Technical Booklet G Resistance to the Passage of Sound·Page 71·3.40
Mass requirement for internal masonry walls
Any loadbearing internal wall or internal wall rigidly connected to a separating floor must have a minimum mass per unit area of 120 kg/m² excluding finish.
The mass per unit area of any loadbearing internal wall or any internal wall rigidly connected to a separating floor should be at least 120 kg/m2 excluding finish.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/Technical Booklet G - Resistance to the Passage of Sound.pdf