Basement Impact Assessments

What are Basement Impact Assessments for?

There has been a number of high-profile cases in London where new basement construction has adversely affected neighbouring properties. Local subsidence and flooding have both been reported as a result of developments across the city.

Several London boroughs now require assessment of the impact of basement construction, on neighbouring properties and the wider environment, prior to granting planning approval. Camden, in particular, has a methodical approach to understanding whether a basement proposal may pose significant risk. A series of screening tests, set out in Camden Planning Guidance 4, are applied in a basement impact assessment (BIA) and, if there are risk factors (such as proximity to the Hampstead Heath ponds, or the basement will go below the local water table), a site-specific assessment is needed.

The Royal Borough of Kensington and Chelsea also has specific requirements, as does Fulham, and several other boroughs have guidelines in draft, such as Westminster.  A BIA may also include a flood risk assessment.

How can we help?

In our experience, very few basement proposals need more than a screening report and simple geotechnical site investigation to demonstrate that any risks are insignificant.  Our concise, site specific, BIA report will put any risk posed by your proposed basement into perspective. We consider all relevant local planning requirements in coming to an informed opinion on the likely impact of basement construction at your property. A firm conclusion is given, and if uncertainties remain, we will make recommendations on how these can be confidently resolved.

If your basement does appear to be in a high risk area then our in-depth understanding of the hydrogeology of London and expertise in groundwater flow modelling will be invaluable in providing a confident estimate of risk.  Perhaps more importantly, we can accurately suggest how the risk can be mitigated.

We also provide a professional peer review service for London Boroughs, local authorities, or neighbours that might be affected by nearby basement proposals, to ensure peace of mind that all proportionate mitigation measures are being taken.