This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol3", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
The right of support is a natural right possessed by the owner or occupier of land that the surface level of his land shall not be disturbed by the removal of means of support either laterally or vertically, either adjacent or subjacent.
This natural right to support is absolute and unlimited, and without consent, actual or implied, the owner of land cannot be deprived of that right, and he has prima facie a right of action against any one by whom the support to which his land is entitled is taken away ; but the right is not infringed until such time as injury results from removal of support.
It is actual interference with the ordinary enjoyment of land which affords the ground of action, and not particular acts which may conduce towards the interruption of enjoyment. The owners of neighbouring tenements, when dealing with their own property, are prima facie entitled to deal with it as they like, and they are under no legal obligation to leave or to substitute support in any particular form.
The obligation only extends either to the leaving sufficient natural support in situ, or to the substitution of other sufficient support in place of the whole or part removed, so as to prevent subsidence of a neighbouring tenement. Until that tenement is injuriously affected it cannot ordinarily be said that the amount of support left or substituted is insufficient. It may be observed that, whatever may be the nature of the soil, the ordinary obligation not to excavate or undermine or otherwise deal with the land of one tenement so as to cause subsidence of the land of a neighbouring tenement remains the same. If a man has a proprietary right to the minerals below the surface of his neighbour's land, and if he cannot find means to get at those minerals without causing the surface land to sink, he must leave the minerals where they are. If, on the other hand, the rocks are so hard and so arranged in the earth that he can take all the minerals away without interference with his neighbour's surface, he may do so. Between these extreme cases there are many others where the conditions are such as to admit of the gradual excavation of minerals or subjacent rocks, and the steady substitution of efficient artificial for natural support. Sometimes the support left is partly artificial and partly natural. It is sufficient if by one means or another, or by different means in association, the surface is adequately supported.
The same principles which apply to any kind of mining or burrowing beneath the surface of a neighbour's land apply to all cases of excavation or burrowing anywhere in the neighbourhood of land, which may possibly be caused to sink as a consequence. The person excavating should take efficient precautions to safeguard his neighbour's land from being made to subside as a result of the excavation, or he should abstain from excavation whenever there appears to be evident consequential danger to his neighbour's property. There is, however, one class of cases which form an exception to the general rule against removal of support. When land is heavily charged with water the surface may owe much of the natural support which keeps it in place to the water filling all interstices in the rocks below. For example, old mines may be filled with water, or spongy rocks may be saturated, and it is easily conceivable (as has, in fact, happened in some reported cases) that removal of the water by drainage may so weaken support as to cause subsidence at the surface. Nevertheless, neighbours cannot be held responsible for damage caused by removal of support as a consequence of the drainage of their land, nor for pumping large volumes of water from their own wells. The general rule would seem to be that, what a surface owner is prima facie entitled to is such solid support as naturally exists under or around the margins of his land, which his neighbours, in the exercise of their several proprietary rights, must not diminish to such an extent in any place or any direction as to cause subsidence of the surface ; or if they wish to do acts which will have the effect of weakening support to a dangerous extent, they must replace the support taken away by efficient substitutes.
A landowner is no doubt entitled to enjoy support from subjacent water while he has it, but he is not entitled to claim that neighbouring owners shall abstain from dealing as they please with water which they find on or under their lands, only because the quantity of water either on, in, or under his land may be diminished in consequence, and surface support thereby weakened.
There is, however, an apparent exception to the general exception in the matter of support by subjacent water. Although there is no general right to claim support of surface land by subjacent water, there is a right of water support for a surface canal or stream. Owners of land in the neighbourhood of a surface stream must not drain off the underground water if the effect is to lower the surface of the upper stream.
Evidently, if it were allowable to draw water under such conditions as to cause a subsidence in the level of a stream, while passing over the land of a neighbour, the effect would be equivalent to a tapping of the stream, and a part at least, if not the whole, of the water drained away might fairly be taken to be the stream water travelling by underground channels. Also in many cases, if such drainage were to be attempted, the underground currents of water, which would tend to become established would undermine the surface land, and carry away more or less considerable quantities of solid particles derived from subterraneous erosion, so that sooner or later solid support for the surface land would be so far weakened that the surface would fall in. The water rights of riparian owners of the stream might also be more or less seriously invaded or threatened if subterranean drainage of the kind indicated were to be practised.