Planning Permission for House Extensions

Learn which house extensions need planning permission and which are permitted development. Covers rear, side, front, and two-storey extensions with size limits and costs.

Do You Need Planning Permission for a House Extension?

Many house extensions in England can be built without planning permission under permitted development rights. But the rules are different for rear extensions, side extensions, front extensions, and two-storey extensions — and they change depending on whether your property is detached, semi-detached, or terraced.

Getting this wrong is costly. Building without the right approvals can result in enforcement action from your council, which may require you to demolish the extension at your own expense.

Single-Storey Rear Extensions

Single-storey rear extensions are the most common type and have the most generous permitted development allowances:

• Detached houses: Can extend up to 4 metres from the rear wall (or up to 8 metres under the Larger Home Extension scheme with prior approval).
• Semi-detached and terraced houses: Can extend up to 3 metres (or up to 6 metres under the Larger Home Extension scheme).
• Maximum height: 4 metres, or the height of the existing house if lower.
• Eaves height: Must not exceed 3 metres if within 2 metres of a boundary.

The Larger Home Extension Scheme (Prior Approval)

The Larger Home Extension scheme allows single-storey rear extensions of up to 8 metres (detached) or 6 metres (semi-detached/terraced). This requires a prior approval application to your council, which costs £120. The council consults your immediate neighbours, and if no objections are raised within 21 days, approval is granted automatically. If objections are received, the council makes a decision based on the impact on neighbouring amenity.

This is not full planning permission — it is a lighter process, but it does require the council's sign-off before you start building.

Two-Storey Rear Extensions

Two-storey rear extensions have stricter limits:

• Maximum depth: 3 metres from the original rear wall.
• Must not be within 7 metres of the rear boundary.
• Ridge height: Must not exceed the ridge height of the original house.
• Matching materials: Must match the existing house in appearance.
• Upper-floor windows: Side-facing windows must be obscure-glazed and non-opening below 1.7 metres.

Two-storey extensions are not permitted development on terraced houses — you will need planning permission.

Side Extensions

Single-storey side extensions are permitted development if:

• The extension is no more than half the width of the original house.
• It is single-storey with a maximum height of 4 metres.
• It does not extend beyond the front elevation.

Two-storey side extensions must also not be within 2 metres of any boundary, and the roof pitch must match the existing house.

In conservation areas, side extensions that face a highway are not permitted development.

Front Extensions and Porches

Front extensions generally require planning permission because they alter the street scene. However, porches are permitted development if:

• The ground area does not exceed 3 square metres.
• The height does not exceed 3 metres.
• No part is within 2 metres of a boundary with a highway.

When You Will Always Need Planning Permission

Regardless of size, you need planning permission if:

• Your property is a flat or maisonette.
• Your property is a listed building (you also need listed building consent).
• Your permitted development rights have been removed by a planning condition or Article 4 direction.
• The extension would result in more than 50% of the garden being covered by buildings.
• The extension is higher than the existing house.
• You are building forward of the principal elevation facing a highway.

How Much Does Planning Permission for an Extension Cost?

If you need planning permission, the application fee is £258 for a householder application in England. This is a flat fee set nationally and is the same at every council. Use our planning fee calculator to check the fee for your specific project type.

A Lawful Development Certificate (LDC), which confirms your extension is permitted development, costs £129. Even if you do not need planning permission, an LDC is worth getting — it provides legal proof that your council agrees the work is lawful, which is valuable when selling.

The Application Process

If you need to apply for planning permission:

1. Get drawings prepared: You need existing and proposed plans, elevations, a site plan, and a block plan. An architect or architectural technologist can do this.
2. Submit the application: Apply through the Planning Portal or directly to your council with the £258 fee.
3. Neighbour consultation: Your council notifies neighbours, who have 21 days to comment or object.
4. Decision: Householder applications are typically decided within 8 weeks.
5. Conditions: Approval often comes with conditions (e.g., matching materials, construction hours, drainage). Read them carefully.

What Your Neighbours Can Object To

Neighbours can object on material planning grounds, which include:

• Loss of light or overshadowing
• Loss of privacy (overlooking)
• Visual impact on the street scene
• Noise and disturbance during construction
• Impact on parking or highway safety

They cannot object on grounds of property value, loss of view, commercial competition, or personal disputes. The council will only consider objections that relate to planning policy.

Building Regulations

Every extension — whether or not it needs planning permission — requires Building Regulations approval. This covers foundations, structure, damp-proofing, insulation, ventilation, drainage, electrics, and fire safety. You can apply through your council's Building Control service or use a private Approved Inspector.

Research What's Been Approved Nearby

Before designing your extension, check what similar projects have been approved on your street or in your neighbourhood. This helps you understand what your council considers acceptable and can strengthen your application.

Search planning applications near your postcode on Planning Signal. You can filter by application type to find extensions and householder projects specifically, and save the search to get alerts when new applications appear.