A claim to ownership of another person's property based on adverse possession does not happen overnight. To gain title, a trespasser must use—essentially, squat on—the property for a number of years. Each state has its own required statutory period, as outlined in these State-By-State Rules on Adverse Possession. Broadly speaking, most states require possession of the disputed piece of property for at least ten continuous years and in many instances twenty.
"Continuous" means the use is regular and uninterrupted, although the possessor certainly doesn't need to maintain a 24-hour daily campsite or vigil. Erecting a fence, planting and caring for a garden, and holding regular parties or events on the plot of land in question could, for example, satisfy this requirement.
If the statutory period for your state is ten years, and you manage to adversely possess a piece of land for nine years before the true owner calls the police, that's obviously not enough time. But what if you possess the land for a total of 11 years, but miss a year in the middle because you temporarily lived in a different state? Unfortunately, this isn't continuous possession. If you took a break at year five, the ten-year clock begins to run from the beginning of your renewed possession.
Fortunately for claimants, if you've already hit the minimum ten-year or other mark, but leave the state after that, you do not lose any of the adverse possession rights you've acquired. That is, a break in possession after the acquisition of title by adverse possession will have no effect on the rights acquired.
Not all property is used 365 days each year even by its true owner. A typical owner probably wouldn't use a pond or swimming pool every day, but would wait for warmer weather. A typical owner also wouldn't use a ski lodge every day; the owner would wait for winter snow.
For a trespasser trying to gain title to these types of pieces of property, seasonal occupation is acceptable as long as it's in a manner consistent with how the true owner would use the property. So, in short, the requirement of continuity of possession is satisfied with activities that are seasonal in character.
If trying to establish adverse possession over a neighbor's pond, for example, you need only swim in it each summer for the statutory period, not in January.
While possession of a piece of land must be continuous for the statutory period, the possession doesn't always need to be by the same person in order to support an adverse possession claim.
If two adverse possessors are in "privity" with one another, then most courts will allow the second adverse possessor to "tack" or combine his or her time on the land with the time spent by the first adverse possessor. Privity is a legal term that essentially means that there's a direct connection between the two parties. It can be established in several ways, such as by lease, descent, or outright sale.
For example, imagine that the statutory period for adverse possession in your state is ten years. Martha has adversely possessed a vacant lot in her neighborhood for seven years, then sells her interest in the lot to Jane.
Jane occupies the land for another three years. This would likely meet the statutory requirement for ten years of continuity, giving Jane the ability to gain title by adverse possession even though she herself did not possess the land for the full ten years.