A "party wall", also called a "wall in common", a "common wall", or a "shared wall" is a dividing wall between two connected and mutually supporting buildings of different owners, or intended to be between a building actually constructed and a contemplated one, usually standing half on the land of each owner, maintained at mutual cost of both owners, and subject to use by each owner consistent with the rights of the other.
A party wall does not need to be located exactly on the boundary line between two adjoining properties. Instead, it may stand entirely upon the land of one owner only. It takes the place of two walls that would have otherwise been erected by adjoining landowners, each owner holding in severalty that cross-portion of the wall on his or her tract, subject to an easement (called cross-easement) by the other owner for use of the wall as a perimeter wall of the owner's respective building, and for its support.
By Statutory Authorization
Statutes may expressly authorize a lot owner to erect a party wall and to enter his or her neighbor's adjoining land to do so, provided the builder complies with certain requirements.
By Contract or Agreement
Unless prohibited by statute, a wall may acquire the status of a party wall pursuant to an express or implied contract or agreement between adjoining landowners.
By Conveyance of Property
A wall may acquire the status of a party wall by the conveyance of land on which it stands or which it adjoins and serves or is intended to serve for building purposes.
By Implied Easement
The conveyance of lands separated by a common wall on the dividing land may give rise to easements in the nature of a party wall.
By Use of the Property
A right to an easement of support in a wall may arise through use during the pertinent prescriptive period, whether the wall rests wholly on the land of one of the adjoining landowners or in part on the land for each.
Party walls generally take one of four primary forms: