Extensions and Party Walls: Planning Permissions Explained

Home extensions are a popular way to gain more space, add value to your property, and customise your home to fit your lifestyle. Whether you’re planning a rear kitchen extension, a two-storey addition, or a loft conversion, it’s vital to understand the legal requirements — especially when your extension involves a shared or adjoining wall, known as a party wall.

In the UK, property owners are often unsure about the distinction between planning permission and party wall agreements. These are separate legal processes that serve different purposes, but both are often required before you can begin work.

In this blog, we’ll explain everything you need to know about planning permission, party wall agreements, and how to ensure your extension project stays compliant and dispute-free.

What is a Party Wall?

A party wall is a wall shared by two adjoining properties. This can include:

• The wall separating terraced or semi-detached houses

• A garden wall that sits on the boundary line

• Floors and ceilings between flats or maisonettes

If your planned extension involves altering, building on, or digging near this wall, the Party Wall etc. Act 1996 may apply.

Do I Need Planning Permission for an Extension?

In many cases, home extensions fall under ‘permitted development rights’, meaning you don’t need planning permission if your extension meets certain criteria. However, this varies depending on:

• The type of property (house, flat, listed building)

• Whether you’re in a conservation area

• The size and height of the extension

• Proximity to boundaries

• Impact on neighbours’ light or privacy

Permitted Development Criteria (Typical Examples):

• Rear extensions no more than 3 metres (semi-detached) or 4 metres (detached)

• Extension does not exceed 50% of the original house footprint

• Maximum eaves height no more than 3 metres near boundaries

• Uses similar materials to the existing house

If your project falls outside these limits, or if your property has had permitted development rights removed, you’ll need to apply for planning permission.

Tip: Always check with your local authority’s planning portal or consult an architect before starting any work.

When Does the Party Wall Act Apply to Extensions?

Even if your extension does not require planning permission, you may still need to serve a party wall notice under the Party Wall etc. Act 1996.

This applies when your work involves:

1. Building on the boundary line

• Constructing a wall directly on or near the dividing line between two properties.

2. Working on an existing party wall

• Cutting into the wall to insert beams

• Raising, thickening or demolishing it

• Removing chimneys that affect the party wall

3. Excavating near a neighbour’s foundation

• Digging within 3 metres and deeper than their foundation level

• Or within 6 metres if your excavation is very deep (e.g., basement)

In these cases, you must serve formal written notice to your neighbour at least 1–2 months before work begins, depending on the type of work.

How Does the Party Wall Process Work?

Step 1: Serve Notice

You serve a written party wall notice detailing:

• Your name and address

• Description of proposed works

• Start date

• Plans or drawings (if applicable)

Step 2: Wait for a Response

Your neighbour has 14 days to:

• Give written consent

• Dissent (and request a surveyor)

• Do nothing (which is treated as dissent)

Step 3: Resolve Disputes (If Needed)

If your neighbour dissents:

• Each party appoints a party wall surveyor, or both agree on one

• Surveyor(s) draft a Party Wall Award, a legally binding document detailing how work will proceed and how to handle disputes or damages

Important: You cannot legally start work until the Award is agreed and served.

Can I Skip the Party Wall Notice if My Neighbour Is Okay With the Work?

No — not legally. Even if your neighbour is agreeable, you must serve notice if your work is covered under the Act. A verbal agreement is not enough, and without a valid notice or award, your project can be challenged in court.

Failure to follow the Act may lead to:

• Legal injunctions

• Costly delays

• Compensation claims

• Tense neighbour relationships

What Happens if I Need Both Planning Permission and Party Wall Consent?

In many cases, both processes will apply, especially for larger extensions. These steps usually follow this order:

Obtain Planning Permission (if required)

Serve Party Wall Notice

Wait for neighbour response or agreement

Appoint surveyors if needed

Receive Party Wall Award

Begin construction legally

Your project should not begin until all required permissions and agreements are fully in place.

Does Building Control Approve Party Wall Works?

No — Building Regulations and Party Wall Agreements are separate. While Building Control ensures construction meets safety and structural standards, they do not handle neighbour boundary issues.

You must comply with all three independently:

• Planning permission

• Building regulations

• Party Wall Act

Planning an extension is an exciting opportunity to add space, style, and value to your home. But without the right permissions and legal safeguards in place, what starts as a dream project can quickly become a stressful nightmare.

For more information you can call Express Party Wall Surveyor at 020 3633 0823 or contact us