Many local authorities within Greater London and its suburbs require a basement impact assessment (BIA) report as part of the planning permission application. This is required to review the impacts on flooding, surrounding structures and the local geology to ensure any known risks are mitigated.

The geological strata typically found within London is of clay formation and is prone to seasonal shrink and swell leading to subsidence and heave. In exaggerated cases this can lead to movement of the foundations and ultimately the superstructure above. The specific ground conditions within the vicinity of the property should be taken into consideration to assess any potential issues during or after the construction of a new basement.

Another key area of the assessment report is to understand and record the proximity of the development to public footpaths and buildings. Any works undertaken must be fully hazard and risk assessed with  proper structural surveys.

One of the most undesirable factors in the construction of a new basement is the presence of groundwater. Understanding the surrounding soil and water table is key to a successful project. If a high water table is present but is known in advance of the commencement of the construction, suitable measures can be put in place to control this from affecting the project and the surrounding area.

Full BIA requirements can vary between each local authority and between each particular project but usually includes the following:-

  • Site inspection visit to review requirements specific to project,
  • Description of Existing Structure,
  • Ground conditions/geology,
  • Research into British Geological Survey maps & borehole data in surrounding area,
  • Potential ground movements to adjoining properties,
  • Assessment of Party Wall Matters,
  • Temporary construction works and methodology,
  • Indicative programme of works,
  • Control of noise, dust and vibration statement,
  • Flood risk assessment,
  • Drainage review,
  • Trees impact review.
  • FullĀ structural surveys

Our team operates in and around: Hemel Hempstead, Harrow, Maidenhead and Hertfordshire.