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Basement impact assessment

Post 17104 of 23788

With land values soaring in recent years in some inner cities particularly London and York developers and homeowners are looking to maximise the value of their properties and building plots by going down – one or even 2 storeys below ground level. Single, double and even treble basements are not uncommon in Chelsea, Kensington and Camden. Issues affecting development which need to be carefully considered are groundwater, foundation depths, stability of the building together with adjoining or neighbouring structures and the adjacent pavement and highway.

Where a proposed development includes a new or extended basement some Local Planning Authorities provide general guidance on meeting their terms. For example Camden Development Policy 27 suggest that the following processes be addressed to establish if a full Basement impact assessment is required:

Impact of proposals on surface flow and flooding

Impact of proposals on groundwater flow

Impact of proposals on structural stability

What information should be included when submitting applications for basement developments?

When submitting applications for basement developments, the level of technical information required will vary according to the type of the development, but is likely to include:

  • Desktop study of existing geological and hydrological conditions of the site and the wider area in order to identify areas susceptible to instability (ground and water movement) and localised flooding, needs to be site specific.
  • Detailed engineering study undertaken by a chartered engineer/geologist to assess local ground conditions, water movement, subsidence and drainage including through the use of Boreholes, potential impacts on adjoining/nearby properties.
  • Identify suitable construction methods and mitigation measures for developments which may affect the stability of the host and neighbouring buildings and/or nearby structures, and hydrology (at the site and within the area), without placing additional pressure on other areas or on the local combined sewer network
  • Devise a method for monitoring local ground conditions, water movement, subsidence and drainage

All technical reports should be prepared by a suitably qualified chartered engineer or chartered geologist, who is a member of the relevant professional body, refer to Section 6.7 of the ARUP Camden geological, hydrogeological and hydrological study for details. Section 8 of the ARUP study sets out a list of issues that need to assessed in the report.