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Hard Surfacing and Tree Roots

hard surfacing

Putting new hard surfacing around a tree can be a stumbling block when it comes to a planning application, but with the correct approach, it needn’t trip you up.

Any new hard surfacing is not going to be good news for tree roots. Roots need water, nutrients and air to survive, and a hard surface can act as a barrier to all three. That’s assuming you haven’t removed the roots in the first place, digging down to put in the sub-base.

When planning new paths, patios, driveways and parking bays close to trees, there are three key things to remember:

  • Tree roots don’t grow like the crown – they spread out wide and shallow, a bit like a wide-bottomed wine glass. Roots get what they need most readily close to the surface, which is where most of them grow. Studies show that, in general, 90% of a tree’s roots will be in the top 600mm soil;
  • Trees need enough root area to keep the crown healthy. If you cover too large an area, the crown may start to die back, starved of what it needs from the roots. The relevant British Standard (BS 5837:2012) recommends that within a tree’s rooting area, no more than 20% of the unsurfaced ground should be covered by new paving, even if it is permeable;
  • Tree roots radiate out from the trunk like the branches do above ground, getting smaller and more numerous with distance. Dig a trench a metre long near the outer edge of the roots and you may lose a relatively small area of fine roots. The same trench close to the trunk may lead to the loss of several major roots, and so all of the finer roots beyond – a lot more damaging.

The best approach is to avoid surfacing altogether. If you can’t do that, then:

  • Keep the area small, below 20% of the unsurfaced ground the tree needs;
  • Used reduced-dig construction – essentially build up on top of the ground, rather than dig into it;
  • Don’t put surfacing ay closer than 1 metre from the trunk. As well as reducing the risk of major root loss, you are far less likely to find that roots damage the surfacing as they grow, too; and
  • Use permeable surfacing if possible. This still allows some water, nutrients and air to reach roots below, helping to keep the tree healthy.

We recommend that you seek the advice of a suitably qualified and experienced Arboriculturist when considering paving. They can help you work out what area you can surface and how to go about it correctly, with minimal impact on trees. This should both help you get your planning permission and ensure your trees remain healthy in the future.

Get in touch

If you need help with new surfaces close to trees, or with any development site where trees are a concern, at agb Environmental we have a wealth of experience that can find you a workable solution. Contact Richard Parmee (Head of Natural Environment) on richard@agbenvironmental.co.uk or call 01638 663226 for more information.

Ecology, News