One of the main causes of structural movement is clay related subsidence. As indicated above, one of the contributing factors in this type of subsidence, is the presence of trees/hedges close to buildings. The roots suck up large volumes of water, thereby drying out the clay sub-soil, causing it to shrink in volume. The amount of water sucked up by the roots will depend on the type of trees/hedges, their age/size and proximity to the building. Generally broad leaved deciduous trees suck up more water than coniferous trees. Oak, Poplar and Willow trees are particularly thirsty. Young trees/hedges will require less water than older more mature trees/hedges. However, even small trees/hedges, if not regularly pruned/managed, will eventually grow and could cause future problems. The proximity of the tree/hedge to the building will determine whether or not the roots are likely to be within influencing distance of the buildings foundations. As a general rule, the tree/hedge roots will spread a horizontal distance of approximately one and a half times the vertical height of the tree/hedge. Apart from contributing to subsidence in clay sub-soils, trees/hedges can also reduce daylight entering a building, while full or partial collapse of large trees in high winds can cause structural damage. Finally tree/hedge roots can interfere with drainage pipes and other underground services. Problems often occur where trees/hedges growing on neighbouring land are suspected of causing damage. Consultation with the adjoining owner/occupant will be essential in order to agree a strategy. Once alerted of the possible risks posed by trees/hedges growing on their land, failure of the land owner to act in a reasonable and timely manner, could result in their being liable for any damage later caused by their inaction (under the law of private nuisance).
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