Rights of support for buildings are in some ways much more obscure, uncertain, and intricate when they come to be dealt with in practice than the natural rights or easements affecting light or air. Support is a statical resistance to displacement under the influence of gravity. It is not a form of motion appreciable by a special sense like light, nor a gaseous substance which spreads in all directions like air, but a steady resistance to change of position.

Most buildings depend for their support upon the ground below and immediately around their base. It is part of the ordinary business of a builder, under the direction of his architect, to take care that the buildings to be erected by him shall rest on sound foundations, which are laid with reference to the estimated qualities of the earth and rocks beneath the surface. If the foundations are not sound or adequate for the support of the building, and damage results, the blame must naturally fall on those persons who are responsible for the bad design or construction.

When valuable buildings are to be erected, efforts are generally made to render the foundations so secure as to leave a large margin of safety for their support. At the best it is often impossible to say with any exactitude what the margin of safety actually is to begin with, or how that margin may be affected by natural or accidental causes as time goes on. Anything which tends to diminish the margin of safety will, pro tanto, jeopardise the safety of the building, and therefore deserves the attention of the owner, architect, and builder.

It is essentially their business to look after the safety of the building, and to provide adequate support for it on the land of the owner, and they should not look to neighbours to provide any part of the support for the building unless some definite special business arrangement is made in this connection. Ordinarily a neighbour has no sort of responsibility or duty in connection with the upholding of his neighbour's newly built house, and as the law now stands he will not incur any responsibility until the house has stood for twenty years, except under such special considerations as are explained in Chapter VI (Hospitals On Open Sites).

Complications are apt to arise when people mine or burrow under the foundations, or excavate friable earth from pits or hollows not very far away from the foundations.

In such cases the margin of safety for the support of the building may be taken away, and more or less serious injury may result. Such cases may present very difficult and delicate problems to deal with, because if the person mining, burrowing, or excavating has prima facie a right to do these things he cannot be held to have exceeded his right until he had actually caused a failure of support, and not always even then, so that the householder may be in the awkward and unpleasant position of knowing that the earth support for his foundations is being weakened, possibly to a dangerous extent for the security of the house in which he lives, and yet not be able to take any really effective steps to avoid the risk.

The ordinary procedure by petition for injunction which is applicable to light and other cases where injury is threatened cannot be evoked in the majority of such cases, because of the generally obscure character of the facts to be dealt with. A man cannot be restrained by injunction from what he is entitled to do as a matter of right because it is possible that he may at some time go beyond his right ; and prima facie, if he has a right to excavate at all, he has a right to go on digging up to the actual point where support for the neighbouring building begins to fail, when he may become liable for damages if the owner of the building has an easement right binding upon his tenement and therefore also upon him. Some of the intricacies and peculiarities of the law relating to support are explained in Chapter VI (Hospitals On Open Sites). The most important practical lessons to be learnt from a study of the law relating to support would seem to be - (1) That every one who wishes to build a heavy or valuable house should ascertain as fully as possible the state of the subjacent earth as regards its solidity of substance and freedom from cavities at any depth. (2) He should be satisfied that sound foundations can be laid, and that nobody else has a right to burrow or dig in the immediate neighbourhood of his foundation, or at such a distance (if the earth is unsound) that support may be withdrawn from the neighbourhood of his foundations by draining or excavation. (3) If the conditions just referred to are unfavourable, some means of protection and safety may be provided by arrangements with the owners of neighbouring tenements.

In some coal-mining districts large tracts of land have been undermined in such manner that where the surface has not already subsided it is liable to do so. In London and some other large towns and cities underground tubes and tunnels are from time to time constructed under the authority of Acts of Parliament by authorised private companies or municipalities.

When these burrowings are effected extreme precautions are commonly taken to safeguard the tubes or channels from any danger of collapse from vertical or lateral pressure, and the same structural arrangements which fortify an underground tube against collapse make it yield strong rigid resistance in the shape of support for ground and houses above. A considerable proportion of the multitudinous operations which are continually being carried out in towns and cities have a natural tendency to affect the foundations, and thus the ultimate stability, of houses, and even the passage of heavy steam rollers along the streets cannot fail to have some effect. Often when small injuries are inflicted nothing is seen or otherwise made evident, and when at last something obviously gives way under circumstances which indicate failure of support, it may be next to impossible to prove conclusively that the result is due to any one particular cause to the exclusion of others, or that any particular person is responsible.