Basement planning package
The engineering reports needed for a basement planning application.
About this package
The basement planning package brings together the engineering reports many London councils expect with a basement planning application. It includes a Basement Impact Assessment, a structural method statement explaining how the basement will be built, and a ground movement assessment predicting the effects on neighbouring buildings. One fixed fee covers all three, prepared together so that they are consistent with each other.
It suits homeowners planning a new basement or lowering an existing cellar, architects preparing the application, and small developers adding lower-ground accommodation. It is especially useful in boroughs with detailed basement policies, such as Camden, Westminster and Kensington and Chelsea, where councils examine these reports closely and an inconsistent submission can lead to delays or repeated requests for more information.
These reports are closely linked. The method statement sets out the construction sequence, the ground movement assessment depends on that sequence, and the impact assessment draws on both alongside the groundwater and drainage picture. Prepared separately, they can contradict each other. Prepared together, they give planning officers and neighbours' surveyors a single, coherent account of how the basement will be built safely.
What the package brings together
- Basement Impact Assessment
- Structural method statement
- Ground movement assessment
Stages
- Basement Impact AssessmentWe screen and assess the basement's effects on ground stability, groundwater, surface water and drainage, and on neighbouring buildings, in line with the council's basement policy and the information available for the site.
- Structural method statementWe explain how the basement will be designed and built: the underpinning or retaining wall approach, temporary works, the sequence of excavation, and how the existing house and neighbours will be supported throughout.
- Ground movement assessmentWe predict the ground movement from excavation and construction and the likely damage category for neighbouring buildings, so the council and adjoining owners can see that the risk is understood and controlled.
Who it suits
- New basements under terraced houses
- Lowering an existing cellar floor
- Lower-ground extensions into the rear garden
- Applications in boroughs with basement policies
- Architects needing consistent engineering reports
How it works
Frequently asked questions
Does every council require a Basement Impact Assessment?
No, but many inner London councils do for most basement applications, and others ask for some form of structural and ground assessment. Requirements differ by borough and site, for example where there are trees, slopes or watercourses nearby. Your council's planning policies and validation checklist will confirm what is needed. Our basement guide gives an overview.
Will I need a ground investigation?
Usually, yes. A basement assessment relies on knowing the soil type, groundwater level and the depth of neighbouring foundations, and some councils require site-specific investigation as part of it. Our ground investigation and factual report provides that information, and the earlier it is done, the more reliable the planning reports will be.
Is the structural method statement the same as the final design?
No. The method statement explains the approach and sequence in enough detail for planning and party wall purposes. The detailed structural design, with calculations and construction drawings, follows once planning is granted and is needed for Building Control and for the builder. The method statement sets the framework that the detailed design then follows.
What damage category is acceptable to councils?
Councils with basement policies generally expect predicted damage to neighbouring buildings to be no worse than very slight, which typically means fine cracks that are easily treated during normal decoration. The exact threshold is set by each council's policy. The ground movement assessment shows the predicted category, and the design is adjusted if needed to bring it within the limit.