Following a dry winter the insurance industry is again concerned about building subsidence and settlement. Tree roots are often cited as one of the causes of soil shrinkage as they take moisture out of the soil.
Clay soil is known to suffer cracking during prolonged periods without adequate rainfall.
Tree roots can also undermine a buildings foundations if planted too close to a property.

Safe Planting Distances by Species

• Yew and most shrubs 15 feet
• Spruce 22 feet
• Rowan, Birch and Hawthorne 35 feet
• Beech and Sycamore 50 feet
• Lime, Ash and Horse Chestnut 65 feet
• Oak 70 feet
• Poplar and Willow 120 feet
• Note the diameter of root spread is generally about half these distances.

Tips and Comments about Tree Roots

• Typically tree roots are relatively shallow but wide spread. Soil conditions create wide variations in root distribution.
• 90% of tree roots are found in the top 2 feet of soil and seldom go deeper than 6 feet.
• Local authorities can make a tree preservation order to prohibit felling, topping, lopping or up-rooting of listed trees. Similar constraints apply to trees in Conservation Areas.
• Your neighbour can chop the roots of your tree along the boundary line and does not need your permission.
• Root barriers can be used when planting new trees but it is better to select a smaller or less vigorous specimen.
• Lopping and pollarding may reduce further root spread and limit transpiration and thus water loss.
• Much advice says be circumspect about removing a specimen that is presumed to be causing a problem. The distances above are insurance company figures and may be belt and braces.

Tree Root Designs

• Taproot systems: where a strong main root descends vertically from the underside of the trunk. Examples include English oak, Scots pine and silver fir.
• Heart root systems: where both large and smaller roots descend diagonally from the trunk. Examples include birch, beech, larch, lime and Norway maple.
• Surface root systems: where large, horizontal, lateral roots extend just below the soil surface, from which small roots branch down vertically. Examples include ash, aspen, Norway spruce and white pine.

Credits
Banyan Tree Roots Black and White by Photomatt28 CC BY-NC-ND 2.0
IMG_0354 by Fun with Fred CC BY-NC-SA 2.0
Tree roots, shack, Kathmandu, Nepal by Wonderlane CC BY 2.0
Forestry Commission for root systems