A party wall is a wall located on or at the dividing line between neighboring premises and used, intended to be used, or available to be used by adjoining landowners in the construction or maintenance of improvements on their respective property. A party wall usually stands half on the land of each owner but may be entirely on the land of one, and is maintained at mutual cost. Each owner of adjoining lands on which a party wall stands owns the part of the wall that stands on the owner's land and has an easement, or right of use, in the other part, unless there is a contrary law or agreement.
Party wall agreements are generally enforceable as covenants running with the land, so that future owners or assignees are bound by the agreement. An adjoining landowner's easement rights in the wall ordinarily continues so long as the wall stands, unless agreed otherwise. Party wall easements are terminated on the accidental destruction of the wall and, under some circumstances, on substantial changes in conditions of the neighborhood.
A party wall has also been defined as follows:
"A party wall may be defined generally as a wall located upon or at the division line between adjoining landowners and used or intended to be used by both in the construction or maintenance of improvements on their respective tracts, or, more briefly, as a dividing wall for the common benefit and convenience of the tenements which it separates. The term ‘wall in common,’ as sometimes used, has the same meaning as party wall. A distinctive feature of a party wall is that the adjacent buildings are so constructed that each derives its support from the common wall. Thus, where each of two persons is seised of a specified half of a wall and nothing more, and no right of support or shelter has been acquired by the one from the other, such a wall is not a party wall."
40 Am. Jur. Party Walls § 2 at 485 (1942).
However, such a division wall may take on the character of a party wall by prescriptive use. For example, some courts have held that a wall erected and continually used as a division wall by adjoining owners for the statutory period is a party wall, even though it does not rest on the division line, but is wholly within the land of one of the adjoining owners. A prescriptive easement in a wall may be based on the support it provides, or other uses, such as protection from the elements. Such cases are decided on an individual basis, and are influenced by factors such as whether the removal of the wall was voluntary or involuntary. For instance, a court held that because a party wall was created by prescription, the plaintifffs obtained the right to continue to have the shelter that the wall provided to their home and the defendant was required to replace the party wall if he caused it to be removed. However, if the wall was destroyed by fire or public condemnation, the defendant would have no such duty to rebuild the portion of the wall removed.