Permitted Development vs Planning Permission for a Rear Extension in London
Permitted development vs planning permission is one of the first questions homeowners ask when considering a rear extension.
The short answer is that some rear extensions may proceed under permitted development, while others require planning permission. London homes often need additional checks because local restrictions, conservation considerations and close relationships with neighbouring properties can affect the available route.
The correct approach depends on the property, its planning history, the site, any local restrictions and the proposed design. If you are considering planning and designing a house extension, an early review can help establish what may be possible before the design develops too far.
What is permitted development?
Permitted development is a national planning permission granted through legislation. It allows certain building work to proceed without a full planning application, provided the proposal complies with every relevant limitation and condition.
These rules can cover matters such as:
The type of property
The extension’s depth and height
Its position in relation to boundaries
The amount of land covered by buildings
The materials and external appearance
Previous extensions and additions
A key concept is the original house. This means the house as it stood on 1 July 1948 if it was built before that date, or as it was first built if constructed later. Previous owners’ additions still count when assessing how much of the permitted development allowance remains.
Permitted development rights can also be restricted or removed. This may happen through an Article 4 direction or a condition attached to an earlier planning permission. The official Permitted development rights for householders: technical guidance explains the national rules, but each property still needs to be checked individually.
What is planning permission?
Rear extension planning permission is normally sought through a full householder application. The local planning authority assesses the proposal against national and local planning policy.
The assessment may consider:
Scale, height and massing
External appearance and materials
The character and context of the property
Daylight, outlook and privacy
The effect on neighbouring homes
The relationship between the extension, house and garden
Planning permission can provide greater design flexibility than permitted development. It may allow proposals that fall outside permitted development limits or respond to a site in a different way.
However, submitting a planning application does not guarantee approval. The design must make a convincing response to the house, its neighbours and the local planning context.
Permitted development vs planning permission at a glance
The main difference between permitted development vs planning permission is how the proposal is authorised and assessed.
Application route
Relies on national rights, subject to detailed conditions and limitations
Requires a full householder planning application
Design limits
Must remain within prescribed rules
Can consider designs outside permitted development limits
What is assessed
Whether the proposal complies with every relevant permitted development requirement
The proposal’s acceptability against national and local planning policy
Neighbour involvement
Usually limited, although consultation applies under the larger home extension prior approval process
Neighbours may be notified and invited to comment
Decision process
Eligibility may be confirmed through a Lawful Development Certificate, or prior approval where required
The local planning authority issues a formal decision
Suitable projects
Straightforward extensions that meet all applicable rules
Larger, more ambitious or context-sensitive proposals
Useful evidence
A Lawful Development Certificate can provide formal evidence that qualifying work is lawful
A decision notice and approved drawings record the consented design
Neither route should be selected on dimensions alone. The property’s planning history, legal status and local restrictions must also be reviewed.
When might a rear extension qualify as permitted development?
A permitted development rear extension may be possible where the property is a house with the relevant rights intact and the proposal meets every applicable condition.
Under current guidance in England, a single-storey rear extension may extend beyond the original rear wall by up to 4 metres for a detached house or 3 metres for another house under the standard route. These dimensions do not establish eligibility on their own.
Other considerations include:
The extension’s overall height and eaves height
Its proximity to a boundary
Whether side and rear elements are being combined
Previous extensions to the original house
The total area of land covered by buildings
The proposed materials and appearance
Whether the house is in an area where additional restrictions apply
Larger single-storey rear extensions may use the prior approval process where that route is available. Before relying on permitted development, it is important to review the complete design and the history of the property rather than treating one measurement as the deciding factor.
What is prior approval?
Prior approval is a process that applies to certain forms of permitted development, including some larger home extensions. A prior approval rear extension is not the same as standard permitted development, but it is also not a full planning application.
For a larger home extension, the local planning authority notifies adjoining neighbours and considers the effect of the proposal on their amenity. If objections are received, the authority assesses the relevant impacts through the prior approval process.
The required procedure must be completed before work begins. The government’s guidance on when permission is required provides further information about permitted development and prior approval.
When is planning permission likely to be required?
Planning permission is likely to be needed when a proposal falls outside the relevant permitted development limitations or the property does not benefit from those rights.
This can include:
Flats and maisonettes, which do not have the same householder permitted development rights as houses
Properties where rights have been removed or restricted
Extensions exceeding the relevant limits
More ambitious or context-sensitive designs
Houses affected by previous extensions
Proposals where conservation-area constraints affect the available rights or design response
Work affecting a listed building may also require listed building consent, whether or not planning permission is needed. This is a separate consent concerned with protecting the building’s special architectural or historic interest.
Being in a conservation area does not automatically mean every rear extension requires planning permission. It does mean that the property’s specific rights, setting and local policies need careful review.
What makes a London rear extension different?
London extension rules combine national planning legislation with borough-level policies and property-specific restrictions. Homes may be within conservation areas or affected by Article 4 directions, which can change what would otherwise be permitted.
The physical context also matters. Closely spaced neighbouring properties can make daylight, outlook and privacy particularly important. A rear extension that appears modest in plan may have a noticeable effect when gardens are shallow or neighbouring windows are close.
The rhythm and character of terraces and period houses can also influence the design. Local planning policies may consider how an extension relates to the original building, established building lines, roof forms, materials and the wider group of properties.
These factors do not necessarily prevent an extension. They help determine the scale, form and planning route most likely to produce a well-resolved proposal.
Is permitted development always the best option?
Permitted development can offer a clear route for a qualifying project, but it is not automatically the best design route.
The largest footprint allowed by the rules may not create the best home. Extension depth can affect daylight within existing rooms, while width and layout influence circulation, room proportions and the connection with the garden. The junction between old and new also needs careful thought.
In some cases, a full planning application can support a more coherent architectural outcome. A different roof form, footprint or material approach may respond better to the property than a design shaped solely around permitted development limits.
The route should follow the house, plot, planning context and homeowner’s priorities. For an example of a design-led response to a terraced property, explore the College Road terrace house extension.
How an architect can help
An architect can assess the planning position while developing a design that responds to how the home should work.
This can include:
Reviewing the property’s planning history
Checking local policies, Article 4 directions and other restrictions
Measuring and identifying the original house
Testing different extension depths, forms and layouts
Advising on permitted development, prior approval or planning permission
Preparing drawings and application information
Coordinating planning with building regulations, structural engineering and party wall considerations
At Marjoram Architects, the aim is not simply to pursue the largest possible footprint. It is to recommend an approach that suits the house, plot and planning context while improving daylight, circulation and the relationship with the garden.
Considering a rear extension in London? Our extension architects in London can assess your property, explore the design possibilities and advise on the most appropriate permitted development vs planning permission route.
Book a consultation to discuss your project.
Frequently asked questions
Do I need planning permission for a three-metre rear extension?
Not necessarily. A three-metre extension may fall within permitted development for some houses, but depth is only one condition. Property type, height, boundaries, previous additions, land coverage and local restrictions must also be checked.
Can I extend a property in a conservation area?
Potentially, yes. Conservation-area status does not automatically prevent an extension or remove every permitted development right. However, additional restrictions, Article 4 directions and local design policies may apply.
Do flats have permitted development rights?
Flats and maisonettes do not benefit from the same householder permitted development rights as houses. An extension to a flat will generally require planning permission, alongside any other necessary property or building consents.
Is prior approval the same as planning permission?
No. Prior approval applies to specified forms of permitted development and considers defined matters, such as neighbour amenity for certain larger home extensions. A full planning application is assessed more broadly against relevant planning policy.
Should I obtain a lawful development certificate?
A Lawful Development Certificate is often advisable if you intend to rely on permitted development. It provides formal evidence that the proposed work was lawful based on the information submitted, which can be useful for future property records or a sale.
Do I still need building regulations approval?
Usually, yes. Planning and building regulations are separate systems. Permitted development or planning permission does not remove the need to address building regulations, structural requirements or responsibilities under the Party Wall Act where these apply.
