As a rule, every person owns the structures on his or her own property, and can do with them as he or she likes. An exception to this rule concerns party walls. A party wall is one located at or near the boundary line. It can be located on both party’s land, or on one party’s land. The key issue is not its precise location, but the intention that it be used by both owners for the construction of maintenance of improvements on both parties’s land. Tate v. Fratt (1896) 112 Cal. 613. For example, if the wall is used by both sides to hold up their garage or some other structure, it is most likely a party wall.
Ideally, party walls are created by express agreements between the parties, and they are governed by the term of the parties’ contract. Equitable Building & Loan Association v. Wolfange (1931) 111 Cal. App. 119. Absent a contrary agreement, either side can increase the size of the party wall, if can be done without causing any injury to other side. Absent a contrary agreement, each side owns that part of the wall, which is on his or her own land, and has an easement in the rest of the wall. (If the wall is entirely on one side’s land, the other side nonetheless has an enforceable easement right in the wall.) If the parties’ have agreed to share the costs of the wall, a lawsuit can be brought to compel the other side to make necessary contributions.
Since both sides have property rights in a party wall, if either side wrongfully removes a party wall or injures a portion of the wall, which is on the other party’s property, then the injured party can sue for damages. Nippert v. Warneke (1900) 128 Cal. 501.
While party walls are based upon agreement between the parties, the Courts will sometimes imply an agreement, even when one side is denying its existence. They do so, when the acts and conduct of one party make it unfair to the other for it to be able to deny that a wall is a party wall. Bank of Escondido v. Thomas (Cal. 1895) 5 Cal. Unreported 94, 41 P. 2d 462.