When building near trees you need to consider both how your building may damage roots, and how roots may damage your building. You can’t usually see where they are until you start digging, so how can you plan your development to take roots in to account?
There are many misconceptions about tree roots. Some claim that what you can see above ground is mirrored below ground, whilst others claim roots spread as far as the crown spreads. To get a better picture, think of a tree like a wine glass, with a flat, spreading root system. The spread may go well beyond the crown spread, particularly if the tree is tall and thin, such as a Lombardy poplar.
Studies have shown that 90 percent of a tree’s roots are within the top 60cm of the ground. Tree roots need water, nutrients and air, all of which are more readily available closer to the surface than deep down, which explains why most are so shallow. They can extend for a considerable distance from the trunk – generally the larger the tree, the further roots will spread, extending radially in all directions like the spokes of a wheel.
The Root Protection Area required for development is normally calculated using the trunk diameter. The spread is often circular, but may be much less regular where there are buildings, roads, rivers and changes in level. Where such features may prevent root growth in one area, it can be more extensive elsewhere – you may find roots further from the trunk than you expect.
The influence of roots can extend well beyond the Root Protection Area, which can be an important consideration in preventing subsidence. Trees take water from the soil over a wide area – you need to know how large the area may be and how this may affect the local soil when designing foundations.
Knowing how tree roots may affect the ground conditions on your site, and how the ground conditions may affect tree roots, is important in designing your development to avoid later building damage or tree removals. Having an arboricultural survey before you start developing your site layout can help identify any problems from the outset, potentially saving you both time and money in the future.
Get in touch
To discuss the influence of development on trees, contact Richard Parmee, Principal Consultant on 01638 663226 or email firstname.lastname@example.org. Richard also works closely with our in house geotechnical team who can advise on the impact of tree roots on foundations.