Two different sets of rules answer this question, and mixing them up is where most boundary rows begin. Planning law decides what you may build; the Party Wall etc. Act 1996 decides what process you must follow when building near the line.
The planning side
Under permitted development, single-storey rear extensions can generally be built up to the boundary itself, subject to height limits (3 metres for a wall on the boundary in most cases, 4 metres detached from it) – but anything two-storey normally needs to stay at least 7 metres from the rear boundary, and side extensions have their own constraints. Conservation areas and Article 4 directions tighten everything. When in doubt, check with the council before committing to drawings.
The Party Wall Act side
Even where planning is satisfied, building close to the line triggers notice duties. A new wall up to or astride the boundary requires one month’s notice. Excavating within 3 metres of a neighbour’s building, deeper than their foundations, requires a Section 6 notice – the 3-metre rule that catches almost every extension footing in London. Within 6 metres, deep excavations can also qualify. No notice means no lawful start, and an injunction risk.
Where exactly is the boundary?
Title plans show general boundaries, not precise lines – fences move, and 100mm matters when a wall sits on the line. If there is any doubt, a boundary survey comparing the title plan with accurate site measurements settles the question before it becomes a dispute.
Before you build
Kingston Surveyors arranges RICS party wall surveyors and boundary surveyors across London and the UK – notices served properly, boundaries established accurately, and neighbour relations kept intact. Call 0204 579 8270 for a free, no-obligation quote before the diggers arrive.
