Establish the surveyed boundary and property history where relevant, document the existing conditions, identify whose land and works require support, and seek jurisdiction-specific professional or legal advice before agreement or construction.
Separate six issues
- Where the legal boundary is.
- Where the wall and its footing or reinforcement sit.
- What land level or work the wall supports.
- How surface and subsoil water are managed.
- What access is required during and after work.
- Which authority, professional, contract and legal pathways apply.
Create a shared factual record
Photograph both sides where safe and permitted, record dimensions and visible conditions, gather surveys and approvals, note recent work and water paths, and keep written proposals. A neutral record is more useful than assigning blame from appearance alone.
Get the right advice for the question
A surveyor can address boundary evidence, an engineer can address structural design, an authority or certifier can address approval pathways, and a lawyer or dispute service can address legal responsibility. A contractor quote does not replace all four.
Boundary and cost responsibility differ by facts and jurisdiction. Obtain property-specific advice before relying on an assumption or starting work that affects adjoining land.