Do I Need Planning Permission for an Extension?

If you’re thinking about extending your home, one of the first questions you’re likely to ask is:

“Do I need planning permission?”

The answer is: sometimes, but not always.

Some house extensions can be built under permitted development rights, meaning you don’t need to make a full planning application. However, permitted development is subject to a number of conditions and limitations, and the rules can be more complicated than they initially appear.

Whether planning permission is required depends on the property, the size and position of the proposed extension, previous extensions and alterations, and sometimes the location of the property. Whether the property is in a conservation area or is a listed building will also be a factor.

At LA Hally Architect, we work with homeowners across Winchester, Hampshire and the surrounding areas to help them understand what may be possible before developing a design.

What is permitted development?

Permitted development rights allow homeowners to carry out certain types of development without applying for planning permission.

For extensions, these rights are subject to specific limitations and conditions. If a proposal falls within those rules, a planning application may not be necessary.

This doesn’t mean that you can build any extension without planning permission.

The permitted development rules cover things such as the size, height and position of an extension, and there are additional restrictions in certain circumstances.

Importantly, previous extensions to the property can also affect what you are able to build under permitted development rights.

When will I need planning permission?

If your proposed extension doesn’t comply with the permitted development rules, you will generally need to make a planning application.

This might be because the extension:

Is too large
Is too high
Extends too far beyond the original house
Is positioned where permitted development rights don’t allow it
Doesn’t meet other permitted development conditions
Is affected by restrictions on permitted development rights

The precise requirements depend on the proposal and the property.

For a typical house extension, the relevant planning application will usually be a Householder Planning Application. This is the form of planning application used for many proposals to alter or enlarge an existing house.

What are the permitted development limits for an extension?

There isn’t one simple size limit that applies to every extension.

For example, the permitted development rules distinguish between rear extensions, side extensions and other forms of enlargement, and the rules can also depend on whether the property is detached or another type of house.

As an example, under the current rules, a single-storey rear extension can extend beyond the rear wall of the original house by up to certain distances, subject to the relevant conditions. The limits differ for detached houses and other houses, and additional rules apply in certain designated areas.

This is why it’s risky to rely on a simple rule such as:

“You can extend four metres without planning permission.”

The actual permitted development calculation can depend on the original house, previous extensions, the position of the extension and the site’s designation, among other things.

The Planning Portal recommends checking the detailed rules for the particular proposal before assuming that planning permission isn’t required.

What is the “original house”?

This is an important part of the permitted development rules.

The rules generally refer to the original dwellinghouse, which means the house as it was originally built, or as it stood on 1 July 1948 if it was built before that date.

This means that an extension built by a previous owner can affect the amount of additional development that may be possible under permitted development.

So even if you haven’t previously extended your house, you shouldn’t assume that you have the full permitted development allowance available.

What about two-storey extensions?

Two-storey extensions are subject to different restrictions from single-storey extensions.

The permitted development rules contain specific requirements concerning their height, position and relationship to the boundaries of the property. For example, a two-storey extension must meet minimum separation requirements from certain boundaries.

If your proposed extension is relatively substantial, particularly if it is two storeys, it is therefore worth establishing the planning position before developing the design too far.

Does being in a Conservation Area make a difference?

Yes.

This is particularly relevant to many properties around Winchester and Hampshire.

Certain areas are subject to additional restrictions under the permitted development rules. These include land covered by Article 2(3) designations, which include Conservation Areas, National Parks, Areas of Outstanding Natural Beauty and World Heritage Sites.

For example, additional restrictions can apply to side extensions and certain forms of enlargement, while external cladding may also be restricted.

There can also be Article 4 Directions, which can remove permitted development rights in particular areas.

Article 4 Directions are particularly common in conservation areas where the local planning authority considers that the character of an area needs additional protection.

This means that two otherwise similar houses can have very different planning situations depending on where they are located.

What if my house is listed?

If your property is a Listed Building, the situation is more complicated.

Planning permission may be required, and Listed Building Consent may also be necessary for works that affect the special architectural or historic interest of the building.

This is one area where specialist architectural and conservation experience can be particularly valuable.

LA Hally Architect has experience working with listed buildings and properties in conservation areas, including projects involving extensions and alterations to historic homes.

For a listed building, it’s important to consider the historic character of the property at the very beginning of the design process rather than treating planning as something to deal with after the design has been completed.

LA Hally Architect often work with heritage consultants who can advise on more complex projects and provide guidance on gaining the required approvals.

What if I don’t need planning permission?

Not needing planning permission doesn’t mean that you don’t need to consider the regulations that apply to the building work.

Planning permission and Building Regulations are separate things.

An extension that qualifies as permitted development will still generally need to comply with the Building Regulations. The Building Regulations cover technical matters such as structure, insulation, fire safety, ventilation and drainage.

You may therefore have a project where:

Planning permission isn’t required

but

Building Regulations approval is required.

This is a common source of confusion for homeowners.

If you’re unsure about the difference between the two processes, we’ve explained it in more detail in our article:

[What is the difference between planning drawings and Building Regulations drawings?]

Can I get confirmation that my extension is permitted development?

Yes.

If you believe your proposed extension falls within permitted development rights, you can seek formal confirmation from your local planning authority.

One option is to apply for a Lawful Development Certificate. This can provide written confirmation that the proposed development is considered lawful and doesn’t require express planning permission.

This can be useful if you want greater certainty about the planning position before proceeding.

It’s important to distinguish this from planning permission: a Lawful Development Certificate doesn’t grant planning permission; it confirms that the development is considered lawful under the relevant rules.

Can an architect tell me whether I need planning permission?

An architect can help you assess the planning position and identify whether a proposal is likely to fall within permitted development or require a planning application.

At LA Hally Architect the process starts by understanding the existing house, the site and what you want to achieve.

The design can then be developed with the planning context in mind.

This is particularly useful because the best solution isn’t necessarily the largest extension that can be built.

An architect can look at questions such as:

How could the extension improve the existing house?
How will it connect with the garden?
Where will the natural light come from?
How will the extension affect neighbouring properties?
Are there important views or trees to consider?
Is the property in a Conservation Area?
Are there restrictions affecting permitted development?
Would planning permission be required?
What approach is likely to be appropriate for the character of the existing house?

These considerations can be particularly important for older and characterful properties.

What happens if planning permission is required?

If your extension doesn’t fall within permitted development, a planning application will normally be required.

The design is developed into the drawings and information needed for the application and submitted to the relevant local planning authority.

At LA Hally Architect, the planning stage develops the agreed design into detailed plans and elevations while considering the planning context of the site and the requirements of the local authority.

Where appropriate, the practice can also advise on obtaining pre-application advice before submitting a formal application.

This can be particularly useful where the planning position is uncertain or the proposed development is more substantial.

Why involve an architect early?

It can be tempting to decide on the size and shape of an extension first and then ask whether planning permission is possible.

In practice, it can be better to approach the process the other way around.

Understanding the site, the existing house and the planning constraints can help shape a better design from the beginning.

For example, a slightly smaller extension with better natural light, a stronger connection to the garden and a more carefully considered relationship with the existing house may produce a much better result than simply maximising the available floor area.

At LA Hally Architect, the design process is collaborative. The practice considers the existing property, the client’s requirements and the opportunities presented by the site before developing the design.

So, do I need planning permission for my extension?

You might — but it depends on the individual property and proposal.

Some extensions can be constructed under permitted development rights, provided they meet all the relevant limitations and conditions.

Others will require planning permission.

And even where an extension appears to qualify as permitted development, there may be additional restrictions because of the property’s location, previous development or planning history.

The safest approach is to establish the planning position before committing to a design or starting work.

The rules can be detailed, and the Planning Portal itself advises that its extension guidance is an introductory guide rather than a definitive source of legal information.

Thinking about extending your home?

If you’re considering an extension in Winchester, Hampshire or the surrounding area, LA Hally Architect can help you understand what may be possible and develop a design that responds to both your home and its surroundings.

From initial ideas through planning, Building Regulations and construction, the practice can provide as much or as little involvement as your project requires.

If you’re considering extending your home and aren’t sure whether you need planning permission, get in touch with LA Hally Architect to discuss your project.