Party Wall 3 Metre and 6 Metre Rules Explained
One of the most common misconceptions about the Party Wall etc. Act 1996 is that any excavation within three metres of a neighbour automatically requires a Party Wall Notice.
That is not correct.
Distance is only part of the test. The depth of the proposed excavation compared with the depth of the neighbouring building’s foundations must also be considered.
There are two principal tests under section 6 of the Act: the three-metre rule and the six-metre rule.
The short answer
A Section 6 Party Wall Notice may be required where:
The three-metre rule: you propose to excavate within three metres of a neighbouring building or structure and any part of your excavation will extend below the bottom of its foundations.
The six-metre rule: you propose to excavate within six metres of a neighbouring building or structure and your excavation will pass below a line drawn downwards at 45 degrees from the bottom of the neighbouring foundations towards your excavation.
If neither test is met, section 6 will not normally apply to that excavation, although other parts of the Party Wall etc. Act could still apply to the project.
Why does the Party Wall Act regulate excavation?
Excavating close to an existing structure can potentially affect the ground supporting its foundations.
This becomes more relevant as excavations become deeper or closer to the adjoining building.
Section 6 therefore provides a statutory process under which an Adjoining Owner can be notified before certain excavations begin and, where necessary, appropriate safeguards can be considered.
The provisions can apply even when every part of the new building and excavation is located wholly within the Building Owner’s own land.
What is the Party Wall 3 metre rule?
Section 6(1) applies where two conditions are met:
- the proposed excavation is within three metres of any part of a neighbouring owner’s building or structure; and
- any part of the proposed excavation will extend below the bottom of that neighbouring building or structure’s foundations.
Both tests have to be satisfied.
This means that being 2.5 metres from your neighbour’s house does not, by itself, make the work notifiable under section 6.
Foundation depth must also be considered.
A simple three-metre example
Assume you are constructing a rear extension.
The new foundations will be approximately two metres from your neighbour’s house.
Your proposed foundations will be excavated to 1.2 metres below ground level.
If the adjoining house has foundations extending only 700mm below ground level, your excavation will be both:
- within three metres; and
- deeper than the bottom of the adjoining foundations.
A Section 6 Notice would therefore normally be required.
Now consider the same extension where reliable information establishes that your neighbour’s foundations extend to 1.5 metres.
Although your excavation remains within three metres, it would not extend below the bottom of those foundations.
Section 6(1) would therefore not normally be triggered.
This is why simply measuring three metres on a site plan is not enough.
What is the Party Wall 6 metre rule?
Section 6(2) deals with deeper excavations that can potentially affect structures further away.
The test applies where excavation takes place within six metres of a neighbouring building or structure and reaches below a plane drawn at 45 degrees downwards from the bottom of the neighbouring foundations towards the proposed excavation.
This is sometimes called the “45-degree rule”.
It becomes particularly relevant to:
- basement excavations;
- deep foundations;
- piled foundations and pile caps;
- substantial changes in ground level; and
- some deeper structural excavations.
Ordinary shallow domestic foundations may satisfy the three-metre test without engaging the six-metre test, whereas deep excavations can bring buildings further away within the scope of section 6.
How is the 45-degree rule measured?
The starting point is the bottom of the adjoining building’s foundations.
From that point, an imaginary plane is projected downwards at 45 degrees towards the proposed excavation.
If the proposed excavation passes below that plane within six metres of the adjoining structure, section 6(2) may apply.
The precise geometry can matter, so this assessment should generally be made using suitable plans and sections rather than estimates made from a site plan alone.
How do I know how deep my neighbour’s foundations are?
This is often the difficult part.
The depth of adjoining foundations may sometimes be reasonably inferred from:
- the age and construction of the building;
- available structural drawings;
- previous building records;
- exposed foundations;
- trial pits;
- previous engineering investigations; or
- information supplied by the Adjoining Owner.
However, foundation depth should not simply be assumed where it materially affects whether statutory notice is required.
Older buildings in Essex can have considerably shallower foundations than modern extensions constructed alongside them.
Conversely, some properties may have deeper foundations because of ground conditions, previous underpinning or later alterations.
Where there is genuine uncertainty, further investigation or professional advice may be appropriate.
Do drawings need to accompany a Section 6 Notice?
Yes.
Unlike some other notices under the Act, section 6 expressly requires plans and sections.
The notice should be accompanied by drawings showing the site and depth of the proposed excavation and, where a new building or structure is proposed, its position.
The notice must also state whether the Building Owner intends to underpin or otherwise strengthen or safeguard the foundations of the adjoining building or structure.
Serving a generic notice without sufficient information can therefore create problems.
How much notice must be given?
A Section 6 Notice must normally be served at least one month before the proposed excavation begins.
The Adjoining Owner then has 14 days in which to indicate whether they consent.
If no written consent is received within that period, a dispute is deemed to have arisen and the section 10 surveyor procedure applies.
The statutory notice period should not be confused with the amount of time the whole Party Wall process may take.
Where surveyors need to be appointed, drawings reviewed, engineering information considered and an Award agreed, the process may take longer than one month.
Early service is therefore advisable.
What if my neighbour consents?
If the Adjoining Owner gives written consent to the proposed section 6 works, the owners do not automatically need Party Wall Surveyors to make an Award.
However, it is often sensible to consider a Schedule of Condition before excavation begins, particularly where the works are relatively deep or close to the adjoining building.
A Schedule of Condition creates a dated written and photographic record of relevant defects before works commence.
It does not prevent damage occurring, but it can make it much easier to distinguish new damage from defects that existed beforehand.
What protection does an Adjoining Owner receive?
Where a dispute arises, the appointed surveyor or surveyors can determine matters connected with the notifiable works that fall within their statutory jurisdiction.
Depending on the circumstances, the Award may deal with matters such as:
- the manner in which excavation is undertaken;
- sequencing of works;
- temporary support;
- safeguarding measures;
- access where statutory rights apply;
- working arrangements;
- making good damage; and
- other matters properly arising from the notified work.
The Adjoining Owner can also require appropriate measures to underpin, strengthen or safeguard their foundations where this is necessary because of the proposed section 6 work.
Does piling automatically require a Party Wall Notice?
Not automatically.
The legal tests under section 6 still need to be considered.
However, piled foundations frequently involve deeper excavation and associated pile caps, ground beams or other foundation construction. They therefore warrant careful review against the three-metre and six-metre tests.
The relationship between the proposed foundation system and the adjoining building should be established from properly dimensioned structural information.
Does the Party Wall Act only apply to the house next door?
No.
For section 6 purposes, an Adjoining Owner can include the owner of a building or structure within the relevant three- or six-metre distance even where another owner’s land or building sits between the two sites.
This can occasionally result in more Adjoining Owners needing notice than first expected.
Frequently asked questions
My extension is less than three metres from my neighbour. Do I definitely need a notice?
No.
You also need to establish whether the proposed excavation extends below the bottom of your neighbour’s foundations.
My extension is more than three metres away. Am I definitely outside the Act?
Not necessarily.
The section 6(2) six-metre test may still apply where sufficiently deep excavation is proposed.
Does the three metres run from the boundary?
No.
The relevant distance is measured in relation to the neighbouring building or structure, not simply from the legal boundary.
Is the six-metre rule just for basements?
No.
Basements are an obvious example because of their depth, but other deep foundations or excavations can potentially trigger section 6(2).
Can my architect decide whether section 6 applies?
Architects and structural engineers will often identify Party Wall implications, but responsibility for complying with the Act remains with the Building Owner.
Where the position is unclear, advice from an experienced Party Wall Surveyor should be obtained.
Section 6 advice from PJF Surveying
PJF Surveying LLP provides Party Wall advice throughout Essex and the South East.
For Building Owners, we can review architectural and structural drawings to establish whether proposed foundations and excavations are likely to fall within section 6 of the Party Wall etc. Act 1996.
Where notice is required, we can identify the relevant Adjoining Owners, prepare and serve notices, prepare Schedules of Condition and act through the dispute-resolution process where necessary.
Early review is particularly worthwhile where piled foundations, deeper excavations or work close to neighbouring buildings is proposed.
Contact PJF Surveying if you would like your proposed drawings reviewed before construction begins.
Author: Peter Furness BSc (Hons), AssocRICS, MCIOB, MFPWS
PJF Surveying LLP – RICS regulated surveying practice
Last reviewed: October 2026
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