Ground heave occurs when the ground beneath a building moves upwards, i.e. the opposite of subsidence. Heave is caused by the expansion of the ground, and is usually associated with clay soils which swell when they get wet.
Ground heave often occurs when a mature tree near a property is removed or dies. Trees act as powerful pumps, and some species such as willow or oak will take a large amount of ground water out of the sub-soil. Once the tree is removed this water will re-hydrate the sub-soil and cause it to expand. Another possible cause of ground heave is water permeating into the subsoil, such as from a broken drain or culvert carrying a watercourse, or if building works on nearby land interfere with existing ground drainage.
Ground heave can also be caused by frost action, as water expands when it freezes; some types of soil are ‘frost susceptible’ – this tends to be a feature of silty and sandy clays.
Heave can cause significant damage to building foundations and structure. Signs of damage include cracks in brickwork, windows and doors sticking as their frames become out of square, and lifting of paths and patios surrounding a property. Remedying such damage can be an expensive job, and a home may be uninhabitable while work is being carried out – in extreme cases a property may have to be demolished.
A survey will indicate if there are any signs of heave in a property. It may also advise on potential dangers should existing trees be removed. If it is necessary to remove an existing tree, or one dies, expert advice should be sought straight away. Care should also be taken when planting trees near a house; varieties which can grow large and draw up a large volume of water should not be planted too close to an existing building.