House extension planning permission is an important consideration when you want to create more space in your home. Whether you are planning a larger kitchen, an additional bedroom, a side extension or a two-storey addition, understanding the planning requirements can help you avoid unexpected costs and delays.
In England, some house extensions can be built under permitted development rights without a formal planning application. However, these rights come with specific limits relating to the extension’s dimensions, location and design. If your plans fall outside those limits, or your property is subject to additional restrictions, you may need planning permission before work begins.
This article explains when house extension planning permission is required, which rules apply to common extension types, how to apply and what to check before starting your project.
Do You Need Planning Permission for a House Extension?
Not every house extension requires planning permission. Certain extensions qualify as permitted development, which allows homeowners to carry out specific building work without submitting a planning application, provided all relevant conditions are met.
You may need planning permission if:
- Your extension exceeds the permitted development limits for its size, height or position.
- You are planning a two-storey or side extension that does not meet the relevant requirements.
- Your property is subject to an Article 4 Direction or a planning condition that removes permitted development rights.
- Your home is a listed building or is located in an area where additional restrictions apply.
- Your property is a flat or maisonette, rather than a qualifying house.
- Your proposal involves alterations that are not covered by the permitted development rules.
The planning history of your property also matters. Previous extensions may affect the development allowance available for further work.
Before commissioning detailed designs or arranging construction, check whether your proposal qualifies as permitted development. Planning Build’s guide to whether you need planning permission provides a useful starting point.
House Extension Planning Permission Rules in England
Permitted development rights allow certain extensions to qualifying houses without a formal planning application. However, the extension must comply with all the relevant limitations and conditions.
The main rules differ according to the type of extension you want to build.
Single-Storey Rear Extensions
A single-storey rear extension is a popular option for homeowners who want a larger kitchen, dining room or living area.
Under the standard permitted development rules in England, a qualifying single-storey rear extension can generally extend beyond the rear wall of the original house by:
- Up to 4 metres for a detached house.
- Up to 3 metres for other qualifying houses, including semi-detached and terraced properties.
Larger single-storey rear extensions may qualify under a separate prior approval procedure. This can allow an extension to project up to 8 metres for a detached house or 6 metres for other qualifying houses, subject to the relevant conditions and neighbour consultation requirements.
This larger-extension route is not automatic permission to build. You must follow the required procedure and satisfy the local planning authority’s requirements before starting work.
Other restrictions apply, including limits on height, eaves near boundaries and the total area covered by extensions and other buildings.
Side Extensions
Side extensions can provide additional space for a utility room, kitchen or other part of the home. However, they are subject to specific restrictions under permitted development rights.
Generally, a qualifying single-storey side extension must:
- Be no more than 4 metres high.
- Have a width no greater than half the width of the original house.
- Remain single-storey.
- Meet the applicable height and boundary conditions.
Additional restrictions apply in designated areas, including conservation areas and National Parks. A side extension that falls outside the relevant limits will generally require planning permission.
Two-Storey Extensions
Two-storey extensions are subject to more detailed requirements.
Under the standard permitted development rules, a qualifying two-storey rear extension must generally project no more than 3 metres beyond the original rear wall and must be at least 7 metres from the relevant boundary opposite that wall.
Additional conditions cover height, roof design and upper-floor windows. For example, certain upper-floor side windows must be obscure-glazed and have restricted opening arrangements to protect privacy.
Two-storey side extensions require planning permission under the standard householder rules. Additional restrictions also apply to extensions of more than one storey in designated areas.
For the full technical requirements, consult the government’s permitted development rights guidance for householders.
How to Apply for House Extension Planning Permission
If your extension does not qualify as permitted development, you will generally need to submit a householder planning application to your local planning authority.
Step 1: Assess Your Proposed Extension
Start by establishing the purpose, size, layout and design of the extension.
Check the property’s planning history and identify any restrictions that could affect your plans. If the proposal is complex or you are unsure which rules apply, consider seeking professional planning advice before finalising the design.
Step 2: Prepare Planning Drawings
A planning application usually requires drawings showing the existing property and the proposed extension.
Depending on the proposal, these may include:
- A location plan showing the property’s position.
- A site plan showing the extension and boundaries.
- Existing and proposed floor plans.
- Existing and proposed elevations.
- Sections or other drawings where necessary.
The drawings should clearly communicate the extension’s dimensions, layout and appearance.
Planning Build’s guide to planning application drawings explains the types of plans you may need.
Step 3: Gather Supporting Documents
Depending on the site and proposal, your local planning authority may require additional information. This could include a planning statement, a Design and Access Statement where applicable, or specialist reports addressing particular site constraints.
Check the authority’s local validation requirements before submitting your application.
Step 4: Submit the Application
You can generally submit a householder planning application through the Planning Portal or your local authority’s application service.
You will need to provide the required forms, drawings and supporting information, as well as pay the applicable planning application fee.
For more detail, read Planning Build’s article on the householder planning application process.
Step 5: Wait for the Decision
Once your application has been validated, the local planning authority will assess the proposal. This may involve consultation with neighbours and other relevant parties.
The authority may grant permission, grant it subject to conditions or refuse the application.
The standard determination period for a typical householder planning application in England is generally eight weeks from validation, although some applications take longer.
You should wait until the necessary permission has been granted before starting work that depends on it.
What If Your House Extension Does Not Qualify as Permitted Development?
If your proposed extension exceeds the permitted development limits, that does not automatically mean you cannot build it. It means you may need to submit a planning application for the authority to assess.
You could revise the design to meet the permitted development requirements or apply for permission for the proposal as planned. The most suitable approach depends on the site, the design and the relevant planning policies.
If you have already built an extension without permission that was required, you may need to consider a retrospective planning application. Approval is not guaranteed, so establish your position before assuming the work is lawful.
Planning Build’s guidance on retrospective planning permission explains the options available in these circumstances.
Do House Extensions Need Building Regulations Approval?
Planning permission and building regulations are separate requirements.
Planning permission considers whether a development is acceptable in planning terms. Building regulations cover technical matters such as structural safety, fire safety, ventilation and energy efficiency.
An extension that qualifies as permitted development may still require building regulations approval. Requirements depend on the nature of the work, and certain types of construction may qualify for specific exemptions.
Check both planning and building regulations requirements before construction begins.
Frequently Asked Questions
How much does house extension planning permission cost?
The cost depends on the applicable planning application fee and any professional services you need. You may also need to budget for drawings, planning advice, surveys and supporting documents. Check the current fee before submitting your application.
Can I build a house extension without planning permission?
Yes, some extensions qualify as permitted development. However, the proposal must meet all the relevant conditions, and restrictions may apply because of the property’s location, planning history or type.
How long does planning permission for a house extension take?
The standard determination period for a typical householder application in England is generally eight weeks from validation. The actual time can be longer if further information is required or the application involves additional considerations.
Can I apply for planning permission myself?
Yes. Homeowners can submit their own planning applications. However, the application must include the required forms, drawings and supporting documents. A planning consultant or architect may help if the proposal is complex or you need assistance understanding the requirements.
Can planning permission for a house extension be refused?
Yes. An application may be refused if the proposal conflicts with relevant planning policies or would cause unacceptable harm, for example through its design, scale or impact on neighbouring properties. Depending on the circumstances, you may be able to revise the proposal or appeal the decision.
Get Help With Your House Extension Plans
Understanding house extension planning permission before construction begins can help you make informed decisions, prepare the right documents and avoid unnecessary complications.
The correct approach depends on your property’s planning history, the dimensions of the proposed extension and any restrictions affecting the site. Checking these factors early can help you determine whether permitted development rights apply or whether a formal application is required.
If you need help assessing your proposal or preparing an application, contact Planning Build to discuss the planning support available for your project.
