Trimble Architects

This article asks: what are the rules on planning permission for extensions? Find out more about planning permission and what size extension you can build without planning permission.

Recently the permitted development rules have been relaxed, and this means that you can build an extension of up to six metres without planning permission.

If your house is detached, you are now permitted to build up to eight metres. An extension or addition to your home is usually considered to be permitted development.

Therefore, you will not need to go through the additional process of getting planning permission as long as:

• The extension you are building is no more than half the area of land around the original house.
• The term "original house" is seen as it was in 1948, or after this date how it was newly built.
• Extensions of more than one storey are not permitted to extend beyond the rear wall of the original house by more than three metres.

Anything more than the allowed three metres, and you would require planning permission for your extension. The maximum eaves and ridge height of your extension must be no higher than the existing house.

Although you might not need planning permission, you will likely need approval under the Building Regulations. There are some classes of new buildings or extensions of existing buildings that do not require Building Regulations approval. Your local planning office will give you advice on what planning permission or building regulations are needed. It is always best to find this out before you start any work on your property.

WHAT IS THE DIFFERENCE BETWEEN LISTED BUILDING CONSENT AND PLANNING PERMISSION?

For any project where planning permission is required, be it a conversion, extension or new build, the process will involve fees paid to the council. Planning fees fall into three sections:

• Rates for statutory planning applications.
• Council charges, including pre-app costs, the Community Infrastructure Levy (CIL) and other payment demands.
• Professional estimates.

The first of these costs is the most certain, prices are set nationally, so are the same throughout the whole of the United Kingdom. Self-builds are exempt from the Community Infrastructure Levy (CIL), so if your building project qualifies then you won’t need to pay this.

Other council expenses can vary and can be considerably costly for things like pre-app or legal agreements. Likewise, professional fees can increase your budget, especially if you require several different professionals for your project.

• Full or detailed planning permission for a house conversion or new house in England is £462.00.
• Outline applications are £462.00 per 0.1 hectares.
• Householder applications, needed for garden buildings or extensions, are £206.00.
• Requests to approve conditions (e.g. landscaping or materials details) are £116.00, or £34.00 for householder applications.
• Multiple conditions can be covered under one request, but submitting via the Planning Portal carries an additional £20 processing charge.

The Neighbour Consultation Scheme, which was due to expire in 2019, has now been made permanent. This scheme allows larger extensions but also gives neighbours the right to raise objections.

Yes – provided they comply with the Party Wall Act, which regulates shared or adjoining structures. Party Fence Walls are covered, though timber fences or screens are not.

This scheme allows:

• Semi-detached or terraced houses to be extended up to 6 metres.
• Detached houses to be extended up to 8 metres.

Neighbours have 21 days to raise objections. After that, the local authority has another 21 days to grant prior approval.

Even with planning permission or permitted development rights, neighbours may still have concerns. Issues such as a Party Wall Agreement or legal challenges may arise, though it is rare for objections to stop a permitted extension entirely.

When extending a property, windows and glazing are a crucial consideration.

Replacing existing windows: Usually does not require planning permission, provided replacements are similar in appearance to the originals.

Adding new windows: May require permission if they overlook neighbours, affect privacy, or alter the external appearance significantly.

Glass and double glazing: Most extensions use modern double glazed panes, which improve insulation and reduce noise.

It’s worth noting that Building Regulations apply to the thermal performance of glazing. This ensures your extension meets current energy efficiency standards.

Many homeowners use extensions as an opportunity to improve the overall energy performance of their home. Double glazing helps reduce heat loss, lowering energy bills and preventing condensation inside the property.

Building Regulations require windows and glazed doors to achieve minimum standards for insulation and performance. The seal on double glazed panes must be secure to prevent drafts, leaks, and heat loss over time.

When planning your extension:

• Think about how glass panes will affect light and comfort in your new space.
• High-quality double glazing reduces outside noise and helps maintain a stable indoor temperature.
• Replacing old windows in the rest of your property at the same time as building an extension can add long-term value.

Many homeowners find that choosing durable, double glazed windows not only improves comfort but also enhances the market value of their home.

If you want to find out more information about whether you need planning permission for your extension building project, you can discuss it with your local architect. If you are looking for an architect in London we can help you with planning permission advice.