Party Wall Agreements: When You Need One and What It Costs

Party wall · Consents

When you need a party wall agreement, the three notices with diagrams, how long each takes, what a party wall surveyor does and what it costs, from a London architect.

Last updated: 30 October 2026 · Reviewed by Graham Sproul RIBA, Design & Operations Director

The figures here are approximate and meant to give you an idea, not a quote. Every house and brief is different, so your costs and programme will depend on your project.

When do you need a party wall agreement?

You need to serve notice on your neighbour when you plan work to a shared wall or structure, build a new wall on or at the boundary, or dig close to and below their foundations. You need an agreement, called a party wall award, only if they dissent or don’t reply in writing within 14 days. The table shows which notice common London projects trigger.

Your work	Notice	Minimum notice	Example on a London terrace
Cutting into a party wall to take a beam	Party structure notice	2 months	Steels for a loft conversion bearing on the party wall
Cutting off a projection from a party wall	Party structure notice	2 months	Removing a chimney breast on a party wall
Raising, underpinning or repairing a party wall	Party structure notice	2 months	Underpinning for a basement; raising the wall for a mansard
Building a new wall on or astride the boundary line	Line of junction notice	1 month	The flank wall of a side return or rear extension built on the boundary
Digging within 3m of a neighbour’s building, deeper than its foundations	Adjacent excavation notice	1 month	Foundations for a rear extension next to the neighbour’s back addition
Digging within 6m, where the dig cuts a 45° line down from their foundations	Adjacent excavation notice	1 month	A basement, or deep piled foundations
Minor work such as plastering, rewiring or putting up shelves	Usually none	·	Fitting kitchen units against the party wall

Notice goes to every owner of the neighbouring property. Notices, awards and fees are per adjoining owner, meaning per legal title, so if the house next door is divided into flats, the freeholder and each leaseholder need their own notice. That’s why party wall costs can be a large part of an extension budget next to a block of flats. You can serve notice between 2 months and a year before you plan to start.

What is a party wall agreement?

A party wall is a wall shared with your neighbour, sometimes called an adjoining or adjacent wall: either one that stands on the boundary or one that separates your building from theirs. A party wall agreement, properly a party wall award, is the document surveyors draw up when a neighbour dissents. It sets out what work will be done, how and when, who pays for what, and records the condition of the neighbour’s property.

Its purpose is to let the building owner do lawful work while protecting the neighbour’s property. It isn’t planning permission: a neighbour can’t use it to stop work the Act allows. The terms below come up in every notice.

Term	What it means
Party wall	A wall that stands on land of two owners and forms part of a building, or a wall that separates buildings belonging to different owners
Party fence wall	A garden wall that stands astride the boundary and separates the two owners’ land, but isn’t part of a building
Party structure	A party wall, and also a floor or other structure that separates buildings or parts of buildings, such as the floor between two flats
Adjoining or adjacent owner	The neighbour whose property is affected by the work
Building owner	The owner who wants to carry out the work and serves the notice
Line of junction	The boundary line between two properties
Award	The surveyors’ document that settles a dispute: what, how, when and who pays
Schedule of condition	A record, with photos, of the neighbour’s property before work starts

The three party wall notices, with diagrams

There are three notices, one for each kind of work the Act covers: a party structure notice for work to a shared wall, a line of junction notice for a new wall on the boundary, and an adjacent excavation notice for digging near a neighbour’s foundations. A project can need more than one, for example a loft and a rear extension on the same house.

Party structure notice

You need it to work on a wall or structure you already share: cutting in to take the bearing of a beam, removing a chimney breast attached to the party wall, raising, underpinning or repairing the wall. A loft conversion with steels set into the party wall is the most common example on a London terrace. Give at least 2 months’ notice. The notice lapses if the work hasn’t started within 12 months of serving it.

Line of junction notice

You need it to build a new wall on or astride the line of junction, the boundary between your land and your neighbour’s. This covers the construction of a new party wall astride the boundary, and a wall built wholly on your side of it. The flank wall of a side return infill or rear extension built right up to the boundary is the usual case. Give at least 1 month’s notice. If the wall sits wholly on your side, the neighbour can’t stop it, but they must still be told.

Adjacent excavation notice and the 45-degree rule

You need it to dig near a neighbour’s building. Within 3m, it applies if your new foundations go deeper than theirs. Within 6m, it applies if your excavation cuts a line drawn down at 45 degrees from the bottom of their foundations: that’s the 45-degree rule. A basement under the house, or deep foundations for an extension, are typical examples. Give at least 1 month’s notice.

How the party wall process works, step by step

You serve notice in writing. Your neighbour has 14 days to reply in writing. If they consent, you can go ahead once the notice period has run. If they dissent, or don’t reply at all, a dispute is treated as having arisen and surveyors are appointed to agree an award. Silence never counts as agreement.

If your neighbour won’t appoint a surveyor, you can appoint one on their behalf, so a silent neighbour can’t stall the work indefinitely. Party wall notices are one of several things settled before building starts, and our guide to the stages of a house extension puts them in order.

Do you need a party wall surveyor?

You don’t need one to serve a notice, but many owners appoint one to do it properly. You do need surveyors if your neighbour dissents or doesn’t reply. You can’t act as your own surveyor. You and your neighbour can share one agreed surveyor, or appoint one each, and the surveyors then agree the award between them.

A party wall surveyor serves the notices, records the neighbour’s property in a schedule of condition, agrees the award with the other surveyor, and settles any later claim that the work caused damage. The schedule of condition matters most: if a crack appears during the works, it shows whether it was there before.

With one agreed surveyor, there’s one fee. If your neighbour appoints their own surveyor, which is their right, you usually pay that surveyor too. As a guide, recent quotes we’ve seen from a London firm (October 2026) were about £1,650 + VAT for an agreed surveyor, and typically £1,200 to £1,700 + VAT for a neighbour’s own surveyor. Treat them as examples: your surveyor will quote for your job.

How much is a party wall agreement?

As published on our fees page, serving a notice costs about £200, and an award, if one is needed, about £900 to £2,000+. You pay for the building work and usually for the process it triggers. Your neighbour pays a share only if the work fixes a defect or disrepair, or if they ask for extra work that benefits them.

Item	Approx. figure	Who usually pays
Serving a notice	About £200 per notice	You (the building owner)
An award, if the neighbour dissents or doesn’t reply	About £900 to £2,000+ per award	You; the award sets how the surveyors’ costs are shared
Budget allowance in AURA’s fee proposals	About £1,000 per neighbour	You
Recent quotes we’ve seen (one London firm, October 2026)	About £1,650 + VAT as an agreed surveyor; £1,200 to £1,700 + VAT for a neighbour’s own surveyor	You, usually for both surveyors
The building work itself	Your build cost	You
Work that fixes a defect or disrepair, or extra work the neighbour asks for	Set in the award	Shared, or the neighbour

A worked example: a rear extension on a mid-terrace

Take a rear and side return extension on a mid-terrace house in SW London. The new flank wall is built on the boundary with one neighbour, and the foundations are within 3m of both neighbours’ houses and deeper than theirs. That’s the typical pair on a terrace extension: a Section 1 (line of junction) notice to the first neighbour, and a Section 6 (adjacent excavation) notice to each. Three notices at about £200 each come to about £600.

If both neighbours consent, that’s the cost. If both dissent, there’s an award for each adjoining owner, at about £900 to £2,000+ each on our fees page figures, so about £1,800 to £4,000+. AURA’s proposals suggest allowing about £1,000 per neighbour, so about £2,000 here. If each neighbour appoints their own surveyor, budget more: you usually pay their surveyor as well as your own. Serve the notices at least 1 month before the work they cover, and allow at least 2 months in the programme.

When to serve notices on your project

We serve notices once the structural design exists, because they need the engineer’s foundation details. Allow at least 2 months from serving to starting work on the party walls, so any award is in place before the builder starts. Party wall is separate from planning and building regulations: you may need all three, and planning approval doesn’t replace notice.

Whether you need planning permission is covered in our planning permission vs permitted development guide.

Party wall costs are one line in the budget. For the build cost itself, see our house extension cost guide.

What can go wrong, and how to avoid it

Most party wall problems are about timing and records. Notices served late push back the start date, notices sent to the wrong people have to be served again, and without a schedule of condition a damage claim turns into one word against another. Each is avoidable with a little planning.

Notices served too late. Two months for a party structure notice is the minimum, and a dissent adds the time to agree an award. Build it into the programme before you book a builder.

The wrong owners. Next to flats, all leaseholders and the freeholder need to be served. Check the title before notices go out.

No schedule of condition. Record the neighbour’s property before work starts, even if they consent. It protects both sides.

Award costs left out of the budget. If a neighbour dissents, you’ll usually pay the surveyors. Budget for it from the start, and keep a good relationship with your neighbours: it keeps a project moving.

Party wall worries turn into planning objections. On our projects, neighbours sometimes raise party wall concerns as objections to the planning application. Planning doesn’t decide party wall matters, but the objection can still slow the decision. Talking to neighbours before you apply, and explaining that the party wall process protects them, helps.

A chimney breast on a shared stack. Removing a chimney breast where the stack is shared with next door is a common cause of delay we’ve seen. It needs a party structure notice, two months ahead, and support for the stack above, so plan it early.

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