Westminster Basement Construction Method Statement

Westminster Structural Methodology Statement

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. Westminster Council requires that, at the Planning stage, all basement construction complies with their City Management Plant Development Plan Document (DPD).

Westminster recently updated their requirements for planning submissions for new basements. Basement designs will be expected to:

incorporate principles of sustainable design, having regard to the London Plan policies including Sustainable Design and Construction (5.3), Retrofitting (5.4), Overheating and Cooling (5.9) and Westminster’s City Plan Strategic Policy S28 (Design).

Westminster Council requires that a Structural Methodology Statement (SMS) be prepared as part of the planning application. This document includes but is not limited to:

  • A thorough desk study to include the site history, age of the property, site survey, geology, historic river courses and underground infrastructure, including utilities services, drains and tunnels. This should also identify other basement developments in the area, so that cumulative effects can be considered.
  • An appraisal of the existing structure including drawings to show the arrangement of the existing structures. The appraisal should identify previous alterations and any obvious defects. It should also assess the condition and location of the building with adjoining buildings. This should include opening up works to investigate the existing structure, which should be summarised on a set of drawings.
  • A site investigation which can be demonstrated to be relevant to the site together with trial pits to show the existing foundations and the material they are founded on, for all walls which may be impacted by the proposals. If groundwater is present, the levels should be monitored for a period of time.
  • Details of the engineering design which should be advanced to detailed proposals stage. Relevant drawings should be provided to show how the designers have addressed the following:
    • ground conditions and groundwater
    • existing trees and infrastructure
    • drainage
    • flooding
    • vertical and horizontal loading
    • structural engineering general arrangement and details; drawing showing underpinning, piled wall etc.
  • An analysis of the Upper Aquifer (when it exists) and how the basement may impact on any groundwater flow.
  • Details of flood risk, surface water flooding, critical drainage areas explaining how these are addressed in the design. A full flood risk assessment will be required in some areas.
  • An assessment of movements expected and how these will affect adjoining or adjacent properties. This needs to include both short term and long term effects. The design and construction should aim to limit damage to all buildings to a maximum of Category 2 as set out in CIRIA Report 580.
  • Details of sequences of construction and temporary propping to demonstrate how the basement can be built to prevent movements exceeding those predicted. It should show how the horizontal and vertical loads are supported and balanced at all stages of construction and consider the interaction between permanent works and temporary works.

Westminster Council also requires the construction stage impacts to be addressed at planning stage: the construction of basements should be in accordance with Westminster City Plan Strategic Policies S29 (Health and Well-being), S31 (Air Quality)and S32 (Noise), which seek to maintain or improve residential amenity of neighbouring residents and minimise noise and air pollution.

A Construction Management Plan is currently required with planning applications for a basement development. This should be site-specific and include sufficient information to demonstrate that the relevant guidance is followed.

The City of Westminster council require that the Structural Statement is prepared and signed off by a Chartered Civil Engineer (MICE) or Structural Engineer (MIStructE). Our engineers at Croft have the qualifications for this requirement: we can assist you in the first step, and beyond, of turning your basement proposal from a concept into a physical reality!