Core service
Basement construction in London
Excavation, underpinning and waterproofing beneath occupied London houses, coordinated with the design team.
Capability
Basement work is the most technically demanding residential construction carried out in London. It is also the work where the consequences of poor sequencing are most severe, for the property itself and for its neighbours. We construct to the temporary and permanent works designs prepared by the appointed engineers, and we manage the site so that the design assumptions hold on the ground.
- Basement excavation
- Basement extensions
- Underpinning
- Structural alteration
- Waterproofing and basement tanking
- Drainage and pumped systems
- Temporary works coordination
- Movement monitoring
- Vibration monitoring
- Consultant coordination
- Mechanical services
- Specialist fit-out
Sequencing and temporary works
Underpinning is carried out in a defined pin sequence with agreed hit-and-miss spacing, each bay excavated, cast and dry-packed before the adjacent bay is opened. Temporary works are installed to the temporary works designer’s scheme, inspected and recorded. We do not vary a sequence on site without the engineer.
Monitoring
On sensitive sites we implement and coordinate movement and vibration monitoring through the relevant works, with readings reviewed against agreed trigger levels and reported to the design team. At Caithness Road in Brook Green, a neighbouring property incorporated a substantial three-storey glass structure; monitoring, controlled excavation sequencing and close coordination with the structural engineer and specialist consultants ran throughout the below-ground works.
Waterproofing
Waterproofing is designed by others and installed by us to that design, typically as a combined system with drained cavity membranes, sump and pump provision with alarm, and maintainable drainage channels. Penetrations, service entries and construction joints are the details that matter, and they are recorded as they are formed.
What we do not do
We do not carry out structural, temporary works, waterproofing or geotechnical design. Those designs are produced by appointed specialists. Our role is construction, coordination and control of the works on site.
How a project runs
A basement project starts with information: a measured survey, a structural appraisal of the existing house, a ground investigation and, in most London boroughs, a basement impact assessment. Party wall notices are served and condition surveys of the neighbouring properties are agreed before anything is dug.
On site the sequence is set by the temporary works and underpinning design. The house is underpinned in a controlled order, the basement is excavated and the new structure cast, and the waterproofing is installed to the specialist's design. Movement and vibration are monitored throughout, and the fit-out follows once the structure is complete and tested.
Our basement projects
Questions we are asked
Do I need planning permission for a basement?
In most London boroughs, yes. Basement excavation normally needs planning permission, and boroughs such as Kensington and Chelsea, Westminster and Camden have specific basement policies and require a basement impact assessment. Your architect will confirm what applies to your house.
Who designs the waterproofing?
A specialist waterproofing designer, working to BS 8102. The design will usually combine a cavity drainage membrane, a waterproof concrete structure or a tanking system, and we install it to that design.
How are the neighbours protected?
Through the party wall process, condition surveys agreed before work starts, temporary works designed by the engineer, a controlled underpinning sequence, and monitoring against agreed trigger levels. At Caithness Road, movement and vibration were monitored throughout because of the neighbouring glass structure.
Can you refurbish an existing basement rather than dig a new one?
Yes. At Achilles Road in West Hampstead we refurbished the existing basement and formed a new bathroom within it, without excavating.