A single-storey extension is a popular way to create extra living space without adding another floor to your home. Whether you want a larger kitchen, an open-plan dining area or an additional living room, extending your property can improve how you use the available space.
Before starting work, however, you need to establish whether planning permission for a single-storey extension is required. Some projects fall under permitted development rights, meaning a formal planning application may not be necessary. Others must receive approval from the local planning authority before construction begins.
The requirements depend on the extension’s size, height, location and design, as well as the property’s planning history. This article explains the main rules in England, the circumstances in which permission is needed and how to prepare for your project.
Do You Need Planning Permission for a Single Storey Extension?
Not always. A single-storey extension to a house in England may qualify as permitted development if it satisfies all the relevant limits and conditions.
Permitted development rights allow certain home improvements to proceed without a full planning application. However, these rights are subject to restrictions, and they may have been removed or limited for particular properties.
You may need planning permission if:
- Your extension exceeds the permitted development size or height limits.
- You want to build an extension at the front of your property or beyond a restricted elevation.
- Your proposal involves a side extension in a location where additional restrictions apply.
- Your property is in a conservation area or another designated location.
- A planning condition or Article 4 Direction restricts permitted development rights.
- Your property is a flat or maisonette rather than a house.
Even where planning permission is not required, building regulations approval may still be necessary.
For a broader explanation of the rules, read Planning Build’s guide to extension planning permission.
Permitted Development Rules for a Single Storey Extension
The permitted development rules vary depending on whether you are extending the rear or side of your house. The following limits are a useful starting point, but all applicable conditions must be satisfied.
1. Single-Storey Rear Extension Limits
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 apply to the extension’s projection from the original rear wall, not simply the distance from the current back door or the edge of an existing extension.
Eligible properties may be able to build a larger single-storey rear extension under the larger home extension prior approval procedure. Subject to the relevant conditions, the maximum projection can increase to eight metres for a detached house and six metres for other houses.
This larger allowance is not automatic. You must follow the required notification and prior approval process with the local planning authority. The larger extension route is also unavailable on certain designated land and Sites of Special Scientific Interest.
You can review the official requirements in the Planning Portal’s extension guidance.
2. Maximum Height
Height is another important factor when determining whether a single-storey extension qualifies as permitted development.
A single-storey rear extension must generally not exceed four metres in height. Additional restrictions apply to the eaves and the relationship between the extension and the existing house.
Where any part of the extension is within two metres of the property’s boundary, the eaves height must generally not exceed three metres.
The extension must also meet the applicable roof and eaves height restrictions in relation to the existing house. A design that satisfies the projection limit may still require planning permission if it exceeds the permitted height.
For this reason, measure the proposed extension carefully before finalising the design.
3. Rules for Side Extensions
A single-storey extension built to the side of a house is subject to different restrictions.
Under the general permitted development rules, a qualifying side extension must:
- Be no more than four metres high.
- Have only one storey.
- Be no wider than half the width of the original house.
Other conditions may apply depending on the property’s layout and the extension’s position.
Restrictions are stricter on designated land, including conservation areas, where extensions beyond a side wall of the original house generally require planning permission.
If your design combines a side extension with a rear extension, both sets of relevant restrictions may apply. It is important to assess the complete proposal rather than considering each section separately.
4. The Original House and Previous Extensions
One of the most common sources of confusion is the meaning of the original house.
For permitted development purposes, the original house generally means the property as first built or as it stood on 1 July 1948 if it was built before that date.
This matters because previous extensions may already have used some of the property’s permitted development allowance. The assessment generally considers the total enlargement, including relevant existing extensions, rather than treating every new project as a separate allowance.
For example, if a previous owner has already built a rear extension, you cannot automatically assume that you can add another extension using the full standard projection limit.
Check the property’s planning history and establish what has already been built before relying on permitted development rights.
When Is Planning Permission Required for a Single Storey Extension?
A full householder planning application is generally required when the proposed extension does not meet the permitted development rules or when those rights are unavailable.
The Extension Is Too Large
If your extension projects further than the applicable limit, exceeds the permitted height or breaches another condition, you may need planning permission.
For example, a proposed rear extension projecting five metres beyond the original rear wall of a semi-detached house would exceed the standard three-metre projection limit. It might qualify under the larger home extension procedure if the property and proposal meet the relevant requirements, but this needs to be checked before work begins.
The Property Has Planning Restrictions
Some properties have conditions or restrictions that remove permitted development rights. An Article 4 Direction may also restrict certain types of development in a particular area.
If your home is listed, you may need listed building consent as well as any required planning permission. Work affecting a listed building’s character can require consent even when the proposed physical extension is relatively small.
The Extension Changes the Front or Side of the Property
Extensions projecting beyond the principal elevation, or beyond a side elevation that fronts a highway, are subject to specific restrictions. A front extension is therefore less likely to qualify as permitted development than a straightforward rear extension.
The exact position of the property and the proposed design matter, so avoid assuming that a small extension will automatically be permitted.
How to Apply for Planning Permission for a Single Storey Extension
If your project requires planning permission, preparing the application carefully can help reduce avoidable delays.
Step 1: Assess Your Proposal
Start by establishing the extension’s purpose, dimensions, location and proposed appearance. Consider how it will relate to the existing house, neighbouring properties and the surrounding area.
This initial assessment can help identify potential planning issues before you invest in detailed design work.
Step 2: Prepare Planning Drawings
Your application will normally need suitable plans and drawings showing the existing property and the proposed extension.
Depending on the project and the local planning authority’s requirements, these may include:
- A location plan identifying the property.
- A site or block plan showing the extension’s position and boundaries.
- Existing and proposed floor plans.
- Existing and proposed elevations.
- Sections or additional drawings where needed to explain the height and design.
Accurate drawings help the planning officer understand the proposal and assess its impact.
Planning Build can help with planning permission drawings and the preparation of supporting application information.
Step 3: Check the Supporting Information
Some proposals may require supporting documents in addition to the drawings. The requirements depend on the location, scale and nature of the development.
For example, a planning statement may help explain the proposal and address relevant planning considerations where one is appropriate. Properties in sensitive locations may also be subject to additional requirements.
Check the local planning authority’s validation requirements before submitting the application.
Step 4: Submit the Application
Applications in England can generally be submitted through the Planning Portal or directly through the relevant local planning authority’s arrangements.
You will need to provide the required forms, drawings and supporting documents, together with the applicable fee.
Once submitted, the authority checks whether the application is valid before proceeding to consultation and assessment.
Step 5: Wait for the Decision
The local planning authority assesses the proposal against the development plan and other relevant planning considerations.
For a typical householder application, the statutory determination period is usually eight weeks from validation, although some applications take longer. The actual timescale can depend on the complexity of the proposal, requests for further information and whether an extension of time is agreed.
You should not begin work that requires planning permission until the necessary approval has been granted and any relevant conditions have been considered.
For more information, see Planning Build’s guide to the planning application process.
Do You Need Building Regulations Approval?
Planning permission and building regulations serve different purposes.
Planning permission considers whether the extension is acceptable in terms of its design, size, position and impact on the surrounding area. Building regulations address technical requirements such as structural stability, fire safety, insulation, ventilation and drainage.
A single-storey extension may qualify as permitted development but still require building regulations approval.
Before construction, confirm which building control route applies to your project and check whether any other permissions or consents are needed. Depending on the work, you may also need to consider party wall procedures or private property restrictions.
How Planning Build Can Help
Understanding the planning rules before designing and building a single-storey extension can help you avoid unnecessary expense and delays.
Planning Build can help you assess your proposal, understand whether a planning application may be required and prepare the information needed to move your project forward.
Whether you are planning a rear kitchen extension or a side addition, professional advice can help you identify relevant restrictions and understand your options before committing to construction.
Explore our planning permission services or contact Planning Build to discuss your proposed extension.
