One of the legal requirements for establishing a claim over another person's property through adverse possession is that the trespasser's possession be "hostile." (The other requirements include that the possession be continuous, actual, exclusive, and open and notorious.) But how "hostile" do the trespasser's actions need to be? Must the trespasser be angry or unpleasant with the true property owner?
The answer is no. "Hostility" does not mean malice or ill will. In the adverse possession context, "hostility" means that the individual claiming possession of a disputed piece of land must demonstrate to a court that his or her possession is an actual invasion of, or infringement upon, the true owner's property rights.
Imagine that you build a fence, honestly believing that you're building it at the border of your yard. Three decades pass. Your neighbor then discovers that your fence was actually built two feet into his property, meaning that you've spent the past 30 years living with a slightly wider yard than you held legal title to.
Even though you didn't realize at the time that you were building the fence on your neighbor's property, your possession of that area of land might still be considered "hostile" within the meaning of your state's law, because your use infringed directly on his property rights. In short, the element of hostility can be found even though the possession occurred inadvertently or by mistake.
However, state laws do vary on this topic. In some, the trespasser must actually be cognizant that he or she has no legal right to be on the property. At the other end of the spectrum, a few states' laws require the trespasser to have made an innocent good faith mistake in occupying the property, such as by relying on an invalid or mistaken land deed.
A claim of ownership through adverse possession will not succeed when the trespasser actually had the authority to be on the premises. A trespasser who uses land by permission from the owner can never gain title by adverse possession, no matter how long that use might continue.
In other words, if your friend tells you that you can swim in his backyard pond whenever you like, and you do so for decades, while he never uses it at all, you can't succeed on an adverse possession claim. There's no hostility, since you were given express permission.
In this spirit, many courts tend to reject adverse possession claims by family members, since it's presumed that family members would give permission to occupy parts of their property. Thus, if you live in your uncle's garage for the required statutory period, or build a shed on your mom's yard, courts will assume that your presence there was not hostile.
Similarly, a renter cannot establish a claim of adverse possession against the owner and landlord of a piece of property. This is generally true regardless of how much rent was paid, or how long the renter possessed the land.
If you are a property owner and you notice that a trespasser or neighbor is using your land, the requirement that the trespasser's use be "hostile" gives you a couple of options to protect your property rights. First, you can speak with the person and give your permission. Or if you prefer not to give permission, you can simply clarify your property rights. Chances are, the trespasser will then simply leave without further ado.
Second, you can have the trespasser sign a rental agreement. For even a nominal amount of money, a signed rental agreement would supply undeniable evidence that the trespasser was using a portion of your property with permission. Once that permission is established, the trespasser isn't really a trespasser. Hence, he or she wouldn't be able to meet the burden of showing hostile possession, and therefore, wouldn't be able to claim title through adverse possession.
Again, however, you're under no legal obligation to provide such permission. This would mostly be appropriate in situations where you really don't mind the person's use, and want to maintain good relations; such as with a neighbor who has planted flowers along your property line. A more direct option in dealing with adverse possession is to contact an attorney and file an action to eject the trespasser, as well as calling the police.