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Basement Impact Assessment

Basement developments are as popular as ever. Do you know the risks?

Basement developments are more popular than ever.

For Londoners, where space is at a premium, they are an alternative to the more traditional extension.

However many do not appreciate how risky such redevelopments can be, not taking into account the site’s history and legacy.

At Soils, we have the technical expertise to provide the geotechnical, environmental engineering and consultancy to ensure that nothing is missed and that everything is within regulations.

As part of any basement development, a Basement Impact Assessment (BIA) must be carried out. The purpose of the BIA is to demonstrate that the development will not result in any of the adverse impacts.

The BIA is made up of the following elements:

– Desk based screening and scoping stage

Flood Risk Assessment – limited scope if site is in a Flood Zone 1

– Investigation of existing foundations

– A soil and groundwater investigation and interpretative report signed off by a Chartered Engineer and ROGEP

– Hydrology report on the effect of the basement on groundwater flow. This must be signed off by a Chartered Geologist (CGeol)

– Impact assessment on the effect of the basement on nearby structures – includes detailed geotechnical design for construction induces ground deflections. This must also be signed off by a Chartered Engineer

Ground Movement Analysis and Damage Category Assessment 

These are essential components of the BIA. Analysis is undertaken using industry standard WALLAP and Oasys PDISP software.

Soils models the ground movement during construction including the effect of temporary and permanent propping, offering advise on movement hold and action values if these are required by the Structural Engineer or Party Wall Surveyors.

Soils Limited staff have the appropriate qualifications and chartered status to sign off the final BIA.

A note on London

London Borough’s give guidance regarding their requirements for a proposed basement in their Basement SPD, if this guidance is not closely followed, they will reject it.

LB Merton DM D2 Design Considerations for Basements states:

“The council will require an assessment of basement and subterranean scheme impacts on drainage, flooding from all sources, groundwater conditions and structural stability where appropriate. The Council will only permit developments that do not cause harm to the built and natural environment and local amenity and do not result in flooding or ground instability.”

Additional Services

In addition to basement developments, Soils Limited also has the technical expertise to provide geotechnical and environmental engineering and consultancy on:

– Small extensions

– Large multi-plot residential developments

– Multi-storey

Have a query? Contact the Soils team here.