These walls are described in the BCA, Part F5, as walls that "separate sole-occupancy units" (also known as inter-tenancy walls). This includes townhouses, high-rise home units, three-storey flats, hotels and similar residential buildings. Except for Class 9c buildings (aged care units); party walls require a minimum sound rating of Rw + Ctr 50.

A party wall that separates one sole-occupancy unit’s wet area (a bathroom, laundry, kitchen etc.) from a habitable room in another sole-occupancy unit is required to be of discontinuous construction.

Discontinuous Construction:

The BCA describes discontinuous construction as "a wall having a minimum 20mm cavity between 2 separate leaves". See downloads for further information.

Where the 2 separate leaves are both masonry, the BCA allows resilient wall ties "if required". As they are rarely required, their omission will not only save money but improve the acoustic performance of cavity (double-leaf masonry) walls.

Discontinuous construction is also required where a wall separates a sole-occupancy unit from a plant room or lift shaft.