Kensington & Chelsea
Basement Impact Assessment (BIA)
Planning is a legal procedure to which standard questions are applied. Croft Structural Engineers has developed and continues to evolve its documents to ensure that they meet the Council’s planning requirements.
The driving document in K&C is the Subterranean Planning Document (SPD). This is linked closely to the SPD supplements Unitary Development Plan Policy CD32 & CL7.
There are numerous areas that are covered in our BIA. As the Council develops its SPD requirements our BIA’s are evolving. Recently RBKC has added an Engineering Design and Construction Statement (EDCS). The EDCS was something that Croft Structural Engineers included in its original BIA.
RBKC have become more stringent on the basements and there is a requirement to consider the impact on the local people. There is a big emphasis on the noise, dust and traffic caused by the basement construction. The traffic concerns are to be covered in a CTMP (Construction Traffic Management Plan); Croft do not provide this in house but are working closely with several firms who can provide this information. Noise and dust concerns are covered as specific elements within our construction method statement.
The BIA must be reviewed and produced by a Chartered Structural Engineer. Within the practice Croft has both Chartered Civil MICE CEng and Chartered Structural Engineers MIStructE CEng. Their expertise will be employed to ensure the report is correct in its contents.
The service Croft Structural Engineers provides would typically follow:
- Site Inspection
- Meeting with an engineer to discuss the needs of the projects and specific requirements
- Walk over survey to determine what the requirements of the site are
- Review of local trees (not a full arboricultarlist report, but one can be commissioned)
- Review of adjacent buildings where access is available
- Are there signs of subsidence locally
- Soil investigations
- Arranging soil investigation report
- Bore holes to confirm ground and water tables
- Reports by a geotechnical engineer
- Desk Study – This forms the bulk of the BIA and will cover
- Structural Schemes of internal layouts
- Proposed use and loadings
- Retaining wall designs
- Anticipate deflections of retaining walls
- Local Stability
- Highway loadings
- Ensure that the scheme “Maintains Structural Stability of the building & Neighbouring Properties”
- Suggestions for monitoring during the works of neighbouring buildings
- Are there slopes that may slip?
- Are landslides a concern?
- Are there signs of subsidence locally?
- Is network rail of the underground near?
- Are there listed buildings close to the site that may be affected?
- Water Flow and Hydrology
- Review of local water tables
- Will the development affect London’s Main aquifer
- Will drinking water supplies be affected
- Local water course reviewed within 100m
- Are we close to drift deposits – springs are likely to occur near changes in ground from sands to clays
- Flood Risk Assessment
- Review on flooding
- Our reports will be in accordance with Policy CE2
- SUDS: Sustainable Drainage Systems;
- RBKC have provided guidance on when flood risk assessments and SuDS designs should be undertaken. What we have noticed is a shift by planners to ignore the guidance and always request SUDS and RFA’s are produced. We now recommend included both an RFA and a SuDS report within our BIA’s.
To reduce the risk of flooding and allow water to enter the ground water RBKC have requirements that only 50% of a garden area is used as a basement and that 1m is provided as soil. This is a good recommendations as it provide an area for rainwater to soak into and reduces flash run off.
- Loss of Open Space or Trees
- Review of local trees, their location and the affect the basement may have
- Arrange appointment of Arboricultarlist if many or impart trees are to be affected
- Construction Process
- Method statement on how the contractor should approach the work to safely complete the design.
Recently added is the initial temporary design details for the basement.
There are other items that may be required to complete the planning procedure and our BIA will not be the only document. You will need a planning drawings and design and access statement. If buildings are listed or near listed building then a Historic planning consultant may be necessary. On specific sites additional geotechnical advice is necessary to confirm soil movements to adjacent properties. We are here to help with the process where we can and will advise and bring people on board where appropriate.
Recently RBKC have made additional non structural requires for Basement planning submissions. These included;
- Pumped drainage
- Construction impacts such as Noise vibration and dust are kept to acceptable limits
- Construction Traffic Management plans is produced to reduce the risk of harm to other road users and pedestrians.
At Croft we ensure that the requirements of CL7, CE2, CD32 are covered in our Basemen Impact Assessments. With our professional approach we have had great success in producing the BIA’s.