Rear Extensions and the Party Wall Act
A rear extension can engage the Act through its foundations, a new wall at the boundary or work to an existing shared structure.
Boundary walls
Section 1 may apply where a new wall is proposed astride or up to the line of junction.
Foundation excavation
Section 6 may apply where new foundations are close to and deeper than neighbouring foundations.
Existing shared walls
Cutting in flashings, beams or roof connections may be notifiable depending on the design.
The 3-metre test
Excavation within 3 metres can be notifiable where it will extend below the bottom of the neighbour’s foundations. Distance alone does not decide the question; depth matters too.
The 6-metre test
The 6-metre provision uses a 45-degree test measured from the bottom of the neighbour’s foundations and is particularly relevant to deeper excavation.
Before serving notice
- Confirm the boundary position and ownership details.
- Obtain plans and foundation sections.
- Identify whether Sections 1, 3 or 6 apply.
- Allow enough time before the intended start date.
Rear extension FAQs
Does planning permission replace Party Wall notice?
No. Planning and the Party Wall Act are separate processes.
Can my neighbour refuse the extension?
The Party Wall Act does not provide a general veto. Dissent normally leads to an Award.
Who pays?
The Building Owner usually pays reasonable Party Wall costs arising from the project.