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Basements & Trees

Author: Abi St. Aubyn

The increasing value of properties in London has made the cost of moving up the property ladder nigh on impossible for all but the super-rich. Extensions seem to be the only option left, however, in central London increasing the footprint of your house up or out is not always possible due to strict planning and Conservation Area controls. Therefore ‘down’ is often the most feasible option.

Basement extensions are increasingly controversial due to a number of issues including noise, vibration, change to drainage patterns and the potential damage to party walls, let along the complexities of physically removing spoil from a deep hole at the back of the site out into a street side skip. The impact on trees is another important issue which must be considered. Many of the London Boroughs have specific Basement Policies, with Supplementary Planning Guidance requiring the retention of trees and the provision of at least 1-1.5m depth of soil above basements in order to support future tree growth.

The extent of a proposed basement is therefore often limited by the presence of nearby trees, some of which may not even be within the site. The rooting pattern of trees is complex. It depends on a number of factors such as the species, age, the soil type and any physical obstructions nearby such as the footings for boundary walls, existing basements/vaults and compacted sub-bases for hard surfacing. The standard circular interpretation for a root protection area (British Standard BS 5837:2012) may need to be adjusted to reflect these other factors. In some cases evidence from carefully supervised trial pits can assist in showing clearly whether a tree has roots which are significant to its long term health within the area earmarked for the proposed basement.

It is often possible to achieve basements in proximity to trees, however the complex rooting pattern of the trees on the site must be understood and the impacts on the trees considered from the outset. Full details of the methodology to protect the trees during the construction process forms an integral part of the planning application. At David Archer Associates we provide advice from the outset, through the planning application process to the supervision and monitoring of the arboricultural aspects of the project during construction. Please give us a call if you would like further information or to discuss a particular project.