Why basements almost always need notice
Basement work typically involves at least two, and often three, separate triggers under the Act:
- Section 6 (adjacent excavation) — this is the big one. If you're excavating within 3 metres of a neighbouring building to a depth lower than their foundations, or within 6 metres if the excavation cuts a line drawn down at 45 degrees from the underside of their foundations, you need to serve a Section 6 notice — even if the dig is entirely on your own land.
- Section 3 (party structure works) — underpinning a shared wall, inserting beams into it, or cutting into it for waterproofing or structural support is party structure work, not excavation, and needs its own Section 3 notice.
- Section 1 (line of junction) — less common, but relevant if any new walls are being built up to or astride the boundary as part of the works.
It's entirely normal for a basement project to need Section 3 and Section 6 notices simultaneously, served on the same neighbour, covering different aspects of the same job.
The depth and distance test
Section 6 notice is triggered by depth relative to the neighbour's foundations, not by an absolute number of metres. A basement dig that only goes 1.5 metres below ground can still trigger notice if the neighbour's foundations are shallower still — which is common in older terraces with historically shallow footings. Conversely, a deeper dig set well back from the boundary might fall outside the 3m/6m bands entirely. This is why basement notices should be based on an actual foundation depth assessment, not a rule of thumb.
Notice periods run separately, not cumulatively
If your project needs both a Section 3 and a Section 6 notice, each runs its own two-month and one-month clock respectively, tied to the specific works it covers. A common misunderstanding is that the longer period governs the whole project — it doesn't. Provided the physical works are genuinely separable, excavation work can proceed once its own notice period has run, even if a party structure notice on the same job is still within its two-month window.
Structural engineer input, then notice
Because basement notices depend on accurate foundation depth and load information, it's worth having your engineer's drawings and calculations finalised — or at least stable — before you serve. A notice built on preliminary numbers that change materially once the structural design is finished may need to be re-served, resetting the clock.
What this means for your notice
If you're using the generator, be specific: describe the works as excavation, underpinning, or both, and include the intended depth. The platform will prompt you for the details that determine which sections apply — but it's the accuracy of what you enter about depth, distance, and the works themselves that determines whether the right notices go out. Get your engineer's numbers first, then generate the notice.
This article is general guidance and not a substitute for advice on your specific project. If your basement works are structurally complex, a party wall surveyor's early input is worth the fee.