If you’re planning an extension or a loft conversion in London or Surrey, there’s a good chance you’ll need a party wall agreement. Most homeowners hear about it late, usually from the builder, and the first question is always the same: what’s this going to cost me?
We build extensions and lofts across Central London, South London and Surrey, so this comes up on almost every job. Here is how it works and what you should budget.
What is a party wall agreement?
A party wall agreement is a legal document that lets you carry out certain building work next to, or on, a wall you share with a neighbour. It comes from the Party Wall etc. Act 1996.
Your neighbour doesn’t get to veto your project. The Act makes sure they are told properly, that their property is protected, and that any damage is put right. If you skip it and something cracks next door, you’re in a weak position.
Do you need one? The usual triggers
You normally need to serve notice if you’re:
- cutting into a shared wall, for example to fit steel beams for a loft conversion
- building a new wall on the boundary line between two properties
- raising, rebuilding or demolishing a shared wall or chimney breast
- digging foundations within 3 metres of a neighbouring building, if your foundations will go deeper than theirs
- digging within 6 metres of a neighbouring building, if the excavation cuts across a 45-degree line down from their foundations
Terraced and semi-detached homes, which make up a lot of South London, almost always trigger one of these. A detached house in Surrey may not, unless you’re building close to the boundary. Our guide to house extensions explains which jobs usually need notice.
How much does a party wall agreement cost?
The cost depends on how your neighbour responds. As rough 2026 estimates for London and Surrey:
| Situation | Typical cost |
|---|---|
| Serving the notices yourself, neighbour consents | £0 to £150 (free templates exist) |
| Notices drafted by a surveyor, neighbour consents | £150 to £500 |
| One agreed surveyor acting for both sides | £700 to £1,500 per neighbour |
| Two separate surveyors (one each) | £1,500 to £3,000+ per neighbour |
London sits at the top end of these ranges. Fees also rise with the size of the job and the number of neighbours.
The building owner pays. That’s you, the person doing the work. In most cases you also cover your neighbour’s reasonable surveyor fees. If you have two adjoining neighbours, as on a typical terrace, double the figures above.
For the full cost of the build itself, see our house extension cost guide for South London.
What happens step by step?
- Serve notice. You send a written notice to each affected neighbour. For work to the party wall itself, give at least two months before it starts. For excavations, give one month.
- Your neighbour has 14 days to respond. They can consent, or dissent and appoint a surveyor.
- A silent neighbour counts as dissent. If you hear nothing within 14 days, a dispute is treated as having started, and surveyors get involved.
- Surveyors agree the award. This is the legal document that sets out what work is allowed, how, and when. It usually includes a schedule of condition recording the state of the neighbour’s property beforehand.
- Work starts. The award is valid for 12 months, so build within that window.
Allow 4 to 8 weeks from serving notice to a signed award if surveyors are involved. This is the part people forget when they plan a start date.
Can a neighbour stop my project?
No. They can’t block work the Act allows, but they can make you do it properly. The surveyor can set conditions on working hours, protection of their property and how the work is carried out. The delay and extra fees are usually the real cost of a difficult neighbour, not a refusal.
A friendly conversation before the notice lands often saves hundreds of pounds. A neighbour who has been told what is happening and why is far more likely to consent in writing and avoid a second surveyor.
Party wall agreement for a loft conversion
Lofts are the most common reason we see these. Fitting steels usually means resting beams on the party wall, which is exactly what the Act covers. If you’re thinking about a loft, read our loft conversion guide alongside this one so you can plan the notice period and the build together. Not sure whether you also need council approval? Read our loft conversion planning permission guide.
Is a party wall agreement the same as planning permission?
No. They are separate processes. Planning permission (or permitted development rights) deals with your local council. A party wall agreement deals with your neighbours. You can have one without the other, and many projects need both. Building regulations approval is a third, separate step.
How to keep costs down
- Talk to your neighbour first. Consent saves you the cost of a second surveyor.
- Suggest one agreed surveyor. It’s usually the cheapest route when both sides are happy with it.
- Start the process early. Don’t leave it until the week before your builder arrives.
- Use a surveyor who knows your area. London and Surrey properties, with old foundations, chimney breasts and shared walls, need local experience.
- Ask your builder what’s included. Some contractors manage the notices as part of the job. If you’re comparing quotes, check who handles this.
How we handle it
At Excel Construction, we explain the party wall process at the quote stage, so there are no surprises on cost or timing. We work with local surveyors across Central London, South London and Surrey, and we plan the start date around the notice periods rather than the other way round.
If you’re planning an extension or loft and want a clear picture of the costs, including the party wall side, get in touch for a free quote.
Party wall agreement FAQs
How much does a party wall agreement cost in London?
Expect roughly £700 to £1,500 per neighbour for one agreed surveyor, and £1,500 to £3,000+ per neighbour if each side appoints their own. You usually pay both sides’ reasonable fees.
Who pays for the party wall surveyor?
The person doing the building work, known as the building owner, pays. This normally includes the neighbour’s surveyor fees as well as your own.
How long does a party wall agreement take?
Notices must be served at least one or two months before work starts, depending on the type of work. With surveyors involved, allow 4 to 8 weeks to reach a signed award.
Do I need a party wall agreement for a loft conversion?
Usually yes, if the work involves cutting into or resting beams on a shared wall, which is typical for semi-detached and terraced houses.
What if my neighbour refuses to sign?
They can’t stop lawful work. If they dissent, or don’t reply within 14 days, surveyors are appointed to agree an award that protects both properties.
Fee ranges are estimates for 2026 and vary by surveyor and project. This guide is general information, not legal advice.
Related: our building regulations guide for extensions and loft conversions in London explains what Building Control inspects and how the completion certificate works.