What is a "Party Wall" and how is it constructed?

At both of Bucci’s condominium developments in Calgary; Tribeca in Mission and Next in Bridgeland, we are using a double wall assembly for  the dividing wall between two adjacent homes. This wall assembly is referred to as the “Party Wall”.  It is designed specifically to meet the established criteria for fire ratings and sound transfer. Generally, it is composed of  two independently constructed walls with a one inch airspace between them.  The walls are 2 x 4 construction with studs placed every 16 inches. The space between the 2 x 4 studs is filled with R-20 insulation on each wall.   A bead of black acoustical caulking is applied to all external studs and top and bottom plates so that when the drywall is added there is a complete seal. The drywall is 5/8 inches thick and fire guard rated. In addition all electrical boxes have a flanged gasket around them to ensure a tight seal when exposed through the drywall. In this video, Kim Morrison of Gauvin Construction, describes a Party Wall assembly at NEXT condos in Bridgeland.