Diagnose the problem before selecting the remedy
RICS distinguishes subsidence from settlement and explains that some movement caused by leaking pipework can be addressed by repairing the leak rather than underpinning the building. The cause and the required structural response need investigation before a contractor is asked to price a predetermined solution. [2]
Ask for a report stating the evidence, the cause considered most likely, any unresolved questions and the options for addressing them. Where an insurance claim may be involved, agree the investigation and repair process with the insurer before commissioning major permanent work.
Underpinning is also used for planned alterations
The June 2023 Temporary Works Forum and ASUC guidance describes circumstances including lowering adjacent ground, installing deep services near existing foundations and increasing loads. It also explains why underpinning associated with a basement can have to act as retaining construction, not only carry vertical loads. [3]
A basement proposal therefore needs a coordinated structural and construction assessment. Ask the engineer to distinguish the permanent basement structure from the temporary support required while excavation proceeds.
How is it carried out?
Traditional underpinning extends support beneath existing foundations through carefully designed, staged work. Other specialist solutions may be considered where that approach is unsuitable. The sequence, load transfer, stability and ground conditions require an engineered design before excavation beneath a wall. [1]
The TWf/ASUC guidance emphasises planning, competent specialists, ground and structural information, and a monitoring strategy. It also identifies circumstances outside the scope of its standard discussion that need specialist advice. Do not treat a generic sketch as suitable for every pier, wall or building. [3]
Safety, neighbours and approvals
Planning Portal's basement safety guidance highlights the risks of working below existing structures and the need to plan construction safely. Ask who is responsible for the temporary works and the contractor's method before excavation begins. [4]
The Party Wall Act may apply to work on shared structures or excavation near a neighbour. GOV.UK identifies relevant works separately from the building-control process. Resolve that assessment before starting; approval from one body does not answer all neighbour-related questions. [5]
What to request before accepting a price
Request an identified design basis, the extent of underpinning, investigation assumptions, temporary support, monitoring, inspection stages and reinstatement. Ask what happens if the ground differs from the investigation and how a change will be authorised and priced.
At completion, retain the final design, site records, monitoring information and building-control documentation. Ask the engineer to identify any continuing observations or maintenance recommendations. No reliable universal price or duration follows from the word “underpinning”: the scope and ground conditions must first be defined.