It is estimated that there are around three billion trees in the UK – that means there are over 45 to each person! They provide shade in summer, add to the beauty of urban and rural landscapes and reduce air pollution. On the other hand, they obstruct light, their leaves block gutters and, in high winds, trees can damage property. More importantly, trees cause cracking, foundation failure and subsidence.
Delegates who attended the latest free CPD seminar in Newton-le-Willows, organised by the regional committee, were informed and entertained by Alistair McLeod from Ascerta Consulting Ltd on the many benefits and problems associated with trees planted near buildings.
Alistair briefly explained the requirements of BS 5837:2012 in relation to tree planting and aftercare, surveys, risk assessment and protection plans. He added that whilst trees can be protected by Tree Preservation Orders, if it can be proved that they have caused damage to buildings by the roots taking out water from the soil, resulting in soil shrinkage (especially in heavy clays), then it is often better to remove the tree. Although 90 per cent of roots are in the top one metre of soil, if the tree remains, even underpinned foundations or root barriers may not completely solve the problem of shrinkage; roots can simply find another path, both under or around them.
Another commonly held assumption is that pruning or crowning trees will reduce root spread and significantly limit damage to buildings. Alistair told delegates that generally this is only a short-term solution – the tree usually recovers after a year or so, and the roots actively spread out in search of water to promote new growth. After five years he estimated that the tree would take up the same amount of water as it had before the intervention.
This seminar demonstrated that, whilst in many cases trees located near buildings will not cause any structural damage, there is guidance available to building engineers setting out sensible tree planting distances. However, this is mainly related to trees growing on shrinkable clay soils and it should be noted that planting distances on other soil types are likely to be different.
31 May 2017