A huge growth in demand has occurred in recent years for the construction of basements in central London. That continues unabated, and increasingly we are being asked to advise on basements in the outer boroughs, and occasionally outside the M25. By January 2016 Gabriel GeoConsulting had advised on over 150 basement projects. The reports we issued in relation to these projects usually comprised one or more of:
- Basement Impact Assessment (BIA), called a ‘Geo-hydrology report’ by Westminster. These include both GMA and DCA components (see below) whenever they are required by the Local Planning Authority.
- Ground Movement Assessment (GMA): These include analyses of vertical heave/ settlement using PDISP software, and estimation of movement alongside the basement using the methodology in CIRIA report C580 (or analysis of bored pile retaining walls using FREW software) in order to enable a Damage Category Assessment (DCA) to be provided.
- Hydrogeological Assessment (groundwater).
- Hydrological Assessment (surface water).
- Flood Risk Assessment, usually required to meet the requirements of PPG25.
The planning authorities in many of the London Boroughs have introduced specific requirements for the technical reports which must be submitted with planning applications. We welcome the opportunity to discuss the particular reports which are likely to be required in relation to your proposed basement scheme; please see our Contacts page.
The majority of these basements are being retro-fitted below existing houses, with the remainder being part of re-developments. The development projects we have assisted our clients with range from small single-storey basements beneath terraced houses or their gardens, to large multi-storey basements beneath large mixed-use developments or multiple blocks of flats linked underground by the basement car park.