House Extension Planning Permission — The Complete 2025 Guide

Understanding Permitted Development Rights

Permitted Development (PD) rights allow certain home improvements without full planning permission. For house extensions, key PD rules include:

• Single-storey rear extensions: Up to 4m for detached houses, 3m for attached houses (semi-detached or terraced)
• Extension height: Maximum 4m height at the eaves
• Materials: Must use similar materials to the existing property
• Volume limits: No more than 50% of the original house's volume (including previous extensions)

Article 4 Directions

Some councils have removed PD rights through Article 4 Directions, requiring full planning permission for even small extensions. This is particularly common in areas of special architectural interest. Notable areas include parts of Hillingdon and Buckinghamshire councils. Always check with your local planning authority before proceeding.

Two-Storey Extensions

Two-storey extensions almost always require full planning permission. This is because they have a greater impact on neighbours through overlooking, overshadowing, and bulk. The exception is if you can demonstrate the extension falls within very limited PD criteria, which is rare.

Side Extensions

Side extensions typically require planning permission as they affect the street scene and neighbours' amenity. Even narrow side extensions usually need approval, though some councils may grant prior approval for certain designs.

Conservation Areas and Listed Buildings

If your property is in a conservation area or is a listed building, you will NOT have Permitted Development rights. This applies to areas like Denham, Beaconsfield Old Town, and Amersham in Buckinghamshire. You will need listed building consent for any significant works.

How to Apply for Planning Permission

The application process involves:

1. Pre-application advice: Many councils offer pre-app meetings for a fee (£50-£150). This can identify issues before you submit.
2. Full application: Submit via the Planning Portal with application form, site location plan, block plan, existing and proposed elevations, and floor plans.
3. Fee: £206 for householder planning applications (2025)
4. Timeline: 8 weeks for determination (13 weeks for major applications)

Prior Approval vs Full Planning

Some extensions can use a "prior approval" process, which is faster and cheaper. This applies to certain larger single-storey rear extensions under the larger home extensions scheme. However, this process still requires neighbour notification and council assessment.

Frequently Asked Questions

What size extension needs planning permission?

As a rule, single-storey rear extensions over 3m (attached) or 4m (detached) need planning permission. However, this depends on your property type and location. Always check with your local council.

How long does planning permission take?

The statutory timeframe is 8 weeks for householder applications, though complex cases can take longer. Pre-application advice can help identify potential issues early.

What is permitted development?

Permitted Development is a set of planning rules that allow certain home improvements without the need for a full planning application. It has specific limits on size, height, and location.

Can a conservation area affect my extension?

Yes. Properties in conservation areas lose their Permitted Development rights. This means even small extensions require planning permission, and the council will consider the impact on the area's character.

Related Pages

• House Extensions
• Builders in Gerrards Cross
• House Extensions in Beaconsfield