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13 Single Storey Extension Ideas For Your Home


A single storey extension can provide our architects with infinite design possibilities. That’s why we love to design them.

Our architects’ favourite part of the design process is working with homeowners to choose incredible new, modern and innovative materials. This means your single storey extension will be truly one of a kind and stand out from the crowd.

The only difficult part is deciding on the design and materials which suit you best, as there are so many to choose from. To help give you some inspiration, we have highlighted thirteen of the most popular types of single-storey extensions.

For each one, we discuss the planning permission aspects, construction costs and some design examples.

1. Side extension – single storey extension idea

1.1. Planning permission

Good news! In the majority of cases, most single-storey side extensions can be built under what’s called ‘Permitted Development’. This allows changes to be made to your house without the need to apply for planning permission. This is a fantastic route to take as it often removes much of the complex red tape associated with the planning system and its sometimes intricate policies.

The following permitted development criteria are exclusive to single-storey side extensions:

  • Your extension cannot exceed four metres in height
  • It can only be single-storey
  • It can only be up to half the width of the original house

If your single-storey side extension idea doesn’t meet the above criteria, then not all is lost. It can actually be a huge advantage. Local planning policies are often far less rigid than permitted development. This means there might be scope to build a bigger extension than you thought….with modern materials.

1.2. Construction cost

There are several factors, which can affect the cost of your extension including size, materials, quality of finish and even the builder you use.

For an average size semi-detached or detached house, the cost of a single-storey side extension would range between £40,000 – £50,000.

1.3. Side extension – design idea

Side extensions don’t need to be big to create a unique and fantastic living space. This side extension measured only 1.5m in width but helped create a stunning open-plan kitchen and living room:

Side extension – single storey extension idea
Transform your existing living space with an elegant side extension

2. Rear extension – single storey extension idea

2.1. Planning permission

When it comes to planning permission vs. permitted development, the main thing to consider for rear extensions is the depth. Here are the allowed depths of permitted development single-storey rear extensions:

  • 3m depth: terraced and semi-detached houses
  • 4m depth: detached houses

Some people think that opting for permitted development will always get you the most space, but that is not necessarily the case. For example, the planning departments of many boroughs in London will allow semi-detached houses to have single-storey rear extensions of 3.5m in depth. This is 500mm more than you would achieve through permitted development. There are many examples like this so you needn’t be worried about exploring the planning permission route – it might just get you more space!

2.2. Construction cost

The easiest way to work out the cost of your extension is to work out how many square metres you want to build. You then multiply that number by the total construction cost/m2.

On average, it costs approximately £1,800 – £2,200/m2 to build a single-storey rear extension.

For an average size extension measuring 4m x 5m the total build cost would range between £36,000 – £44,000.

2.3. Rear extension – design idea

The living space of this semi-detached house was a little small and cramped and far too small for the growing family. This single-storey rear extension was designed with huge bi-fold doors to flood the new living space with natural light:

Rear extension – single storey extension idea
This 3m deep extension helped create an entirely new kitchen and huge living space

3. Wrap around – single storey extension idea

3.1. Planning permission

Wrap-around single-storey extensions are the perfect option if you’re looking to create the maximum amount of floor space. In terms of planning permission, they are a little trickier to successfully take through the planning system when compared to some other types of extension. The reason is that they fall within neither side extension nor the rear extension permitted development guidance.

The good news is that our team of architects and planning consultants have designed and built hundreds of wraparound extensions. If this is something you had in mind, feel free to arrange a free 30-minute consultation with one of our architects. We’re always free to chat about your ideas.

3.2. Construction Cost

Because wraparound extensions have the potential to add so much space, they also cost more to build.

For a typical semi-detached house, we would estimate that a side and rear wrap-around extension would be approximately 50m2.

At £1,800 – £2,000 per m2, the total construction cost for an average size wraparound extension would be £90,000 – £110,000.

3.3. Wrap around extension – design idea

Wrap around – single storey extension idea
This stunning wrap-around extension makes more efficient use of a space the family rarely used

4. Side return – single storey extension idea

4.1. Planning permission

Side return extensions are usually found on terraced houses. Although they aren’t the largest extensions you can build, they have three main advantages.

1. They make fantastic use of the area to the side of your house, which is often overshadowed.

2. As they are relatively small the construction costs are low compared to other types of extension.

3. They can help transform your existing small space into something far more usable if you go down the open plan route.

As most infill side extensions are relatively narrow, they can often be built under permitted development. This means you avoid needing to deal with much of the red tape associated with the planning permission route.

4.2. Construction Cost

The construction costs of side return extensions can vary quite a bit depending on your location.

Outside Londonthe cost per m2 can range between £3,000 – £4,000/m2. This means the cost of an average 15m2 extension will range between £45,000 – £60,000.

Inside London – construction costs are higher, ranging from £4,500 – £6,000 per m2. The average cost of a side infill extension would range between £67,500 – £90,000.

4.3. Side return extension – design idea

Side return - single storey extension idea
If your terraced house has a narrow side return even a relatively narrow extension can help create an incredible new living space

5. Flat roof – single storey extension idea

5.1. Planning permission

In most cases, you won’t need to apply for planning permission for a flat roof rear extension as most fall under permitted development. But there are some exceptions to this rule. If you live in any of the following, you may not have permitted development rights and might need to apply for planning permission:

  • Flat
  • Maisonette
  • Listed Building
  • Conservation Area

5.2. Pros and Cons of flat roof extensions


  • Cheaper than a pitched roof
  • More contemporary and modern
  • A slight pitch prevents water collecting
  • Easy to install skylights


  • Internal ceiling heights might be low
  • Short life span compared to a pitched roof
  • May need extra maintenance
  • Not very energy efficient

5.3. Flat roof extension – design idea

A picture of a brick flat roof extension
The flat roof on this traditional brick built extension helps give it a contemporary twist

6. Pitched roof – single storey extension idea

6.1. Planning permission

When it comes to pitched roof extensions the good news is these can often be built under permitted development as long as they don’t exceed 4m in height. Also, if your extension would be located within 2m of your fence, the eaves height (usually the height of your gutters) cannot exceed more than 3m in height.

6.2. Pros and Cons of a pitched roof extension


  • Traditional in appearance
  • Relatively easy to maintain
  • Efficient at clearing rainwater


  • More expensive than a flat roof
  • More problematic to build with complex extensions
  • Difficult to clean

6.3. Pitched roof extension – design idea

We love designing pitched roofs because of the incredibly high ceilings they can achieve. Even in a small extension, the increased sense of space from a pitched roof will help make your entire living space appear larger.

A picture taken from the inside of a pitched roof extension
The high ceilings created from a pitched roof will help any extension feel bright and airy

7. Offset pitched roof – single storey extension idea

7.1. Planning permission

The planning and permitted development policies for offset pitched roof extensions are almost identical to pitched roofs. There is nothing in the permitted development legislation which stipulates that your ridge must be in the centre of your extension (as long as it doesn’t exceed more than 4m in height).

When going down the planning permission route, planning officers often like something a little different or modern. This means there is plenty of scope to be creative, even if your extension falls outside permitted development legislation.

7.2. Construction cost

Pitched roofs are often more expensive than flat roofs. The main reason for this is that pitched roofs are more complicated to build and also use more materials when compared to flat roofs.

For an average size 20 m2 single-storey rear extension, a pitched roof with a gable end would cost approximately £7,000 more than a flat roof.

7.3. Offset pitched roof extension – design idea

Offset pitched roof – single storey extension idea
This offset pitched roof extension adds a modern twist to a traditional design

8. Huge skylights – single storey extension idea

8.1. Planning permission

The best part about skylights is that they don’t require planning permission. You can use as many as you like on your roof to help flood your new living space with as much natural light as possible.

8.2. Construction cost

The cost of rooflights just comes down to the size you wish to install.

On the smaller side, a skylight measuring 55cm x 98 cm (manually controlled) would cost in the region £500.

On the larger side, a rooflight measuring 114cm x 252cm (manually controlled) would cost approximately £2,200.

8.3. Huge skylight – Design idea

A picture taken from inside an extension with large rooflights
Flood your living room with natural light by installing these huge skylights

9. Glass roof – single storey extension idea

9.1. Planning permission

If you want to make a statement, why not go for an entire glass roof? In terms of planning, the policies and legislation for glass roofs are similar to roof lights. There are no real limits to the amount of glazing you’re allowed to have within your roof.

9.2. Construction cost

A fully glazed roof is far more expensive than the flat or pitched roof alternatives.

The average cost per m2 would be in the region of £2,000.

This means for an average 20 m2 extension the cost of a fully glazed roof would be £40,000.

But you may decide it’s worth it when you see your neighbours peeking over the fence to marvel at your incredible new extension!

9.3. Glass roof extension – design idea

A picture of a modern extension with a glass roof
Make all your dinner party guests jealous with this incredible glass roof extension

10. Timber cladding – single storey extension idea

10.1. Planning permission

Cladding is a relative innovation when you think about how long bricks have been used to build extensions. From a planning point of view, something a little modern like timber cladding can be more difficult to get through the planning system when compared to bricks.

The reason is that under permitted development the materials of your new extension need to match the materials of your house. So, if you are like most homeowners and have a house made of brick, a timber-clad extension wouldn’t meet this criterion.

This leaves you having to go down the planning permission route. To help convince your local planning authority to accept such a modern material, we would advise asking your architect to provide lots of design examples showing your desired cladding. It will certainly help bring the planners over to your side if they have any reservations.

10.2. Construction cost

On average timber cladding costs between £40 – £60 per m2.

Bear in mind that it is far quicker to install when compared to a brick-built exterior wall so you will certainly save on labour.

10.3. Timber cladding extension – design idea

A picture of a modern extension clad with timber
If you’d like your extension to stand out from the crowd look no further than timber cladding

11. Zinc cladding extension – single storey extension idea

11.1. Planning permission

The planning factors to consider when installing zinc cladding are very similar to timber. As they won’t match the existing materials of your house this unfortunately rules out the permitted development route.

When submitting your plans to the local authority, ask your architect to include as many real work examples as possible. This will help your planners to appreciate how your extension would enhance the character of the area, making them more likely to approve your application.

11.2. Construction cost

Zinc is one of the most expensive types of cladding you could buy. It ranges from £140 – £180 per m2.

11.3. Zinc cladding extension – design idea

A picture of a modern zinc cladding extension
Why not be bold and opt for this contemporary zinc cladding?

12. Orangery – single storey extension idea

12.1. Planning permission

If you’re a fan of designs that are more traditional, look no further than an orangery. As there are so many different designs, sizes, and materials, these often fall under the permitted development category.

If you’re looking for a wraparound extension, this is also good news because local authority planning officers often prefer traditional over modern as it conforms better with the character of an area.

12.2. Construction cost

The average cost of an orangery is around £2,250/m². This includes supply and builds costs, along with electrics, plastering and lighting. 

12.3. Orangery extension – design idea

A picture taken from the inside of an orangery extension
For those with more traditional taste an orangery is the perfect extension

13. Glass box – single storey extension idea

13.1. Planning permission

If I could build my dream extension it would 100% be entirely made out of glass as they look stunning! They are however not the easiest of extensions to get successfully through the planning system. As most houses are made of brick, entirely glass extensions are not considered to be permitted developments as they wouldn’t match the bricks of your house.

The planning permission route can also be a little challenging as glass extensions are very contemporary and sometimes at odds with other extensions you might find on the same street.

That being said, at Adara, our team of architects and planning consultants have a huge amount of experience when it comes to glass extensions. If you have any design or planning permission-related questions please contact one of our architects at any time for a free 30 minute consultation.

13.2. Construction cost

Glass extensions range in cost but on average expect to pay approximately £2,800 – £3,200 per m2.

So for a typical extension measuring 25m2, the overall cost would be between £70,000 – £80,000.

13.3. Glass box extension – design idea

A picture of an extension made entirely of glass
Do you enjoy looking at the stars while sitting on your sofa? If so, a glass box extension is one of the only ways to do it


At Adara, our team of architects and planning permission experts love to help homeowners design unique and stunning extensions.

We will always do our best to give you something truly unique and help you stand out from the crowd.

If you have any ideas you would like to discuss, feel free to book a free 30-min consultation with our architects. We’re always on hand to hear about your ideas (and hopefully share some of our own).

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