Image of subsidence. Brick wall with a crack running vertically across it

Don’t Crack Up: All About Subsidence

What is subsidence?

Subsidence is the downward movement (shrinkage) of the ground on which a building is supported.

Causes:

• Sub Soil – clay soils shrink as the moisture level decreases for example over periods of drought.
• Trees and shrubs – massive quantities of water are absorbed from the ground by the roots of trees and large shrubs causing shrinkage of the soil. Damage is also caused by the roots themselves as they extend further attempting to find water during dry periods. Trees can also seek water from drains causing damage to the underground service pipes due to tree root intrusion
• Damaged drains – this is a particular problem in older buildings, the water from leaking pipework can wash away soil under foundations.
• Location – some properties have been built over mines or land fills.

Other forms of ground movement:

• Heave – The movement of land in an upwards direction caused by the removal of trees and large shrubs or the swelling of saturated soil.
• Landslip/slide – The movement of land down an incline caused by excessive rainfall on already saturated ground or coastal erosion.

What can be done to avoid subsidence?

• Try to avoid planting trees or shrubs close to any buildings or main drains not only on your own property but neighbouring properties.
• Regularly maintain your property checking for blocked or leaking drains and clearing leaves from gutters.
• Have your trees and shrubs pruned, by restricting the leaf growth you restrict the spread of the roots and the absorption of moisture from the ground.
• When paving a large area, ensure that it is permeable so that water can penetrate through the hard surface into the ground below. If water sits or goes straight to the drainage system, nearby trees and shrub’s roots will continue to extend their search for water and cause drying out of the ground.
• If there is already a substantial tree near a building or public highway, you should consider having it professionally surveyed every 3 years to assess its health and to determine whether any pruning or felling is required. Keep these reports in a safe place, as they may be required in the event of a claim.

Did you know?

• Most trees cause no damage.
• Tree roots spread up to three times the height of the tree.
• Properties built after 1980 usually have deeper foundations and are therefore less likely to be affected.
• London clay is worst soil for subsidence issues, especially during periods of drought
• A tree is the property and responsibility of the land owner, who may be liable for any damage caused to a third party.
• Before you carry out work on a tree you should check with the Local Planning Authority as to whether a Tree Preservation Order is in place.

Are your trees too close?

  • Tree Species

  • Apple/pear
  • Ash
  • Beach
  • Birch
  • Cypress
  • Cherry
  • Damson
  • Elm
  • Hawthorn
  • Holly
  • Horse Chestnut
  • Laburnum
  • Laurel
  • Magnolia
  • Maple
  • Oak
  • Pine
  • Plum
  • Poplar
  • Sycamore
  • Spruce
  • Walnut
  • White Beam/Mountain Ash/Rowan
  • Willow
  • Yew
  • Safe Distance in Metres*

  • 10
  • 21
  • 15
  • 17
  • 20
  • 11
  • 11
  • 30
  • 12
  • 1
  • 23
  • 9
  • 6
  • 5
  • 20
  • 30
  • 8
  • 11
  • 35
  • 17
  • 7
  • 14
  • 11
  • 40
  • 5

*Estimated safe distance from property in metres

As opinions differ slightly dependant upon whom you speak to (insurers/loss adjusters, horticultural societies, nursery suppliers or arborists), this table is for general information only. Brownhill Insurance Group Ltd does not accept liability in relation to its use

What signs you should look out for.

• Diagonal cracks in plasterwork and brickwork.
• Usually with a thickness of a £1 coin (3mm).
• Doors and windows sticking.
• Sloping floor; try placing a ping pong ball or a coin on it’s edge on the floor and see if it rolls.

What to do if you suspect your property is suffering from subsidence.

Contact your insurance provider, if it is confirmed that your policy covers subsidence, they will organise a qualified surveyor to assess the situation and find the cause of the problem.

If subsidence is confirmed (as apposed to general wear and tear and/ or natural/historic movement which is not an insured peril) the cause of the subsidence will then be eliminated followed by a period of monitoring. Once the subsidence has been stabilised the necessary repair work can be carried out.

Further reading:

Valuing London’s Urban Forest
Geology of Britain Viewer
Tree Preservation Order