Basement Impact Assessment (BIA)

Given the relatively high land and property values in London (and its outer suburbs), basement construction has become increasingly popular in recent years. Several local authorities have recognised that the construction of basements has the potential to impact on flooding, groundwater, land stability and the structural stability of adjoining/neighbouring properties.

Therefore, a number of London Boroughs, notably Camden, Westminster, Kensington & Chelsea require a specific Basement Impact Assessment (BIA) at the planning stage to assess the hydrogeological, hydrological and geotechnical impact of a basement construction on neighbouring properties.

In 2009, the London Borough of Kensington and Chelsea produced their own planning guidance document entitled “Subterranean Development”. The London Borough of Camden adopted a similar approach for their use in planning applications involving basements (Camden development policy DP27). The Camden Basement Development document (CPG4) presents a structured approach which identifies the potential risks in a five stage Basement Impact Assessment (BIA) process. The overall process has now also being adopted by a number of other London Boroughs as a template for their own assessment of basement construction applications.

bia2Southern Testing has produced a significant number of Basement Impact Assessments (BIA) in the last few years to comply with Local Authority planning requirements. Our Clients have included both individual householders, architects, structural engineers and specialist basement design and construction companies. We can provide Geotechnical, Hydrogeological and Hydrological Basement Impact Reports to support planning submissions. As now required by many London Boroughs, our experienced geological, geotechnical and hydrogeological specialists have the relevant Chartered Engineering, Geologist and Environmental qualifications to act as signatories.

Our Basement Impact Assessment (BIA) services include:

Stage 1 and 2 – Screening and Scoping Reports; Risk based reports to assess the potential impact on factors such as surface flow and flooding, local groundwater flow, land stability and the structural stability of adjoining/neighbouring properties.

Stage 3 – Ground Investigation Reports; We can specify and carry out the ground investigation to establish soil and groundwater conditions. We operate a variety of drilling equipment to enable ground investigation in restricted access site environments such as within existing basements, light-wells, buildings, low headroom areas, rear gardens and on steep slopes, where conventional equipment cannot be mobilised.

Stage 4 – Impact analysis; We carry out detailed analyses (if required) on the effects of the basement construction in terms of ground movements and damage category assessment of neighbouring structures, slope stability and groundwater flows using specialist analytical software such as Pdisp, Xdisp, SlopeW and ModFlow (three-dimensional finite-difference groundwater modelling).

Close liaison with the Clients’ Architect and Structural Engineer at all stages is essential.

Get in touch

If you have any questions about our services or would like to discuss how we could help you, please get in touch using our contact form below. Please provide as much information as possible about the nature of your enquiry, particularly the purpose of the investigation, the site address and postcode.

Any existing or proposed site plans are useful and can be attached beneath the message box. Please provide a contact address, email and telephone number. We will get in touch as soon as possible.


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Southern Testing are continuing to work through the Coronavirus (COVID-19) emergency, including carrying out site work where it is safe to do so.

The Government have given express support to the Construction sector and have issued specific guidance for working on site. The Construction Leadership Council have also issued guidance.

We have revised our travelling and working practices to ensure that our staff are protected, and to meet the particular requirements of the guidance as well as our own risk assessments. The guidance and our working practices are under constant review.

Most site investigation work can be undertaken safely under the current restrictions.

We are committed to helping all our clients, old and new, during this difficult time. Should you have any site investigation requirements, or wish to discuss a particular project, please do not hesitate to contact us.