If your extension needs foundations within 3 metres of your neighbour's building, Section 6 of the Party Wall etc. Act 1996 may apply - but only if you're also going deeper than the bottom of their foundations.
Section 6(1) applies where you excavate within 3 metres measured horizontally from any part of a neighbour's building, and any part of that excavation will go lower than the level of the bottom of their foundations. Section 6(2) adds a second trigger: within 6 metres, where your excavation would meet a 45-degree plane drawn downwards from the bottom of their foundations.
No. Distance alone isn't enough. You need both proximity (within 3m) and depth (lower than the bottom of their foundations) under Section 6(1). If you're within 3m but shallower than their foundations, Section 6(1) doesn't apply.
It's strictly the bottom of their foundations. The Act says "the level of the bottom of the foundations" - not ground level, not the top of the footing. That's why knowing their actual foundation depth matters.
Separate from the 3m rule. If you're between 3m and 6m away, Section 6(2) applies if your excavation would intersect a 45-degree line drawn down from the bottom of their foundations. Common with deeper excavations like basements or piled foundations.
Yes. Piling is still excavation for Section 6 purposes - the Act covers works to "excavate, or excavate for and erect a building." Depth is measured the same way. Flag piling specifically to your surveyor, since it can engage Section 6(2) even at 6m.
You often don't, initially - that's why Section 6 notices include proposed foundation details, and why surveyors often request trial holes. You serve based on your proposed depth and a reasonable assumption, then agree the details in the award if needed.
The Act doesn't precisely define "building or structure" for Section 6 purposes, but it's read broadly. Government guidance explicitly includes garages as qualifying structures, and practitioner commentary suggests even substantial garden walls and fences with concrete-set posts can count. In practice, most solid boundary features - walls, garages, outbuildings - are likely to qualify, so it's safer to assume Section 6 could apply than to assume a structure is too minor to count.
Every extension is different. Rather than guess your neighbour's foundation depth, describe your actual project to the Notice Checker and get an immediate, plain-English indication of what applies.
Try the Notice CheckerThis page is general information about the Party Wall etc. Act 1996, not professional advice about your specific project. Whether a notice is required, and what it must contain, should always be confirmed directly with a qualified Party Wall Surveyor before any works begin or any notice is served.