Building near trees

Most trees growing near our buildings cause no significant damage. However, there are instances where combination of shrinkable soils and trees could be viewed as a hazard to a building structure. Trees, hedgerows and various shrubs extract moisture from the ground and, in soils with volume change potential such as Clay, this can result in movement.

What damage can trees cause to our property?

Trees affect building in many ways:

  • Structural damage caused by subsidence: this is generally a problem on shrinkable Clay soils, especially for buildings which have shallow foundations. Clay subsoil shrinks and expands in volume due to changes in the soil moisture content. Even where this is within normal limits, it will cause the building to lift slightly during wet weather and sink slightly when it is dry. Ground movement has the potential to affect foundations and damage the supported structure.
  • Drain damage: tree roots can penetrate drainage system by ingression into the pipes that can cause blockages. Roots can also put pressure and strain on the pipe lining causing escape of water or sewer spillage. The escape of water could cause the underlying soil to soften, giving it reduced ability to support weight of the property, and causing the foundations to subside.
  • Physical damage: tree roots can lift paving, lightweight structures such as garages or sheds, and create a tripping hazards. Also, tree branches can cause damage to roofs and guttering.

Different trees have different water demands which translate into radius of influence. Therefore, it is imperative to not only consider tree presence on our plot but also on adjacent sites. In order to avoid damage to building foundations, it is advisable to consult an experienced and qualified professional like our structural engineer Croydon. We thoroughly check type of trees present on your building plot, outline respective radius of influence on our drawing documentation, and specify adequate foundation system.

Rules and regulations around building near trees

Chapter 4.2 of the NHBC standards covers guidance on building near trees. This chapter focuses on how footings are affected by trees when they are founded on cohesive soils. It also covers areas like heave precautions and drainage protection. If you are unsure how to best protect your new foundations next to tree, please rest assured that GL Design Services are here to help. As a chartered engineers we are happy to help out with foundation design near trees and specify minimum embedment depth considering the type of tree and its water demands, location and distance for the proposed footings and plasticity index of the soil.

What is a Root Protection Area (RPA)?

The Root Protection Area (RPA) is defined in BS 5837. It is a minimum area around the bottom of a tree that would support and provide enough volume for the tree rooting system to grow successfully. Based on Arboricultural Method Statement, a qualified structural engineer will be able to specify the right type of foundations taking into account root protection zone and soil volume change potential.

What is a Tree Preservation Order (TPO)?

TPO is an order made by a Local Planning Authority in England to protect specific trees, groups of trees or woodlands with the aim of protecting them. This is a legal protection enforcement which makes it an offence to cut down, uproot, wilfully damage or wilfully destroy a tree without the Council’s consent. Owners of protected tree, hedge, bush or shrub must not carry out or cause or permit the carrying out of, any of the prohibited activities without the written consent of the local authority.

Carrying out works to a TPO tree without the relevant consent is an offence and can end up the landowner being fined. It is a criminal offence and, if convicted, a magistrate’s court can impose a fine of up to £20,000. In serious cases a person may have to go to the Crown Court and be liable to an unlimited fine.

Trees in Conservation Areas

Trees in Conservation Area (TREES) refers to an area of special architecture and historic interest where threes are given special protection by the local planning authorities. All trees in conservation area are protected by TPH. Therefore, before any works can be carried out on protected trees you must apply to your Local Planning Authority (LPA) and follow the relevant rules and restrictions this sets out. LPA has usually six weeks to consider the proposal and respond. Planning works cannot proceed until LPA has responded or six weeks period has passed.