What is a Party Wall - Bruce Spenser MSc MCIOB

• “party fence wall” means a wall (not being part of a building) which stands on lands of different owners and is used or constructed to be used for separating such adjoining lands, but does not include a wall constructed on the land of one owner the artificially formed support of which projects into the land of another owner;

• “party structure” means a party wall and also a floor partition or other structure separating buildings or parts of buildings approached solely by separate staircases or separate entrances;

• “party wall” means—

  (a)

  a wall which forms part of a building and stands on lands of different owners to a greater extent than the projection of any artificially formed support on which the wall rests; and

  (b)

  so much of a wall not being a wall referred to in paragraph (a) above as separates buildings belonging to different owners;

and of course there is very much case law the original and most famous being Watson v Gray (1880) 

Most importantly you also have Bruce’s Cyclopedia of Party Walls