Basements, cellars and party walls
Digging down beside a neighbour is the most involved kind of party wall work. Basement and cellar conversions almost always need notices for excavation, and usually for underpinning the party wall too.
Which notices are needed?
- Section 6 (adjacent excavation), one month's notice. This applies to digging within 3 metres of a neighbouring building below its foundations, or within 6 metres where the dig cuts below a 45° line drawn down from the bottom of those foundations. Basements usually trigger both tests. The notice must include plans and sections.
- Section 2 (party wall work), two months' notice. This applies to underpinning or lowering the foundations of the party wall, cutting into it, or any other work to it.
- Section 1 (line of junction), one month's notice. This applies if a new wall will be built at the boundary, such as a new basement retaining wall.
In Hampshire, full basements are less common than in London. Cellar conversions and lowering existing cellars are more typical, especially in the Victorian terraces of Southsea and Southampton. The same rules apply.
What a basement award usually covers
- The engineer's construction method statement, the temporary propping and the sequence of underpinning
- Movement monitoring of the neighbouring property, with trigger levels at which work must pause
- A detailed schedule of condition, often including crack measurements
- Groundwater and drainage arrangements
- Working hours, noise and vibration limits
- Security for expenses: the adjoining owner can ask for money to be held as security in case the work is abandoned partway through
Allow time. Basement awards involve more technical review than most. Serve notices early, and involve your structural engineer from the start.
Costs
Basement awards are priced individually, because the technical review is more involved. Notices are £100 per neighbour, covering all the notices they need. Contact us with your drawings for a fixed quote. See full pricing.
Basement questions
Does lowering the floor of an existing cellar need a party wall notice?
Usually, yes. Lowering the floor typically means digging below the party wall's existing foundations and underpinning it. That's notifiable under sections 2 and 6.
What is security for expenses?
Under section 12 of the Act, an adjoining owner can ask for the building owner to provide security, usually money held by the surveyors or a solicitor, before work starts. It protects them if the work is left unfinished. It's most often requested for basements.
Not sure if the Act applies to your project?
Tell us what you're planning. We'll tell you, free of charge, whether you need to serve notice and what happens next.