Party Wall Agreement: Do You Need One for Your Extension?

If you live in a terraced or semi-detached house, there's a good chance your extension or loft conversion will touch the Party Wall Act. It's not a planning rule and the council won't remind you about it. But if you skip it, it can cause delays, cost you money and sour things with the people next door. The good news is that it's mostly paperwork, and it goes smoothly when you start early.

The short answer

You need to follow the Party Wall etc. Act 1996 if your work involves any of these:

• Building a new wall on, or right up to, the boundary line with your neighbour.
• Doing work to a wall you share with your neighbour, such as cutting into it to put in a steel beam, raising it, or taking out a chimney breast.
• Digging foundations close to your neighbour's building and going deeper than their foundations.

If any of those apply, you have to give your neighbour written notice before you start. If they agree in writing, that's what most people mean by a party wall agreement. If they don't agree, or don't reply, two surveyors (or one shared one) draw up a document called a party wall award that sets out how the work will be done.

If none of them apply, for example a detached house with an extension well away from the boundary, you probably don't need to do anything under the Act.

The three types of notice

The kind of notice depends on the work. Many extensions need more than one.

Type of work	Notice	Minimum notice before work
A new wall on or up to the boundary line	Line of junction notice	One month
Work to an existing shared wall (beams, raising it, cutting in flashings)	Party structure notice	Two months
Digging within 3 metres of a neighbour's building and deeper than their foundations	Notice of adjacent excavation	One month

There's a wider rule for digging too. If you're within 6 metres of a neighbour's building and your excavation would cut through a line drawn down at 45 degrees from the bottom of their foundations, that also needs notice. Deep foundations for a two-storey extension, or a basement, are the usual cases.

You can serve notice earlier than the minimum, and it's a good idea to. A notice runs out if the work hasn't started within a year.

Common projects and what usually applies

• Single-storey rear extension on a semi or terrace: often a line of junction notice for the side wall on the boundary, plus an adjacent excavation notice for the foundations.
• Loft conversion: steel beams are often set into the party wall, so a party structure notice is very common. Our loft conversion service covers this as part of the design.
• Two-storey side extension next to a neighbour's house: usually an adjacent excavation notice, and sometimes a line of junction notice.
• Removing a chimney breast on a shared wall: a party structure notice.

Every house is different, so treat these as a starting point. Your drawings show exactly what's needed.

What happens after you serve notice

1. Your neighbour has 14 days to reply. They can agree in writing, or they can disagree.
2. If they agree, you can go ahead once the notice period ends, or sooner if they agree to that in writing. Many people still record the condition of the neighbour's side before work starts, with photos, so there's no argument later about cracks.
3. If they disagree, or don't reply within 14 days, the Act treats it as a dispute. That sounds worse than it is. It just means surveyors get involved.
4. Surveyors are appointed. You can share one agreed surveyor, or each side can appoint their own. They then agree a party wall award.
5. The award is issued. It sets out what work will be done, how and when, and usually includes a record of the condition of the neighbour's property. Then work can start.

The person doing the work usually pays the reasonable surveyor fees for both sides. That's why a friendly chat before the notice lands is worth a lot.

What the Act doesn't do

• It doesn't replace planning permission. That's a separate question. Our guide to whether you need planning permission covers it.
• It doesn't replace building regulations. You still need building control sign-off. See how long it takes to sign off an extension.
• It doesn't cover public sewers. If you're building near a sewer, that's a build over agreement with the water company.
• It doesn't let your neighbour veto the work. It controls how the work is done, not whether it happens.
• It isn't enforced by the council. It's a civil matter. If you start without serving notice, your neighbour can go to court to stop the work until it's sorted out, which is slow and expensive.

England and Wales

The Party Wall etc. Act 1996 applies in both England and Wales. The notices, the 14-day reply period and the time limits are the same in both. Planning and building regulations differ between the two countries, but party wall rules don't. Our page on planning permission in Wales covers the parts that do change.

When to start

Talk to your neighbour as soon as you know roughly what you want to build. Serve notice once you have drawings that show the wall and the foundations, and well before you book a builder's start date. If surveyors are needed, the award can take several weeks on top of the notice period, so it's one of the things that most often pushes a start date back.

Party wall costs are also easy to forget when you're budgeting. Put a line in for them from day one. Our extension budget planner helps you see the whole cost, and our guide to avoiding unexpected costs lists the other usual surprises.

Check your home first

Use the planning checker to see what rules apply to your plot, and the local authority finder to find your council's planning and building control teams. If you're still weighing up whether to extend at all, the Build, Wait or Move framework is a good place to start.

Talk it through

If your extension will sit on the boundary or share a wall and you're not sure what that means for timing and cost, bring it to a free Build, Wait or Move Call. We'll look at your plans, explain which notices are likely to apply and how they fit around planning and building regulations. If the honest answer is that a different design, or waiting, would make life easier with the neighbours, we'll say so.