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.