Party wall (or parti-wall) is a dividing partition between two adjoining buildings (or units) that is shared by the tenants of each residence or business. The wall is sometimes constructed over the center of the property line dividing two terraced flats or row houses so that one half of the wall is on each property. They are sometimes two abutting walls built at different times.
Party walls are typically made of non-combustible material. Where required by code, the party wall could be a fire wall. The wall starts at the foundation and continues up to a parapet, creating two separate and structurally independent buildings on either side. The term can be also used to describe a division between separate units within a multi-unit apartment complex. Very often the wall in this case is non-structural but designed to meet established criteria for sound and/or fire protection between residential units.
In the United Kingdom, the legal rights and obligations governing work to or adjacent to a Party wall are governed by the Party Wall etc. Act 1996 and Party Wall Surveyors specialise in managing the negotiation process between adjoining owners and resolving disputes. Apart from special statutory definitions, the term "Party Wall" may be used in four different legal senses.
Less commonly, it may also be spelled Parti Wall.
In the USA, the term most commonly refers to the wall within a condominium complex that separates two neighboring units or the wall between two adjacent rowhouses. Additionally, "Parti Wall" is not an acceptable spelling in the USA.