Definition of a party wall from RICS and GOV websites
If you live in a semi-detached or terrace house you share a wall (or walls) with your neighbour – that wall is known as a party wall.
Since the Party Wall etc Act 1996 came into force, owners in England and Wales have had a procedure to follow when building work involves a party wall or party fence wall, some excavations close to neighbouring buildings, and new walls at boundaries.
The Act covers:
•new building on or at the boundary of 2 properties
•work to an existing party wall or party structure
•excavation near to and below the foundation level of neighbouring buildings
If you propose to excavate, even on your own land, you may be required to give notice to your neighbour, one month before starting.
Links to useful pdf files