The short answer
You need to serve a Section 6 notice (an “adjacent excavation” notice) at least one month before you start if you plan to excavate:
- within 3 metres of a neighbour’s building or structure and deeper than the bottom of their foundations, or
- within 6 metres of it and any part of your excavation would cut a line drawn down at 45° from the bottom of their foundations.
Rule 1: within 3 metres
Measure horizontally from any part of the neighbour’s building or structure. If your excavation, or the foundations you’re putting in it, will go deeper than the bottom of their foundations within that 3 metres, Section 6(1) applies. Most rear extensions next to older houses fall into this category, because modern footings are usually deeper than Victorian or inter-war ones.
Rule 2: within 6 metres (the 45° line)
For deeper excavations further away, such as basements, imagine a line drawn down at 45° from the bottom of the neighbour’s foundation, starting at the outside face of their wall and running towards your dig. If any part of your excavation within 6 metres would meet that line, Section 6(2) applies.
What the notice must include
- Whether you propose to underpin or otherwise strengthen or safeguard the neighbour’s foundations.
- Plans and sections showing the site and depth of the excavation and, where relevant, the site of any building you’re putting up.
- At least one month’s notice before the excavation starts.
What happens next
Your neighbour has 14 days to respond. If they consent, you can go ahead once the notice period has passed. If they don’t reply within 14 days, a dispute is treated as having arisen, and surveyors are appointed to agree a Party Wall Award. A Section 6 notice lapses if the work hasn’t started within 12 months.
Source: Party Wall etc. Act 1996, section 6 (legislation.gov.uk). General guidance only, not legal advice.
