74,000
100m2 £54,000 to £60,000 £30,000 to £36,000 £4000 to £5500 £88,000 to £101,500

Types of Double-Storey Extension

We’ll now take a closer look at the various design choices available when it comes to constructing a two-storey extension.

In each of the following subsections, we’ll lay out the features, costs, and pros & cons of these options.

Rear Extension Cost

One of the most common extension designs, simply involves adding structure at the back of a property. This tends to involve extending into the back garden. Rear extensions are well-suited to detached and semi-detached houses or a terraced house with sufficient garden space.

Double storey extension build

In many cases, a rear extension may be the only viable choice. Depending on the size and quality of the double-storey rear extension, it will likely cost between £26,000 and £100,000 to build.


✔ Can be less expensive than other types

✔ May provide better lighting opportunities

✔ Provides a quick access point to the outdoors


✖ Uses up garden space

✖ Construction may be challenging if garden space is minimal

Side Return Extension Cost

Unlike a rear extension, a side return extension is constructed to the side of a property. While this means no garden space is used up, not all properties will be well suited for it.

Side return double storey extension

However, if you have enough room, most detached and semi-detached homes could have a side-return extension added, although how large it could be will depend on how much land you own to the side of your house.

Again, depending on the size and quality of the extension, installation prices will likely range from £40,000 to £90,000.


✔ Double-storey side extension will not use up garden space

✔ Eco-friendly


✖ Not suited to as many properties as a rear extension

✖ You may be limited with the space you can use

✖ Likely to block your home’s side entrance

Wraparound Extension Cost

Though not the most common choice, a wraparound extension is the largest design option as it is essentially a combination of a rear and side return extension.

Wrap around double storey extension

To maximise house space, this might be the right choice for you, assuming that you have sufficient room to the side and back of your home for construction.

It is generally suited to semi-detached and detached houses. On average, it costs about £30,000 to £100,000 to build a wraparound extension. It is the most expensive option.


✔ Large and spacious extension

✔ A trial excavation is needed


✖ Could be particularly expensive

✖ Tends to be more time-consuming

✖ Complex to build

Front Extension Cost

One of the least common extension types is a front extension. This type of extension is self-explanatory and is essentially a rear extension on the other side of the property.

Front double storey extension

However, given that it alters the outer appearance of a property the most, building regulations are, unsurprisingly stricter. The average cost of a front extension is £26,000 to £100,000.


✔ Generally not as expensive as a wraparound extension


✖ Significantly alters the appearance of the property

✖ Building regulations are stricter

What Does Building a Double-Storey Extension Involve?

In this section, we’ll take a look at what is involved in the process of building a two-storey extension, step-by-step.

1. Planning and Hiring Professionals

Building a two-storey extension requires plenty of planning. First and foremost, you’ll need to consider whether the Party Wall Act of 1996 may apply to have an extension built on your property.

There are also many building regulations and planning permission rules to take into account.

Then, you’ll need to decide on a design. It’s best to go through a range of double-storey extension ideas.

In the previous section, we looked at the pros & cons of the various design options, but either on your own accord or with the help of a professional, you can go into more detail with your design choices and personalise the extension based on your preferences.

It is best to hire an architect or professional designer to create an in-depth plan for your double story extension.

Once you have the design complete, you should get in touch with contractors/companies. You should obtain a minimum of three quotes before making a decision. It’s also worth asking for some references too, before coming to a decision.

2. Laying the Foundations

On the first day of construction, the foundations must be measured and dug out in accordance with your design plans. Building control will come by to assess the work.

They’ll also make suggestions such as whether reinforcement is needed for the extension’s foundations. Next, the pipework and drainage will need to undergo modification prior to concrete being added.

Plenty of landscape work is likely to follow, particularly if the new extension is set to extend into your back garden and if a new door is required, to provide access to the outdoors.

A path or new patio may also be on the books, depending on your plans. Landscape work could take place at a later stage in the project but it is generally considered ideal to do so around the beginning.

This will allow new plants the time they need to grow and establish their presence.

3. Building the Extension

For this step, the actual extension will be constructed. As soon as the foundations have been laid, the extensions’ external walls can be built.

Scaffolding will most likely prove necessary. As soon as the external walls have been constructed, the internal walls may be built. Next, the roof and covering will be added.

Then, windows, doors, guttering, and external pipes will be added, alongside any other infrastructure required to complete the body of the extension.

4. Add the Fittings

At this stage, carpentry, plumbing and electric work will be undertaken within the extension. Other internal fittings may include a stud wall or steel joists for reinforcement.

Then, plastering, decorating (painting or wallpapering), and adding the flooring will follow. Once everything is in place, the electrics can be turned on and the plumbing connections finalised.

5. Additional Work

Once the extension is complete, you may wish to have a variety of appliances fitted such as radiators. To add a new radiator would cost about £200 to £300 per unit.

To have a new kitchen installed would set you back somewhere in the range of £4000 to £20,000, depending on the size and quality of the kitchen.

Building a double storey extension

If you’d like to install a new upstairs bathroom, expect to pay approximately £4500 to £9000, again varying based on the quality and size of the installation. To have both rooms painted would set you back roughly £600 to £1000.

Underfloor heating would likely cost £1500 to £2500 with the price landing about £1500 to £2000 for a new boiler system, and £500 to £1000 if a party wall agreement is required.

If you chose to hire an architect as part of the project, you’d like to pay around £800 to £2500, while surveyors charge about £500 to £2000 altogether.

DIY Double-Storey Extension

Unfortunately, building a double-storey extension is not a DIY job. Some work in particular will require the work of professionals such as electrical tasks.

The same is true of plumbing, gas work, and structural jobs. Of course, some work can be undertaken DIY, such as painting and decorating and adding a professional finish.

By taking on some of the work yourself, you can save money. The extent of the work you should undertake DIY will depend on how confident you are in your skills and knowledge that are required for those specific tasks and whether or not it is actually legally allowed for a DIY enthusiast to perform such jobs. Double storey extension with scaffolding

If you are unsure about anything, contact your local council for advice.

A contractor may be needed to sign off the work. As with any DIY work, there are risks that need to be considered. If your work involves working with heavy equipment or materials, you could accidentally harm yourself, such as if an object struck you or if you were to strain your back while carrying a heavy load.

It’s important that you take all of the necessary safety precautions and consider what safety equipment you may need. Beyond that, performing DIY work incorrectly could mean that expensive repairs will be required.

Potential Problems and Pitfalls

As with all construction work, there are some disadvantages to two-storey extensions. Firstly, having a double-storey extension built is an expensive and time consuming task.

Not only that but an extension with two-storeys is more likely to come with challenges in terms of double-storey extension planning permission approval and there is a danger that your neighbours will not approve of the project, potentially leading to conflict and interpersonal disputes.

Tradespeople building a double storey extension

If your application(s) for planning permission or/and building regulations were rejected, you would need to apply again with the appropriate changes made to your new application(s). However, in most cases, any applications that are needed are approved the first time.

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Sam J

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