Some home extensions and loft conversions need a planning application. Others may be covered by permitted development rights, provided the property and proposal meet the relevant conditions. The right route depends on the actual building, its history and the detailed design.
For London homeowners, the useful starting point is a property-specific check. A project looking similar to one down the road does not establish that it can follow the same approval route.
What does permitted development mean?
Permitted development is a form of planning permission granted nationally for specified development. It can remove the need for an individual planning application, but only where every applicable limitation and condition is satisfied.
It is therefore more accurate to ask whether your proposal qualifies than whether it is “small enough”. Size matters, alongside matters such as position, height, property type and restrictions affecting the site. Some permitted development routes also involve a prior approval process.
The government's technical guidance for householders explains the framework in England. Use it with professional advice on your own proposal, rather than treating an isolated diagram as a complete answer.
Check the property before the proposal
Establish whether the home is a house, flat or maisonette and check its planning history. Householder permitted development rights for common alterations do not generally apply to flats and maisonettes in the same way.
Your designer should also check whether rights have been restricted by a planning condition or an Article 4 direction, and whether the property is on designated land. Conservation-area status can affect what is permitted, and listed buildings require separate consideration.
Previous extensions or roof alterations may also matter. Provide historic plans and decisions if you have them. What looks like the original rear wall today may already be part of an earlier enlargement, so measuring only from the current footprint can give a misleading result.
Assess the exact design
For an extension, ask your designer to review the footprint, height, relationship to boundaries and how the proposal relates to the original house. For a loft, roof shape, added volume and the position of the enlargement are among the relevant considerations.
Do not approve a concept on the assumption that any necessary adjustment will be minor. A change to roof form or wall position can alter the room layout, structure and cost. Confirm the intended planning route while those decisions are still flexible.
Keep a record of the assumptions used in the assessment. If the design changes later, ask whether its planning position also needs review. Compliance is attached to the proposal actually built, not simply to an earlier conversation.
When a planning application is needed
Where a proposal does not qualify under the applicable permitted development rights, a planning application may be required. That does not automatically mean the project is unsuitable; it means it needs assessment through a different route.
A useful submission explains the proposal clearly through the required drawings and supporting information. Your team should consider relevant local policies and the relationship with neighbouring properties, rather than preparing the application as a paperwork exercise after the design is settled.
Before instructing detailed work, ask what the main planning uncertainties are and whether pre-application advice would be useful. Its value depends on the project and local service available. No application strategy can promise an approval.
What is a lawful development certificate for?
A proposed lawful development certificate can provide formal confirmation of a proposal's lawfulness. It is distinct from applying for discretionary planning permission. The evidence and drawings need to accurately describe the work for which confirmation is sought.
Ask your designer whether applying would be appropriate. Keep any certificate and approved supporting documents with your property records. Future buyers and advisers may need to understand the basis on which the work was carried out.
The certificate should not be treated as permission to make unreviewed changes. If dimensions, appearance or position change, seek advice on the revised proposal before construction proceeds on that basis.
Planning is one part of the approvals picture
Building regulations address a separate set of requirements. A project that does not need an individual planning application can still need building regulations approval. Neither route replaces consideration of party wall matters, ownership restrictions or permissions required under a lease.
Create a short approvals schedule with your project team. Record each requirement, the responsible person, the current status and the point by which it must be resolved. This is more reliable than a general statement that “the permissions are sorted”.
If an approval includes conditions, identify which need action before work starts or before a particular stage. Keep responsibility for those actions explicit in the programme.
Prepare for your first design discussion
Bring the address, existing drawings, photographs and any information about previous works. Explain the accommodation you need and the budget available. Ask for an outline of the likely route and the checks needed to confirm it.
A good early discussion should leave you clearer about the next decision, even if it cannot answer every question immediately. It should also distinguish confirmed facts from assumptions still being investigated.
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Official guidance
GOV.UK: lawful development certificates; Planning Portal: permitted development rights; GOV.UK: planning permission; GOV.UK: building regulations. Guidance relates to England and was checked on 15 October 2026. Confirm requirements for the specific property and final design.
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