Most buildings would be either useless or of very little value if they could not be adequately lighted and ventilated. Dwelling-houses, offices, and workshops specially require plenty of daylight and fresh air in nearly every part of the interior, in order that they may be cheerful, healthy, and efficient places to live or work in. Therefore anyone who is concerned in designing modern buildings must of necessity give considerable thought and attention to some of the practical problems which may arise when a scheme for lighting or ventilating new premises has to be decided upon.

Often there are collateral circumstances which interfere with the execution of an ideal scheme, and must be taken into account. For example, there may be persons owning neighbouring land or buildings who might have a right to interrupt the free passage of light and air across their property, or perhaps the same or some other neighbours, by virtue of their proprietary rights, may enjoy some easements over the land whereon it is proposed to build, so as to have a right to object to the new buildings, wholly or in part, as an interruption of the enjoyment of their easement.

In such cases it may be necessary to depart more or less widely from an ideal scheme, unless it is found possible to arrive at some agreement with the neighbours concerning those matters about which there appears to be a conflict of rights and interests.

Also, it may be necessary or expedient in many cases to take account of probable or possible future developments or dealings with the property, or separate parts of it.

For example, suppose it is intended to develop a large estate where the proprietary rights of the whole are vested in the same person or group of persons acting as one. In such cases there would be no immediate conflict of interest between the owners of neighbouring plots within the estate (the owner being the same) ; but it would be certainly imprudent for that reason to neglect to take into account the way in which each plot, and the building upon it, or to be afterwards erected, would be affected by the buildings on neighbouring plots. Evidently the ultimate value of the whole property will depend upon the sum of the value of the separate parts, and when the property begins to be broken up by the sale of separate plots or buildings conflicts of interest may immediately arise between the vendors and the vendees of the detached parts, and also between the several vendees.

The means by which conflicts of interest relating to the access and ingress of light and air to buildings may arise between neighbours are really very numerous, and often by no means easy to adjust. In towns, especially in congested neighbourhoods, when anybody wishes to build (whether by way of adding to old buildings or by pulling them down and erecting new ones), the complexity of the problem to be solved may be such that there may be practically no way out of the difficulty short of buying up, if possible, several or all of the surrounding land and buildings, or abandonment of the project.

Much will always depend upon how far neighbouring proprietors are disposed to stand upon their real or supposed rights to light and air, or their disposition and power to legally obstruct the light and air which might be desired or necessary for the proposed new buildings.

No one owning old buildings with what are commonly called "ancient lights" can afford to ignore building operations of his neighbours which seriously affect his lights, or he may lose his rights partially or altogether after an interruption of a year, and his property may then suffer a very heavy fall in value. On the other hand, the possession of " ancient lights " may confer a greatly enhanced value upon any kind of building. Also a careful and watchful preservation of the easement will often confer a considerably increased value upon the site, because if the particular building is pulled down to make way for a better one the easement may be preserved, and new windows in the same positions may be opened in any new building erected on the site without infringing the rights of neighbours.

The same reasons which make it advisable for a proprietor to jealously guard any special rights of light and air which he may enjoy as easements appertaining to his property will induce prudent proprietors generally to be watchful and on guard lest new easements may be acquired for neighbouring properties which may impose new burthens on theirs.

Speaking generally, the acquisition of an easement of light for one tenement is more or less decidedly inimical to the interests of neighbouring properties, so that owners of houses and building sites are scarcely, if at all, less interested in protecting their property from the gradual accrual of new easements, which may impose additional restrictive burdens upon their property, than are the owners of dominant tenements in sustaining the rights of easement already appertaining to their property.

Sometimes the ownership of very insignificant buildings possessing ancient lights will afford opportunities to the owners to put forward most extortionate demands for compensation for obstruction of the lights, or for the purchase of the houses, and great and useful schemes for the improvement of old neighbourhoods may be seriously retarded or financially crippled by the extortionate demands made. Courts of Equity will not regard with favour any attempts at extortion by this or other means, but law suits may be costly and last long, and doubt or delay may be very injurious to the people concerned with building, so that in a large proportion of cases extortionate demands are paid right and left to clear away opposition and facilitate rapid progress.

So far as possible people concerned with building schemes should make arrangements in good time to secure freedom from opposition or extortion when work is in progress.

The builder, or those persons who are directing building operations, should especially take care so to arrange matters in advance, if possible, as not to be liable to be blackmailed by people who, by standing upon their real or alleged rights, might be able seriously to obstruct progress, and to demand a big price for ceasing to be obnoxious and obstructive.

On the other hand, while a builder should be careful to counteract the designs of blackmailing property owners, who would take the utmost advantage of his necessities to extort money if opportunity offered, he must also be careful to respect the honest claims of those who have rights which they use and enjoy. He should not so act as to confer fictitious fanciful values on property intrinsically of little value ; while he must not, on the other hand, invade the rights of people whose property might be seriously injured in value by obstruction of lights really useful to them for health, comfort, or business purposes.

A builder or architect is not generally so much concerned about other people's air as he may be about their lights.

He should look after the efficient ventilation of his own buildings. He should see that the inlets and outlets for his ventilation are in convenient places where they are not liable to be easily obstructed, or the incoming air to be easily contaminated with objectionable matter.

Concerning the neighbours, he is not in an ordinary way very likely to block their ventilating inlets or outlets, especially if these are in or near the walls of the neighbouring houses, and on the neighbours' own lands. Air, unlike light, can travel round corners, and by all kinds of routes towards a hole in the wall ; and nothing short of building quite close up to a wall will ordinarily stop access of air in such fashion as to afford a good ground of action.

It is to be understood that a natural right to sufficient air does not include a right to a breeze in any particular direction towards the building, so as to prevent a neighbour from obstructing breezes by building on his land.

Cases like the Nottingham cellar ventilation case, referred to in Chapter V (Air)., where the ventilating outlet is on a neighbour's land, are not common. All necessary provisions for ventilation are ordinarily made upon or in immediate association with the premises to be ventilated, so that without trespassing it is nearly impossible for a neighbour to stop access of air.

Concerning pollution of air, as a general rule a man cannot pollute air to the injury of his neighbours and their property without also injuring himself and his property to a like or generally to a greater extent; and when buildings for habitation are in question everybody is interested in having the air as sweet and pure as circumstances permit, and owners or occupiers are not likely to attempt to set up or to acquire easements to make offensive smells, or otherwise to poison or pollute the air. Sanitary inspectors or neighbours would soon take effective steps to stop nuisances of this kind if any attempt were made to perpetuate them by frequent repetition.

In practice the only people likely to be permitted to pollute air in a wholesale way, and as a regular habit, are public bodies of various kinds, and factory owners carrying on trades and manufactures which from their very nature must be more or less offensive to neighbours. Such trades and manufactures as are dangerous to life and health are generally subject to official inspection and regulation, and the proprietors may be compelled to carry on their operations in ways which are least objectionable, so that altogether there is a tendency in modern days towards increased purity of atmosphere nearly everywhere rather than the reverse. There are still places where large quantities of more or less acrid fumes and smoke and smells escape into the atmosphere, and many of the places from which the nuisances originate have acquired easement rights by long uninterrupted use and enjoyment; but pressure of various kinds can be and often is brought to bear upon the owners and occupiers of buildings where these obnoxious and dangerous trades are carried on to confine their rights of pollution to the narrowest limits consistent with the successful carrying on of those trades.