Do I Need a Party Wall Agreement?
Written by James Walker · Last reviewed 15 August 2026
James Walker has 2 degrees in construction (BSc (Hons) Building Surveying · MSc Environmental Design of Buildings) and an extensive background in issue resolution, resolving over £4 billion of consumer issues.
The short answer
- Three situations trigger it: work on a shared wall, building on the boundary line, and excavation near a neighbour's building.
- The excavation rules catch most extensions: within 3 metres of a neighbour's building and deeper than their foundations.
- Both tests must be met for the 3-metre rule, distance alone is not enough.
- Notice periods are real. Serve late and the whole project waits.
- It is separate from planning permission and Building Regulations. Needing one says nothing about the others.
On this page
Applies to England and Wales.
When it applies
Work on a party wall. Cutting into it, inserting beams, raising it, underpinning it, removing chimney breasts.
Building on the boundary line. A new wall on or astride the line.
Excavation near a neighbour's building. The rules that catch most domestic projects:
- Within 3 metres of any part of a neighbour's building or structure, and excavating deeper than the bottom of their foundations. Both conditions must be true.
- Within 6 metres, where the excavation would cut a plane drawn downward at 45 degrees from the bottom of their foundations. This catches deeper work, basements, piling.
The 3 metres is measured from their building, not the boundary. If their house sits hard against the line, almost any excavation along that flank is caught.
Why this catches so many extensions
Most modern extension foundations go down around a metre or more. Older neighbouring properties frequently have shallower foundations than that.
So a routine rear extension on a terrace or semi, dug to normal depth within 3 metres of next door, will usually trigger a notice. Drainage trenches and inspection chambers can too, because they go deeper than people expect.
Notice and timing
Serve notice in writing on the affected neighbour. For excavation work, notice is generally served at least one month before the planned start.
The neighbour has 14 days to respond. Consent, and you proceed. No reply or a dissent means a dispute has arisen under the Act, and surveyors are appointed to produce an award setting out what may be done and how.
A notice lapses if work does not begin within 12 months.
This is why the timing matters. Projects are routinely delayed because notices were served when scaffolding was already booked.
The condition record
Where surveyors are appointed, the award normally includes a record of the neighbour's property condition before work starts.
That record protects both sides. It is the evidence if damage is later alleged, and equally the evidence if a crack was already there.
Who pays
Generally the party carrying out the work, including the adjoining owner's surveyor's fees where one is appointed.
How it works
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Related guides
Common questions
- Do I need one if my neighbour is happy?
- You still serve notice. They can consent in writing, which avoids surveyors.
- What if they ignore it?
- No reply after 14 days is treated as a dispute, and the surveyor route follows.
- Can I ignore the Act?
- Ignoring it can bring work to a halt under injunction and expose you to damages.
- Does my builder handle it?
- Usually not. Confirm who is responsible.