The 3-metre rule
You must serve a Section 6 notice if any part of your proposed excavation lies within three metres of an adjoining owner's building or structure, AND the lowest point of your excavation will be lower than the bottom of their foundations. Most rear extensions trigger this rule because foundations are commonly 1.0–1.2m deep — deeper than typical Victorian footings.
The 6-metre rule
You must also serve a Section 6 notice if any part of your excavation lies within six metres of the adjoining owner's structure AND your excavation, projected at a 45° angle, would intersect with the bottom of their foundations. This is the rule that catches deep basement digs — even when the excavation is several metres from the boundary.
Statutory notice period
Section 6 requires one month of notice. The notice must be accompanied by drawings and sections showing the proposed excavation and any new foundations.
Mandatory drawings
Unlike Sections 1 and 3, the Act explicitly requires drawings with a Section 6 notice. The wizard prompts you to upload these — typically a foundation plan, a section through the excavation, and the proposed sequence of work. Without the drawings the notice is invalid.
Common scenarios
- Rear extensions with deeper foundations than the neighbour's.
- Basement conversions and lightwells.
- Deep underpinning works adjacent to a shared boundary.
- New garage builds with strip foundations close to the AO's structure.
Adjoining owner response options
Within fourteen days the AO may consent to the works in writing, dissent and concur in the appointment of an Agreed Surveyor, or dissent and appoint their own surveyor. Because Section 6 works carry the highest risk of damage (subsidence, vibration, wall movement), the appointment of a surveyor and a Schedule of Condition is almost always advisable — even where the AO is willing to consent.