Basement developments are becoming increasingly popular as a way of gaining additional space without having to relocate; particularly across London and densely built areas where space is a premium. Whilst such developments are seen to improve areas of limited space and increase the value of the property, the potential adverse impact on the stability of existing buildings and the natural environment has been recognised by Local Authorities.
Many Local Authorities, especially within Greater London, now require a Basement Impact Assessment to support a planning application. The requirements of a Basement Impact Assessment can differ significantly from one London Borough to another, with each Local Authority developing their own in-house requirements. In general, however, each Basement Impact Assessment will need to include an assessment of the following components:
Groundwater - quality and flow obstruction
Surface Water – drainage and flooding
We have gained valuable experience preparing Basement Impact Assessments for a variety of developments within London. To meet your requirements and those of the Local Authority, we ensure that each Basement Impact Assessment is prepared in accordance with specific planning guidance. For most sites, a desk top study is sufficient to support a planning application. For some sites however, usually those located within an environmental sensitivity area, an intrusive Ground Investigation may also be required as a condition of the planning application. Any additional intrusive investigation is advised to be carried out upon receipt of a successful Decision Notice and following the guidance given by the local authority.
If required, the intrusive investigation can also be combined with a geotechnical investigation to inform detailed design.
Is the proposed development an extension of an existing basement? If an existing basement is present, will access be available during a site walkover?
Do you have any previous investigation data or knowledge of the ground conditions underlying the site? A previous investigation may remove the need to carry out additional investigation as part of the Basement Impact Assessment.
Do you have existing and / or proposed drainage plans? All Basement Impact Assessments need to assess the potential impact on drainage systems.
Do you have a structural engineer on working on your project? Most Basement Impact Assessments are required prior to detailed design and will therefore include some general assumptions regarding construction methods, basement design etc. If, however, a structural engineer has been instructed, liaison and combined planning can be invaluable.
We will usually require 2 to 3 weeks from instruction to complete a desk based study and 4 to 6 weeks if an intrusive ground investigation is required. However, if you have deadline to meet, please contact us so that we can consider options to help you.