Most trees growing near buildings will not cause a problem. There are many trees that have been growing near buildings for years so it would be wrong to assume that all trees growing close to buildings will cause damage. Factors such as the height of the hedge, soil type and the extent of the foundations of a property will determine whether roots will cause damage.
Many factors, both of the site and tree, can affect root spread. Roots grow in proportion to the height of the hedge. If a Leylandii hedge is kept to a reasonable height 2-3m (6-10ft) then the root system will be much less substantial (and much less likely to cause damage) than if the trees are left to grow to 10m (30ft). Roots often extend for a radius wider than the hedge height.
Structural damage is generally limited to properties on shrinkable clay soils. Trees taking moisture out of these soils can cause soil shrinkage and this can result in subsidence. Conversely removing large trees from clay soils can cause the ground to swell, again leading to structural displacement.
Buildings built before the 1950s are most at risk, as they frequently have foundations only 50cm (20in) deep.
Drain damage - roots may block drains, which burst as a result. This can lead to the formation of cavities as the water from the drain flows into the soil. In general, roots will not break into drains but will enter existing cracks and poorly sealed joints. Older drains with poor seals and rigid joints are most susceptible.