Planning an extension? One of the first questions to answer is: do you need planning permission for an extension?
The good news is that many single-storey extensions, and some two-storey extensions, can be built without making a full planning application. This is because certain projects fall within permitted development rights.
However, permitted development comes with strict rules covering the size, height, position and design of your extension. If your plans fall outside these limits, you may need to apply for planning permission before building work starts.
Building an extension without the required permission can lead to enforcement action and, in some circumstances, you could be required to alter or remove the extension.
This guide covers
- Permitted development rules for single-storey extensions
- Planning permission for two-storey extensions
- Kitchen and garage extension rules
- When planning permission is required
- Retrospective planning permission
- Planning application costs
- What to check before building an extension
Do I need planning permission for an extension?
You may not need planning permission if your extension falls within your property’s permitted development rights.
Permitted development rights allow homeowners to carry out certain building projects and alterations without submitting a standard planning application, provided the work meets the relevant conditions and limitations.
However, not every property benefits from the same rights.
Permitted development rights can be restricted or removed in some circumstances. Flats and maisonettes, for example, don’t benefit from the same permitted development rights as houses. Restrictions may also apply to certain properties, locations and homes that have previously undergone a change of use.
That’s why it’s important to check with your local planning authority (LPA) before starting work.
Do you need planning permission for a single-storey extension?
Many single-storey extensions can be built under permitted development, provided they remain within the relevant limits.
As a general guide, a single-storey rear extension may extend up to:
- 6 metres beyond the original rear wall of an attached house
- 8 metres beyond the original rear wall of a detached house
The extension must also comply with the applicable height and design restrictions. A single-storey extension will generally have a maximum overall height of 4 metres.
Where an extension is close to a property boundary, additional height restrictions can apply.
The rules depend on the property, the extension’s position and its design, so it’s worth speaking to your local planning authority and an experienced architect or architectural designer before committing to the project.
Do you need planning permission for a kitchen extension?
A kitchen extension isn’t treated as a separate category simply because the new space will contain a kitchen.
Instead, the normal extension planning permission and permitted development rules apply.
That means a single-storey kitchen extension may not require planning permission if its size, height, location and design all comply with permitted development requirements.
If you’re planning a large open-plan kitchen extension, side-return extension or wraparound extension, check the plans carefully. The size and position of these projects can mean that planning permission is required.
Do you need planning permission for a garage extension?
Whether you need planning permission for a garage depends on factors including its size, location, design and intended use.
Different rules can also apply depending on whether you’re building a new detached garage, adding an attached garage to your home or converting an existing garage.
Don’t assume that a garage is automatically covered by permitted development. Check with your local planning authority before starting construction, particularly if the garage will be close to a boundary or used as habitable accommodation.
You’ll also need to consider Building Regulations, which are separate from planning permission.
Do you need planning permission for a two-storey extension?
Some two-storey rear extensions can fall within permitted development rights, but the restrictions are tighter than they are for many single-storey projects.
The permitted development rules can place limits on:
- How far the extension projects from the original house
- Eaves and overall roof height
- Distance from property boundaries
- Materials and external appearance
- Upper-floor windows
- Balconies and verandas
- How much of the land surrounding the original house is covered by extensions and outbuildings
As a general rule, a two-storey rear extension under permitted development can extend up to 3 metres from the original rear wall, subject to the other applicable restrictions.
The materials used should normally be similar in appearance to those of the existing property.
There are also privacy requirements for certain upper-floor side windows. Obscure glazing and restrictions on opening windows can be required.
Two storey extensions to the front or side of the original house will generally require planning permission.
Given the size and cost of a double-storey extension, getting professional design and planning advice early in the project can help you make better use of the available space and reduce the risk of planning problems later.
When do you need planning permission for an extension?
You will generally need to apply for planning permission when your proposed extension doesn’t meet the requirements for permitted development.
Planning permission may also be necessary where permitted development rights don’t apply to the property or have been restricted.
This can include situations where:
- The extension exceeds permitted size or height limits
- You’re proposing certain front or side extensions
- Your home is a flat or maisonette
- Permitted development rights have been removed
- The property is subject to specific planning restrictions
- Previous alterations affect the permitted development available
- The proposed design falls outside permitted development conditions
Properties in designated areas can also be subject to additional restrictions.
Before finalising your plans, contact your local planning authority to establish which rules apply to your property.
Planning permission vs Building Regulations
Planning permission and Building Regulations are not the same thing.
Planning permission focuses primarily on whether a development is acceptable in planning terms, including its size, appearance, location and impact.
Building Regulations deal with how the extension is constructed, covering areas such as structural safety, insulation, ventilation and fire safety.
An extension that doesn’t require planning permission can still require Building Regulations approval.
Make sure you check both requirements before construction starts.
How much does planning permission for an extension cost?
Planning application fees vary depending on where you live in the UK and the type of application you’re making.
A typical extension to one house will usually require a householder planning application where planning permission is necessary.
Application fees are reviewed periodically, so always check the current fee with your local planning authority before applying.
Remember that the planning application fee is only one part of the overall cost. Depending on your project, you may also need to budget for an architect or designer, structural engineer, surveys, drawings and other professional services.
What happens if you build an extension without planning permission?
If your extension required planning permission and you built it without obtaining approval, the local planning authority may take enforcement action.
One option may be to submit a retrospective planning application.
Retrospective planning permission allows you to seek approval for work that has already been completed or started without the necessary permission.
However, submitting a retrospective application doesn’t guarantee that permission will be granted.
The local authority will assess the development against the relevant planning policies, much as it would have done if you had applied before construction.
If permission is refused and an enforcement notice is issued, you may have to alter or remove the unauthorised development unless an appeal or another appropriate route is successful.
For that reason, it’s much safer to establish whether permission is required before building your extension.
Should you get a Lawful Development Certificate?
Even when planning permission isn’t required, you may want to apply for a Lawful Development Certificate (LDC).
A Lawful Development Certificate can provide formal confirmation that your proposed extension is lawful under permitted development rules.
Although it isn’t the same as planning permission, having documentary evidence that an extension was lawful can provide valuable reassurance and may be useful when you eventually sell your property.
What should you check before building an extension?
Before starting your extension:
- Check your permitted development rights. Confirm that they apply to your property and haven’t been restricted or removed.
- Measure the proposed extension carefully. Check its depth, height, eaves, position and distance from boundaries against the relevant permitted development limits.
- Speak to your local planning authority. Confirm whether planning permission or another form of consent is required.
- Check Building Regulations. Remember that Building Regulations approval can be required even when planning permission isn’t.
- Consider a Lawful Development Certificate. This can provide formal evidence that your extension is permitted development.
- Get professional advice. An architect, architectural designer or other experienced extension specialist can help you understand the rules and maximise the space available.
FAQs about planning permission for extensions
How big can an extension be without planning permission?
The maximum size depends on factors including the type of property, where the extension is positioned, its height and whether it’s single or two storeys.
Under permitted development, some single-storey rear extensions can extend up to 6 metres from an attached house or 8 metres from a detached house, subject to the relevant conditions and procedures.
Always check the rules applying to your individual property before building.
Can I build an extension without planning permission?
Yes. Many home extensions can be built without a full planning application when they qualify as permitted development.
You’ll still need to comply with all applicable permitted development conditions and check whether other approvals, including Building Regulations, are required.
Does a kitchen extension need planning permission?
Not necessarily. Kitchen extensions follow the same planning rules as other extensions. If the project meets permitted development requirements, a planning application may not be needed.
Does a two storey extension need planning permission?
Not always. Certain two-storey rear extensions can qualify for permitted development, but the rules are more restrictive. Two-storey side and front extensions will generally require planning permission.
Can my neighbour object to my extension?
Neighbours can comment on a planning application, but an objection doesn’t automatically mean permission will be refused. The local planning authority considers relevant planning matters when deciding an application.
Different procedures can apply to certain extensions being constructed under permitted development, so check the specific route applying to your proposed project.
Can I get retrospective planning permission for an extension?
You can apply retrospectively where development has taken place without the necessary planning permission. However, approval isn’t guaranteed, and enforcement action may follow if the development is unacceptable.
What should you do before starting an extension?
Before starting work, establish which planning route applies to your proposed extension. This may mean checking whether the project falls within permitted development rights or whether a planning application or prior approval is required.
It is also important to remember that planning permission and Building Regulations are separate. A project that does not require a planning application may still need Building Regulations approval and may involve other considerations such as party walls, drainage, structural design or restrictions affecting the property.
If you are relying on permitted development rights, consider obtaining confirmation from your local planning authority before committing significant money to the project. A Lawful Development Certificate can provide formal confirmation that a proposed development is lawful for planning purposes.
Understand your extension before you commit
BetterPlanHomes project packs bring together the key planning, cost, design and risk considerations for common home improvement projects, helping you research your options and make a better-informed decision before progressing further.