Which notice type applies?
A rear extension on a terraced or semi-detached property usually triggers two parts of the Act. Section 3 applies because the new flank wall is built off the party wall and the party wall is often raised or cut into. Section 6 applies because the foundations are typically excavated within 3 m of the neighbouring building (and deeper than the neighbour's foundations). Both notices are commonly served as a single combined document.
Common scenarios where this notice is needed
- Building a new flank wall off the existing party wall.
- Raising the party wall to accept the new extension roof.
- Excavating strip or trench-fill foundations within 3 m of the adjoining building.
- Underpinning or piling within 6 m of the neighbour where the new foundation is deeper than a 45-degree line drawn down from the neighbour's foundation.
- Cutting in flashings or chasing the party wall for the new roof junction.
The notice period and what to expect
If both Section 3 and Section 6 apply, you serve both notices and the longer period (two months under Section 3) governs when works can begin. The notices are usually combined into a single document.
Once served, the adjoining owner has fourteen days to respond. If they consent, you can proceed once the notice period expires. If they dissent (or fail to respond), the Section 10 surveyor process begins and a Party Wall Award is produced before the relevant works can start.
Typical cost for this project type
The notice itself costs £48 inc VAT through our generator (less for multiple notices). Surveyor fees only apply if the adjoining owner dissents — typically £600–£1,200 for an Agreed Surveyor or £1,200–£3,000 for two-surveyor matters on a standard domestic project. For a full breakdown, see our cost guide.
How to generate the right notice
Our notice generator walks you through the relevant questions for your project type and produces a statutorily compliant notice ready to print and serve. The wizard recommends the right section automatically based on what you describe — there's no need to know which section applies before you start.
Frequently asked questions
Do I need a Party Wall notice for a single-storey rear extension on a detached house?
Section 3 is unlikely to apply because there is no shared wall. Section 6 may still apply if you are excavating within 3 m of a neighbouring building — for example, an outbuilding or a neighbour's garage — and your foundation is deeper than theirs. Use our checker to confirm.
What if I'm only doing a small kitchen extension?
Size doesn't matter for the Act — what matters is whether the works engage Section 3 (party structure) or Section 6 (excavation depth and proximity). Even a 3 m × 3 m extension can require both notices on a terraced property.
Can I serve the notice after I've started the foundations?
No. The notice period must elapse before any notifiable work begins. Serving retrospectively is a breach of the Act and exposes you to an injunction.