Wall height and ground conditions affect foundation design; the legal boundary and proposed wall position determine whether a line of junction notice may apply.
Start with the wall's actual purpose
A free-standing brick garden wall, a retaining wall that holds back higher ground and a wall supporting another structure carry different loads. Retaining walls can be affected by water pressure as well as soil weight and often need specialist design. Do not use one generic trench-depth rule for all three. A builder or engineer should consider ground conditions, height, exposure and the possibility of nearby drains or tree roots.
Check the setting-out line
If the new wall is proposed along a property boundary, establish whether it is wholly on your land or intended to straddle the line. A line of junction notice can apply to a new wall built up to the boundary. Building a new party wall astride it requires the adjoining owner's written consent. Title plans and old fence positions may not settle a disputed boundary, so resolve that question before concrete is poured.
Avoid undermining existing structures
Excavation close to a neighbouring building or wall needs an assessment of stability and, in some circumstances, section 6 of the Party Wall Act. The statutory test is not simply whether the trench is within three metres; the relationship to neighbouring foundation depth matters. If the work is a substantial retaining wall or an unusually deep footing, ask for professional structural and party wall advice before digging.
Plan drainage and future maintenance
Keep water from collecting behind a retaining wall or being diverted onto the neighbour's property. Think about the finished top level, coping details and access for repointing. Where a wall is jointly owned, agree the proposed finish, who undertakes the work and any need for a formal statutory notice. A signed neighbour note about costs is not necessarily the same document as a Party Wall Act notice.
Does this project need a party wall notice?
A garden wall at a boundary can fall within section 1, and certain works to a party fence wall are covered elsewhere in the Act. Nearby excavation can also be separately notifiable under section 6. The automated builder covers selected simple section 1 or 3 scenarios, not excavation notices or structural design.
Checklist before work begins
- Confirm boundary ownership and precise position.
- Choose a foundation design for the actual height and ground.
- Check drains, tree roots and nearby buildings before excavation.
- Deal with written consent and any relevant notice in advance.
Think you may need a notice?
Check your work for free. A personalised £4.99 PDF is available only if it fits the builder’s supported notice types.
Related guides
GOV.UK party wall explanatory booklet ↗ · Party Wall etc. Act 1996 ↗
Last reviewed: 22 October 2026. Information is not a substitute for professional assessment of your project.