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Basement developments

We have prepared a Good Practice Guide on Basement Developments(pdf, 862KB), which provides advice on both planning as well as non-planning matters. It also covers permits and requirements, and local amenity, construction and design issues.

A Basement Assessment User Guide (2021) (pdf, 230 KB) has also been produced which provides advice where proposals include a basement, cellar, or other subsurface structure. It is designed to guide users through the Basement Assessment process and ensure that the correct supporting information is submitted with a planning application.

Permits and requirements

Basement developments have to comply with a wide range of legislation and different permissions can be required:

Local amenity and construction issues

Excavation and construction of a basement needs to be carefully planned and co-ordinated to avoid problems such as highway/parking impacts, noise, dust, vibration and disturbance to neighbours. For this reason, all basement developments in the borough are required to prepare and submit a Construction Management Statement. See the Local Validation Checklist for further information on its required contents. Developers of basements are also expected to sign up to a Considerate Construction Scheme.

Design issues

The following are common design issues that should be considered when proposing basement works:


Just as overly large extensions above ground level can dominate a building, an extension below ground can be of an inappropriate scale.

Trees and root protection

The presence of trees and tree roots is an additional factor that may mean proposals for new or expanded basements may be over-development, including street trees and trees on or adjoining the site, and their required root protection zone.

Garden and biodiversity

Proposals for basement development that take up more than half the front and/or half the rear garden of a property may not be accepted.

Rainwater and sustainable drainage systems

A basement development should provide an appropriate proportion of planted material to allow for rainwater to be absorbed.

Basements as living accommodation

The Local Plan, the Residential Development Standards SPD and the London Plan seek to ensure high quality housing and neighbourhoods with a good standard of sunlight, daylight, outlook and privacy.

Further information

Up to: Planning

Updated: 07 October 2022

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