A terraced house extension works within tighter limits than an extension on a detached house. The house shares walls with its neighbours on one or both sides, the garden is often narrow, and there may be no way round to the back except through the front door. None of that rules out a good extension, but it does shape what you can build, how it is approved and how the build is run.
This guide covers the usual ways to extend a terraced house, the permitted development limits that apply to terraces, when prior approval or planning permission is needed, the party wall position, and the practical points that come up on almost every terrace: getting materials in, keeping light in the middle of the house, and dealing with shared drains and boundaries. For how we take on extension projects, see our page on house extensions across West Sussex.
What are the options for extending a terraced house?
The main options for extending a terraced house are a single storey rear extension, a side return extension that fills the strip beside a rear projection, a wraparound that combines the two, and a two storey rear extension. Which one works depends on the shape of the house, the garden and the planning position.
A rear extension pushes the back of the house out into the garden across part or all of its width. A side return extension fills the narrow passage that runs alongside a rear projection, where the house has one. A wraparound fills the side return and also extends beyond the end of the projection, so it is an L shape in plan. A two storey rear extension adds space on the first floor as well, but it faces stricter limits on a terrace, covered below.
Our guide to rear extensions and side extensions compares the two positions in general, and our guide to single storey and double storey extensions looks at the choice of storeys. This guide is about what changes when the house is a terrace.
What is a side return extension?
A side return extension fills the side passage beside a rear projection on a terraced house. The passage is often too narrow to be much use as garden, so building over it can widen the kitchen or living space behind the main house without taking much of the main garden.
Many terraced houses have a narrower section at the back, sometimes called an outrigger or back addition, with a strip of outdoor space running along one side of it. The side return extension builds over that strip, usually up to the boundary with the neighbour, and often removes the old side wall of the projection to open the two spaces into one room.
Because the extension sits against the boundary, the height of the wall on that side and the shape of the roof matter. A sloping or glazed roof that drops towards the boundary keeps the wall lower on the neighbour’s side, which helps with both the permitted development limits and the light reaching the neighbour’s window.
How far can you extend a terraced house without planning permission?
Under permitted development, a single storey rear extension on a terraced house can extend up to 3m beyond the original rear wall and be up to 4m high. Through the prior approval scheme, the limit rises to 6m. A side extension must be single storey, no more than 4m high and no wider than half the original house.
These figures come from Class A of the householder permitted development rules, as set out in the GOV.UK technical guidance. For permitted development, a terrace house means a house in a row of three or more. The main limits for a terraced house are:
| Type of extension | Permitted development limit |
|---|---|
| Single storey rear | Up to 3m beyond the original rear wall, up to 4m high |
| Single storey rear, through prior approval | Up to 6m beyond the original rear wall, up to 4m high (not on article 2(3) land) |
| Side extension | Single storey, up to 4m high, no wider than half the width of the original house |
| More than one storey at the rear | Up to 3m beyond the original rear wall, and at least 7m from the boundary opposite the rear wall |
| Within 2m of a boundary | Eaves no higher than 3m |
| Any extension | Not higher than the existing roof or eaves, similar materials, and buildings covering no more than half the garden and grounds |
“Original” means the house as it stood on 1 July 1948, or as it was built if it is newer. Any earlier extension counts against the limits, so a house that has already been extended at the back may have less allowance left.
How the limits apply to a side return
A side return extension usually counts as both a side extension and a rear extension. The GOV.UK guidance says that where an extension fills the area between a side elevation and a rear wall, the restrictions on both apply. The side wall of the rear projection counts as a side elevation, and the back wall of the main house behind the side return counts as a rear wall.
In practice, that means the side return must stay single storey, no more than 4m high, no wider than half the width of the original house, and within the depth limit measured from the rear wall of the main house. A side return that runs the full length of a long rear projection can go past that depth limit, which is one of the reasons many side return extensions on terraced houses go through planning permission rather than permitted development. A wraparound faces the same tests.
When does a terraced house extension need prior approval or planning permission?
A terraced house extension needs prior approval to use the larger 6m limit, and it needs planning permission if it goes beyond the permitted development limits, if the house is on article 2(3) land such as a conservation area or the National Park, or if permitted development rights have been removed.
Prior approval for a larger rear extension
The prior approval scheme lets a single storey rear extension on a terraced house go up to 6m deep. The homeowner notifies the council, and the council gives the adjoining neighbours notice and the chance to object. Work cannot start until the council confirms that prior approval is not needed, grants it, or 42 days pass without a decision. The scheme does not apply on article 2(3) land.
When planning permission is needed
Planning permission is needed where the extension goes past any of the limits above. It is also needed on article 2(3) land, which includes conservation areas and National Parks, for any side extension or any rear extension of more than one storey. Councils can remove permitted development rights across an area with an Article 4 direction, and an earlier planning permission for the house may have removed them too. Permitted development rights for extensions do not apply to flats or maisonettes.
Confirming the position before you build
The GOV.UK guidance advises checking with the local planning authority before starting any work. Where an extension falls within permitted development, a Lawful Development Certificate from the council confirms it in writing. That is useful when you come to sell the house, and it settles any doubt about how the depth of a side return has been measured. Apex can prepare and submit Lawful Development Certificate and planning applications on the homeowner’s behalf.
How does the Party Wall Act affect a terraced house extension?
Most terraced house extensions involve the Party Wall etc. Act 1996, because the work is close to, on or at the boundary with at least one neighbour. Typical triggers are cutting into the party wall for steel beams, building a new wall on the boundary line, and digging foundations near the neighbour’s foundations.
The homeowner, not the builder, is responsible for giving notice to the neighbours. GOV.UK says notice should be given between two months and a year before the work starts. A neighbour has 14 days to give written consent, and no response cannot be taken as agreement. Where a neighbour does not consent, a party wall surveyor is appointed, either jointly or one for each side. On a mid-terrace house, notices may be needed for the neighbours on both sides.
Our guide to the party wall agreement for an extension explains the notices, the surveyor’s role and the award in more detail. Party wall matters should be discussed with a party wall surveyor early, because the notice period can affect when the build can start.
How do materials get in when the only access is through the house?
On many terraced houses there is no side access, so everything for the extension, from bricks and steel to the waste from digging foundations, has to come through the front door and the hall. The build programme is planned around that route, with the route protected and the house still usable.
This is how it is usually handled:
- Check for another way in. Some terraces have a rear lane, a shared alley or a gate from a neighbouring plot. Where there is one, materials can go round the back, but rights of way and the neighbours’ agreement need checking first.
- Protect the route. Floors, stairs and door frames along the route are covered with protective boards and sheets, and fittings in the way may be taken down and refitted afterwards.
- Plan deliveries around the route. Long items such as steel beams and roof timbers are measured against the hall and doorways before they are ordered. Large deliveries are timed so they go straight through the house and are not left on the pavement.
- Get the permits for the street. A skip or scaffolding on the road or pavement needs a permit or licence from the highway authority. Where a skip will not fit, waste can go out in bags through the house.
- Seal off the house from the build. Once the back of the house is opened up, a temporary dust screen keeps the rest of the house clean and secure.
Living in the house during the build is often possible, but the kitchen is usually the room being extended, so a temporary kitchen elsewhere in the house is worth planning for.
How do you keep light in the house after extending?
The main risk on a terraced house extension is a dark middle room. Once the back of the house is extended, the room between the front and the new extension can lose its only window. Rooflights, a glazed roof over a side return, and glazed doors at the back are the usual ways to bring light into the depth of the plan.
The roof of a side return extension is often the best place for glazing, because it sits right beside the middle of the house. A run of glazing along the side return, or a glazed strip where the new roof meets the old wall, puts daylight into the area that would otherwise be darkest. Rooflights in a flat roof over a rear extension do the same job for a full-width extension.
Light also matters for the neighbours. The permitted development rule that limits eaves to 3m within 2m of the boundary keeps the wall on the boundary low, and under prior approval the council considers the effect on adjoining houses. A roof that slopes down towards the boundary is one way to keep the extension within the limits and reduce its effect on the house next door.
What happens to drains and shared boundaries?
Drains are one of the first things to check on a terraced house extension, because many terraces share drain runs behind the houses. Since 1 October 2011, drains shared by more than one property have been public sewers, so building over or near one usually needs the water company’s agreement.
In Sussex the water company is Southern Water. Its guidance asks for a build-over application for any structure built over or within 3m of a public sewer, measured from the outside of the pipe or manhole to the outside of the new foundations. A survey of the drains, often with a camera, shows where the runs and manholes are before the design is fixed. A manhole inside the footprint of an extension may need to be moved or replaced with a sealed cover, and that is agreed with the water company and Building Control.
The boundary itself needs the same care. Garden walls and fences between terraced houses are often shared, and a new extension wall built on or up to the line falls under the Party Wall Act. Gutters and roof edges must not overhang the neighbour’s land, and rainwater from the new roof has to go into a suitable drain or soakaway on your side. These details are worked out in the drawings so they do not become disputes on site.
Who handles what on a terraced house extension?
Apex works with trusted architectural partners who survey the house, draw up the design and check it against the permitted development limits and the Building Regulations. Apex can prepare and submit planning and Lawful Development Certificate applications on the homeowner’s behalf, then build the extension to the approved drawings and work with the Building Control inspector on site.
The homeowner makes the Building Regulations application, either to the council’s building control service or to a registered building control approver, and serves any party wall notices on the neighbours.
Please note: this guide summarises the GOV.UK householder permitted development guidance and party wall guidance for houses in England. Every house is different, and the council decides whether a particular extension needs planning permission or prior approval. Before any work starts, the homeowner should confirm the planning position with their local council and discuss any party wall matters with a party wall surveyor. Apex can prepare planning and Lawful Development Certificate applications, but it does not serve party wall notices or submit Building Control applications.
Thinking about extending your terraced house?
The best starting point is a look at the house. Get in touch with Apex Lofts & Construction and we will visit, talk through the options for your terrace, and explain how the planning, party wall and access points apply to your home.
Frequently Asked Questions
Can I build a side return extension without planning permission?
Sometimes. A side return extension counts as both a side and a rear extension, so it must meet both sets of permitted development limits: single storey, no more than 4m high, no wider than half the original house, and within the rear depth limit. Many go beyond the depth limit and need planning permission, and side extensions always need it on article 2(3) land such as a conservation area.
Do I need a party wall agreement for a terraced house extension?
Usually, yes. Most terraced house extensions cut into a party wall, build on the boundary or dig near a neighbour’s foundations, which all fall under the Party Wall etc. Act 1996. The homeowner gives notice to the neighbours, and if a neighbour does not consent in writing within 14 days, a party wall surveyor is appointed.
Can you build a two storey extension on a terraced house?
Yes, but the limits are tight. Under permitted development, a rear extension of more than one storey can go up to 3m beyond the original rear wall and must stay at least 7m from the boundary opposite the rear wall. Many terraced gardens are too short for that, so a two storey extension on a terrace often needs planning permission.
How long does prior approval take for a rear extension?
The council has 42 days. Once the homeowner notifies the council about a larger single storey rear extension, the council gives the adjoining neighbours notice and the chance to object. Work cannot start until the council confirms that prior approval is not needed, grants it, or the 42 days pass without a decision.
Can an extension be built over a shared drain?
Often, with the water company’s agreement. Drains shared by more than one property became public sewers on 1 October 2011, and in Sussex Southern Water asks for a build-over application for any structure over or within 3m of a public sewer. A drain survey before the design is fixed shows where the runs and manholes are.
Does Apex Lofts & Construction design terraced house extensions?
Yes. We work with trusted architectural partners who survey the house and draw up the design, and we can prepare and submit planning and Lawful Development Certificate applications. The homeowner makes the Building Regulations application and serves any party wall notices. We then build the extension to the approved drawings and work with the Building Control inspector on site.