Do I need a party wall agreement?
The Party Wall Act catches people out. It's completely separate from planning permission — you can have full planning consent and still be acting unlawfully if you haven't served notice.
Please read: this tool gives general information, not advice. It's based on the Party Wall etc. Act 1996 (England & Wales). It cannot see your property or your boundary. Always confirm your position before starting work.
Which of these will your work involve?
Tick everything that applies. If in doubt, tick it — it's better to know.
⚠️ Two things people get badly wrong:
- Silence is not consent. If your neighbour doesn't respond within 14 days, they are deemed to have dissented — a dispute is treated as having arisen, and surveyors must be appointed.
- Serving notice late. The notice periods run before work starts. Discovering this when the steels are booked is one of the most expensive mistakes on an extension.
General information only, not advice. Cheshire Design & Build NW accepts no liability for reliance on this tool. England & Wales. Based on the Party Wall etc. Act 1996.
Rules taken from the Party Wall etc. Act 1996 (sections 1, 3 and 6). Verified July 2026.
The three types of party wall notice
The Party Wall etc. Act 1996 covers three separate situations. Each has its own notice period, and the one that catches most people out is the third — because it applies even when you never touch your neighbour's wall.
1. Building on the line of junction — 1 month's notice
If you're building a new wall on or at the boundary, you must give your neighbour at least one month's notice before work starts. This catches the flank wall of most side extensions.
2. Work to an existing party wall — 2 months' notice
Cutting a steel beam into a shared wall, removing a chimney breast, underpinning, raising the wall, or inserting a damp-proof course all count. This requires the longest notice period: two months. It is extremely common on structural alterations and loft conversions in terraced and semi-detached houses.
3. Excavation near a neighbouring building — 1 month's notice
This is the one people don't see coming. You must serve notice if you are excavating:
- within 3 metres of a neighbouring structure, to a depth lower than the bottom of their foundations; or
- within 6 metres of a neighbouring structure, where your excavation cuts a line drawn downwards at 45° from the bottom of their foundations.
Standard extension foundations frequently trigger this — and basement and cellar work almost always does.
Do you also need planning permission?
Separate question, separate answer. Many extensions and loft conversions don't need a full planning application at all — they fall under permitted development. Find out where you stand with our free planning permission checker.
What happens if you don't serve notice
Your neighbour can seek an injunction to stop the work. You lose the protections the Act gives you, and you're exposed if they later claim your work caused damage. It's a private legal matter — the council won't police it, but your neighbour's solicitor will.
We flag party wall issues at the free site visit, so they're dealt with in good time rather than discovered when the steels are due on site.
Party Wall FAQs
Do I need a party wall agreement for an extension?
It depends on the work, not the project. You need to serve notice under the Party Wall etc. Act 1996 if you are building a new wall on or at the boundary, doing work to an existing party wall (such as cutting in a steel beam or removing a chimney breast), or excavating within 3 metres of a neighbouring building to a depth below their foundations — or within 6 metres if your excavation cuts a 45-degree line down from the bottom of their foundations.
How much notice do I have to give my neighbour?
It depends which part of the Act applies. Building a new wall on or at the boundary requires at least 1 month’s notice. Work to an existing party wall or party structure requires at least 2 months’ notice. Excavation near a neighbouring building requires at least 1 month’s notice. Serving notice late is one of the most common — and most expensive — mistakes on an extension.
What happens if my neighbour does not reply?
If an adjoining owner does not respond within 14 days of being served, they are deemed to have dissented, and a dispute is treated as having arisen. That means surveyors must be appointed and a party wall award drawn up. Silence is not consent — which is why serving notice early matters.
Is a party wall agreement the same as planning permission?
No — they are completely separate. Planning permission is about whether you can build. The Party Wall Act is a private legal matter between you and your neighbour, and it applies whether or not you need planning permission. You can have full planning permission and still be acting unlawfully if you have not served party wall notice.
Do you handle the party wall process?
We flag it at the free site visit, so it is dealt with in good time rather than discovered when the steels are due on site. Where a formal award is required, a party wall surveyor is appointed — we coordinate that alongside the build programme so it does not hold the job up.
Planning an extension or loft?
Book a free site visit. We'll flag any party wall issues early — before they cost you time or money.