The so-called 3 metre rule comes from section 6 of the Party Wall etc. Act 1996. It concerns qualifying excavations within three metres of a neighbouring building or structure, where the new excavation is deeper than the bottom of that neighbour's foundations.
Does any digging within three metres need notice?
No. The key test involves the proximity and depth of the proposed excavation relative to the existing neighbouring foundations. A shallow excavation may not meet the section 6 condition. You cannot reliably decide the issue just by measuring from a fence.
What counts as a neighbouring building?
Section 6 can apply to a relevant neighbouring building or structure; the affected owner need not always be the owner of the property immediately next door. Correctly identifying adjoining owners and foundations is important.
How much notice must be given?
Qualifying section 6 excavation ordinarily requires at least one month's notice. Plans and sections showing the location and depth of excavation or foundation and the proposed building or structure must accompany the notice, together with required information about safeguarding the neighbour's foundations.
Also check the related 6 metre rule, which applies using a different geometrical test.
Based on the GOV.UK explanatory booklet and the Party Wall etc. Act 1996. This is general guidance for England and Wales; the applicable rules depend on the actual work and affected owners.
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