Planning an extension can give you more living space, improve your home’s layout and increase its practicality. However, before starting work, one important question needs answering: do you need planning permission for an extension, or can you build under permitted development rights?
The answer depends on the type, size, height and position of the proposed extension, as well as the property’s location and planning history. Some house extensions can be built without a formal planning application, provided they meet specific conditions. Others require approval from the local planning authority before construction begins.
This article explains when planning permission is needed for an extension in England, the permitted development rules to consider, and how to check your proposal before committing to building work.
Do I Need Planning Permission for an Extension?
You may not need planning permission if your extension qualifies as permitted development. These rights allow certain homeowners to extend their properties without submitting a full planning application, provided the work meets all applicable limitations and conditions.
However, permitted development is not available for every property or project. You are more likely to need planning permission if your extension exceeds the relevant size limits, adds another storey, significantly changes the property’s appearance or falls outside the permitted development rules.
You may also need permission if your home is a flat or maisonette, is in a conservation area with relevant restrictions, or has had its permitted development rights removed.
Before deciding, consider:
- The type of extension you want to build, such as a rear, side or two-storey extension.
- How far the extension will project from the original house.
- Its proposed height and width.
- Previous extensions and other development on the property.
- Whether local restrictions affect your permitted development rights.
You can read more about the wider requirements in our guide to planning permission rules.
When Can You Build an Extension Without Planning Permission?
Many extensions to houses in England can qualify as permitted development, but only when they meet the relevant rules. The following examples explain some of the main requirements.
Single-Storey Rear Extensions
A single-storey rear extension may qualify as permitted development if it does not project beyond the rear wall of the original house by more than:
- Four metres for a detached house.
- Three metres for any other type of house, including semi-detached and terraced houses.
Under the larger home extension scheme, eligible single-storey rear extensions may project up to eight metres for detached houses or six metres for other houses, subject to prior approval and the applicable conditions. This is not automatic permission to build a larger extension; you must follow the relevant notification and prior approval procedure.
Other restrictions apply. For example, a single-storey rear extension must generally not exceed four metres in height. Additional limits apply to eaves height, boundary distances, the amount of land covered and the relationship with the original house.
For more detail, see the Planning Portal’s extension guidance.
Side Extensions
Side extensions are subject to additional restrictions under permitted development rules.
A qualifying side extension must generally be single-storey, no higher than four metres and no wider than half the width of the original house. Other conditions concerning the position, height and appearance of the extension must also be satisfied.
Side extensions on certain designated land, including conservation areas and other protected locations, generally require planning permission where they extend beyond the side elevation of the original house.
If your design includes both a side and rear extension, the relevant limits can apply together. You should assess the entire proposal rather than checking each section in isolation.
Two-Storey Extensions
Two-storey extensions are more restricted and require careful assessment.
Under the general permitted development rules, a qualifying extension of more than one storey must not project beyond the rear wall of the original house by more than three metres. It must also be at least seven metres from any boundary opposite that rear wall.
Additional requirements concern roof design, overall height, windows facing side boundaries and the materials used. Side extensions of more than one storey generally require planning permission.
Where the proposal involves changes to the existing roof as well as an extension, additional permitted development rules may apply.
Other Conditions That May Affect Your Extension
Meeting the projection limits alone does not guarantee that an extension qualifies as permitted development.
Other general conditions may include:
- The extension must not extend beyond the principal elevation or a side elevation that fronts a highway.
- The extension must not be higher than the highest part of the existing roof, or higher at the eaves than the existing eaves, subject to the applicable rules.
- Where the extension is within two metres of a boundary, its eaves height must generally not exceed three metres.
- Extensions and other buildings must not cover more than half the land around the original house.
- External materials must generally have a similar appearance to those of the existing house.
The rules also take previous extensions into account. Work carried out by a previous owner may affect how much additional development is permitted.
For a detailed explanation, consult the government’s permitted development technical guidance.
When Do You Need Planning Permission for an Extension?
You will generally need a planning application if your proposal does not qualify as permitted development or another relevant permission does not already authorise the work.
Common situations include:
Your extension exceeds the permitted limits. If the proposed dimensions, height or position fall outside the applicable rules, you may need householder planning permission.
You want to build a substantial or multi-storey extension. Larger proposals often need a closer assessment, particularly where they affect neighbouring properties, the street scene or the character of the area.
Your property has restrictions. Article 4 Directions, planning conditions and certain designated locations can remove or restrict permitted development rights.
Your property is a flat or maisonette. The usual householder permitted development rights for extensions do not apply in the same way to flats and maisonettes.
Your property is listed. Planning permission may be required for the proposed extension, and listed building consent may also be necessary where the work affects the building’s special architectural or historic character.
Your design affects neighbouring properties or local character. Even if a proposal appears modest, its location and design may mean it needs formal consideration.
If you are unsure about your position, Planning Build can help you assess your options through its planning permission advice service.
How to Check Whether Your Extension Needs Planning Permission
Before paying for construction work or appointing a contractor, take time to establish which rules apply to your property.
1. Define Your Proposed Extension
Start with a clear outline of the project. Identify whether it will extend to the rear, side or front of the house, whether it will have one or more storeys, and its intended dimensions.
The more accurately you define the proposal, the easier it will be to assess against the relevant planning requirements.
2. Review the Original House and Previous Work
Permitted development limits are generally assessed against the original house, meaning the house as first built or as it stood on 1 July 1948 if built before that date.
Previous extensions can affect the remaining permitted development allowance. Check the property’s planning history and establish whether earlier work was approved or carried out under permitted development rights.
3. Check for Local Restrictions
Contact your local planning authority or review its planning records to establish whether an Article 4 Direction, planning condition or other restriction affects the property.
You should also check whether the house is listed or lies within a conservation area or another designated location.
4. Prepare Suitable Drawings
Accurate drawings help establish the extension’s dimensions, layout, height and position relative to the existing house and boundaries.
Depending on the proposal, you may need existing and proposed floor plans, elevations, a site plan and a location plan. These drawings can also help identify whether the design needs to change to meet permitted development requirements.
Planning Build can support this stage through its planning permission drawings service.
5. Seek Confirmation Before Starting Work
If the extension appears to qualify as permitted development, you can consider applying for a Lawful Development Certificate from the local planning authority. This provides formal written confirmation of whether the proposed development is lawful for planning purposes.
If a full application is required, you will need to prepare and submit the appropriate documents and pay the applicable application fee. You can learn more about the steps involved in our guide to the planning application process.
What Happens If You Build an Extension Without Required Permission?
Starting construction without the necessary planning permission can create problems if the local planning authority later determines that approval was required.
The authority may investigate the development and, where appropriate, take enforcement action. This can include requiring changes to the extension or removal of unauthorised work.
You may be able to apply for retrospective planning permission, but approval is not guaranteed. The proposal will be assessed against the relevant planning considerations, just as an application made before construction would be.
Retrospective permission should not be treated as a substitute for checking the requirements in advance. Establishing your position before work begins can reduce the risk of additional costs and delays.
Do You Need Building Regulations Approval as Well?
Planning permission and building regulations are separate requirements.
Planning permission considers matters such as the development’s size, appearance, location and effect on the surrounding area. Building regulations address technical standards, including structural safety, fire safety, insulation, ventilation and drainage.
Even if your extension qualifies as permitted development, building regulations approval may still be required. You may also need to consider party wall procedures, property covenants or other consents depending on the circumstances.
Make sure you understand all relevant requirements before construction begins.
How Planning Build Can Help
Establishing whether an extension needs planning permission is an important early step in any home improvement project. Getting it wrong can lead to redesigns, unexpected fees and delays.
Planning Build can help you assess your proposed extension, understand the applicable planning requirements and identify the appropriate route forward. Whether you need advice on permitted development or support preparing a planning application, getting the right guidance early can help you make more informed decisions.
Explore our planning permission services or contact Planning Build to discuss your proposed extension.
