The Property Rights of Airspace
In property law, owning land includes owning the earth under the surface and air above the surface. While ownership under the surface theoretically extends to the center of the earth, ownership of the air above the surface doesn’t extend endlessly into space.
Defining boundaries in the air
A landowner owns as much of the air above the surface as she can reasonably use in connection with the surface. That isn’t a clear line, obviously. Land wouldn’t be useable at all if one didn’t own some of the air above the surface; almost any use of the land requires using some airspace above the surface.
Certainly building any kind of structure on the surface occupies airspace. Because you have the right to reasonably use your land as long as you don’t unreasonably interfere with others doing the same, you have the right to reasonably use both the surface and the air above it unless you thereby interfere with someone else’s use of property.
So even though you may occupy only 20 feet of the air for a long time, under the common law principle, you can later decide to build a 200-foot building unless it would be a nuisance.
Although the upper limit of an owner’s airspace isn’t clearly defined, it certainly doesn’t extend into navigable airspace. The upper airspace belongs to the public and is open to air travel.
Using and protecting airspace
Ownership of airspace is just like ownership of land. The owner can use and enjoy it reasonably. Zoning and other statutes often restrict the height of buildings. Such statutes don’t actually declare the unused airspace to belong to the public, however; they merely restrain the owner’s use of that space. So landowners may own more airspace than the law allows them to use.
Not only can the landowner use and enjoy the airspace, but she can also convey it to others. For example, a condominium may divide up airspace among individual unit owners. An owner can also give another party, such as a utility company, an easement to use some of the airspace.
An entry into another’s airspace is a trespass even if the trespasser doesn’t touch the surface of the earth. Airplanes may trespass by flying low over a person’s property, for example. An airplane trespasses by flying low enough over the surface to interfere with the owner’s reasonable use and enjoyment of her surface.
Of course, if the airplane doesn’t fly over a person’s surface, just nearby, the airplane’s interference with the surface because of noise and light wouldn’t be a trespass — but it could be a nuisance. And if the government’s flying the plane, the landowner could only seek just compensation for the government taking an easement through her airspace.