Rear, side and wrap-around extensions transform London homes, but they frequently trigger obligations under the Party Wall etc. Act 1996. As RICS-accredited party wall surveyors serving all London boroughs, we help owners identify which notices apply and keep good relations with neighbours throughout the build.
When does an extension need a party wall notice?
Not every extension is notifiable, but many are. The Act is engaged when you build on or into a shared party wall, build up to the line of junction, or excavate for new foundations close to a neighbouring structure. Single-storey rear extensions, side-return infills, wrap-arounds and kitchen extensions commonly involve at least one of these. Serving the correct party wall notice is the first legal step.
Typical extension works that engage the Act
- Building a new flank wall astride, or up against, the boundary line.
- Cutting into the party wall to insert a beam, flashing or damp-proof course — a Section 2 activity requiring a party structure notice.
- Excavating foundations within three or six metres of a neighbour’s building under Section 6.
- Removing a garden wall that is a party fence wall and rebuilding it.
Foundations near the boundary
Foundation depth is the most common trigger for extension disputes. Where you dig within three metres of a neighbour’s structure and below the level of their foundations, or within six metres under a 45-degree line, Section 6 applies. Our 3 and 6 metre rule guide explains how to measure this. Traditional strip foundations, and even shallower rafts, can readily fall within these distances on a compact London plot.
| Extension type | Likely section | Notice period |
|---|---|---|
| Rear extension with foundations near boundary | Section 6 | 1 month |
| Side-return built up to the line of junction | Section 1 | 1 month |
| Beam cut into the party wall | Section 2 | 2 months |
| Wrap-around combining the above | Sections 1, 2 & 6 | 1–2 months |
Building on the line of junction
Section 1 deals with building a new wall at the boundary where none previously stood astride it. You may build wholly on your own land, or, with the neighbour’s agreement, astride the line as a new party wall. Notice under Section 1 is served at least one month before starting. Even when you build entirely on your own side, you retain footing and projection rights that a surveyor can help you exercise correctly. See our overview of the types of party wall works.
Consent, dissent and appointing surveyors
Once served, each adjoining owner has 14 days to consent or dissent. Written consent avoids the need for surveyors on that element, though a schedule of condition remains wise. If they dissent or do not respond, a dispute is deemed to arise and surveyors are appointed — either a single agreed surveyor or one for each side, with a third surveyor on standby. The outcome is a party wall award governing the works. Our guides for building owners and adjoining owners explain each side’s rights.
FAQs
My extension is on my own land — do I still need notice?
Possibly. If you excavate near your neighbour’s foundations under Section 6, or build up to the boundary under Section 1, notice is required even though the structure sits on your side.
Who pays the surveyor’s fees for an extension?
Generally the building owner, as the works are for their benefit. Reasonable fees are determined within the award; see our costs and process guide.
Can I start as soon as I have served notice?
No. You must allow the statutory notice period — one month for Sections 1 and 6, two months for Section 2 — and resolve any dispute through an award first.
Plan your extension with confidence
If you are extending a London property, our RICS-accredited surveyors will confirm exactly which notices apply, protect your neighbour’s property with a schedule of condition and deliver a fair award. Please contact us to get your extension underway smoothly.