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Terraced House Extensions: Design Ideas and Planning Advice

Design Ideas

We love to design terraced house extensions!

Why? Because it gives us the opportunity to get creative with our designs.

As terraced houses can be narrower than either semi-detached or detached houses, it can make extending them a little more challenging.

However with some innovative ideas from a creative team of architects with a lot of experience of terraced house extensions, any terraced house can be transformed into a truly stunning place to live.

For those of you who are looking to add that much-needed living space, our guide below covers everything you need to know about extending your terraced home. We cover planning policy, permitted development & construction costs.

We have also included some incredible design ideas we hope help inspire you to transform your own home.

1. Single storey rear – terraced house extension

1.1 Permitted development

We’re not sure if you know this, but there are lots of different types of extensions you can build without the need to apply for planning permission. This is what’s known as ‘Permitted Development Rights’. Below are the permitted development rules and regulations covering single storey rear extensions to terraced houses:

Area: Only 50% of the land around your “original house” can be covered by extensions.

Height: Extensions cannot be higher at the eaves (the area below your gutters) than the existing eaves and cannot exceed an overall height of 4m.

Proximity to the boundary: Where the extension comes within two metres of the boundary, the height at the eaves cannot exceed three metres.

Location: Extensions cannot be built forward of the principal elevation (usually the front of your house).

Conservation Areas: If you live in a Conservation Area, the building work for a terraced house extension cannot include cladding on the outside of your house.

Materials: The materials used in any exterior work must be of a similar appearance to those on the exterior of the existing house.

Depth: For terraced houses, single-storey rear extensions cannot extend beyond the rear wall of the original house by more than 3m.

1.2. Planning Permission

If you don’t meet the requirements of the above legislation, all is not lost. Although going down the Permitted Development route can mean less paperwork, it can be restrictive depending on the type of design you would like. There are some advantages to going down the planning permission route.

Materials: When it comes to Permitted Development, it’s important that the materials of your extension match those of the main house. For example, if your house is made of red brick, your extension would also need to be built using red brick. This is not the same when it come sot planning.

Room for creativity: When it comes to planning permission, there is far more scope to be creative. Your local authority planning officers will also have more flexibility to work with you to create a more unique space. One of the best ways to transform how your rear extension looks through the planning permission route is to use external cladding. These are different types of materials that can be attached to the exterior frame of your house.

Common cladding materials:

– Timber

– Brick

– Stone

– Render

– Zinc

– Copper

There are hundreds if not thousands of materials to choose from!

Timber cladding extension
Transform any extension with this modern timber cladding

1.3. Construction cost

The construction cost for an average size single storey rear extension to a terraced house will cost approximately £40,000 – £50,000.

Ways to reduce construction costs: Terraced house extensions can be expensive. However, there are a number of ways you can do your best to bring the overall extension cost down to an acceptable level. Some possible ways include:

– Avoid moving load bearing walls

– Work with your architect to choose the right construction system

– Choose skylights over glass ceilings

– Generate your own party wall notice

– Ask your architect to prepare a ‘schedule of works’

1.4. Design ideas

Modern glass terraced house extension
Flood your living area with natural light with a stunning glass extension
Side return extension for a terraced house
The use of both glass and brick for this terraced house rear extension is an idea we love!

2. Single storey side – terraced house extension

2.1. Permitted Development

L-shaped terraced houses: Most terraced homes don’t have space towards the side which could accommodate an extension. However, there are lots of terraced houses built in an L-shape. These types of houses have a narrow passageway running down the rear of the house. This part of your house can be extended under Permitted Development depending on the depth.

Legislation: In addition to the rear extension Permitted Development legislation highlighted above, the following Permitted Development criteria are specific to side extensions for terraced homes. If you meet these requirements, you will not need to apply for planning permission.

Height: Your extension cannot exceed four metres.

No. of storeys: Can only be a single storey.

Width: Can only be up to half the width of the original house.

Conservation Areas: If your house is located within a conservation area, any side extension would require planning permission.

2.2. Planning Permission

For those of you who want to maximise space and create the biggest possible living area with your terraced house extension, the planning permission route might be best.

Wrap around extensions: The best way to maximise space if you own an L-shaped terraced house is with a wraparound design. These types of extensions do not meet the requirements of Permitted Development which means you need to go down the planning permission route. It’s not all doom and gloom though, as there are lots of advantages.

Character of the area: The main consideration your local planning authority will have when assessing your wraparound side extension is how it impacts the character of the area. The best way to assess this yourself is to hop onto the 3D view of google maps and take a look at other houses on your street. The character of your street would encompass all your neighbours’ houses. If they have similar extensions to the kind you’d like, the chances are the planners will say it conforms to your street’s character. Make sure to include any relevant examples when you finally apply for planning permission. Planners like that sort of proactive thinking!

Impact on your neighbours: The second most important factor your local authority planning department will consider is how your extension affects your neighbours. As terraced houses tend to be narrower than semi-detached or detached houses, most extensions are built right up against your boundary wall. This proximity to neighbouring gardens could be cause for concern. If either you or your architect think this aspect of your terraced house extension might be a concern, there are some creative design solutions available. The most effective is to reduce the height of the extension at the point it meets your neighbour’s boundary. This leaves you with that much-needed floorspace while reducing any chance that your extension might overshadow their garden.

Glass roofs: One way to reduce the impact of your extension and also raise support from your local planning department is to include a glass roof in your design. The transparency will reduce the overall impact on the area’s character and your neighbours, but it will also let in a huge amount of natural light.

Glass roof terraced house extension
A glass roof can help open up the living space in terraced houses

2.3. Construction cost

Outside London, the cost of a side extension is typically between £2,000 – £2,400 per square metre, and in London, it can be as expensive as £3,500 per square metre.

Normal side return: If you’re looking to simply extend the relatively narrow gap between you and your neighbour’s house, the overall build cost will be less than usual. Side infill extensions can be conducted for as little as £20,000 due to the limited amount of construction work involved. If you’d like to create a large open plan kitchen/living room, bear in mind the average cost to remove each supporting wall is between £3,000 and £4,000.

Wrap around side/rear extension: These types of extensions can be more expensive to build because not only are you building a side and rear extension, but you’re also linking them together.

In order to help reduce the overall cost of this type of extension, make sure your architect prepares either a ‘schedule of works’ or a ‘bill of quantities’. These are essentially detailed lists of all the labour and materials involved in your extension. This will help make your builder’s quote far more accurate as they will simply include a price next to each item. Although the outlay to prepare these documents can range between £1,000 – £1,500 for a terraced house, it will save you money in the long run as the more detailed the tender package the more detailed the quote you receive.

Modern side extension for a terraced house
Give your modern extension a traditional twist with Crittall windows

3. Terraced House: Loft extension

3.1. Permitted development

Unlike other types of extensions, the largest loft extensions are usually built through Permitted Development.

Here are the main Permitted Development criteria when it comes to loft conversions as part of your terraced house extension:

Materials: Materials must be similar in appearance to the existing house

Volume:  If you own a terraced house, you cannot add more than 40 cubic metres of space (measured externally).

Height: Must not exceed the height of the existing roof.

Location: Your loft extension should not extend onto the principal elevation of the house (usually the front).

Eaves: The eaves of the original roof are maintained (or reinstated).

Overhang: The roof enlargement does not overhang the outer face of the wall of the original house.

If your new loft extension would not meet the above requirements, you would need to apply for planning permission.

3.2. Planning Permission

When it comes to loft conversions in your terraced house extension, going down the planning permission route often gets you less space when compared to Permitted Development. The reason is that most local authority planning policies are more restrictive when it comes to roofs. Although local planning policies differ from borough to borough, the principal deciding factor is that they should not dominate the roof slope.

Dormer window size: In terms of size, dormer windows which are half the height and width of the roof slope are generally acceptable. Unfortunately, that will often give you limited new space within your loft when compared to what could be achieved through Permitted Development. Make sure your architect has carefully explored the Permitted Development route before applying for planning permission.

3.3. Construction Cost

Velux loft conversion: The average cost of a terraced house loft conversion will depend on the type of conversion you’re carrying out. Velux loft conversions are usually the cheapest option to convert your loft as they involve minimal building works. The cost of a Velux loft conversion in a terraced house is approximately £27,500. However, bear in mind that it will only make the existing space within your loft usable rather than create extra space, as the options below do.

Dormer window: The best way to add space to the loft of a terraced house is to create the largest dormer window possible. A dormer window loft conversion to a terraced house will cost in the region of £50,000 – £60,000 depending on the size. However, this will transform even the smallest of spaces into a stunning master bedroom and potentially an en-suite bathroom.

Mansard Loft Conversion: A mansard style loft conversion creates the largest space possible in terraced houses. Bear in mind though that it’s also the most expensive option with an average cost of around £60,000 – £70,000. They’re expensive because they involve replacing most of the original room which requires more labour and materials.

3.4. Design Ideas

Velux conversion terraced house
Huge roof lights can make the smallest loft appear bright and open
Dormer loft extension for a terraced house
A stunning zinc clad dormer window

4. Other terraced house renovation ideas

4.1. Kitchen Upgrade

If you’re like my family, you spend the most time in the kitchen. This is why a recent ‘Nationwide’ survey found that a new kitchen was at the top of future buyer requirements when it came to looking for a new house. As terraced houses can be narrow, a great option for your terraced house conversion is to remove any internal walls and create a jaw dropping open plan kitchen & living room. Unlike the examples above, taking down internal walls and fitting a brand-new kitchen does not require planning permission.

4.2. Bathroom Upgrade

Lots of terraced houses only have bathrooms on the first floor. To avoid needing to give your guests directions when entertaining, why not install a downstairs toilet? It can also avoid any accidents if you have young children. Downstairs toilets are relatively cheap to fit, ranging from £3,000 – £5,000.

Bathrooms are often humid places and get old and tired more quickly when compared to other rooms in your house. A stunning new bathroom is a great way to add that extra value to your home. A new bathroom can cost in the region of £6,000 – £7,000.

5. What other permissions do I need to consider for a terraced house extension?

5.1. Party Wall Agreement

What is a party wall? A party wall is a wall that sits directly on the boundary of land between neighbours. If you live in a mid-terraced house, you will have two party walls. They separate you from the neighbours either side, and these walls need to be considered when thinking about your terraced house extension.

What is a party wall agreement? A party wall agreement is needed if you plan on carrying out any building work near or on a party wall. This would cover any rear or side extensions or loft conversions. It can also include removing any supporting walls, as the steel beams needed to support them may need to sit on or close to a party wall shared with your neighbour.

What are the steps involved? You must advise your neighbours of any planned building works, provide them with a Party Wall Notice and prepare a Party Wall Agreement in writing. If you are carrying out any works which you feel might involve a party wall agreement, we would suggest contacting a Party Wall Surveyor. They are experts in all such matters and will be able to guide you through the process.

5.2. Right of light

Essentially, a person’s ‘right to light’ is enshrined under common law by the Prescription Act 1832.

This means that a window that has received more than 20 years of unobstructed daylight has automatically earned itself ‘a right to light’. This is particularly important when designing extensions to terraced houses because they are often built the full width of a plot and close to your neighbours’ windows.

Before you submit any designs for a new extension to planning, we think it’s a good idea to have a word with your neighbours. Not only is this the ‘neighbourly’ thing to do, but it may reduce the chances that your neighbours make any sort of right to light claim against you.

5.3. Building regulations

If you’re planning a terraced house extension, you will need to comply with the building regulations.

What are building regulations? Building regulations is the technical step after you have obtained the relevant planning permission or consents for your extension. They ensure that renovations and extensions are safe and high performing.

Building Regulations cover specific topics, including structural integrity, fire protection, accessibility, energy performance, acoustic performance, protection against falls, electrical and gas safety.

Architect involvement: Your architect will be the best person to help you through the building regulations stage. They will prepare a set of detailed drawings demonstrating that your extension meets all the relevant British Standards. Details will include fountains, steel beams, insulation, waste etc.

Engineer involvement: Once your architect has prepared their detailed drawings these will be sent to an engineer. Your engineer will then prepare a set of structural drawings and structural calculations to show that the foundations and appropriate steels have been included to make sure the structure is well supported.

6. FAQs

6.1. Pitched roof

Pros: Many terraced houses are traditional in design which tend to lend themselves better to extensions with pitched roofs. The second advantage is that pitched roofs can help achieve higher internal floor to ceiling heights, adding to an increased sense of space in your terraced house extension.

Cons: The two main disadvantages of pitched roofs are that they are more expensive to build when compared to flat roofs. They also take a little longer to build as the structure is more complex.

6.2. Flat roof

Pros: Flat roofs add a more contemporary feel to terraced house extensions. The juxtaposition of a traditional terraced house with the more modern extension is a relationship which often looks fantastic.

Cons: Flat roofs often require more maintenance compared to pitched roofs and the overall floor to ceiling heights are lower.

6.3. Glazed internal doors:

Completely glazed internal doors are a great way to get that little bit of extra natural light into your terraced house. Not only that, but they can really help small spaces feel that much larger as it adds more transparency to your living spaces.

Internal glass panels
Help bring light through your house with these internal glass panels

6.4. New staircase

Terraced properties can be narrow, and lots of the space towards the middle of your house is taken up by a staircase.  Open stair treads and glass balustrades not only look stunning but will flood your house with natural light, helping the space appear much larger than it is.

Open Stairs
Open stairs can be a fantastic way to increase the sense of space in the narrowest of homes

6.5. Skylights and glass roofs:

Did you know that horizontal windows let in 3 times more light than vertical windows? Roof lights and glass panels are not only limited to extensions. Why not include them in the hallway or bedroom on the top floor? These are a very cost effect solution to transforming your home.


Extending or renovating your terraced house can be a huge undertaking.

Our experienced team of creative architects and planning have a huge amount of experience when it comes to transforming terraced houses.

If you would like any planning permission advice about your terraced house extension, or you would like to talk about your ideas, why not book a free 30 min consultation with one of our team?

We’re always here to help!

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