A rear extension is one of the most popular ways to create additional space in a home. Whether you want a larger kitchen, an open-plan dining area or an extended living room, building towards the back of your property can improve the layout without changing the appearance of the front of the house.
However, before starting construction, you need to establish whether rear extension planning permission is required. Some projects qualify as permitted development, while others need a full planning application or approval through a separate prior approval procedure.
The requirements depend on the extension’s depth, height, position and design, as well as the property’s location and planning history. This article explains the rules in England, how to check which route applies and what to do before building.
Do You Need Planning Permission for a Rear Extension?
Not always. A rear extension to a house in England may qualify as permitted development, meaning you can carry out the work without submitting a full planning application if you meet all the relevant conditions.
However, permitted development rights have limits. You may need planning permission if your extension exceeds the permitted dimensions, affects a restricted elevation or is proposed on a property where permitted development rights have been removed.
You should also check whether the house is listed, located in a conservation area or subject to other planning restrictions.
Before deciding whether permission is needed, consider:
- How far the extension will project beyond the original rear wall.
- Whether the extension will have one storey or more.
- The proposed height and distance from the boundaries.
- Whether previous extensions affect the permitted development allowance.
- Whether local restrictions apply to your property.
For a broader explanation of the rules, see Planning Build’s guide to planning permission rules.
How Far Can You Extend the Rear of a House Without Planning Permission?
The permitted projection depends on whether the extension has one storey or more and whether you are using the standard rules or the larger home extension procedure.
Single-Storey Rear Extensions
Under the standard permitted development rules in England, a single-storey rear extension must not project beyond the rear wall of the original house by more than:
- Four metres for a detached house.
- Three metres for any other house, including semi-detached and terraced houses.
These limits are measured from the original rear wall, not necessarily the back of a previous extension.
If your property already has an extension, you cannot automatically assume that you have the full allowance available for another addition. The existing and proposed development may need to be considered together.
Larger Single-Storey Rear Extensions
Eligible homeowners may be able to build a larger single-storey rear extension through the larger home extension prior approval procedure.
Under this route, the maximum projection may increase to:
- Eight metres for a detached house.
- Six metres for any other house.
The extension must generally remain no more than four metres high and satisfy the other applicable conditions.
This route is not automatic permission to build a larger extension. You must notify the local planning authority and follow the required prior approval process, which includes consultation with adjoining neighbours. The authority may need to consider the impact on neighbouring properties before the work can proceed.
The larger-extension procedure is not available in certain designated locations, including conservation areas and other land covered by the relevant restrictions, or on Sites of Special Scientific Interest.
Two-Storey Rear Extensions
Two-storey rear extensions are subject to stricter limits.
Under the general permitted development rules, an extension with more than one storey must not project beyond the original rear wall by more than three metres. It must also be at least seven metres from any boundary opposite that rear wall.
Additional restrictions apply to the extension’s height, roof design and upper-floor side windows. Two-storey rear extensions on designated land generally require planning permission.
If your proposed extension is larger than these limits, you will usually need to consider a householder planning application rather than the larger home extension prior approval procedure, which applies to qualifying single-storey rear extensions.
You can review the official requirements in the Planning Portal’s extension guidance.
What Height Can a Rear Extension Be?
Height is another important factor when determining whether a rear extension qualifies as permitted development.
A single-storey rear extension must generally not exceed four metres in height. Where any part of the extension is within two metres of the property’s boundary, its eaves height must generally not exceed three metres.
Additional rules apply to the relationship between the extension’s eaves and roof height and those of the existing house.
For two-storey extensions, the conditions are more restrictive. The extension must generally not be higher than the highest part of the existing roof or have eaves higher than the existing eaves. Upper-floor side windows must also meet the applicable privacy requirements.
A proposal can fall within the permitted depth limit but still require planning permission if it breaches another condition. Check the height, roof design and boundary distances together rather than assessing each requirement in isolation.
When Is Planning Permission Required for a Rear Extension?
A rear extension will generally require a planning application if it does not qualify as permitted development or if the relevant rights do not apply to the property.
The Extension Exceeds the Permitted Limits
If your proposed extension is deeper or higher than the applicable limits, you may need full planning permission.
For example, a rear extension projecting five metres beyond the original rear wall of a semi-detached house exceeds the standard three-metre limit. It may qualify under the larger home extension procedure if it is single-storey and meets the relevant requirements, but you must follow that procedure before proceeding.
Your Property Has Restricted Permitted Development Rights
Permitted development rights may have been removed by a planning condition or an Article 4 Direction. If so, a rear extension that would normally qualify may still require planning permission.
Check the property’s planning history and ask the local planning authority whether any restrictions apply.
Your Home Is Listed or in a Designated Area
Properties in conservation areas and other designated locations can be subject to additional restrictions. Under the general rules, a rear extension of more than one storey is not permitted development on designated land.
Listed buildings require particular care. Depending on the proposal, you may need planning permission, listed building consent or both.
Previous Extensions Have Used the Available Allowance
The permitted development rules consider relevant previous extensions and the total enlargement of the original house. If a previous owner has already extended the property, the remaining scope for further work may be limited.
Review the existing layout and planning history before assuming that a new rear extension qualifies.
What Will the Council Consider When Assessing a Rear Extension?
Where planning permission is required, the local planning authority assesses the proposal against the development plan and other relevant planning considerations.
Important factors may include:
Design and appearance: The council may consider the extension’s scale, proportions, materials, roof design and relationship with the existing house.
Impact on neighbouring properties: The extension should be assessed for potential effects on daylight, privacy and the outlook from neighbouring homes.
Overbearing impact: A deep or tall extension close to a boundary may appear dominant from an adjoining garden or property. Its size and position can be important.
Local character: The design may need to respond appropriately to the surrounding buildings and any relevant heritage considerations.
Site layout: The location of the extension, remaining garden space and relationship with boundaries may also affect the assessment.
There is no guarantee of approval based on size alone. The acceptability of a rear extension depends on the design and the circumstances of the site.
If you need help assessing the planning requirements, Planning Build offers planning permission advice to help you understand your options before submitting an application.
How to Apply for Rear Extension Planning Permission
If your project requires full planning permission, preparing the application carefully can help the local authority assess the proposal.
1. Establish the Planning Requirements
Confirm whether the extension qualifies as permitted development, falls within the larger home extension prior approval procedure or requires a full planning application.
Check the property’s planning history, existing extensions and any restrictions affecting the site.
2. Prepare the Extension Design
Define the proposed extension’s dimensions, height, layout and appearance. Consider how it will connect to the existing house and how close it will be to neighbouring properties.
An early review can help identify potential issues before detailed design work is completed.
3. Prepare Planning Drawings
Depending on the proposal, you may need:
- A location plan identifying the property.
- A site or block plan showing the extension and boundaries.
- Existing and proposed floor plans.
- Existing and proposed elevations.
- Sections or additional drawings where necessary.
The drawings should accurately show the proposed dimensions and the extension’s relationship with the existing house.
Planning Build can support this stage through its planning permission drawings service.
4. Submit the Application
In England, applications can generally be submitted through the Planning Portal or the relevant local planning authority’s application arrangements.
You will need to provide the required forms, drawings and supporting documents, together with the applicable fee.
The council will check whether the application is valid before proceeding to consultation and assessment.
5. Await the Decision
The usual statutory determination period for a householder planning application is eight weeks from validation, although some applications take longer. The timescale can depend on the complexity of the proposal, requests for additional information and whether an extension of time is agreed.
Do not begin work that requires planning permission before approval has been granted. You should also review any conditions attached to the decision before construction begins.
For further information, see Planning Build’s guide to the planning application process.
Do You Need Building Regulations Approval for a Rear Extension?
Planning permission and building regulations are separate requirements.
Planning permission considers whether the extension is acceptable in planning terms, including its design, size and impact on the surrounding area. Building regulations cover technical standards such as structural safety, fire safety, insulation, ventilation and drainage.
Even if your rear extension qualifies as permitted development, building regulations approval may still be required.
Depending on the project, you may also need to consider party wall procedures, private property restrictions or other consents. Establishing these requirements early can help prevent avoidable delays during construction.
How Planning Build Can Help
Understanding the planning requirements before building a rear extension can help you make informed decisions about the design, budget and next steps.
Planning Build can help you assess your proposal, understand whether permitted development or a planning application may be appropriate, and prepare the drawings and supporting information needed for the process.
Explore our planning permission services or contact Planning Build to discuss your proposed rear extension.
