If you are planning a rear extension, loft conversion, or any structural work close to a shared boundary in London, you will almost certainly need to deal with the Party Wall etc. Act 1996. This guide explains what it means in practice and what to expect.
What is the Party Wall Act?
The Party Wall etc. Act 1996 is a piece of legislation that governs building work that affects party walls, party structures, or excavations near neighbouring buildings. It applies across England and Wales.
Its purpose is to prevent disputes between neighbours by establishing a clear notice and agreement process before work starts. It protects both the person doing the work and the adjoining owner.
When does the Party Wall Act apply?
The Act applies to three types of work:
1. Work to a party wall or party structure
This includes cutting into a party wall (for example, to install a steel beam), raising or underpinning a party wall, and demolishing and rebuilding a party wall. Relevant for most structural alterations, rear extensions with side walls on the boundary, and loft conversions in terraced or semi-detached properties.
2. Building a new wall on or at the boundary
If you are building a new wall on the line of junction between your property and your neighbour's — or within 3 metres of their structure — the Act applies.
3. Excavation near neighbouring buildings
If you are excavating within 3 metres of a neighbouring building to a depth lower than the bottom of their foundations, or within 6 metres if your excavation would intersect a line drawn downwards at 45 degrees from the bottom of their foundations, the Act applies.
This catches most new extension foundations in London, where properties are close together and Victorian or Edwardian foundations are typically shallow.
What do you need to do?
Serve a Party Wall Notice
Before starting any notifiable work, you must serve a written Party Wall Notice on every adjoining owner (including freeholders of flats where relevant). The notice must describe the work, give the address, and include a start date. Notice must be served at least two months before work begins for party wall work, and one month for excavation notices.
Wait for a response
The adjoining owner has 14 days to respond. They can:
- Consent in writing — work can proceed without a formal award. Most straightforward outcome.
- Dissent and agree to appoint an agreed surveyor — one surveyor acts for both parties.
- Dissent and appoint their own surveyor — you each appoint a surveyor; the two surveyors produce a Party Wall Award together.
- Not respond within 14 days — this is deemed dissent and triggers the surveyor process.
Party Wall Award
If a surveyor (or surveyors) is appointed, they produce a Party Wall Award — a legal document that sets out how the work is to be carried out, records the condition of the neighbour's property before work starts, and establishes how any damage will be assessed and remedied. The award protects both parties.
How much does it cost?
If your neighbour consents in writing, there is no surveyor fee — just the cost of the notice itself (which you can serve yourself, or ask your contractor to help with).
If surveyors are appointed, costs typically run:
- Agreed surveyor (acting for both): £800–£1,500
- Two surveyors (one each): £1,500–£3,000+ total — the building owner typically pays both fees
In London, where property is dense and neighbours are cautious, it is common for adjoining owners to dissent even if they have no real objection — this is sometimes done simply to ensure a condition schedule is taken before work starts. This is reasonable and protects everyone.
How long does it take?
Allow at least 2 months from serving the notice to starting notifiable work. If there is dissent and a full surveyor process, allow 3–4 months before work begins if the neighbour is slow to engage their surveyor.
This timeline is important to factor into your project programme. Many delays on London extension and loft projects stem from party wall notices being served too late.
Common party wall scenarios in London
Terraced house rear extension
If your extension has a side wall on or close to the boundary, and you are cutting into the rear wall of the existing house (a party wall in a terrace), a notice is likely required. This is the most common scenario for East and South London terraces.
Semi-detached loft conversion
An L-shaped dormer or hip-to-gable loft conversion on a semi-detached property will typically require a party wall notice — both because of work to the shared gable wall and because dormer construction involves work to the roofline close to the party wall line.
Basement excavation
Any basement extension in London almost certainly triggers the Act due to excavation depths and proximity to neighbouring foundations.
Structural alteration with steel beam
If a structural opening requires a beam that bears onto a party wall or requires pockets cut into the party wall, a notice is required.
Can your contractor serve the notice?
Yes — your contractor can prepare and serve the notice on your behalf, but the notice must be from you as the building owner. RCB helps clients with the notice process and can advise on what needs to be served, but the legal appointment of a surveyor (if required) is your decision.
What happens if you do not serve a notice?
Building without serving a required notice is not illegal, but it means the protections of the Act do not apply. If the neighbour suffers damage and you have no Party Wall Award, you have no agreed record of pre-existing conditions — and any dispute must go through the courts rather than the lower-cost surveyor process. You also risk an injunction stopping the works.
See how RCB handles structural alterations, including party wall coordination →
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