Basement excavation can require a Party Wall Act notice when it falls within the distance-and-depth tests relating to a neighbour's foundations. The 3-metre and 6-metre distances are not automatic exclusion zones, and work on a party structure can require a separate notice. Planning and building regulations approvals do not replace this process. [1] [2]
The two excavation tests
Under the government's explanation of section 6, notice is required for excavation within 3 metres of a neighbouring building or structure where the work goes below the neighbour's foundations. Within 6 metres, the relevant test is whether the excavation meets a line drawn down at 45 degrees towards it from the bottom of those foundations. [1]
Measure the relationship to the neighbouring building or structure, not simply the property boundary. The assessment therefore needs proposed excavation levels and reliable information about relevant foundations. A plan showing a 3-metre circle without depths does not answer the test. [1]
Allow for more than one type of notice
An excavation notice normally needs at least one month's notice. Work to an existing party structure normally needs two months. A basement may engage both provisions, so the programme should identify the applicable notices rather than assigning one general “party wall period” to the entire project. [1]
The excavation notice needs plans and sections showing the proposed work and its depth. If there is no written consent within 14 days, the statutory dispute process applies; silence should not be treated as permission to proceed. [1]
Provide the surveyor with an engineered proposal
The notice exercise should be coordinated with the structural design. Existing foundation information, proposed support and the construction sequence need to tell a consistent story. The government's guidance explains the information accompanying the notice, while HSE separately requires the stability of neighbouring structures to be protected during excavation. [1] [3]
Ask the engineer to identify which assumptions still depend on investigation. Do not let the surveyor's involvement become a substitute for designing the temporary works or resolving uncertain foundations. The underpinning good-practice guidance treats those engineering responsibilities as essential parts of the work. [4]
Protection during the project
Ask how existing condition will be recorded, how relevant movement will be monitored and who receives readings. These are practical protection questions to coordinate with the engineers and the party wall arrangements. Islington's basement guidance also emphasises competent engineering involvement and monitoring through construction. [5]
Any agreement or award should be read alongside the current drawings and method. Where a construction change affects the notified works, refer it back before proceeding rather than assuming the earlier documents cover any later variation. This follows the need to keep design and construction responsibilities coordinated. [6]
Keep the approvals separate
The Party Wall Act does not decide whether the basement is acceptable in planning terms or demonstrate building regulations compliance. Likewise, a planning approval is not an instruction that a neighbour must accept an unsupported excavation method. Keep the planning, building control and party wall records as separate but coordinated parts of the project. [2] [7]
A party wall surveyor or solicitor should advise on the notices, rights and dispute procedure for the particular properties. [1]