A larger kitchen, a proper dining area, or more space for family life can make extending your home an attractive alternative to moving. Before you commit to a design, however, there is one question to answer: do you need planning permission for a house extension?
Not always. Some house extensions in London can be built under permitted development rights, provided they meet all the relevant conditions. Others require a prior approval application or householder planning permission. The route depends on the property, the proposed work and any restrictions affecting the address.
At London’s Prestige, we recommend establishing these requirements early. Knowing what is possible helps you plan the layout, budget and construction programme with greater confidence.
What Is Permitted Development?
Permitted development is a national grant of planning permission for certain types of work. Where an extension meets the applicable rules, you do not need to submit a conventional planning application.
However, these rights are not available for every property. The house extension rules do not apply to flats or maisonettes, and some homes created through permitted development conversions are also excluded. Planning conditions and Article 4 directions can restrict the rights available at a particular address.
This is why a neighbour’s extension is useful inspiration but cannot confirm what you can build. Your home may have a different planning history, original layout or set of restrictions.
How Far Can You Extend Without a Householder Planning Application?
For an eligible house, the standard single-storey rear extension depth limits are:
Property type | Standard maximum projection beyond the original rear wall |
Detached house | 4 metres |
Semi-detached or terraced house | 3 metres |
These are depth limits, not a complete eligibility test. A single-storey rear extension must also stay within the relevant height limits. Its overall height cannot exceed four metres, and where it comes within two metres of a boundary, its eaves cannot exceed three metres. Other conditions still apply.
The measurements relate to the original house: the house as first built, or as it stood on 1 July 1948 if older. Previous extensions matter, including those built before you bought the property. You cannot simply measure a fresh allowance from the end of an existing addition.
Before designing around a particular depth, arrange an accurate survey and review the property’s planning history.
Can You Build a Larger Rear Extension?
Some eligible houses can use the larger home extension route. This allows single-storey rear extensions of up to eight metres for detached houses and six metres for other houses, subject to the relevant conditions.
This route requires a prior approval application before work starts, including a neighbour consultation process. It is not an automatic entitlement to build to the maximum depth.
The larger rear extension allowance does not apply on designated land such as conservation areas, or on Sites of Special Scientific Interest.
For homeowners, the practical point is simple: a six-metre extension and a three-metre extension may follow different approval routes, even when both are described as permitted development.
What About Side Returns and Two-Storey Extensions?
Side returns can be appealing where an unused passage sits beside the kitchen. However, their shape needs careful assessment.
Under the relevant permitted development rules, a side extension must be single storey, no more than four metres high and no wider than half the original house. A proposal extending beyond both a side wall and a rear wall must satisfy both sets of restrictions.
Some two-storey rear extensions can also qualify, subject to stricter conditions, including depth and boundary separation. Two-storey side extensions do not qualify under these house extension rights.
For a wraparound design, ask your designer to assess the complete proposal. Treating the side and rear sections as unrelated additions can give a misleading picture of what is allowed.
Why Your London Address Matters
The national rules are only part of the assessment. You also need to understand the controls affecting your property.
Conservation areas and Article 4 directions
Check your borough’s conservation area maps and any Article 4 directions covering your address. Read what the direction actually removes; it may relate to particular alterations rather than every form of development.
For example, Islington Council identifies Article 4 directions affecting conservation areas and explains that certain changes may require permission as a result. The relevant restrictions need to be checked against the proposed work.
Listed buildings
Listed building consent is a separate consideration. If an extension affects the character of a listed building as a place of special architectural or historic interest, consent is required. Planning permission may also be necessary.
For a period home, investigate its status before settling on glazing, roof forms or changes to existing walls. Early design advice gives you a better basis for developing the proposal.
Should You Get a Lawful Development Certificate?
If your extension qualifies as permitted development, consider applying for a Lawful Development Certificate for the proposed work.
This provides a formal decision on whether the specified proposal would be lawful for planning purposes. It is different from a planning application: the assessment concerns compliance with the relevant legal requirements rather than whether the council favours the design.
The certificate applies to the proposal described in the application. If you change the design, do not assume the original certificate still covers it.
Keep the certificate, drawings and supporting information with your property records.
Planning Permission and Building Regulations Are Separate
An extension can qualify as permitted development and still require building regulations approval.
Building regulations cover the construction and extension of buildings. Establish the appropriate building control route before work begins, even where a householder planning application is unnecessary.
Party wall procedures are also separate. Depending on the work, an extension may involve obligations relating to shared walls, boundary construction or nearby excavation. Planning approval does not replace those requirements.
Build these steps into the programme early so that the construction start date reflects everything the project needs.
What Happens If You Need Planning Permission?
Needing permission does not mean you need to abandon your preferred design. It means the council must assess the proposal through the planning application process.
Your designer should prepare the drawings and supporting information required by the borough. The council considers the proposal against its development plan, including matters such as size, layout, appearance and effects on the surrounding area.
Allow time for this stage before committing to a construction date. Government guidance says most planning applications are decided within eight weeks, but this is not a guaranteed project timeline. Surveying, drawing preparation, revisions and other approvals also need space in your schedule.
Plan Your Extension Around How You Live
Once the approval route is clear, focus on what the extra space needs to achieve.
Would a wider kitchen solve the problem, or do you need a separate utility room? Where will the dining table sit? Will the existing middle room still receive enough daylight? How will you move between the house and garden?
At London’s Prestige, we approach home extensions as part of the wider home. The layout, materials and finish should work together, with a clear scope before construction begins.
Frequently Asked Questions
Does a small extension always avoid planning permission?
No. Size is only one factor. The type of property, previous extensions and restrictions affecting the address also determine whether permitted development rights apply.
Can I extend a ground-floor flat under householder permitted development rights?
The permitted development rights described for house extensions do not apply to flats or maisonettes. A private garden does not change that distinction. Check the planning route with your local authority.
Is prior approval the same as planning permission?
Prior approval is a procedure attached to certain permitted development rights. For an eligible larger rear extension, it involves an application and neighbour consultation before work starts. It follows a different route from a householder planning application.
Do I still need building control if my extension is permitted development?
Yes, a typical house extension still needs the appropriate building regulations process. Permitted development addresses planning requirements; it does not remove building regulations obligations.