Quick answer: The three-metre rule can apply where proposed excavation is within three metres of a neighbour’s building or structure and goes below the bottom of its foundations. The six-metre rule uses both distance and a 45-degree plane drawn from the bottom of the neighbour’s foundations, so not every excavation within six metres is notifiable.
This article concerns England and Wales. It provides general information, not legal advice. The application of the Party Wall etc. Act 1996 depends on the facts, ownership and proposed work.
The three-metre test
Measure the shortest horizontal distance from the proposed excavation to the neighbouring building or structure. Notice is normally required only if the excavation will extend lower than the neighbour’s foundation bottom.
The six-metre test
This applies to deeper excavation where part of the proposed excavation falls within six metres and beneath a line drawn downwards at 45 degrees from the bottom of the neighbour’s foundation, in the manner described by section 6.
Why foundation levels must be checked
Assumptions can produce the wrong result. Trial pits, historic drawings or professional investigation may be needed to establish the adjoining foundation depth and profile.
What the notice should include
The notice should state whether underpinning or safeguarding is proposed and be accompanied by plans and sections showing the site, excavation depth and proposed building or structure.
Frequently asked questions
Is every excavation within three metres notifiable?
No. The proposed excavation must also be deeper than the neighbour’s foundation bottom.
Do piles count as excavation?
Piled and basement designs can engage section 6; obtain project-specific professional advice.
Authoritative sources and further help
Read the official GOV.UK explanatory booklet and the Party Wall etc. Act 1996 on legislation.gov.uk. For the wider process see our building owners guide, adjoining owners guide and notice guidance.
Reviewed: 16 July 2026. Seek advice from a suitably experienced party wall surveyor or solicitor where the facts or legal position are disputed.