Which notice type applies?
A basement conversion almost always requires a Section 6 notice (because the excavation is within 3 m of a neighbouring building and deeper than their foundations) and usually a Section 3 notice (because the party wall is underpinned, lowered, or cut into for new structural members). Both notices require detailed drawings showing the depth, sequence and method of excavation. Because the consequences of a basement failure are severe, dissent and full Section 10 surveyor involvement is the norm — not the exception.
Common scenarios where this notice is needed
- Lowering the existing basement floor to gain head height.
- Underpinning the party wall to extend the basement laterally.
- Excavating a new lightwell or rear extension below ground level.
- Sequential needling and pinning of the party wall.
- Diaphragm or sheet piling adjacent to the party wall.
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
Why are basement notices treated more seriously than other Party Wall notices?
Because basement works carry the highest risk of damage to the adjoining property — including subsidence, cracking, and in extreme cases catastrophic structural failure. Most adjoining owners will dissent and appoint a surveyor to ensure a Schedule of Condition, monitoring regime and method statement are agreed before works start.
Do I need engineering drawings before serving the notice?
Yes — for Section 6 you must include drawings showing the depth and proximity of the proposed excavation. The Act does not specify the level of detail, but in practice a basement notice without method statements and structural drawings will be rejected by any competent adjoining owner's surveyor.
How long does the Party Wall process typically take for a basement?
Allow two months for the notice period plus four to twelve weeks for the surveyor process — so plan for three to five months from service to start of works. Complex basements with multiple adjoining owners can take longer.