What is a Party Wall? Semi-detached and terraced houses generally share at least one wall with an adjoining owner(s). These shared walls are known as "Party Walls". Will having a Loft Conversion affect the Party Wall? Generally yes. In most cases the conversion of a loft space into a useable room involves carrying out some work on the Party Wall, if there is one. Who has ownership of the Party Wall? When carrying out building work involving a Party Wall you are obliged to act