London Planning Permission for House Extensions

Navigating the planning system can feel daunting, but understanding the rules helps you avoid costly mistakes and delays. This guide explains when you need planning permission for a house extension, how permitted development works, and what to expect from the application process.

Do I Need Planning Permission for an Extension?

Not all extensions require planning permission. The UK planning system includes ‘permitted development rights’ that allow certain building works without a formal application. However, these rights come with strict limitations.

Permitted Development Rules for Extensions

Under permitted development, you may be able to build a rear extension without planning permission if it meets these criteria:

• Single storey rear extensions: Up to 3 metres from the original rear wall (attached houses) or 4 metres (detached houses)
• Under the Prior Approval scheme: Up to 6 metres (attached) or 8 metres (detached)
• Maximum height: 4 metres
• Eaves must not exceed the height of the existing house
• Materials must be similar in appearance to the existing house
• No extension beyond the side elevation facing a highway
• Side extensions limited to half the width of the original house

When You Always Need Planning Permission

Planning permission is required if:

• Your property is a flat or maisonette
• You live in a conservation area, National Park, or Area of Outstanding Natural Beauty
• Your property is listed or in the curtilage of a listed building
• You want to extend forward of the principal elevation facing a highway
• Your extension exceeds permitted development limits
• Your permitted development rights have been removed by a condition or Article 4 direction

How Long Does Planning Permission Last?

Once granted, planning permission is typically valid for three years. You must begin the approved development within this period, or the permission expires. ‘Begin development’ usually means more than just clearing the site – you need to have started substantive construction work.

If your permission is about to expire, you can apply for a new permission or, in some cases, apply to extend the time limit.

The Planning Application Process

Step 1: Pre-Application Advice

Before submitting a formal application, consider requesting pre-application advice from your local planning authority. This typically costs £100-£500 and provides:

• Informal feedback on your proposal
• Guidance on planning policy constraints
• Information about potential objections
• Advice on application requirements

Pre-application advice is particularly valuable for complex sites, conservation areas, or ambitious designs.

Step 2: Prepare Your Application

A householder planning application requires:

• Completed application form
• Site location plan (1:1250 or 1:2500 scale with north point)
• Site/block plan (1:500 or 1:200 scale)
• Existing and proposed floor plans (1:50 or 1:100 scale)
• Existing and proposed elevations (1:50 or 1:100 scale)
• Design and access statement
• Application fee (currently £258 for householder applications)

Step 3: Submission and Validation

Applications are submitted through the Planning Portal or directly to your local authority. The council will validate your application, checking all required documents are included. Invalid applications are returned, causing delays.

Step 4: Consultation

The council consults neighbours and statutory consultees. A site notice may be posted, and the application appears on the council’s planning register. Consultees typically have 21 days to comment.

Step 5: Decision

The target decision period for householder applications is 8 weeks. Most applications are decided by planning officers under delegated powers. Complex or contentious applications may go to a planning committee.

Possible outcomes include:

• Approval: Permission granted, possibly with conditions
• Refusal: Permission denied with reasons stated
• Request for amendments: Officer suggests changes to make the scheme acceptable

Planning Conditions Explained

Approved applications often come with conditions. Common conditions include:

• Time limit: Development must begin within 3 years
• Approved plans: Work must accord with submitted drawings
• Materials: Samples to be approved before construction
• Hours of work: Restrictions on construction times
• Landscaping: Requirements for planting or boundary treatment

Breaching conditions can result in enforcement action, so ensure you understand and comply with all conditions.

What If Planning Permission Is Refused?

If your application is refused, you have options:

Negotiate and Resubmit

Discuss the reasons for refusal with the planning officer. Often, a revised scheme addressing their concerns will be approved. There’s no fee for a resubmission within 12 months of the original decision.

Appeal

You can appeal to the Planning Inspectorate within 12 weeks of the decision. Appeals are free but can take 6-12 months to determine. Success rates for householder appeals are around 30-40%, so consider whether your case has merit.

Planning in Conservation Areas

Extensions in conservation areas face additional scrutiny. You’re more likely to need planning permission (as permitted development rights are often restricted), and proposals must preserve or enhance the character of the area.

Key considerations include:

• Materials must be appropriate to the conservation area
• Design should respect local architectural character
• Scale and massing should be sympathetic to surroundings
• Views and settings of historic buildings must be protected

Listed Building Consent

If your property is listed, you need listed building consent for any works affecting its character as a building of special architectural or historic interest. This applies to internal works as well as extensions.

Listed building consent is separate from planning permission – you may need both. There’s no fee for listed building consent applications, but they require detailed justification of how the proposal affects the building’s significance.

How We Can Help

Navigating planning can be complex, particularly in London and Surrey where conservation areas, Article 4 directions, and local policies add layers of complexity. Composition Design Architects has extensive experience securing planning permissions across the region.

We offer:

• Feasibility assessments to identify what’s achievable on your site
• Pre-application discussions with planning officers
• Full planning application preparation and submission
• Negotiation with planners if issues arise
• Appeal support if necessary

Learn more about how we work and our design process, or view our portfolio to see completed projects.

Contact us to discuss your project and understand your planning options.

We work with homeowners across London and Surrey, including Wandsworth, Wimbledon, Clapham, Fulham, Kensington, Richmond, Kingston, Guildford, and Cobham.