A single-storey extension can create valuable extra space in your home, whether you want a larger kitchen, a more practical dining area or an additional living room. Before you start designing or building, however, it is important to understand the planning permission requirements that apply to your property.
Some single-storey extensions can be built under permitted development rights without a full planning application. Others require householder planning permission, while certain larger rear extensions may follow a separate prior approval process.
Understanding which route applies to your project can help you avoid unnecessary costs, redesigns and delays. This article explains the planning permission requirements for single-storey extensions in England, the rules that affect approval and the steps to take before construction begins.
Does a Single-Storey Extension Need Planning Permission?
Not every single-storey extension requires planning permission. Under permitted development rights, certain extensions to houses can be built without submitting a full planning application, provided they meet specific limits and conditions.
However, permitted development is not a blanket exemption. The extension must satisfy the relevant requirements concerning its size, height, position and appearance. The property’s planning history and location must also be considered.
You may need planning permission if:
- The extension exceeds the permitted development limits.
- Your design involves a front extension or extends beyond a restricted elevation.
- The proposal involves a side extension on designated land.
- Previous extensions have used up the available permitted development allowance.
- An Article 4 Direction or planning condition restricts your permitted development rights.
- The property is a flat or maisonette, or another type of building that does not qualify for the usual householder rights.
If you are unsure which rules apply, start by reviewing the property’s planning history and the requirements explained in Planning Build’s guide to planning permission rules.
What Are the Permitted Development Rules for Single-Storey Extensions?
Permitted development rules determine whether certain extensions can proceed without a full planning application. The main limits for single-storey extensions in England depend on the extension’s position and dimensions.
Rear Extension Limits
Under the standard permitted development rules, 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 relate to the original house, rather than necessarily the current rear wall if the property has already been extended.
Eligible homeowners may be able to build a larger single-storey rear extension under the larger home extension prior approval procedure. Under this route, the maximum projection can increase to eight metres for a detached house or six metres for another house, subject to the applicable conditions.
This is not the same as unrestricted permitted development. You must notify the local planning authority through the relevant prior approval process, which includes consultation with adjoining neighbours. The authority may need to assess the impact on neighbouring properties before the extension can proceed.
The larger-extension procedure is not available in certain designated locations or on Sites of Special Scientific Interest.
For the official requirements, see the Planning Portal’s extension planning permission guidance.
Height and Boundary Restrictions
A single-storey rear extension must generally not exceed four metres in height under permitted development rules.
Where any part of the extension is within two metres of the property’s boundary, the eaves height must generally not exceed three metres. Other conditions apply to the height of the extension in relation to the existing house.
These restrictions matter even if the extension falls within the permitted projection limit. A design that is too high or breaches another condition may still require planning permission.
Side Extension Requirements
A qualifying single-storey side extension must generally:
- Be no more than four metres high.
- Be limited to one storey.
- Be no wider than half the width of the original house.
Additional restrictions apply to side extensions on designated land, including conservation areas, where extensions beyond a side wall of the original house generally require planning permission.
The permitted development rules also limit how much of the land around the original house can be covered by extensions and other buildings. Generally, these additions must not cover more than half the relevant land area.
Previous extensions, sheds and other outbuildings may affect this calculation.
When Is Full Planning Permission Required?
If your proposed extension does not satisfy the permitted development requirements, you will generally need to apply for householder planning permission.
Your Extension Exceeds the Limits
If your proposed extension is too deep, too high or too wide to qualify under the relevant rules, you may need a planning application.
For example, a rear extension projecting five metres beyond the original rear wall of a semi-detached house would exceed the standard three-metre limit. It may qualify under the larger home extension procedure if the property and proposal meet the requirements, but that route must be checked before construction begins.
Your Property Has Restrictions
Some homes have planning conditions or Article 4 Directions that restrict permitted development rights. In these cases, even an extension that would ordinarily qualify may need planning permission.
Listed buildings require particular care. Depending on the proposed work, you may need planning permission and listed building consent. The applicable requirements depend on the building’s status, the nature of the extension and its potential effect on the building’s special character.
Your Design Affects the Front or Side of the House
Permitted development rights restrict extensions that project beyond the principal elevation or, where it fronts a highway, a side elevation of the original house.
A design that extends around the side and rear of a property may also need to satisfy both sets of restrictions. Assessing the whole design is therefore important before deciding whether a planning application is required.
What Does the Council Consider When Assessing an Extension?
Where planning permission is required, the local planning authority assesses the proposal against the development plan and other relevant planning considerations.
Important factors can include:
Design and appearance: The extension should be considered in relation to the existing house and the character of the surrounding area. Its scale, roof form, materials and proportions may all be relevant.
Impact on neighbouring properties: The council may consider whether the extension would cause unacceptable overlooking, loss of privacy, an overbearing effect or loss of daylight to neighbouring homes.
Site layout and boundaries: The extension’s position, proximity to neighbouring buildings and relationship with the street can affect the planning assessment.
Local planning policies: Policies may address design, heritage, residential amenity, environmental considerations and other issues relevant to the site.
Approval is not guaranteed simply because an extension is relatively small. The local context and the details of the proposal matter.
If you need support assessing your proposal before applying, Planning Build offers planning permission advice to help you understand the requirements and possible next steps.
How to Apply for Planning Permission for a Single-Storey Extension
If your project requires full planning permission, the following steps can help you prepare.
1. Establish the Planning Requirements
Confirm whether the extension qualifies as permitted development or needs a full application. Check the property’s planning history and identify any restrictions that could affect the proposal.
If the extension falls under the larger home extension procedure, establish the prior approval requirements before proceeding.
2. Prepare the Extension Design
Develop a clear proposal showing the extension’s intended size, layout, height and appearance. Consider how it will connect to the existing house and how it will sit within the available site.
An early assessment can help identify design changes that may be needed to address planning requirements.
3. Prepare the Required Drawings
A householder planning application will generally need appropriate drawings, which may include:
- A location plan.
- A site or block plan.
- Existing and proposed floor plans.
- Existing and proposed elevations.
- Sections or other supporting drawings where necessary.
The exact requirements depend on the proposal and the local planning authority’s validation requirements.
Planning Build can help with planning permission drawings and the supporting information needed for an application.
4. Submit the Application
Applications in England can generally be submitted through the Planning Portal or using the relevant local authority’s application arrangements.
You will need to provide the required forms, plans and supporting documents, along with the applicable fee. The council will check the submission for validity before moving to the assessment stage.
5. Respond to the Council and Await a Decision
The authority may consult neighbours, assess the proposal against planning policies and request further information where necessary.
The usual statutory determination period for a householder planning application is eight weeks from validation, although some applications take longer. The timescale can be affected by the complexity of the proposal and whether additional information or an extension of time is agreed.
Do not begin work that requires planning permission until approval has been granted and you have checked any conditions attached to the decision.
For more information, read Planning Build’s guide to the planning application process.
Do You Need Building Regulations Approval?
Planning permission and building regulations are separate requirements.
Planning permission addresses whether the proposed extension is acceptable in planning terms. Building regulations deal with technical standards, including structural safety, fire safety, energy efficiency, ventilation and drainage.
Even when a single-storey extension qualifies as permitted development, building regulations approval may still be required.
You should also check whether other requirements apply, such as party wall procedures, private property covenants or additional consents for a listed building.
How Planning Build Can Support Your Extension Project
Determining the correct planning route is an important part of preparing for a single-storey extension. Checking the requirements early can help you understand whether you need a full planning application, whether a prior approval process may apply and what information to prepare.
Planning Build can support you with planning advice, drawings and application preparation, helping you understand the requirements relevant to your proposed development.
To discuss your project, explore our planning permission services or contact Planning Build.
