Trespass and Nuisnace
The common law tort of trespass is often misunderstood, often to the defendant's detriment, and plaintiff's benefit, for one simple reason: the requirement of knowledge, or rather, lack of knowledge.
Trespass is defined as the intentional entry upon land in possession of another without consent. There are two critical factors to keep in mind: (a) harm or damage is not needed for trespass to occur; and crucially (b) knowledge that the land is owned by another is not necessary, even if both parties are mistaken.
Simply put, the law doesn't care whether you intentionally entered land that you knew belonged to somebody else, merely that you intentionally entered onto that particular parcel of land is sufficient to trigger a trespass cause of action.
Accidental trespass, which implies a lack of intent, is devoid of liability. Consent to trespass intuitively absolves the defendant of any liability. And necessity to trespass, either in a public or private sense -- that is, either the protect the community or to protect oneself -- is also a viable defense. Note however that a public necessity defense is a so-called complete defense which affords a complete avoidance of damages, while a private necessity defense is an incomplete defense which means defendant may be liable for damages.
Another defense against trespass is entry to abate a nuisance; see below.
(1) Defendant needs to turn his car around on a narrow street and intentionally enters onto the driveway of a home to perform the maneuver. He is liable for trespass because he intentionally entered the driveway; whether he knew the driveway belonged to another is irrelevant, merely that he intended to enter the driveway is all that matters.
(2) Same as above except that defendant enters onto the driveway of another by accident because he got a flat tire causing him to inadvertently enter the driveway. Here he is not liable because it was a mistake, it was unintentional.
(3) Same as above except that this time defendant enters onto the driveway of another because he swerved to avoid an oncoming car. Here he is likewise not liable because it was a private necessity to save himself from a head-on collision. However, when entering onto the property, he damaged some plants and collided with a parked car, so he is potentially liable for damages. On the other hand, it could be argued that his defensive maneuver was also to protect the oncoming driver, in which case it was arguably a public necessity, thus relieving him of any damages.
A nuisance in this context is a type of trespass that generally implies an ongoing affair, rather than a singular event.
Nuisance is defined as a substantial and unreasonable interference with one's use and enjoyment of property, typically of the non-material sort such as odors.
As with many causes of action, a nuisance cause of action needs to rise to a "substantial and unreasonable" level of interference with their property. This means that for a reasonable person in that situation, it would cause undue hardship.
Entry to abate a nuisance may be used as a defense against a trespass cause of action. In order to raise this defense, (1) the defendant must be the owner of the property which is being adversely impacted by the nuisance; (2) defendant must make a demand to abate the nuisance; (3) the entry onto the property must be reasonable; and (4) the force used to make the demand must likewise be reasonable.
(1) Plaintiff's neighbors occasionally enjoy a wood-burning firepit in their garden. Sometimes, the wind current cause the smoke to enter onto plaintiff's property. Result: no nuisance cause of action.
(2) Same as above except that neighbors burn the wood-burning firepit nearly every night for hours at a time, and the excess smoke permeates plaintiff's home and causes plaintiff to suffer asthma attacks and difficulty sleeping. Result: possible nuisance cause of action.
(3) Defendant's neighbor has been accumulating foul smelling garbage in the immediately adjacent parking lot and has seemingly left the property for an indefinite amount of time. The stench of the garbage has become nauseating. Defendant first tries to contact plaintiff, but to no avail. Defendant then walks onto plaintiff's driveway and beings clearing out the garbage. Result: no successful trespass claim against defendant.