Building Foundations and Tree Roots

Trees can be found in almost every example of the built environment. As well as being aesthetically pleasing, they absorb CO2 emissions, produce oxygen, and provide habitat for urban wildlife. Trees and buildings go together, but occasionally there is an issue with building foundations near tree roots. Problems can arise when either a tree and its root structure have grown larger than might have been planned for, or new building work is planned in the vicinity of existing trees.

What damage can tree roots cause?

There are two types of damage that tree roots can cause, direct and indirect.

Direct damage is caused by the roots themselves exerting force on the building as they grow. If the force of the roots is greater than the resisting force of the building, damage will occur. Tree roots are lazy and will follow the easiest path to find water, meaning the roots will usually divert course rather than trying to fight existing building work. Direct damage can be caused to walls, where foundations are likely to be structurally weaker, or in drains, where broken pipework has allowed the tree roots to seek out an abundant supply of water. Tree roots will grow to take advantage and subsequent drain damage is not uncommon.

Indirect damage

The second type of damage is caused by the removal of water, as the tree roots draw moisture from the ground. Excessive moisture draw, for example in times of drought, can cause the soil to shrink in volume. This is known as subsidence, and is a significant problem for buildings. Subsidence occurs often when you have a moisture rich clay-based soil.

Indirect damage and dealing with subsidence

Subsidence can be complex and costly to deal with. It is not as simple as removing a tree suspected of causing the subsidence. Tree removal, with the subsequent root death, can exacerbate the problem. Additionally, many older and established trees may be subject to a tree preservation order. If damage to the building has already occurred, structural underpinning work may be required, providing additional support for the building’s foundations. To help avoid subsidence, pruning the tree and reducing the canopy is often done proactively, as it lessens the moisture draw of the tree root system, which reduces the risk of subsidence occurring in the first place.

What is a tree preservation order (TPO)?

A tree preservation order is defined by the government as

“An order made by a local planning authority in England to protect specific trees, groups of trees or woodlands in the interests of amenity. An Order prohibits the:

  • cutting down
  • topping
  • lopping
  • uprooting
  • wilful damage
  • wilful destruction

of trees without the local planning authority’s written consent.”

Your local authority will be able to assist you in identifying whether a tree is subject to a TPO. Where damage to property is an issue and a tree needs to remove, there is often a requirement to replant an appropriate replacement. Failure to comply with a TPO can result in fines up to £20,000.

What is a root protection area (RPA)?

In addition to tree protection orders, there is also planning consideration for the root structures of trees. Root Protection Areas are commonly used in the planning process where existing trees are being retained within the development area. It is designed both to protect trees and to help avoid future issues from direct and indirect root damage to building foundations. The RPA is calculated using the diameter of the trunk at a height 1.5m above ground level. For trees with a single stem, the RPA is calculated as an area equivalent to a circle with a radius 12 times the stem diameter. This is based on the minimum area around a tree deemed to contain sufficient roots to ensure the tree’s viability and health.

All UK planning applications take trees into account and RPA rules apply to both new building projects as well as extension and alteration work.

What to do if you suspect an issue with tree roots?

The key to minimising the problem of tree roots and building foundations is to act quickly before serious damage is caused. It is also important to plan ahead, either when planting new trees or considering new building work in the vicinity of existing trees.

One of our specialist team will be able to help determine the scale of any problem and the most effective solution. Give us a ring on 01380 850885 to see how we can be of assistance.