The Party wall etc Act 1996 has two definitions of a party wall known by the clauses that they are defined within section 20 of the Act as type a) and type b) party walls.

Type a) party walls are walls that form part of a building and stands on land of different owners. This describes the common party wall between two semi-detached properties or in many terraces of houses where the boundary passes through the centre of the wall. The wall has therefore been constructed “astride” the boundary with a part of the wall being either side of the boundary.

Type b) party walls also divide two different owners but the wall is not astride the boundary and can be wholly owned by one of the two properties. This type of wall is often found where a neighbour has constructed against a boundary wall belonging to the adjoining owner. Most often this is found in historic locations as generally most owners in recent years have an increased awareness of their rights and have prevented the neighbour from using their wall.

To make matters much more complicated in many older properties both type a) and type b) properties may exist on the same house. In some location where a type b) party wall exists it may only be a party wall up to a certain height and thereafter revert to a boundary wall. In complex situations it will be necessary to appoint an experienced party wall surveyor to assist you.

One other thing to be aware of is that the Act is called the Party Wall etc. Act and therefore may apply to you and your property even if there is no party wall present. In particular where there are flats the structure that separates flats owned by different owners may be deemed a Party structure. The Act also includes reference to excavation on or near the boundary and the construction of new walls on the line of junction between properties of different owners.

In complex situations an experienced Party Wall surveyor will need to attend site to inspect the property and evaluate the location of the wall relative to any known boundary and the amount of enclosure that has occurred to the wall. It is common for a wall to have been built as a party wall between terraced house and semi-detached houses. However, where those houses are staggered or built at different levels the party wall may have been continued as a boundary wall. It is not uncommon for two surveyors to meet and discuss the situation before agreeing on whether a wall is a party wall or not.