The short answer
Basement excavations raise real concern about encroachment onto adjoining land, which affects ownership, future development, structural design and value. The Act gives no general right to build on or under the neighbour’s land, but a party wall award can manage the risk through clear drawings, method statements, safeguards and careful setting out.
Why it matters
Basement work happens in confined conditions, and once concrete is poured it is hard to check exactly where every face sits. Engineers and building control focus on safety and compliance, not legal boundaries, so there is often no routine boundary measurement once excavation is underway, and encroachment may only surface years later when the neighbour excavates. If a wall, underpinning or foundation projects into adjoining land it may block the neighbour’s future basement, require expensive cutting back, create compensation arguments, affect title and saleability, and lead to proceedings outside the Act. Discovered encroachment is often unsafe or disproportionate to demolish, needing specialist cutting and temporary support at substantial cost.
What to do now
- As a building owner, obtain accurate survey information and ensure drawings clearly show boundaries and proposed structures.
- Instruct competent contractors, keep clear records of setting out, and avoid designs that rely on informal assumptions about the boundary.
- As an adjoining owner, raise concerns early — before concrete is cast and before practical options narrow.
Common mistakes
- Relying on informal assumptions about where the boundary sits.
- Assuming building control or engineers will police encroachment.
- Raising concerns only after the structure is built.
When to call Coburns
If a basement is proposed next to your boundary, on either side, send us the drawings early and we will make sure setting out and safeguards are properly addressed.